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Subsurface sources contribute substantially to fine‐grained suspended sediment transported in a tropical West African watershed in Burkina Faso Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-16 Michael Rode; Felix op de Hipt; Adrian L. Collins; Yusheng Zhang; Philipp Theuring; Uwe‐Karsten Schkade; Bernd Diekkrüger
Increasing watershed sediment yields is an important problem in Africa, but the sources of these sediment yields have only very rarely been investigated. This study therefore aims to discriminate subsurface and surface sources of fine‐grained sediments in a representative mesoscale (580 km2) West African savanna watershed. We used a sediment source fingerprinting approach for source apportionment including geochemical and radionuclide (137Cs, 210Pbex, and 7Be) composite signatures where 7Be was used as a tracer for the first time in the African environment. Two field campaigns were conducted collecting a total of 258 geochemical and 66 isotope samples. We found that subsurface source categories, dominantly river bank, contributed an unexpected high share of 43% (geochemistry) and 45% (radionuclides) to the sampled fine‐grained sediments. Pairwise comparison of the averaged frequency distributions for predicted source proportions using five geochemical signatures with the frequency distribution generated using the single radionuclide signature suggested that the two distributions are not statistically different. Extrapolating our measured contribution of subsurface erosion to areas with similar yields in comparable environmental settings, we can assume that subsurface sources are an important component of sediment loss across large areas of West Africa. Subsurface erosion, primarily associated with bank rather than gully erosion, is likely to increase in the future with projected rises in run‐off due to land use and climate change. Source tracing studies need to be undertaken more widely across Africa to help mitigation planning for sediment‐related and land degradation problems.
Environmental risk resulting from historical land degradation in alluvial plains considered for dam planning Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-16 Mateja Breg Valjavec; Mitja Janža; Aleš Smrekar
Land degradation of alluvial plains is an environmental risk for groundwater contamination, stemming from the mobilization of contaminants that can occur from waste‐filled gravel pits. This risk can be increased by river damming and consequential rises in groundwater levels. The presence and characteristics of former historical land degradation of alluvial plains should therefore be considered when planning hydroelectric projects. The aim of this study was to assess the hydrological and environmental impacts of the planned damming of the Sava River on the groundwater, which is the drinking water source for the Slovenian capital Ljubljana. It introduces an integrative approach for determining the characteristics of old waste‐filled gravel pits with stereo image processing of historical aerial photographs and electrical resistivity tomography (ERT) in combination with hydrological modelling. Thirty gravel pits in the study area (17 km2) were identified by stereo image analysis, and three were selected to test results in the field using non‐invasive ERT. Integrating this information with the results of hydrological modelling, we assessed the risk of groundwater contamination from the scenario of the planned damming of the River Sava. The results indicate that the thickness of the unsaturated zone below the identified gravel pits will be reduced by an average of 4 m at median groundwater level conditions during damming, which will increase the vulnerability of groundwater to contamination.
Effects of grazing exclusion on soil–vegetation relationships in a semiarid grassland on the Loess Plateau, China Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-16 Guohua Ren; Caixia Wang; Kuanhu Dong; Huisen Zhu; Yongcui Wang; Xiang Zhao
Grazing exclusion (GE) is regarded as an effective practice to restore degraded grasslands. However, the patterns of vegetation recovery and related regulating factors in response to fencing have not been fully recognized. Hence, quantitative analysis of vegetation–soil relationships in response to GE was conducted in a semiarid grassland located on the Loess Plateau, North China. The results revealed that enclosure establishment significantly increased vegetation cover, height, and productivity but reduced plant diversity. Soil bulk density (0–20 cm) and pH (0–50 cm) clearly decreased after GE, whereas soil water (0–20 cm), organic matter (0–10 cm and 30–40 cm), and nutrient concentration (0–20 cm) increased significantly. Redundancy analysis of vegetation and environmental variables suggested that edaphic properties, including soil water, soil pH, total N, bulk density, and organic matter, was associated with plant community composition. Subsequent canonical correlation analysis indicated that soil bulk density, organic matter, and total N played an important role in shaping vegetation patterns in response to fencing whereas variations in soil pH and total N were the major contributors to variations in grazing rangeland. This work emphasized that fencing is a positive grassland management approach and suitable changes in grazing stock and soil variability are required to quantify vegetation recovery in response to grazing exclusion.
Continuous‐cropping tobacco caused variance of chemical properties and structure of bacterial network in soils Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-16 Shu Chen; Gaofu Qi; Tian Luo; Hongchun Zhang; Qiankun Jiang; Rui Wang; Xiuyun Zhao
Continuous cropping of the same crop leads to land degradation. This is also called the continuous‐cropping obstacle. Here, we investigated how long‐term continuous cropping of tobacco influences soil biochemical properties and bacterial networks in the mountain lands of China. Two different fields were sampled: one with 25 years of continuous cropping tobacco and one with noncontinuous cropping tobacco. Soil chemical and biological properties were measured including available phosphorus and potassium, soil organic matter, pH, alkali‐hydrolysable nitrogen, micronutrients contents, and activity of urease, catalase, invertase, and phosphatase as well as tobacco agronomic characteristics. Bacterial communities of the two different soils were sequenced by metabarcoding of the 16S ribosomal RNA, and, with these data, network analysis was done. Soil chemical properties and tobacco agronomical properties were negatively affected by the continuous‐cropping obstacle, and this treatment has a less complex network (less modules, nodes, and connectivity) than the soil with noncontinuous cropping treatment. For continuous cropping, there were less generalists, which were key species that connect network, than noncontinuous cropping. Moreover, the taxonomic composition of bacterial network was different in the two different treatments. In the continuous‐cropping network, 40% nodes had negative interactions, suggesting that more competition or antagonism existed among bacterial species. It concluded that continuous cropping has a detrimental effect on soil chemical and that the bacterial network properties under continuous cropping are more sensitive to soil variables (so more unstable and inefficient) because there are less bacterial species that interact each other and this is due to limited nutrients or excessive toxic nutrient.
Post‐little ice age paraglacial processes and landforms in the high Iberian mountains: A review Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-16 Enrique Serrano; Marc Oliva; María González‐García; Juan Ignacio López‐Moreno; Juan González‐Trueba; Raúl Martín‐Moreno; Manuel Gómez‐Lende; Jordi Martín‐Díaz; Jordi Nofre; Pedro Palma
Three Iberian mountain ranges encompassed glaciers during the Little Ice Age (LIA): the Pyrenees, Cantabrian Mountains, and Sierra Nevada. The gradual warming trend initiated during the second half of the 19th century promoted the progressive shrinking of these glaciers, which completely melted during the first half of the 20th century in the Cantabrian mountains and Sierra Nevada and reduced by 80% of their LIA extent in the Pyrenees. In these formerly glaciated environments, the transition between glacial and periglacial conditions results in an accelerated paraglacial readjustment, with very active geomorphic processes. Cirque walls generate a large amount of sediments through rock‐falls and slides. LIA moraines, devoid of vegetation and composed of highly unstable sediments, are being intensely mobilized by slope processes. Inside the moraines, the shrinking of LIA glaciers favoured the development of buried ice patches, with permafrost‐related landforms, small periglacial features generated by solifluction, and cryoturbation processes and remarkable hydrological changes. Present‐day morphodynamics is mostly related to seasonal frost, though patches of permafrost have formed in contact with the buried ice, undergoing a process of degradation because it is not balanced with present‐day climate. This is reflected in the occurrence of multiple collapses and subsidence of the debris cover where the frozen bodies sit. Next to the small glaciated environments in the highest Pyrenean massifs, there is a permafrost belt undergoing also rapid geomorphic changes. Based on the observed processes, we discuss spatio‐temporal patterns of paraglacial readjustment in Iberian mountains and compare it with other midlatitude mountain environments.
Vegetation restoration changes topsoil biophysical regulations of carbon fluxes in an eroding soil landscape Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-16 Jianye Li; Bojie Fu; Shuguang Liu; Paul Dargush; Guangyao Gao; Jianbo Liu; Fangli Wei
The dynamics of biophysical regulations of carbon fluxes can have a major effect on an ecosystems' carbon budget. Only a handful of comprehensive assessments of such dynamics exist. To better understand the carbon cycle, we measured all major carbon flux by biophysical regulations including rainfall, runoff, infiltration, and sediment yield at eight runoff plots in an eroding soil landscape on the Chinese Loess Plateau, a typical vegetation restoration area for the region. Results show that topsoil carbon flux by infiltration into deep soil layers was the largest efflux from topsoil in plots with vegetation, followed by runoff and sediment carbon effluxes. On the contrary, the carbon flux by sediment was the largest efflux from topsoil in plot without vegetation, followed by infiltration and runoff carbon effluxes. Total topsoil carbon flux by biophysical regulations to the deep layer is about 71 ± 10% of the typical carbon sequestration rate in the region. Topsoil carbon sequestration capacity might be underestimated by up to 43 ± 3% if the infiltrated carbon was not factored into estimates. The results of this study improve understanding of soil carbon dynamics and expand the dynamic carbon replacement hypothesis; photosynthesis replaces not only lateral carbon lost by erosion but also vertical carbon lost by infiltration.
FORAGE GRASS CULTIVATION INCREASES SOIL ORGANIC CARBON AND NITROGEN POOLS IN A KARST REGION, SOUTHWEST CHINA Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-16 Dejun Li; Jing Liu; Hao Chen; Liang Zheng; Li Wen; Kelin Wang
Whether conservation agriculture systems can increase soil organic carbon (SOC) and total nitrogen (TN) pools remains unresolved. We measured SOC and TN pools in maize‐soybean rotation fields and three types of conservation agriculture systems with mature forests being selected for comparison in southwest China' karst areas. The three types of conservation agriculture systems were fields of mulberry, forage grass and sugarcane. The objective was mainly to evaluate whether replacement of maize‐soybean fields by the other three types of agricultural fields would significantly increase SOC and TN pools. Across the 0‐30 cm soil profile, SOC and TN pools were not significantly higher in the mulberry and sugarcane fields than in the maize‐soybean fields (47.42 ± 6.34 Mg C ha‐1 and 5.47 ± 0.49 Mg N ha‐1). Nevertheless, SOC and TN pools in the forage grass fields (74.12 ± 5.30 Mg C ha‐1 and 7.09 ± 0.41 Mg N ha‐1) were higher by 56.3% and 29.4% relative to the maize‐soybean fields, but were lower by 38.3% and 21.8% compared to the forests, respectively. Microbial biomass C (MBC) and N (MBN) concentrations varied in similar patterns as SOC and TN pools. The MBC: SOC and MBN: TN ratios were higher in the forage grass fields, suggesting increased soil organic matter quality compared to the other types of agricultural fields. Our findings suggest that whether conservation agriculture can enhance SOC and TN pools largely depends on crop type with forage grass cultivation being identified as an efficient solution to promote SOC and TN pools.
RESILIENCE OF RED FERRALITIC SOILS IN THE KARST REGIONS OF MAYABEQUE PROVINCE, CUBA Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-13 José M. Febles González; J.M. Febles Díaz; Nelson Moura B. Amaral Sobrinho; A. Tolón Becerra; X. Lastra‐Bravo; G.F. Botta
There is an ongoing global debate on soil degradation, its magnitude and agro‐environmental impact, where long‐term experimentation provides quantitative criteria for its capacity for restauration with rational use and management. In this context, research in the last 30 years has confirmed that the resilience of Red Ferralitic soils in the karst regions of western Cuba is a multifactorial process, conditioned not only by the intrinsic properties of the soil surface and use conditions, but also dependent on geological‐geomorphological and use conditions. This study determined the capacity of Red Ferralitic soils for blocking karst‐erosion to be a period of 50 years in the San Jose de Las Lajas polje. They would recover, but depending on the amount of limestone impurities, it would take from 100 to 600 years. In any case, there are very few similar studies, not only because of the time necessary to achieve reliable results, but because in the case of karst ecosystems, they are subjected to constant disturbances impeding resilience research.
Effects of soil moisture and vegetation cover on biomass growth in water‐limited environments Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-13 Javier Lozano‐Parra; Susanne Schnabel; Manuel Pulido; Álvaro Gómez‐Gutiérrez; Francisco Lavado‐Contador
Soil moisture has a direct influence on biomass production, food security and ecosystem functioning, thus resources management in water‐limited environments could be improved if feedbacks between water and vegetation were fully understood. This study tries to define the sensitivity of annual pastures under the influence of different vegetation covers to soil water availability during two contrasting growing seasons, dry and wet. For this reason, soil water content was continuously monitored during two complete hydrological years using capacitance sensors, which were gathered in soil moisture stations located in open grasslands and beneath tree canopies. Pasture growth was recorded by measurements of its height and by biomass cuts. The study was conducted on three private farms located in savanna‐like ecosystems of Spain (dehesa) with Mediterranean climate. Results highlighted the importance of the topsoil (first 15 cm) as the main layer for water supply of natural grasses. Soils below canopies registered longer and more intense water deficits than those located in grasslands. This was reflected in biomass growth, given that when growing conditions were dry, pasture yield decreased more than 40% in grasslands and more than 50% below tree canopies. The studied ecosystems occupy millions of hectares in Spain and Portugal and present a canopy cover up to 40%. If dry episodes become more frequent in the present century due to climate change an important surface, especially under trees, could become drier, less productive and, therefore, more prone to land degradation.
ADVANTAGE OF MIXED TREE STANDS IN RESTORATION OF UPPER SOIL LAYERS ON POST‐MINING SITES: A FIVE‐YEAR LEAF LITTER DECOMPOSITION EXPERIMENT Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-13 Paweł Horodecki; Mirosław Nowiński; Andrzej M. Jagodziński
No in‐depth studies covering litter decomposition were previously conducted on afforested post‐mining sites. We aimed to compare leaf litter decomposition rates of 14 tree species growing in mixed stands on a post‐mining spoil heap, and to compare their decay rates with those obtained in pure stands of tree species that are very often planted in post‐mining areas. The study was conducted on the Bełchatów Lignite Mine spoil heap, central Poland. We studied litter decomposition rates over five years using the litterbag method. Leaf litter decomposition rates (k constants; year‐1) after five years of the experiment were arranged from highest to lowest as follows: Prunus serotina (1.04), Alnus glutinosa (0.86), Fraxinus excelsior (0.81), Ulmus laevis (0.73), Acer pseudoplatanus (0.68), Populus tremula (0.63), Populus × canadensis (0.59), Betula pendula (0.54), Populus nigra 'Italica' (0.38), Quercus rubra (0.36), Pinus sylvestris (0.34), Robinia pseudoacacia (0.34), Fagus sylvatica (0.25) and Quercus robur (0.22). Decomposition rates increased with Mg, Ca and summed Mg+Ca+P+K contents in freshly fallen leaves (%). All species‐specific decomposition rates were higher in mixed than in Scots pine stands. Half of them were also higher than in pure stands of other tree species. Our results indicate that tree species composition could significantly affect the physiochemical properties of upper soil horizons on reclaimed areas. Based on these findings we recommend planting high share of A. pseudoplatanus, A. glutinosa, and U. laevis, but also F. sylvatica and Q.robur in stands on post‐mining spoil heaps, because mixed stands can accelerate soil development more than pure stands.
Integrated spatial assessment of inland excess water hazard on the Great Hungarian Plain Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-12 Csaba Bozán; Katalin Takács; János Körösparti; Annamária Laborczi; Norbert Túri; László Pásztor
Inland excess water (IEW) is a form of surplus surface water, often regarded as a specific flood type. However, it occurs most frequently in local depressions of large flat areas, irrespective of river floods and the surface water networks. IEW is considered to be a typical Carpathian Basin problem, as it can cause major land degradation problems in the agricultural areas of Hungary mainly located on the Great Hungarian Plain (GHP). An innovative method for mapping the probability of IEW inundation is proposed in this study. This method is based on the geostatistical modelling of the relationship between the natural and human driving factors and the occurrence of IEW inundations. The results show that significant part of the GHP (about 500,000 hectares) is moderately or highly affected by IEW inundations where the combination of multiple influencing factors simultaneously occur. The resulted IEW inundation probability map can be used to meet future challenges in agricultural management and the adaptations to climate change effects.
NITROGEN ADDITION CAN IMPROVE SEEDLING ESTABLISHMENT OF N‐SENSsITIVE SPECIES IN DEGRADED SALINE SOILS Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-10 Hongxiang Zhang; Yang Xiang; Louis J. Irving; Qiang Li; Daowei Zhou
Salinization is an important cause of land degradation globally and these soils are usually nutrient deficient, which inhibits plant establishment and growth. Medicago sativa and Leymus chinensis are important legume and grass forage species, respectively, in China and are frequently used in pasture establishment. We aim to test whether nitrogen (N) addition can increase the salt tolerance of these two glycophytes and whether the two species inhibit each other at the germination and seedling emergence stages. M. sativa and L. chinensis seeds were germinated separately or together in 0, 100, 200 mM NaCl solutions with supplemental 0, 20, or 40 mM N solutions. N addition increased germination percentage and rate, shoot length and seedling N concentration under moderate NaCl conditions for L. chinensis, but had no effect on Na+ concentrations. Conversely, N addition stimulated Na+ uptake in M. sativa, but it had little effect on germination parameters, with salt suppressing N uptake. The presence of M. sativa stimulated L. chinensis germination percentage in mixed treatments. Our results suggest that proper N application may aid establishment of N‐sensitive species L. chinensis in grass‐legume mixtures in degraded saline soils, through both direct influence as a nutritional and/or osmotic resource and indirect effect by increasing salt sequestration by M. sativa. N application had little effect on establishment of the N‐fixing species M. sativa.
SOIL MAPPING AND DELINEATION OF MANAGEMENT ZONES IN THE WESTERN GHATS OF COASTAL INDIA Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-10 Ram Ratan Verma; Begur Lakshminarasimha Manjunath; Narendra Pratap Singh; Anil Kumar; Trupti Asolkar; Virendra Chavan; Tapendra Kumar Srivastava; Pushpa Singh
The pace of land degradation has almost doubled across the Western Ghats of India, one of the world's 'hotspots' for biodiversity, owing to soil erosion, mining and rampant urbanization. The arising nutrient depletion vis‐à‐vis land degradation is thus a serious threat to agricultural sustainability in this region. Delineation of spatial soil property maps for nutrient management is an effective strategy for precision agriculture. The present investigation was carried out in North Goa District in Western Ghats, a seldom researched domain in the Indian coastal region. The study involved spatial array analysis of soil properties of 383 geo‐referenced soil samples and used fuzzy k‐means clustering for delineation of management zones (MZs). Soils were found highly acidic with low available N, P and medium exchangeable K with a widespread Zn, Cu, Fe deficiency and sporadic salinity. Soil properties exhibited low to high levels of skewness except for soil pH and Mn. Correlations between soil pH and K, Zn, and Mn, between EC and Fe, between soil organic carbon (SOC) and N, P, K, Cu and Mn was positive and significant (P=0.01). Geostatistical analysis revealed varied distribution pattern for soil properties with Gaussian (pH, P, Cu), spherical (EC), stable (SOC), hole effect (N), K‐Bessel (K, Fe), exponential (Zn) and circular (Mn) as best fit semivariogram models with weak and strong spatial dependence. The spatial variability was mapped and two MZs were delineated. The developed maps will be crucial in site‐specific nutrient management for agricultural and ecological sustainability in the Western Ghats of India.
Grazing Exclusion – An Effective Approach for Naturally Restoring Degraded Grasslands in Northern China Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-10 Li Wang; Martin Wiesmeier; Guiqin Zhao; Ruiyang Zhang; Fujiang Hou; Guodong Han; Kadambot H.M. Siddique; Yantai Gan
Nearly 90% of the 390 million hectares of grasslands in northern China were degraded. 'Grazing exclusion' has been implemented as a 'nature‐based' solution to rejuvenate degraded grasslands, but the effectiveness of the rejuvenation processes is uncertain. Here, we investigated the effects of grazing exclusion on aboveground plant community traits, soil physiochemical and biological properties, and the mechanisms responsible for enhanced grassland rejuvenation. A meta‐analysis across various studies was used to assess the effectiveness. On average, grazing exclusion improved vegetation coverage by 18.5 percentage points, and increased aboveground biomass by 1.13 t ha–1 and root biomass by 1.27 t ha–1, which represent an increase of 84%, 246%, and 31%, respectively, compared to continuous grazing practices. Grazing exclusion reduced soil bulk density by 13.7% and increased soil water content by 68.9%. Grasslands under grazing exclusion increased soil organic carbon (SOC) in the 0‐15 cm depth by 3.95 (±0.35 Std Err) t ha–1, and total soil N, available N, and total soil P in the 0‐40 cm depth by 2.39 (±0.14), 0.83 (±0.37), and 1.96 (±0.44) t ha–1, respectively, compared to continuous grazing; these values represent an increase of 31%, 25%, 23%, and 14%, respectively. Prolonging the duration (years) of grazing practices enlarged the differences in SOC and soil N content between grazing exclusion and continuous grazing. Grazing exclusion has improved plant community traits and enhanced soil physiochemical and biological properties of degraded grasslands, and thus this 'nature‐based' approach can serve as an effective means to rejuvenate degraded grasslands.
GRAZING PRACTICES AFFECT THE SOIL MICROBIAL COMMUNITY COMPOSITION IN A TIBETAN ALPINE MEADOW Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-06 Fei Yang; Kechang Niu; Courtney G. Collins; Xuebin Yan; Yangguang Ji; Ning Ling; Xianhui Zhou; Guozhen Du; Hui Guo; Shuijin Hu
Grazing is the primary land‐use activity on the Tibetan Plateau and can affect soil microbes and their function through aboveground vegetation removal, animal trampling and manure deposition. Two distinct grazing systems (i.e., winter grazing, WG, and annual grazing, AG) dominate on the Tibetan Plateau but their effects on soil microbes have rarely been assessed. Taking advantage of a 5‐yr field experiment that controlled timing and density of grazers via fence exclosures, we examined impacts of different grazing practices on the biomass, diversity and composition of the soil microbial community in a Tibetan alpine meadow. Based on high‐throughput sequencing, we found that grazing had no significant effects on bacterial and fungal α‐diversities, but altered their community compositions. While total soil carbon (TC) and nitrogen (TN), and C/N were related to both bacterial and fungal community compositions, plant shoot biomass only correlated with bacteria, and soil pH and moisture significantly influenced fungi under grazing. Also, grazing altered plant community composition but did not lead to corresponding changes in bacterial or fungal community composition. Moreover, grazing practices affected the relative abundance of specific bacterial and fungal taxa, reducing Actinobacteria but increasing Basidiomycete fungi in WG. Soil TC and TN were higher and the soil microbial community was more stable in AG than WG, likely due to more stable litter inputs in AG. Together, these results showed that AG was less disruptive to soil microbes, suggesting that AG may provide a viable option for sustainable utilization and conservation of these fragile alpine systems.
SOIL MICROBIAL COMMUNITY RESPONSES TO FORAGE GRASS CULTIVATION IN DEGRADED KARST SOILS, SOUTHWEST CHINA Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-06 Dejun Li; Jing Liu; Hao Chen; Liang Zheng; Kelin Wang
Variation of soil microbial community abundance and structure has great implications for soil fertility and nutrient cycling. A better understanding of soil microbial community dynamics under different land use types is undoubtedly needed in order to develop sustainable land use schemes. The current study aimed to assess how soil microbial community changed after replacement of maize‐soybean field by sugarcane, mulberry or forage grass field in a karst area of southwest China. Mature forests were included for comparison. Phospholipid fatty acid (PLFA) method was used to characterize soil microbial community abundance and structure. The abundances of total PLFAs and PLFAs of bacteria, fungi, actinomycetes and arbuscular mycorrhizal fungi were significantly increased in the forage grass field, but not in the sugarcane and mulberry fields relative to the maize‐soybean field. Total PLFAs' abundance in the forage grass field was increased by 81% compared to that in the maize‐soybean field, but was about 52% lower than that in the forest. The microbial community structure was not distinguished as much as the microbial abundance among the five land use types. Soil organic carbon (SOC) was identified as the primary factor affecting both soil microbial abundance and structure. Soil microbial community abundance was positively correlated with SOC, but the ratios of fungal to bacterial PLFAs and Gram‐positive to Gram‐negative bacterial PLFAs were negatively correlated with SOC. Our findings suggest that the replacement of the maize‐soybean rotation system by forage grass cultivation has the potential to improve soil fertility in the karst region, southwest China.
Why do smallholder farmers dis‐adopt conservation agriculture? Insights from Malawi Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-06 Edna Chinseu; Andrew Dougill; Lindsay Stringer
International donors and advisory bodies, governments and non‐governmental organisations (NGOs) are actively promoting conservation agriculture (CA) to improve agricultural productivity and resilience to climate change impacts. However, many smallholder farmers continue to dis‐adopt (abandon) the technology. Reasons for dis‐adoption are not well known. This article examines farmers' lived experiences and perceptions of CA to understand why smallholder farmers dis‐adopt CA in Malawi. Improving understanding of dis‐adoption of this seemingly appropriate intervention is important to achieve sustained adoption and for ensuring long‐lasting impacts of agricultural development project interventions. A mixed methods approach was used, involving household questionnaire survey and focus group discussions with smallholder farmers. Findings reveal that while drivers of dis‐adoption are multi‐dimensional and multi‐layered, they are rooted in shortfalls of CA promoters' implementation arrangements. While CA proponents market CA as a time‐saving, labour‐saving and yield‐improving technology, respondents report contrary experiences. Our findings show that farmers lack sufficient technical support and encounter technological, social, institutional and economic challenges. These, coupled with unfulfilled expectations, undermine ownership of CA projects and lead to dis‐adoption. This highlights a need to: (1) collaboratively design projects to better suit local needs and context with inclusive implementation arrangements; (2) emphasise climate resilience benefits of CA rather than economic benefits to manage farmers' expectations; (3) intensify multi‐disciplinary research that incorporates farmers' knowledge and experiences to develop suitable, flexible and low‐input CA packages; (4) provide regular hands‐on technical extension support to farmers.
Difference in wind erosion characteristics between loamy and sandy farmlands and the implications for soil dust emission potential Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 Rende Wang; Na Zhou; Qing Li; Chunping Chang; Zhongling Guo; Jifeng Li
Dust emission depends directly and indirectly on soil particle distribution, but little information is available that examines dust emission potential and its relationship with wind erosion for different soils. This study aimed to elucidate the difference in wind erosion characteristics between loamy farmland (LF) and sandy farmland (SF) and discuss the influence of this difference on dust emission potential. Field observations were conducted during 2012–2016 in Bashang district, north China. With increasing friction wind speed, the horizontal mass flux increased exponentially in LF, but obeyed the power function in SF. The horizontal mass flux was higher in SF than in LF, but the gap narrowed from 766 times at friction wind speed of 0.3 m s−1 to 50 times at 0.6 m s−1. The dry aggregate size distribution of sediment in LF was finer than in SF. Fine particle content (diameter < 0.05 mm) in windblown sediment was much higher in LF (31.39%) than in SF (5.92%), which was influenced by parent soils. With height increasing, the mass percentage of sediment decreased more rapidly in SF than in LF, with 86% and 66% of sediment clustering at height 0–20 cm, respectively. Since the horizontal mass flux and dust content in sediment both increased more quickly in LF than in SF with increasing friction wind speed, the dust emission potential was larger in LF than in SF under strong winds. The adverse effect of dust emission in loamy soils on atmospheric pollution should receive more attention in strong wind erosion events.
A farmer‐scientist investigation of soil carbon sequestration potential in a chronosequence establishment of perennial pastures Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 Natasha Pauli; Lynette K. Abbott; Rob Rex; Caroline Rex; Zakaria M. Solaiman
Australian agricultural soils have sustained a substantial loss of naturally low levels of soil organic carbon (SOC) through conversion of native vegetation to cropping. Recently, government programs focused on greenhouse gas emission abatement have provided incentives for conversion of cropland to permanent pastures. Concurrently, some farmers are pursuing innovative pasture grazing practices, such as the use of perennial pastures and rotational grazing. While gaining carbon credits is generally not the main driver for uptake of these practices, there is significant potential for soil carbon sequestration. We investigated soil organic carbon (SOC) stocks across a chronosequence of pastures sown with temperate, perennial grasses in south‐western Australia. This study presents a rare insight into short‐ and long‐term carbon dynamics in a novel agricultural system, which has potential for greater uptake within this region. SOC stocks for the upper 30 cm of soil ranged from 64.9 t ha‐1 in the longest established pasture (sown in 2003 and sampled in 2012 and 2014) to 25.2 t ha‐1 in a poorly performing pasture (sown in 2007). SOC stocks at two of the sampled sites showed large (19.7 to 22.0 t ha‐1) fluctuations over a two year period, which was likely linked to targeted management practices intended to increase pasture productivity. Taking into account farmers' needs for experimenting with management practices, and their detailed local knowledge of why certain locations responded in different ways, is paramount for developing longer‐term and larger‐scale approaches to improving soil health through novel agricultural practices.
Reducing Emissions from Deforestation and forest Degradation (REDD+) in Angola: insights from the Scarp Forest conservation hotspot Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 Ana Leite; Aimy Cáceres; Martim Melo; Michael S.L. Mills; Antonio T. Monteiro
The depletion of forests in conservation hotspots is a poorly known societal concern of the post‐conflict society of Angola. Rapid economic and population growth, fragile environmental regulation, enforcement and planning threat these invaluable forests and their biodiversity. By mitigating climate change through a sustainable management of forests, REDD+ could also favour the preservation of biodiversity. This study addresses the depletion of forests in Angolan conservation hotspots under a REDD+ perspective. In the Scarp forest, a centre of endemism, activity data and emission factors were assessed between 2001‐2014. Next, spatial factors associated to deforestation were identified using generalized linear modelling and it was provided a view on how REDD+ may support sustainable forest management in conservation hotspots. Activity data based on an error‐corrected estimate indicated a deforested area of 4856.3 ± 653.1 ha between 2001‐2014. Field mean aboveground carbon content amounted to 89.4 ± 126.4 tCha‐1. Among the most relevant factors associated to deforestation were elevation, density of bare land, north‐south exposure (aspect) and distance to trails. All negatively related to deforestation. Overall, the threatened Scarp forest conservation hotspot seems to have significant potential for reducing carbon emissions and beneficiate from REDD+. Yet, the considerable uncertainty in our estimates limited the discussions in the magnitude of forest depletion and carbon emissions. In view of performance‐based payments for development, additional field surveying seem necessary to boost the accuracies presented by new forest monitoring tools that can reduce technical difficulties and sustain the eligibility of Angola for international REDD+ funding sources.
Enantioselectivity in degradation and ecological risk of the chiral pesticide ethiprole Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 Qing Zhang; Wu Xiong; Beibei Gao; Zachary Cryder; Zhaoxian Zhang; Mingming Tian; Edmond Sanganyado; Haiyan Shi; Minghua Wang
Intensive agricultural activities have caused land degradation due to soil pollution, particularly by pesticides. However, the degradation, metabolism, and toxicity of chiral pesticides by soil microorganisms is often enantioselective. This study aimed to determine the effect of chirality on the degradation of the enantiomers of ethiprole in soil and their impact on soil microbial communities. (R)‐ethiprole underwent directional chiral conversion to the (S) enantiomer in a paddy soil microcosm, leading to elevated concentrations of (S)‐ethiprole. Initially, the bacterial operational taxonomic units (OTUs) significantly decreased after three days of incubation with rac‐ethiprole, (R)‐ethiprole and (S)‐ethiprole but gradually increased in the later stage. Principal coordinate analysis revealed that the bacterial community structure was enantioselectively affected by the ethiprole enantiomers. Within three days, both rac‐ethiprole and (R)‐ethiprole reshaped the original stochastic microbial community into a deterministic community (variable selection). Thus, we propose that the enantioselective behavior and ecotoxicology of chiral pesticides need to be considered, especially since there are numerous chiral pesticides currently in use within agricultural management. The comprehensive understanding of the ecological risk of chiral pesticide enantiomers is vital to the process of improving sustainable production and environmental health in agricultural ecosystems.
Analysis of drought and vulnerability in the North Darfur Region of Sudan Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 Alnail Mohmmed; Ke Zhang; Martin Kabenge; Saskia Keesstra; Artemi Cerdà; Makomere Reuben; Mohammed M.A. Elbashier; Twecan Dalson; Albashir A.S. Ali
North Darfur of Sudan is located on the edge of the Sahara desert and endures frequent droughts due to water shortages and high summer temperatures. Monitoring and understanding drought characteristics is essential for integrated drought risk mitigation and prevetion of land degradation. This study evaluates drought conditions in North Darfur by analyzing the spatiotemporal distribution of drought using three drought indices (Standardized Precipitation Index–SPI, Vegetation Condition Index–VCI, and Soil Moisture Content Index–SMCI) and their combined drought index (CDI) from 2004‐2013. Biophysical and socioeconomic indicators are further used to measure vulnerability to drought risk and its three components (exposure, sensitivity and adaptive capacity) through a comprehensive risk assessment framework. The results show that most of North Darfur has experienced prolonged droughts during the study period, especially from 2007‐2011. There is also a significant correlation between the monsoon season CDI and annual crop yield anomaly. The results confirm the validity of the CDI index, which provides a comprehensive description of the drought situation by combing four drought indices quantifying different drought aspects. The vulnerability results show that the majority of this region is highly exposed and sensitive to drought risks. In particular, the northern zone of the region is highly vulnerable, which is categorized by less crop diversity, higher land degradation, frequent droughts and high poverty levels. This study provides valuable information for coping with climate change‐induced drought risk in this region and demonstrates that there is still a large room for enhancing the adaptation capacity in this region.
SUNFLOWER (Helianthus annuus L.) HARVEST: TRACTOR AND GRAIN CHASER TRAFFIC EFFECTS ON SOIL COMPACTION AND CROP YIELDS Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 G.F. Botta; A. Tolón‐Becerra; F. Bienvenido; D. Rivero; D. Laureda; A. Ezquerra‐Canalejo; E. Contessotto
Previous studies have defined compaction as an important degradation process of agricultural soils. However, there is very little information (under field conditions) on the effects of tractor and grain chaser traffic during harvest operations on soil cropped for 15 years under no‐till cultivation methods. The aim of this study was to quantify the effects of 2 different total loads of tractor and grain chaser traffic on soil physical properties and sunflower (Helianthus annuus L.) yields. The treatments included a control plot with no tractor or grain chaser traffic (T1), a plot with tractor and grain chaser traffic with a total load of 275.8 kN (94.35 kN/km/ha) (T2) and a plot with tractor and grain chaser traffic with a load of 332.2 kN (123 kN/km/ha) (T3). Soil physical properties and sunflower yields were analysed over three growing seasons in the western part of the Pampa region, Argentina. In the topsoil (0 to 200 mm), the results showed that after one pass of T2 and T3, infiltration decreased significantly compared with that in T1; a similar trend was observed for total topsoil porosity. Cone index values in T3 were > 2.5 MPa and between 3.33 and 4.90 MPa in the subsoil (200 to 600 mm). Dry bulk density values in T3 were > 1.70 Mg m‐3 in the topsoil and in the subsoil. This study also demonstrated that as the wheel load and ground contact pressure increase, sunflower yields decrease and subsoil compaction increases, even in soils with a high bearing capacity.
Labile organic matter plays a more important role than the autotrophic bacterial community in regulating microbial CO2 fixation in an eroded watershed Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 Jieyu Jiang; Zhongwu Li; Haibing Xiao; Danyang Wang; Chun Liu; Xuqin Zhang; Hao Peng; Guangming Zeng
Understanding the effect of soil erosion on soil carbon (C) fixation is of great significance for evaluating the complicated connection between land degradation and C cycle. To investigate erosion‐induced changes in autotrophic bacterial community and microbial carbon dioxide (CO2) fixation, three typical eroding sites and three depositional sites were selected in the hilly red soil region of southern China with severe erosion. Positive responses of autotrophic microbial abundance to soil deposition were observed, while no obvious changes in microbial diversity were observed between eroding and depositional sites. The relative abundances of obligate autotrophic bacteria, such as Rhodopseudomonas and Pseudonocardia, were enhanced in the eroding sites. Deposition of organic matter‐rich soil was not conducive to the growth of obligate autotrophic bacteria. The average rate and amount of microbial CO2 fixation at the depositional sites (30.86 Mg C km‐2 yr‐1 and 0.05 g kg‐1) were higher than those at the eroding sites (18.04 Mg C km‐2 yr‐1 and 0.025 g kg‐1), which indicated that soil deposition significantly enhanced autotrophic microbial CO2 fixation. In addition, multiple stepwise linear regression showed that compared with microbial properties (abundance, diversity), dissolved organic carbon is a more important explanation factor for the change of microbial CO2 fixation rate (68.8%, P=0.001).
From active to stable: Paraglacial transition of Alpine lateral moraine slopes Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-01 Jana Eichel; Daniel Draebing; Nele Meyer
Many retreating Alpine valley glaciers leave large lateral moraines behind. Reworking of these landforms by geomorphic processes is one of the most important paraglacial processes in many Alpine environments. Although several studies investigated moraine reworking by gullying processes, it is not well known what happens when gullying ceases and why and when lateral moraine slopes become stable. This study improves the understanding of the paraglacial transition from active to stable Alpine lateral moraine slopes by assessing potential influencing factors, indicators for completed paraglacial adjustment, and its spatiotemporal patterns using a combination of geomorphic and ecologic data. A geomorphic and ecologic permanent plot survey and geomorphic mapping were carried out on three lateral moraine complexes in the Turtmann glacier foreland (Switzerland). Subsequently, permanent plot data were analysed using multivariate statistics. Our study suggests that ecosystem engineering by colonizing plant species, slope geomorphometry, and material properties are important factors influencing the paraglacial transition from active to stable slopes. Geomorphic processes are often absent once vertical vegetation layers and soil horizons develop, showing that mature vegetation and advanced soil development are valuable indicators for slope stability and completed paraglacial adjustment. In a conceptual model, we describe the paraglacial transition of Alpine lateral moraine slopes as a temporal sequence in which gullying (Stage I), solifluction (Stage II), and finally stabilization (Stage III) follow one after another. In space, paraglacial adjustment is heterogeneous, and resulting patterns can be explained by the identified influencing factors.
Increasing Wind Erosion Resistance of Aeolian Sandy Soil by Microbially Induced Calcium Carbonate Precipitation Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 Kanliang Tian; Yuyao Wu; Huili Zhang; Duo Li; Kangyi Nie; Shican Zhang
Wind erosion of aeolian sandy soil can cause serious land degradation and other environmental problems, and thus their prevention and control is very important. However, there has not been a very effective way to prevent this severe wind erosion until now, and traditional measures such as mechanical methods, chemical sand‐fixing methods and agronomic methods also have many disadvantages. The main objective of this study is to evaluate feasibility of microbially induced calcite precipitation (MICP), as a novel soil‐strengthening technique, to cement aeolian sandy soil and reduce wind erosion risk. For this purpose, aeolian sandy soil was cemented with Sporosarcina pasteurii through MICP technique, and the physical and mechanical properties and wind erosion resistance of cemented aeolian sandy soil were tested. The results show that wind erosion resistance of aeolian sandy soil can be effectively improved by spraying S. pasteurii solution and cementing solution (Equal concentration of urea and calcium chloride mixture) into it from the surface, and the cemented aeolian sandy soil had good wind erosion resistance. Finally, morphology of precipitated CaCO3 crystals was studied using scanning electron microscope (SEM), optical microscope and X‐ray diffraction (XRD). The calcium carbonate crystals produced in aeolian sandy soil were calcite, and the calcium carbonate crystals had polyhedral spherical or flower clusters crystal morphology. The results of this study demonstrate an effective way to use MICP technology to cement aeolian sandy soil and prevent wind erosion, and provide a new way for wind erosion prevention.
Effects of Soil Type, Temperature, Moisture, Application Dose, Fertilizer and Organic Amendments on Chemical and Bio‐degradation of Dimethyl Disulfide in Soil Land Degrad. Dev. (IF 7.27) Pub Date : 2018-10-02 Dawei Han; Dongdong Yan; Qiuxia Wang; Wensheng Fang; Xianli Wang; Jun Li; Dong Wang; Yuan Li; Canbin Ouyang; Aocheng Cao
Dimethyl disulfide (DMDS) is a potential alternative to Methyl bromide (MB) for soil fumigation to control soil borne disease. Laboratory experiments were conducted to investigate the effects of combinations of soil and environmental factors of DMDS degradation in soil. The results showed that soil pH and soil organic matter content are the major factors influencing the degradation of DMDS in soil. Generally, DMDS degradation was significantly slower in acidic and high organic content soils. The degradation rate increased with temperature and water content. However, when the temperature exceeded 35°C the degradation rate decreased, and when the soil water content was raised to 10% the change in DMDS degradation was not significant in Fangshan soil. The degradation of DMDS in soil depended on the initial application rate. Degradation slowed down as the fumigant application rate increased. DMDS degradation in soil was restrained by the addition of organic matter to soil, and the effect was enhanced by increased dosage. DMDS degradation in soil was also restrained by the use of chemical fertilizers except when amended with sodium dihydrogen phosphate and sodium thiosulfate. The impact of fumigant application rates and chemical fertilizers on bacterial communities in soil was determined by 16S rRNA amplicon sequencing. The results showed that bacterial diversity was affected by different treatments. Our study provides useful information for evaluate environmental safety assessments of DMDS in soil.
Prevalent sediment source shift after revegetation in the Loess Plateau of China: Implications from sediment fingerprinting in a small catchment Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-27 Wendi Wang; Nufang Fang; Zhihua Shi; Xixi Lu
As an important soil and water conversation endeavor, the 'Grain for Green' project launched by the Chinese Central Government almost doubled the vegetation cover on the Loess Plateau between 1999 and 2013. The corresponding vegetation restoration considerably diminished slope erosion throughout the Loess Plateau, although erosion in gullies remains poorly understood. In this paper, a composite fingerprinting approach was employed to assess the relative importance of the erosion of gully and slope soils within a typical dam‐controlled catchment of the Loess Plateau. A total of 23 couplets were identified based on the deposited layer thicknesses and extreme rainfall event records along the sediment profile. The results suggest that gullies contributed 71% to the overall sediment proportion, and those sediments had an increased tendency to accumulate during 2010–2016 under the 'Grain for Green' project. The sediment inputs from slope areas were predicted to be 29%. The eroded gullies materials mainly consisted of silt‐sized particles, which dominated the eroded sediment. Silt particles with sizes of 0.02–0.05 mm constituted the main particles in both deposit sediments and gully materials, whereas the slope areas mainly contained particle sizes of <0.01 mm. The check dam proved to be effective at trapping coarse silt with 27–42% of the total sediment content. This study presents reliable information on the importance of gullies as sediment source materials and verifies the applicability of tracing procedures for collecting information on sediment effluxes from both slopes and gullies.
Soil salinity prediction and mapping by machine learning regression in Central Mesopotamia, Iraq Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-27 Weicheng Wu; Claudio Zucca; Ahmad S. Muhaimeed; Waleed M. Al‐Shafie; Ayad M. Fadhil Al‐Quraishi; Vinay Nangia; Minqiang Zhu; Guangping Liu
Soil salinization affects crop production and food security. Mapping spatial distribution and severity of salinity is essential for agricultural management and development. This study was aimed to test the effectiveness of machine learning algorithms for soil salinity mapping taking the Mussaib area in Central Mesopotamia as an example. A combined dataset consisting of Landsat 5 Thematic Mapper (TM) and ALOS L‐band radar data acquired at the same time was used for fulfilling the task. Relevant biophysical indicators were derived from the TM images, and the soil component was retrieved by removing the vegetation contribution from the L‐band radar backscattering coefficients. Field‐measured salinity at the three corner plots of triangles were averaged to represent the salinity of these triangular areas. These averaged plots were converted into raster by either direct rasterization or buffering‐based rasterization into different cell size to create the training set (TS). One of the three triangle corners was randomly selected to constitute a validation set (VS). Using this TS, the support vector regression (SVR) and random forest regression (RFR) algorithms were then applied to the combined dataset for salinity prediction. Results revealed that RFR performed better than SVR with higher accuracy (93.4–94.2% vs. 85.2–89.4%) and less normalized root mean square error (NRMSE; 6.10–7.69% vs. 10.29–10.52%) when calibrated with both TS and VS. In comparison, prediction by multivariate linear regression (MLR) achieved in our previous study using the same datasets also showed less NRMSE than SVR. Hence, both RFR and MLR are recommended for soil salinity mapping.
Natural regeneration on land degraded by coal mining in a tropical climate: Lessons for ecological restoration from Indonesia Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-27 Vivi Novianti; Rob H. Marrs; Devi N. Choesin; Djoko T. Iskandar; Didik Suprayogo
There are few examples of primary succession from tropical conditions, especially on land degraded by human activity, for example, mine wastes. Such studies would assist in informing ecological restoration of these degraded sites. Here, a chronosequence approach was used to investigate early‐stage primary succession on overburden spoil wastes derived from coal mining in a tropical climate over a 64‐month period. Plant species composition and several microclimatic and spoil physicochemical and microbial properties were measured, and responses analysed using regression and multivariate (nonmetric multidimensional scaling) analyses. A clear primary successional process was described showing that vegetation cover and species richness generally increased through time with a successional pathway from graminoids and herbs as the early dominants, shrubs in midsuccession, and trees in the later‐successional stages. Two important differences were noted between our results and primary successions elsewhere; a lower abundance of nitrogen‐fixing species and the colonization by some late‐successional shrubs and trees at the start. During the succession, aggregate stability and organic matter (total C) increased—whereas electrical conductivity and some potentially toxic elements (Al, B) decreased. The constant high spoil moisture content appears to be an important determinant of vegetation development during primary succession and may be a factor in the rapid pace of succession detected here. The lessons for ecological restoration for coal overburden spoil under tropical conditions are that succession can proceed relatively rapidly.
Modelling environment and poverty factors for sustainable agriculture in the Three Gorges Reservoir Regions of China Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-25 Xin Cheng; Chuanmin Shuai; Jiali Liu; Jing Wang; Yue Liu; Wenjing Li; Jing Shuai
Modelling is a good tool for understanding the complex interactions of the agricultural systems; however, few studies have used a combined method of text mining and system dynamics to analyse and simulate the agricultural system. We propose the topic modelling–system dynamics modelling (TM‐SDM) analytical framework to extract, synthesise, and dynamically simulate the factors of land management, disaster, pollution, and poverty in the system. Specifically, 1,598 English language publications were collected to analyse the main concerns and conceptual structure of the sustainable development in the case study area based on topic modelling. Historical data from 2000 to 2014 are used for simulation and prediction based on system dynamics modelling, exploring and comparing different policy scenarios. The results show that policies about education and training, sewage treatment, infrastructure construction, and soil erosion control would help poverty reduction significantly. Sewage treatment policy reduces the incidence of human disease and sewage discharge significantly. Education and training policy has the greatest impact on the improvement of poverty reduction and yield of crops, and the environmental protection scenario has the best performance on maintaining the cultivated land. The balanced development scenario benefits both the poverty reduction and environmental protection concurrently. Focussing on a systems approach to improve the sustainability of agriculture, this paper could have a positive impact on the development and implementation of sustainable agricultural systems. The TM‐SDM analysis and modelling framework that we proposed has a generic nature, which could be applied to the further research and decision‐making on sustainable agriculture and other fields involving complex systems.
Paraglacial coasts responses to glacier retreat and associated shifts in river floodplains over decadal timescales (1966–2016), Kongsfjorden, Svalbard Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-25 Marine Bourriquen; Denis Mercier; Agnès Baltzer; Jérôme Fournier; Stéphane Costa; Erwan Roussel
The aim of this paper is to quantify and map the impact of the post‐Little Ice Age climate change on the coastal evolution on three glacier catchments in the Kongsfjorden area in Svalbard. Climatic data at Ny‐Ålesund indicate an increase in the annual mean air temperature of +4 °C from 1969 to 2016 and an increase in precipitation. On the northern coast of the Brøgger Peninsula, the Austre Lovénbreen, Midtre Lovénbreen, and Vestre Lovénbreen glaciers have experienced a net retreat in response to changing meteorological conditions. Because of this retreat, the glaciers have disclosed a large area of 7 km2 composed of terrigenous sediments. These sediments are transported by runoff and created coastal sandur deltas. Channel network behavior has been studied using the computation of the active floodplain width by photointerpretation, which decreased in average from 1966 to 2010. This demonstrated a contraction of the active braided belt and a decrease in the number of braided channels. A photointerpretation analysis combined with acquisition of dGPS data during field work shows a mean shoreline progradation of +0.16 m a−1 from 1966 to 2016, with a maximal advance of +82 m seaward. Since 1966, coastal progradation has decreased in time with higher mean values at the beginning of the studied period and an erosional trend from 1990. The sublittoral area was studied using analog side scan sonar in 2009, 2011, 2012, and 2017. Three prodeltas were identified and underwent a huge extension from 2009 to 2017. In the light of this knowledge, our main conclusion is that, by retreating, glaciers have an impact on the sediment availability and on the capacity of the fluvial system to effectively transport sediment to the shoreline. These two factors control the overall coastal evolution by regulating the sediment supply to the coastal area. The coastal zones that were fed with sediments by runoff have experienced a coastal progradation, and those that lost this supply have undergone a coastal recession. Due to the contraction of proglacial floodplains, current progradation concerns restricted coastal areas.
Spatial modelling of gully erosion using evidential belief function, logistic regression, and a new ensemble of evidential belief function–logistic regression algorithm Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-25 Alireza Arabameri; Biswajeet Pradhan; Khalil Rezaei; Mojtaba Yamani; Hamid Reza Pourghasemi; Luigi Lombardo
This study aims to assess gully erosion susceptibility and delineate gully erosion‐prone areas in Toroud Watershed, Semnan Province, Iran. Two different methods, namely, logistic regression (LR) and evidential belief function (EBF), were evaluated, and a new ensemble method was proposed using the combination of both methods. We initially created a gully erosion inventory map using different resources, including early reports, Google Earth images, and Global Positioning System‐aided field surveys. We subsequently split this information randomly and selected 70% (90) of the gullies for calibration and 30% (38) for validation. The method was constructed using a combination of morphometric and thematic predictors that include 16 conditioning parameters. We also assessed the following: (a) potential multicollinearity issues using tolerance and variance inflation factor indices and (b) covariate effects using LR coefficients and EBF class weights. Results show that land use/land cover, lithology, and distance to roads dominate the method with the greatest effect on gully occurrences. We produced three susceptibility maps and evaluated their predictive power through area under the curve (AUC) and seed cell area index analyses. AUC results revealed that the ensemble method presented a considerably higher performance (AUC = 0.909) than did the individual LR (0.802) and EBF (0.821) methods. Similarly, seed cell area index displayed a constant decrease from the ensemble to single methods. The resulted gully erosion‐susceptibility map could be used by decision makers and local managers for soil conservation, and for minimising damages in development activities including construction of infrastructures such as roads and the route of gas and electricity transmission lines.
Relationships between aboveground and belowground trait responses of a dominant plant species to alterations in watertable depth Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-25 Wei Mao; Andrew J. Felton; Yunhua Ma; Tonghui Zhang; Zhibin Sun; Xueyong Zhao; Melinda D. Smith
Drought impacts to plant growth can be indicated by changes in key functional traits. However, previous research has focused on aboveground trait responses to precipitation deficits, with less emphasis on concomitant belowground impacts and deep soil drought from groundwater depletion. We assessed changes in a suite of aboveground and belowground traits of a dominant plant, Phragmites communis, in response to an experimental gradient of underground watertable depth. Our study occurred within the northeastern Inner Mongolia region, where changes to groundwater tables have been pervasive in recent years. In general, the results indicate that both aboveground and belowground traits responded positively, yet eventually negatively, to continual increases in watertable depth, indicative of reduced access to soil moisture as watertable depths increased. Key adjustments include changes to the ratio of coarse roots to fine roots, and the distribution of fine roots within the soil profile. These changes in belowground traits had strong correlations with changes in aboveground traits. In particular, specific root length of fine roots was positively correlated with leaf area, height, and aboveground biomass, whereas root biomass was linked to leaf area, specific root length of coarse roots, and root length density. Fine and coarse root production also had positive and negative relationships with aboveground biomass, respectively, suggestive of biomass allocation tradeoffs. We suggest that biomass production responses of this species to changes in watertable depths may largely be driven by interactions between the distribution of fine and coarse roots in the soil profile and changes to leaf area.
Bt rice cultivation does not cause soil biological degradation in terms of C, N, and P cycles Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-25 Zhaolei Li; Bingxue Wang; Dashuan Tian; Jinsong Wang
Preventing soil biological degradation under the cultivation of Bacillus thuringiensis (Bt) crops is crucial to soil health. Despite studies concerning environmental risks of Bt crops, we surprisingly know little about whether soil biological degradation occurs under Bt crop cultivations. To fill this gap, we calculated the index of resistance (IR) and resilience (IR′) of 13 soil properties (the activities of enzymes, the rates of ecosystem processes, soil microbial biomass, and soil carbon and nutrients) using soil samples collected from an 8‐year Bt rice cultivation experiment, including three treatments, that is, continual cultivation of Bt rice (GM) and non‐Bt rice (non‐GM), and rotation between Bt and non‐Bt rice every 2 years (GM/non‐GM rotation). In GM and GM/non‐GM rotation, the IR of the activities of dehydrogenase, acid phosphatase, methane production rates was significantly greater than that in non‐GM. Further, the IR of denitrification, methane oxidation, microbial carbon, and microbial nitrogen was significantly lowered in GM, and the IR of microbial carbon in GM/non‐GM rotation was significantly decreased compared with that in non‐GM. However, the results of IR′ showed no significant differences in these soil properties between treatments, except for methane oxidation and urease in GM and microbial nitrogen in GM/non‐GM rotation. Taking into consideration of soil resistance and resilience, the most soil properties remained relatively stable. These findings suggest that the Bt rice cultivations have not significantly resulted in soil biological degradation.
Major forest increase on the Loess Plateau, China (2001–2016) Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-22 Yuhang Wang; Martin Brandt; Mingfei Zhao; Xiaowei Tong; Kaixiong Xing; Feng Xue; Muyi Kang; Lanhui Wang; Yuan Jiang; Rasmus Fensholt
The Loess Plateau in China is prone to widespread land degradation (soil erosion, deforestation and water loss) and therefore ecological restoration programmes aiming to re‐establish the ecosystem by revegetation have been implemented during recent decades. Consequently, a widespread increase in vegetation cover has been reported, but the state and dynamics of forests remain largely unknown. Here we used field and satellite data to produce annual forest probability scores at 250×250 m between 2001 and 2016. We classified the forest dynamics into three types: net gain, net loss and fluctuation. Assuming that an increasing probability score reflects forest growth, we categorised the annual forest areas into different growing stages indicating the transition between planting and mature forest. In total, the area of forest increase was 48,786 km2 and the percentage of forested areas of the region changed from 8.19% to 15.82% within 16 years. In areas of forest net gain, there was a clear transition from low to high probability forest areas, providing evidence that a general forest transition is occurring on the Loess Plateau. The method developed for continuous monitoring of forest probability scores offers a benchmarking for further decision‐making on ecological restoration of the region and for mapping of afforestation projects elsewhere. The findings on major forest increases demonstrate that land degradation is in fact reversible, with implications for many ecosystem services (e.g. carbon storage, provisioning of forest products).
Solute evidence for hydrological connectivity of geographically isolated wetlands Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-21 Josefin Thorslund; Matthew J. Cohen; James W. Jawitz; Georgia Destouni; Irena F. Creed; Mark C. Rains; Pascal Badiou; Jerker Jarsjö
Hydrological connectivity describes the water‐mediated transfer of mass, energy, and organisms between landscape elements and is the foundation for understanding how individual elements such as wetlands and streams integrate to support ecosystem services and nature‐based solutions in the landscape. Hydrological connectivity of geographically isolated wetlands (GIWs)—that is, wetlands without persistent surface water connections—is particularly poorly understood. To better understand GIW hydrological connectivity, we use a novel chloride mass‐balance approach to quantify the local runoff generation (defined as precipitation minus evapotranspiration, assuming negligible long‐term water storage) for 260 GIW subcatchments across North America. To evaluate hydrological connectivity, we compare the estimated local runoff from GIW subcatchments with the catchment‐average runoff. These comparisons provide three novel insights regarding the magnitude and variability of GIW hydrological connectivity. First, across 10 study regions, GIW subcatchments generate runoff at 120% of the mean catchment rate, implying they are well‐connected elements of the larger hydrologic landscape. Second, there is substantial heterogeneity in runoff generation among GIW subcatchments, which may enable support for a wide array of ecosystem functions and services. Finally, observed heterogeneity in runoff generation was largely uncorrelated to simple linear geographic predictors, indicating that GIW landscape position cannot reliably predict hydrological connectivity. In stark contrast to a priori legal assumptions that GIWs exhibit low or no hydrological connectivity, our results suggest that GIW subcatchments are active landscape features in runoff generation.
Increasing plant diversity and forb ratio during the re‐vegetation processes of trampling road enhance soil infiltration Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-20 Lei Su; Yongsheng Yang; Xiaoya Li; Dong Wang; Yanchun Liu; Yinzhan Liu; Zhongling Yang; Mingming Li
Livestock breeding and production activities provide the livelihood for herdsmen; nevertheless, the accompanying trampling has the potential to negatively influence the physiochemical environment of soil. The policy of returning grazing land to grassland has greatly influenced both biodiversity and ecosystem services. However, the regulatory mechanism behind changes of soil infiltration capacity remains largely unexplored. Here, three sites (a 1‐year (R1) and a 3‐year (R3) restoration grassland, which were both trampling‐induced roads, and an untrampled grassland) were sampled on the Mongolian Plateau of China. The infiltration parameters, soil properties, root channels area, and plant community were determined for each site. The results showed that the species richness, above‐ground biomass, and the proportion of forbs in the R3 grassland were 2.7, 5.5, and 30.8 times higher than those of the R1 grassland, respectively. The soil infiltration rates and cumulative infiltration increased with species richness, above‐ground biomass and the proportion of forbs. Importantly, all values of species richness, above‐ground biomass, and forbs ratio increased with progressing restoration. Overall, our results indicate that grasses recovered first after trampling ceased. Along with the improvement of soil surface conditions, forb species with greater root channels area increased gradually, which increased the soil infiltration rate. Our research highlights the changes in plant community of trampled roads and the regulatory influence of re‐vegetation on the soil infiltration ability.
Negative priming effect of three kinds of biochar on the mineralization of native soil organic carbon Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-19 Yuxue Liu; Ying Chen; Yuying Wang; Haohao Lu; Lili He; Shengmao Yang
This study was conducted to improve our understanding of the effect of biochar on the degradation of original soil organic carbon (SOC) and the resulting net C sequestration. A 120‐day incubation experiment was conducted to detect the CO2 evolution from soil amended with three kinds of biochar, namely, rice husk biochar (RH), pecan shell biochar (PS), and bamboo biochar (BB), at biochar to soil ratios of 0% (as control), 1%, 2%, and 5%, as well as 100% pure biochar, and to evaluate their priming effect on SOC mineralization. Results showed that the cumulative mineralized amounts of SOC decreased by 7.95–10.7% with 5% RH, PS, and BB treatments, whereas there were no significant differences in 1% or 2% biochar treatments after 120 days of incubation compared with the control. Biochar had a suppressing influence on native SOC decomposition, and the effect increased with the amount of applied biochar increasing. The negative priming effect of biochar on the mineralization of SOC was mainly observed after 15 days of incubation and increased with incubation time. The negative effects of BB and RH were significantly stronger than that of PS at the 5% application ratio. This was mainly due to the less pores and smaller specific surface area of PS, which resulted in the weaker encapsulation and adsorption protection effect of PS than RH and BB, and inhibited the degradation of the adsorbed native SOC. Therefore, BB and RH have great potential for C sequestration and mitigation, especially in soils with low organic C.
'Decoupling' land productivity and greenhouse gas footprints: a review Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-19 Li Wang; Herb Cutforth; Rattan Lal; Qiang Chai; Cai Zhao; Yantai Gan; Kadambot H.M. Siddique
A major challenge of our time is to produce sufficient nutrient‐rich food for the ever‐growing human population with limited land resources. There is a huge gap between current yields and genetic potential in many crops, which can be narrowed by enhancing land productivity. High‐input cropping increases crop yields, but heavy fertilizer and pesticide use can lead to land degradation, increase greenhouse gas footprint, and carry significant risks for eutrophication. What efforts can be taken to 'decouple' land productivity and the environmental footprint? Can land productivity increase while concurrently minimizing the environmental footprint? Here, we show that an integrated systems approach can minimize the tradeoff to achieve an effective 'decoupling' outcome. Some key components that can be integrated into a system include: (i) intensifying crop rotations to enhance carbon conversion from atmospheric CO2 to plant biomass; (ii) diversifying cropping systems to enhance residual soil water and nutrient use and increase systems resilience; (iii) including N2‐fixing pulse crops in rotations to reduce synthetic fertilizer use; (iv) improving fertilizer‐N use efficiency to lower N2O emissions; and (v) sequestering more carbon to the soil to potentially offset CO2 equivalent emissions from cropping inputs. Integration of these proven cropping practices into a system creates a powerful synergy among individual components, thereby improving land productivity and systems resilience for long‐term sustainability. Relevant economic and agro‐environmental policies are needed to reinforce the adoption of a systems approach at the local farm level.
CONVERSION FROM TEMPERATE SECONDARY FORESTS INTO PLANTATIONS (LARIX SPP.): IMPACT ON BELOWGROUND CARBON AND NUTRIENT POOLS IN NORTHEASTERN CHINA Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-17 Kai Yang; Jiaojun Zhu; Shuang Xu; Xiao Zheng
Conversions from natural broadleaved forests into conifer plantations have been increasing over the past half century worldwide, especially in China. However, the impacts of plantation afforestation on macro‐ and micronutrient pools combined with litter, soil and roots have not been well quantified. We compared macro‐ and micronutrients pools in litter, fine roots, and at 0‐80 cm soil depths of paired secondary forests and larch plantations. The results showed that compared with natural forest soils, plantation soils exhibited lower concentrations and stocks of C, as well as lower fine root biomass at 0‐10 cm depth. In contrast, the K, Fe, Mn, and Cu pools in the larch plantations were greater by 27‐44% for the 20‐40 cm depth. Furthermore, soil N, P, Ca, Mg pools and stoichiometry of C/N/P in litter, soil, and fine roots did not differ significantly in the larch plantation relative to secondary forests. These results suggest that the conversion from secondary forests to larch plantations only decreases soil C pools but does not lead to reductions in other nutrient pools. Our results also showed there was less C and nutrients in roots and more C and nutrients accumulated in litter of larch plantations compared with secondary forests. In conclusion, converting secondary forests to larch plantations changed the vertical distribution of C and nutrient pools in litter, soil and root. The results suggest that C and nutrient pools in soils should be considered at levels below 40 cm in depth when evaluating C and nutrient change with afforestation.
DOES GRAZING CAUSE LAND DEGRADATION? EVIDENCE FROM THE SANDY FERLO IN NORTHERN SENEGAL Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-17 Kjeld Rasmussen; Martin Brandt; Xiaoye Tong; Pierre Hiernaux; Abdoul Aziz Diouf; Mohamed Habibou Assouma; Compton J. Tucker; Rasmus Fensholt
It has been widely asserted that a high grazing pressure has led to a reduction in vegetation production at decadal time scales, implying land degradation, in African drylands, and in the Sahel in particular. We test this hypothesis by analyzing spatio‐temporal patterns of vegetation production in the north‐western Ferlo in Senegal. Normalized Difference Vegetation Index (NDVI) patterns, here used to represent vegetation production, were determined on the basis of Earth observation MODIS and PROBA‐V data. Furthermore, woody cover was assessed by very high spatial resolution (VHR) imagery. Since livestock is concentrated around deep wells in the dry season for watering, while for management they concentrate daily around pastoral family settlements or camps all year round, we studied the dependence of NDVI on distance from deep wells and camps. Locations of wells and camps were determined by visual inspection of VHR images. We found that 'inverse grazing gradients', defined as decreasing NDVI/production with increasing distance, dominated both around wells and camps. Further we found neither decrease nor increase in woody cover with distance to wells. Both positive and negative trends in wet season NDVI over the period 2000‐2016 were identified within the study area, yet temporal trends were predominantly positive in proximity to deep wells. Around pastoral camps, positive NDVI trends were generally elevated relative to the regional average. The results question the validity of claims that high grazing pressure causes land degradation at the landscape scale, yet they show that grazing does lead to substantial spatial redistribution of vegetation production
Controls of soil and aggregate‐associated organic carbon variations following natural vegetation restoration on the Loess Plateau in China Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-17 Lei Deng; Dong‐Gill Kim; Changhui Peng; Zhouping Shangguan
Natural vegetation restoration can enhance soil organic carbon (SOC) sequestration, but the mechanisms and control factors underlying SOC sequestration are still unknown. The objectives of the study are to quantify the temporal variation of soil and aggregate‐associated organic carbon (OC) and identify factors controlling the variation following natural vegetation restoration after farmland abandonment. We collected soils from sites having 5, 30, 60, 100, and 160 years of a natural vegetation restoration chronosequence after farmland abandonment in the Loess Plateau, China. The results showed that natural vegetation restoration increased macroaggregates (0.25–2 mm; 46.6% to 73.9%), SOC (2.27 to 9.81 g kg−1), and aggregate OC (7.33 to 36.98 g kg−1) in the top 20‐cm soil compared with abandoned farmland, and the increases mainly occurred in the early stage (<60 years). The increase of SOC was contributed by OC accumulated in macroaggregates (0.25–2 mm) rather than microaggregates (≤0.25 mm). Moreover, SOC sequestration in the topsoil (0–10 cm) was mainly determined by fine root biomass (FR), labile organic carbon (LOC), and microbial biomass carbon (MBC). And in the subsoil (10–20 cm), SOC sequestration was mainly determined by the proportion of macroaggregates. The results suggest that natural vegetation restoration increased SOC and aggregate OC, and FR, MBC, LOC, and the physical protection of aggregates played important roles in regulating SOC and aggregate OC.
The effects of different land uses on soil hydraulic properties in the Loess Plateau, Northern China Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-17 Shahmir Ali Kalhoro; Xuexuan Xu; Kang Ding; Wenyuan Chen; Abdul Ghaffar Shar; Muhammad Rashid
Some agriculture practices are unsuitable in the northern hilly region of the Chinese Loess Plateau and have resulted in the degradation of the native vegetation ecosystems and unfavorable soil hydraulic properties, which cause serious soil losses. The objective of this study was to ascertain the influence of land use changes on soil infiltration rate and other related soil properties in this region. A total of 90 infiltration tests were run on six different land uses (natural grassland, apple orchard, abandoned apple orchard, farmland wheat, farmland maize, and scrub grassland). For studying the infiltration rate, a triplicate of infiltration tests had been taken using a disc permeameter with different pressure heads. Infiltration rate was high in abandoned apple orchard (10 mm min−1) whereas very low in apple orchard (0.6 mm min−1). The statistical analysis showed that the main soil properties were affected by changes of land use types or vegetation cover. Compared with that in the natural grassland and abandoned apple orchard sites, a notable reduction of soil root biomass, infiltration, and bulk density in apple orchard was recorded. The root image analysis showed that the natural grassland and abandoned apple orchard have strong root systems, that is, root length density 6.97 ± 0.344 cm cm−3, root surface area 1.56 ± 0.24 cm2 cm−3, and average root diameter 0.814 ± 0.24 mm, in comparison with other sites. The limited root length density, root surface area, and average diameter were recorded in apple orchard 0.51 ± 0.03 cm cm−3, 0.49 ± 0.12 cm2 cm−3, and 1.88 ± 0.24 mm. Conclusively, our study suggests that converting farmland apple orchard into grassland or scrubland may change soil hydraulic properties, which may help to reduce soil losses in the Loess Plateau.
Quantifying the economic impact of soil constraints on Australian agriculture: A case‐study of wheat Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-14 Thomas G. Orton; Thilak Mallawaarachchi; Matthew J. Pringle; Neal W. Menzies; Ram C. Dalal; Peter M. Kopittke; Ross Searle; Zvi Hochman; Yash P. Dang
Soil sodicity, acidity, and salinity are important soil constraints to wheat production in many cropping regions across Australia, and the Australian agricultural industry needs accurate information on their economic impacts to guide investment decisions on remediation and minimize productivity losses. We present a modelling framework that maps the effects of soil constraints on wheat yield, quantifying forfeited wheat yields due to specific soil constraints at a broad spatial scale and assessing the economic benefit of managing these constraints. Of the three soil constraints considered (sodicity, acidity, and salinity), sodicity caused the largest magnitude of yield gaps across most of the wheat‐cropping areas of Australia, with an average yield gap of 0.13 t ha−1yr−1. Yield gaps due to acidity were more concentrated spatially in the high‐rainfall regions of Western Australia, Victoria, and New South Wales, and averaged 0.04 t ha−1yr−1 across the wheat‐cropping areas of Australia, whereas the yield gap due to salinity was estimated to be 0.02 t ha−1yr−1. The lost opportunity associated with soil sodicity for wheat production was estimated to be worth A$1,300 million per annum, for soil acidity, A$400 million per annum, and for salinity, A$200 million per annum. The results of this work should prove useful to guide national investment decisions on the allocation of resources and to target areas where more detailed information would be required in order to reduce the yield gap associated with soil constraints on wheat yields in Australia.
Successes and failures reported in a multiscaled framework constituted by biophilic projects engineered toward environmental recovery Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-14 Alexandre Marco da Silva; Karen Regina Castelli; Ludmila Araujo Bortoleto; Pablo Bettio Mendes; Kristiane Ramos Primo; Rosiane Argenton e Silva
The process of landscapes' fragmentation has led to having two realistic complementary options: (a) developing techniques and approaches for conserving the healthy remaining forest fragments and (b) restoring degraded places. The second option can be conducted by projects that focus on restoring or rehabilitating the degraded environment. In this research, a framework was tested through a set of pilot‐scale projects in a highly urbanized Municipality of the southeastern Brazilian region (Sorocaba, São Paulo State). Four projects were carried out in order to test the efficacy of techniques devoted to solving different problems of environmental degradation (isolation of fragments, loss of biodiversity, soil erosion, and bioinvasion) in different environments (terrestrial [forested and nonforested] and aquatic [rivers]) through the acceleration and orientation of the process of restoration. Here, we show the main findings, discuss the potential and weaknesses found in each project, and offer some recommendations for future potential users. The projects are constituted of techniques and approaches that are all cheap, naturally based, and easy to be implemented and with a high probability of social comprehension and acceptance. In each project, we got interesting outcomes, considering all successes and limitations (for example, a high reappearance of vegetation in streams and strong control of soil erosion). This model embraces the main aspects of environmental recovering through a feasible, realistic, and socioecological approach, and it brings high potential to be used by other researchers and also for technicians and decision makers who search for feasible and realistic projects.
Increased ammonia emissions from synthetic fertilizers and land degradation associated with reduction in arable land area in China Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-14 Wei Ouyang; Zhongmin Lian; Xin Hao; Xiang Gu; Fanghua Hao; Chunye Lin; Feng Zhou
For a long time, there has been an excessive use of synthetic fertilizers applied to the decreasing area of arable land to help meet the increasing food demand, which causes NH3 volatilization and land degradation. In this study, we conducted a nationwide inventory of NH3 emissions from synthetic nitrogen fertilizers in China from 1991 to 2013. We estimated that NH3 emissions increased from 3.20 to 5.21 Tg NH3 yr−1. Because of the different agricultural practices, fertilizer use schedules, and ambient temperature, monthly NH3 emissions have varied greatly. NH3 emissions during the spring and summer accounted for approximately 83% of the national total in 1991, 1998, 2005, and 2013. Similarly, the spatial distribution of NH3 emissions exhibited large heterogeneity in 1991, 1998, 2005, and 2013. High emissions occurred in the eastern and central provinces and eastern Sichuan. Based on NH3 emissions in Chinese counties for 1991–1998, 1999–2005, and 2006–2013, the Pearson correlation coefficient was applied to compute the changing trends in NH3 emissions and fertilization rates. The results showed that the NH3 emissions from the major grain‐producing regions increased, whereas those from the eastern provinces, which experienced rapid economic development, decreased. In addition, fertilizer amount, arable land area, grain yield, and primary industry have been shown to be largely correlated to NH3 emissions based on principal component analysis. Therefore, the results of this study have significant implications for improving the efficient use of fertilizers and preventing soil and/or land degradation.
Assessment of periglacial response to increased runoff: An Arctic hydrosystem bears witness Land Degrad. Dev. (IF 7.27) Pub Date : 2018-07-16 Eric Bernard; Jean Michel Friedt; Sophie Schiavone; Florian Tolle; Madeleine Griselin
In the general context of global warming, the cryosphere appears as an environment that exhibits a strong sensitivity to climate variations. Overall, glacier systems are now known to be reliable indicators of climate trends. Although glacier dynamics are subject to international monitoring networks, periglacial environments are much less observed. However, these newly deglaciated areas get wider since glaciers are retreating, and their dynamics become increasingly significant. The observed increase in water fluxes, temperature and precipitation, permafrost melting, and reduced cold periods induce a combined control on modifications of the glacier and periglacial dynamics. Such consequences are also visible on the landscape, hinting at an adaptation of the environment to the climatic forcing.
Long‐term afforestation significantly improves the fertility of abandoned farmland along a soil clay gradient on the Chinese Loess Plateau Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-11 Yan Zhang; Liyun Wei; Xiaorong Wei; Xuetong Liu; Mingan Shao
In China, almost half of the total land area is degraded, mainly due to the unreasonable use of land for agricultural production. During the past half‐century, afforestation has become a popular management option to remedy degraded soils. In this paper, we studied the long‐term effects of afforestation on the major properties of soils with different textures. We measured the changes in soil physical, chemical, and fertility properties after 10, 20, and 30 years of afforestation with black locust (Robinia pseudoacacia) on abandoned farmland at five sites on the Loess Plateau, China, which is characterized by a temperate monsoon climate. The soil clay contents varied significantly among sites. The objectives were to understand how long‐term afforestation affects soil properties and whether such effects depend on the soil texture. Averaged across the five sites and the depths of 0–10 and 10–20 cm, afforestation resulted in significant increases in the proportion of macroaggregates (+22.5%), saturated hydraulic conductivity (+185.4%), organic matter content (+110.5%), and total nitrogen content (+110.5%) but significant decreases in the proportion of microaggregates (−21.9%) and bulk density (−10.8%). The silt + clay fraction, soil pH, and nitrate content were minimally affected by afforestation. The effects of afforestation were greater at 0–10 cm than at 10–20 cm, but they varied between sites. Furthermore, most soil metrics linearly responded to the time of afforestation, and such responses were dependent on the soil clay content. Our results suggest that long‐term afforestation improves soil fertility better in soils with a clay content of approximately 20%.
Management initiatives in support of the soil quality of urban allotment gardens: Examples from Nantes (France) Land Degrad. Dev. (IF 7.27) Pub Date : 2018-08-09 Cécile Le Guern; Liliane Jean‐Soro; Béatrice Béchet; Thierry Lebeau; Dorine Bouquet
Urban allotment gardens (UAGs) are important for the provision of foodstuffs, social cohesion, residents' well‐being, and prevention of the formation of local heat islands during summer. The soils of these gardens however may be adversely affected by pollution threats and thus create health risks. In such cases, appropriate management becomes necessary. For several gardens exhibiting soil contamination (e.g., Pb at 100–400 mg kg−1) in the city of Nantes, local actors collaborated, including scientists, the municipality's Parks and Open Space Department, elected officials, sanitary administration, and each site's gardeners' association. The soil characterization step was performed along with a sanitary risk evaluation and discussion of management options, based on both the pollution characteristics and local context. The most frequent option consisted of replacing the polluted soils with clean soils. Managing the excavated polluted soils on‐site (e.g., for ornamental purposes) limited the economic and environmental impacts associated with this solution. Alternative solutions, including a combined system of nonaccumulative cropping vegetables at the time of phytoextraction, were also employed to maintain gardening uses. In some cases, land use (gardening) was changed into, for example, an orchard, open space, or ornamental space. A combination of solutions was introduced in several gardens. The various options available for managing polluted soils, as implemented in Nantes' UAGs and based mainly on nature‐based solution, can be applied more generally in order to improve soil quality. In addition to enhancing the quality of both residents' lives and biodiversity, several solutions allow preserving or even restoring soil functions.
Cropland abandonment enhances soil inorganic nitrogen retention and carbon stock in China: A meta‐analysis Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-11 Dashuan Tian; Yangzhou Xiang; Bingxue Wang; Meiling Li; Yanshu Liu; Jinsong Wang; Zhaolei Li; Shuli Niu
Transforming cropland into a semi‐natural ecosystem is an effective approach to increase soil organic carbon (SOC) and nitrogen sequestration. However, we know little about large‐scale response patterns of SOC, soil inorganic nitrogen (SIN), and their interactions over long time of ecosystem restoration. Here, we conducted a meta‐analysis to examine changes in SOC, SIN, and their relationship along 50 year's ecosystem development from cropland transformation in China's 'Grain for Green' Programme. Our results showed that SOC and SIN were consistently enhanced by 57% and 35% with transformation, respectively. Similar with SOC, SIN had higher response magnitudes when cropland was restored to forests (47%) than to shrublands (36%) and grasslands (24%). Both SOC and SIN response ratios showed a quadratic relationship with precipitation. Moreover, we found a strong linear relationship (R2 = 0.36) between SOC and SIN response ratio, with the slope indicating a 0.43% increase in SIN per 1% of increasing SOC. This SIN retention capacity (the slope) significantly increased with restoration time but reduced with precipitation, temperature, and initial SOC. Restored forest had a lower SIN retention capacity than had shrubland and grassland. Overall, this study represents the first to regionally uncover SIN retention mechanism with increasing SOC during ecosystem development. It suggests that ecosystem restoration will contribute more to relieving serious environmental problems (i.e., N leaching and N2O emission) by enhancing SIN retention in China's Grain for Green Programme.
Incision and aggradation in proglacial rivers: Post‐Little Ice Age long‐profile adjustments of Southern Iceland outwash plains Land Degrad. Dev. (IF 7.27) Pub Date : 2018-08-12 Erwan Roussel; Philip M. Marren; Etienne Cossart; Jean‐Pierre Toumazet; Marie Chenet; Delphine Grancher; Vincent Jomelli
The retreat of glaciers in response to climate warming leads to substantial changes in meltwater and sediment yield. Glacial shrinkage also induces the emergence and growth of proglacial margin landforms, which strongly affect water and sedimentary transfers from the glacier to the outwash plains. On a decadal timescale, field observations show that outwash plains of retreating glaciers typically exhibit proximal incision, which decreases in magnitude downstream and stops at an inflection point where aggradation begins. Nevertheless, there is a lack of knowledge about the rates and magnitude of this fluvial adjustment and the effects of the proglacial margin configuration on the temperance or the aggravation of this fluvial adjustment to glacier retreat. This paper investigates the proglacial rivers of 14 retreating glaciers in south‐east Iceland over a post‐Little Ice Age timescale, combining fluvial deposits mapping, lichenometric dating, and long‐profile measurements of proglacial fluvial terraces. Our results demonstrate that (a) proximal incision, associated with distal aggradation and downstream migration of the inflection point, is the dominant pattern of proglacial river response to post‐Little Ice Age glacier retreat in Iceland; (b) estimated mean rates of downstream migration of the inflection point range between 5 and 46 m·a−1; and (c) the downstream migration rate of the inflection point is positively correlated with the proportion of proglacial lakes within the glacier foreland. These findings suggest that proglacial margins dominated by proglacial lakes intensify the rates of proximal incision and inflection point migration.
Land degradation monitoring using terrestrial ecosystem carbon sinks/sources and their response to climate change in China Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-05 Xiaowei Chuai; Xinxian Qi; Xiuying Zhang; Jiasheng Li; Ye Yuan; Xiaomin Guo; Xianjin Huang; Soojin Park; Rongqin Zhao; Xianli Xie; Jianxi Feng; Shuangshuang Tang; Tianhui Zuo; Junyu Lu; Jianbao Li; Xiao Lv
Global warming, which is mainly caused by greenhouse gases, can greatly aggravate land degradation; therefore, the examination of the NEP (net ecosystem productivity) and the analysis of its response to climate change are very critical for understanding carbon cycling. Based on Moderate Resolution Imaging Spectroradiometer data, meteorological data, and soil organic carbon data, this study examined the NEP from 2000 to 2013 and investigated how ongoing climate change affects the NEP. The study results indicate that the terrestrial ecosystems in China generally act as net carbon sinks with increasing NEP values. The western inland region and part of northeast China mainly act as carbon sources, with the NEP exhibiting an increasing trend, whereas the other regions mainly act as carbon sinks, with the NEP showing a decreasing trend across large areas of southern China, where the most obvious land degradation occurs. Homogeneity and heterogeneity co‐occur. The general pattern is that ecosystems with high biomass usually have a high NEP value, acting as high carbon sinks in relatively wet and warm environments, but have a low value and even act as carbon sources in dry and cold environments. Both moderate precipitation and temperature are essential in increasing the NEP, whereas lower precipitation and temperatures might have negative effects. Heterogeneity also widely breaks up the general pattern. Temporally, more NEP grids were positively correlated with changes in temperature and showed stronger correlation coefficients with temperature than with precipitation, but the grids showing a significant correlation with these factors accounted for only a small proportion of the total for both precipitation and temperature.
Agroforestry systems: Meta‐analysis of soil carbon stocks, sequestration processes, and future potentials Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-04 Lingling Shi; Wenting Feng; Jianchu Xu; Yakov Kuzyakov
Agroforestry (AF) has the potential to restore degraded lands, provide a broader range of ecosystem goods and services such as carbon (C) sequestration and high biodiversity, and increase soil fertility and ecosystem stability through additional C input from trees, erosion prevention, and microclimate improvement. Advantages and processes for global C sequestration in AF are unknown. We used a meta‐analysis of 427 soil C stock data pairs grouped into four main AF systems—alley cropping, windbreaks, silvopastures, and homegardens—and evaluated changes in AF and adjacent control cropland or pasture. Mean soil C stocks in AF (1‐m depth) were 126 Mg C·ha−1, which is 19% more than that in cropland or pasture. The highest C stocks in soil were in subtropical homegardens, AF with younger trees, and topsoil (0–20 cm). Increased soil C stocks in AF were lower than aboveground C stocks in most AF systems, except alley cropping. Homegardens stored the highest C in both aboveground and belowground, especially in the subsoil (20–100 cm). Advantages of AF ecosystem services focusing on mechanisms of belowground C sequestration were analyzed. AF could store 5.3 × 109 Mg additional C in soil on 944 Mha globally, with most in the tropics and subtropics. AF systems could greatly contribute to global soil C sequestration if used in larger areas. Future investigations of AF should include (a) mechanistic‐ and process‐based studies (instead of common monitoring and inventories), (b) models linking forest and crop growth with soil water and C and nutrient cycling, and (c) accurate assessments of the AF area worldwide based on the remote sensing approaches.
Land degradation and restoration in the arid and semiarid zones of China: Quantified evidence and implications from satellites Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-03 Dehua Mao; Zongming Wang; Bingfang Wu; Yuan Zeng; Ling Luo; Bai Zhang
Quantified information on land degradation and restoration is needed to support policies for sustainable ecosystem management and socioeconomic development. The arid and semiarid zones of China (ASZC) have experienced significant land degradation, and in response to such degradation, multiple ecological projects were implemented. In this study, remote sensing was used to identify degrading areas and where the degraded areas have been restored from 1990 in this ecologically sensitive region. Specifically, we integrated datasets from the ChinaCover and Moderate Resolution Imaging Spectroradiometer products to characterize changes in vegetation, ecosystems, and environmental conditions. The results confirmed that deforestation, desertification, grassland degradation, wetland loss, and the encroachment upon farmlands were notable in the ASZC. Agricultural activity has cultivated extensive areas of natural ecosystems (46,474 km2). The expansion of built‐up lands in terms of national policies has destroyed large areas of natural (5,487 km2) and agricultural (4,138 km2) ecosystems and continually results in negative impacts on ecological conservation. China has restored some lands (7,732 km2 from farmlands and 24,904 km2 from barren lands) and improved ecosystems, as characterized by increases in the normalized different vegetation index, leaf area index, net primary productivity, and gross primary productivity values in the ASZC, especially after the implementation of many ecological projects. However, it is also necessary to document the conclusions and lessons from these projects to guide future ecological policies and projects in the context of the substantial new challenges facing the protection of this ecologically sensitive environment.
Estimating the very fine sand fraction for calculating the soil erodibility K‐factor Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-03 Eva Corral‐Pazos‐de‐Provens; Juan M. Domingo‐Santos; Ígor Rapp‐Arrarás
The K‐factor of the universal soil loss equation is a core component in many erosion models, as a measure of soil erodibility. It can be estimated by a nomograph, where the summed fractions of silt and very fine sand (VFS) are basic inputs. Frequently, only the three broad particle‐size classes of sand, silt, and clay are measured in laboratories; thus, the VFS fraction must be estimated. Three models are currently available for this estimation, namely, (a) the Revised Universal Soil Loss Equation formula, (b) the European Soil Data Centre method, and (c) the Shirazi–Boersma theory, all three use just the sand fraction as explanatory variable. Nevertheless, their accuracy has never been assessed, and this is the main purpose of this study. The data used to test the VFS estimation methods were drawn from the National Cooperative Soil Survey Soil Characterization Database, incorporating data from more than 300,000 soil horizon samples. The test results show a poor performance of the models, all of which were found to be unsuitable for 31.1% of the textural triangle, accounting for 32.3% of the soil samples. Moreover, it is demonstrated that any conceivable model based solely on the broad particle‐size classes would suffer from a high degree of uncertainty. Consequently, the number of explanatory variables should be increased in order to improve the performance of models. An alternative prediction chart is provided for the first approximation of K‐factor, based on the textural triangle.
Links between Nordic and Arctic hydroclimate and vegetation changes: Contribution to possible landscape‐scale nature‐based solutions Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-02 Elisabeth Groß; Johanna Mård; Zahra Kalantari; Arvid Bring
In Nordic and Arctic regions, the rapidly warming climate sustains hydroclimatic and vegetation changes in the landscape. There is evidence for an increase in vegetation density in some regions, a trend that is expected as a response to increasing temperature and precipitation. If the hydroclimatic changes are linked to vegetation response, it could be viewed as a landscape‐scale nature‐based solution (NBS) that could moderate the runoff response, as denser vegetation should lead to increased evapotranspiration and lower runoff. In this paper, we investigate and compare hydroclimatic changes over a set of basins in the Nordic region and northwest America and compare with changes in vegetation density, analyzed using the normalized difference vegetation index (NDVI) for three time periods: 1973–1978, 1993–1998, and 2013–2016.
Forms and vertical distributions of soil phosphorus in newly formed coastal wetlands in the Yellow River Delta estuary Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-02 Fanzhu Qu; Hongbo Shao; Ling Meng; Junbao Yu; Jiangbao Xia; Jingkuan Sun; Yunzhao Li
To study the forms and vertical distributions of soil phosphorus (P) in a newly formed coastal wetland in the Yellow River Delta estuary, China, two transects from the Yellow River bank to the bare beach that encompassed a variety of vegetation covers were selected for soil sampling and field monitoring. A modified sequential fractionation method was used to partition the soil P, and the related properties were measured. The soils in this newly formed estuarine coastal wetland, only covered by salt‐tolerant plant communities, are strongly alkaline (pH 8.4–9.2) with high soil salinity (mean, 6.23‰). The content of total P (Pt) ranged from 548.3 to 728.5 mg kg−1 in these soils. Dil.HCl‐Pi (extracted with 1 M HCl) was the highest P fraction (mean, 58.1–72.8%), whereas NaHCO3‐Pi was the lowest fraction (mean, 0.4–1.7%) of all the P forms. Vertical distributions showed a surface accumulation of Resin‐P. Resin‐P, NaHCO3‐Pi, NaOH‐Pi, and Conc.HCl‐Pi (extracted with 11.3 M HCl) were positively or negatively correlated with some properties. Attributed to the spatial deposition and hydrology, Dil.HCl‐Pi presented a poor correlation with Ca. The results also showed some clear differences in the P forms and P availability among vegetation covers. The vegetation cover could modify the soil quality, and Suaeda heteroptera, as the pioneer plant community species, significantly enhanced the freely exchangeable Pi and increased P availability, providing important ideas for salt‐soil sustainable use.
Denudation variability of the Sila Massif upland (Italy) from decades to millennia using 10Be and 239+240Pu Land Degrad. Dev. (IF 7.27) Pub Date : 2018-09-02 Gerald Raab; Fabio Scarciglia; Kevin Norton; Dennis Dahms; Dagmar Brandová; Raquel de Castro Portes; Marcus Christl; Michael E. Ketterer; Annina Ruppli; Markus Egli
Landscapes and soils evolve in non‐linear ways over millennia. Current knowledge is incomplete as only average denudation (or erosion) rates are normally estimated, neglecting the temporal discontinuities of these processes. The determination of regressive and progressive phases of soil evolution is important to our understanding of how soils and landscapes respond to environmental changes. The Sila Massif (Italy) provides a well‐defined geomorphological and geological setting to unravel temporal variations in soil redistribution rates. We used a combination of in situ cosmogenic radionuclide measurements (10Be) along tor (residual rock) height profiles, coupled with fallout radionuclides (239+240Pu) in soils, to model soil denudation rates over the last 100 ka. We measured rates prior to the Last Glacial Maximum (LGM) of ≤30 t km−2 yr−1 (~0.036 mm yr−1). Following the LGM, during the transition from the Pleistocene to the Holocene, these rates increased to ~150–200 t km−2 yr−1 and appeared to be above soil production rates, causing regressive soil evolution. For the last ~50 years, we even describe erosion rates of ≥1,000 t km−2 yr−1 (~1.23 mm yr−1) and consider human impact as the decisive factor for this development. Consequently, the natural soil production rates cannot cope with the current erosion rates. Thus, a distinct regressive phase of soil formation exists, which will give rise to shallowing of soils over time. Overall, our multimethod approach traced denudation and erosion histories over geologic and human timescales and made a new archive to soil science and geomorphology accessible.
The smart growth of Chinese cities: Opportunities offered by vacant land Land Degrad. Dev. (IF 7.27) Pub Date : 2018-08-30 Weifeng Li; Weiqi Zhou; Yang Bai; Steward T.A. Pickett; Lijian Han
Despite the publicly accepted concept of 'smart growth' of urban areas and its wide implications in developed countries, there is less concern about this in a newly emerging economy like China. Yet, due to the unprecedented urbanization rates in many developing countries, how to control unordered urban sprawl is becoming a severe challenge to multiple levels of governments. This study is the first to comprehensively evaluate the spatial and temporal change of vacant land within the built‐up area of a large city in China. We used the core city of Shanghai as a case‐study to systematically investigate the spatial–temporal distribution of vacant land at the fine scale. The boundaries of vacant land patches and of other urban land use types were delineated using visual interpretation, based on 0.3‐m resolution aerial photos collected in 2000, 2005, and 2010. We find that (a) vacant land plays a very important role in the composition of the urban landscape of central Shanghai, accounting for 9.3%, 11.3%, and 10.4% of the core city area in 2000, 2005, and 2010, respectively; (b) there exists obvious spatial–temporal change of transformation between vacant land and other land use types during the 10 years studied; and (c) the considerable amounts of vacant land and its change dynamic have important policy implications for smart growth of cities in China. Making the best planning and management decisions about these vacant lands might be one promising smart growth principle for China's cities.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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