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Influence of irrigation regimes and nitrogen fertilizer management on the performance of spring wheat in Bangladesh

A field experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University from November 2016 to March 2017 to find out the effect of irrigation regimes and nitrogen (N) fertilization on the yield performance of spring wheat. The experiment was comprised five levels of irrigation viz., no irrigation (I0); CRI (crown root initiation stage) (I1); CRI + maximum tillering stage (I2); CRI + maximum tillering stage + flowering Stage (I3); CRI + maximum tillering stage + flowering stage + grain formation stage (I4); and six levels of nitrogen viz., 0, 60, 80, 100, 120 and 140 kg ha under Split Plot design with three replicates. Except few all the yield contributing characters and yield of wheat were significantly influence by the application of irrigation and nitrogen. The highest number of total tillers hill (4.15), effective tillers hill (3.63), number of spikelets spike (14.67), grain yield (2.862 t ha), straw yield (3.45 t ha), biological yield (6.312 t ha) and harvest index (45.34%) were obtained from two irrigation at CRI+ Maximum tillering stage. In nitrogen management, the highest plant height (91.17 cm), number of spikelets spike (15.24), number of grains spike (44.46), spike length (10.89 cm), grain yield (2.93 t ha), straw yield (3.478 t ha) and biological yield (6.408) and harvest index (45.72%) were obtained from application of 120 kg N ha. In interaction, the highest grain (3.897 t ha), straw (4.76 t ha) and biological yield (8.661 t ha) and harvest index (45.02%) were achieved from two irrigation at CRI + maximum tillering stage with application of 120 kg N ha. The lowest grain yield (1.22 t ha) was achieved from one irrigation at CRI with no nitrogen application. Whereas, the lowest straw (2.13 t ha) and biological yield (3.78 t ha) were achieved from no irrigation with 60 kg N ha. Based on these results it may conclude here that farmers may apply two irrigations (one at CRI and another at maximum tillering stage) with 120 kg N ha to obtain the higher yield of wheat under Bangladesh context.


Introduction
Wheat (Triticum aestivum L.) is one of the most important grain and primary food for more than one third of the world population. After maize and rice, it covers the more land area than any other food crop and wheat production is the third largest cereal production in the world. It is estimated that global grain demand will be doubled by the year 2050 (Cassmann, 1999;Tilman et al., 2002) [1,2] . By 2050, the demand for wheat in the developing world is projected to increase 60% from now (FAO, 2013) [3] . Wheat grains contain 33% Protein, 29% Carbohydrate, 5% Fat (USDA, 2014) [4] . Currently about 65% of wheat crop is used for food, 17% for animal feed and 12% in industrial applications (FAO, 2013) [3] . In Bangladesh, wheat is the second important cereal crop next to rice (Al-Musa et al., 2012) [5] and the area under wheat cultivation during 2015 was 436814 ha producing 1347926 ton of wheat with an average yields of 3.033 ton ha -1 (BBS, 2015) [6] . Whereas, in the year of 2016-17 wheat was cultivated in 444805 hectares of land producing 13, 11,473 tons of wheat with an average yields of 3.158 ton ha -1 (BBS, 2018) [7] . However, the average yield of wheat in Bangladesh can be raised up to 6.8 ton ha -1 (BARI, 2010) [8] . The low yield of wheat in Bangladesh is attributable to a number of reasons, viz. the traditional cultural practices, poor field management, lack of using proper plant densities, late planting, unavailability of quality seed, use of local cultivars, climatic hazards, intensive cropping and non-replenishment of soil nutrients, inadequate fertilizer use, irregular irrigation and fertilizer management including splitting of N application (Bukhari et al., 1991;Arabinda et al., 1994;Jahiruddin and Hossain, 1994;Ahmed and Meisner, 1996) [9,10,11,12] . In Bangladesh, wheat is grown during Rabi season and the duration extends from the month of November to March. The rabi season in Bangladesh is dry and as such, the inadequate soil moisture in this season limits the use of fertilizers, specially nitrogen and consequently results in decreased grain yield. About 42.78% of the total wheat area in the country is irrigated and the rest of the area is cultivated under rainfed condition (BBS, 2015) [6] . Irrigation plays a vital role in terms of bringing good growth and development of wheat. Insufficient soil moisture affects both the germination of seed and uptake of nutrients from soil. Irrigation frequency also has a significant influence of growth and yield of wheat (Khajanij and Swivedi, 1988) [13] . These suggested irrigation water should be supplied precisely at the peak period of crop growth, which may provide good yield of this crop. Fertilizers are necessary for enhancing productivity in crops, especially in wheat, indiscriminate use of macronutrients and low use of micronutrients leading to an imbalance of soil chemical. A proper fertilization program with macronutrients and micronutrients in plant nutrition is very essential in the high production with good quality products, so there is a need of balance use of fertilizers and proper agronomic practices are needed to increase yield of this crop. High yielding varieties of wheat need adequate N fertilization to satisfy crop demands. Generally the total crop N demand increases with the potential biomass and grain yields. Nitrogen plays an important role to increase the tillering capacity of plants which ultimately increase production. Very low level of nitrogen fertilizer does not supply proper nutrients to plants while high levels encourage vegetative growth rather than reproductive growth, which eventually reduces the yield. Optimum supply of nitrogen raises the protein content, nutritive value of grain and also improves backing qualities (Filipov, 2000) [14] . Thus, a careful and judicious application of nitrogen and water is necessary. Therefore, the present study was undertaken to evaluate the effect of irrigation regimes and nitrogen level irrigation regimes on the yield performance of spring wheat in Rabi season in Bangladesh.

Materials and Methods Experimental Site
The field experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh which is located at 24.75°N latitude and 90.50°E longitude of 18 m above the sea level. The experimental site belongs to the Old Brahmaputra Floodplain (AEZ-9). The experimental field was of a medium high land having silty clay loam soil, more or less neutral in reaction, low in organic matter content (1.29%) and its general fertility level was also low with soil bulk density (1.33 g cm -1 ). The experimental area is situated under a subtropical climate, which is characterized by scantly rainfall and low temperature during October to March. The average temperature (from October to March) was 13-26 0 C, rainfall 7 mm and relative humidity 80.5%. The test crop was wheat variety BARI Gam 24 (Pradip), developed by the scientists of Bangladesh Agricultural Research Institute (BARI) at 2005, can be grown all over the country.

Experimental design and treatments
The two sets of treatments were included in the experiment: A-Irrigation regimes (5): No irrigation (I 0 ), CRI-Crown Root Initiation Stage (I 1 ), CRI + Maximum tillering stage (I 2 ), CRI + Maximum tillering stage + Flowering Stage (I 3 ), CRI + Maximum tillering stage + Flowering stage + Grain formation stage (I 4 ). B-Nitrogen levels (6): No nitrogen (N 0 ), 60 kg N ha -1 (N 1 ), 80 kg N ha -1 (N 2 ), 100 kg N ha -1 (N 3 ), 120 kg N ha -1 (N 4 ), and 140 kg N ha -1 (N 5 ). The experiment was laid out in a split-plot design with three replications. Each replication was divided into five main plots and each of the main plots was then subdivided into six unit plots. The total number of plots was 90 (5×6×3) with each plot area 10 m 2 (4.0 m × 2.5 m). The irrigation regime was assigned to the main plots and nitrogen fertilizer level in sub-plot within each replication. The distances between the plot and block were 0.75 m and 1.0 m, respectively having a provision of irrigation channel.

Crop Husbandry
The land was prepared by repeated ploughing by a power tiller. Weeds and stubble of the previous crop were collected and removed from the field. After leveling, the experimental plots were laid out as per the treatments and design. All the fertilizers except nitrogenous were applied at the rate of BARI recommended dose as 180 kg ha -1 Triple Super Phosphate (TSP), 50 kg ha -1 Muriate of Potash (MoP), 120 kg ha -1 Gypsum (BARI, 2010) [8] . Nitrogen was applied as per experimental specification through urea. The total amount of TSP, MOP, gypsum and one third of the urea were applied at the time of final land preparation prior to sowing. The remaining two-thirds of urea were top-dressed in two equal splits on 20 and 55 days after sowing (DAS). Seeds were sown in the field at the rate of 120 kg ha -1 in 25 cm apart rows. Intercultural operations were done to ensure normal growth of the crop. Irrigations were done according to the treatment. Weeding was done twice during the whole growing period, one after 20 DAS and the other after 55 DAS. The crop was harvested at maturity when 90% of the grains became golden yellow in color from each plot were bundled separately and brought to the threshing floor. The crops were threshed and sundry weights of both the grain and straw were recorded for every plot and the weight in g plot -1 was converted to kg ha -1 .

Data collection
For collecting data on plant characters, five plants were selected at random and uprooted from each plot prior to harvesting. The grain and straw yields were recorded plotwise at 14% moisture basis and expressed as ton ha -1 . The data on the yield and yield contributing parameters (presented in the tables) were recorded accordingly. The harvest index was calculated as follows: Biological yield= Grain yield + Straw yield

Data analysis
The recorded data were subjected to statistical analysis. Analysis of variance was done following two factors Split Plot Design with the help of computer package MSTAT-C. The mean differences among the treatments were adjusted by Duncan's Multiple Range Test (DMRT) at 5% level of significance.

Results and Discussion 1. Effect of irrigation regimes on yield characters and yield
The yield contributing characteristics and yield varied significantly with different level of irrigations ( Table 1). The highest number of tillers hill -1 (4.15), number of effective tillers hill -1 (3.63), number of spikelets spike -1 (14.67), grain yield (2.862 t ha -1 ), straw yield (3.45 t ha -1 ), biological yield (6.312 t ha -1 ) and harvest index (45.34%) were observed by the application of two irrigations. The lowest number of tillers hill -1 (3.71), number of effective tillers hill -1 (3.25) from three irrigation, number of spikelets spike -1 (14.32) from four irrigation, grain yield (1.487 t ha -1 ), straw yield (2.28 t ha -1 ), biological yield (3.767 t ha -1 ) and harvest index (39.47%) from control (no irrigation) were observed. The plant height, number of non-effective tillers hill -1 , number of sterile spikelet spike -1 , number of grains spike -1 , spike length and 1000-grain weight were not significantly influenced by the irrigations. The highest plant height (86.92 cm), number of grains spike -1 (41.23), spike length (10.72 cm), 1000-grain weight (53.57g) from two irrigations, number of non-effective tillers hill -1 (0.56), number of grains spike -1 (39.38) from one irrigation, number of sterile spikelet spike-1(3.12) from control (no irrigation) were recorded. The lowest plant height (84.20 cm), number of sterile spikelet spike -1 (2.86) from two irrigations, number of non-effective tillers hill -1 (0.46), 1000grain weight (53.24g) from three irrigations, spike length (10.26 cm) from control (no irrigation) and were recorded. The plant height is a varietal character of wheat, which may be influenced to some extent by irrigation/soil moisture condition. Shirazi et al. (2014) [15] observed that plant height was gradually increased with increasing number of irrigations. Islam et al. (2018) [16] and Rummana et al. (2018) [17] also observed similar results. Patel et al. (1992) [18] explained that 12 cm depth of irrigation significantly increased the plant height compared with 6 cm irrigation. Irrigation from tillering to heading of wheat had a beneficial effect on tiller plant -1 (Massunaka et al., 1992) [19] . Effective tillers plant -1 was significantly superior in irrigation treatments to no irrigation treatment (Singh and Singh, 1991) [ 20] . Irrigation plays a positive role in increasing the number of tillers plant -1 (Ali and Amin 2007) [21] of wheat. Hefni et al. (1983) [22] found that the number of grains spike -1 and ear length reduced significantly if irrigation would be stopped at tillering and booting stages of wheat. Wheat plant growth was poor and spike length was low at rain fed condition (Singh and Singh, 1996) [23] . The fertile spikelets spike -1 was increased significantly under four irrigation and six irrigation treatments than two irrigations (Naik et al., 1997) [24] . Bhoi et al. (1993) [25] explained that irrigation applied at critical growth stages showed maximum number of grains spike -1 . Number of grains spike -1 dominated by irrigation (Wajid et al. 2016) [26] . Water stress reduced grain number of winter wheat by 33% (Music and Duseck, 1980) [27] while the single mild drought at heading significantly decreased the grain yield, by 18.34% (Ding et al. 2018) [28]. Thousand grain weights declined or decreased with the increase in moisture regime (Naik et al., 1997) [24] or the irrigation frequencies (Joarder et al., 1986) [29] . Bhoi et al. (1993) [25] reported that 1000-grains weight was maximum when irrigations were applied at critical stages. Naser (1996) [30] reported that two irrigations at 30 and 50 DAS significantly increased grain and straw yields over control. The highest spike length, grain and straw yields, the maximum number of tillering plant -1 , number of grains spike -' were recorded where two irrigations were applied. Two irrigation treatment increased grain and straw yields by 58.1% and 54.5%, respectively, over control.

Interaction effect of irrigation regime and nitrogen levels on yield characters and yield
Crop yield contributing characteristics and yield response significantly to the interaction effect of different irrigation regime and nitrogen levels ( Table 3). The highest plant at harvest (100.4 cm), number of tillers hill -1 (4.8), number of effective tillers hill -1 (4.13), number of spikelets spike -1 (15.84), number of grains spike -1 (46.36), grain yield (3.897 t ha -1 ), straw yield (4.76 t ha -1 ), biological yield (8.661t ha -1 ) and harvest index (45.02%) at two irrigation with nitrogen application @ 120 kg ha -1 , number of non-effective tillers hill -1 (0.73) at one irrigation with nitrogen application @ 60 kg ha -1 , number of sterile spikelet spike -1 (3.39) from control (no irrigation and nitrogen) were observed. The spike length and 1000-grain weight was not significantly influenced by the interaction. The highest spike length (11.65 cm) & 1000-grain weight (54.45 g) at two irrigation with nitrogen application @ 120 kg ha -1 were observed. The lowest plant at harvest (66.0 cm), number of tillers hill -1 (2.93), number of effective tillers hill -1 (2.53), grain yield (1.22 t ha -1 ) & harvest index (29.12%) at one irrigation with control nitrogen, number of noneffective tillers hill -1 (0.27) at two irrigation with control nitrogen, number of spikelets spike -1 (12.78) at four irrigation with control nitrogen, number of sterile spikelet spike -1 (2.6) at one irrigation with nitrogen application @ 80 kg ha -1 , spike length (9.46 cm), number of grains spike -1 (35.47) & 1000grain weight (52.90 g) at four irrigation with nitrogen application @ 140 kg ha -1 , straw yield (2.13 t ha -1 ) & biological yield (2.28 t ha -1 ) at control irrigation with nitrogen application @ 60 kg ha -1 were observed. Gangwar et al. (2018) [36] reported that yield contributing factors and yield were significantly affected by different doses of nitrogen and irrigation regimes.120:60:60 NPK kg ha -1 application and fourth irrigation have found most suitable and economic combination for wheat crop under the existing conditions of Bundelkh and region in Uttar Prodesh. Shirazi et al. (2014) [15] found the interaction between 200 mm irrigation and 120 kg N ha −1 was the best combination treatment to obtain maximum grain yield in wheat cv. Kanchan. Parvej et al. (2010) [37] found he highest grain yield (4.82 t ha -1 ) was obtained with 280k g Flobond ha -1 as chemical water retainer and 100 kg N ha -1 . The lowest one (1.53 t ha -1 ) was obtained from 35 kg Flobond ha -1 and no nitrogen. On the other hand, the highest straw yield (6.68 t ha -1 ) was obtained with 100 kg N ha -1 under two irrigation and the lowest one (3.42 t ha -1 ) was found in 35 kg Flobond ha -1 and with no nitrogen. Rahman et al. (2000) [38] reported that maximum plant height, dry matter accumulation, leaf area index, crop growth rate, tiller number per plant and grain and straw yields were recorded from an irrigation depth of 6 cm. Nitrogen at 100 kg ha -1 when top dressed just after irrigation, also improved all the attributes (Saren et al., 2001) [39] . Singh et al. (1996) [23] reported that grain yield was maximum (4.47 t ha -1 ) with presowing irrigation plus irrigation at crown root initiation stages at a nitrogen level of 150 kg ha -1 .   Control, N1 = Nitrogen application @ 60 kg ha -1 , N2 = Nitrogen application @ 80 kg ha -1 , N3 = Nitrogen application @ 100 kg ha -1 , N4 = Nitrogen application @ 120 kg ha -1 , N5 = Nitrogen application @ 140 kg ha -1 . In a column, figures with same letter (s) or without letter do not differ significantly whereas figures with dissimilar letter differ significantly (as per DMRT) ** =Significant at 1% level of probability, * =Significant at 5% level of probability, NS = Not significant.

Conclusion
From the above results of the present study, it may be stated that BARI Gam 24 was grown successfully for obtaining higher yield by two times irrigation (at Crown Root Initiation + Maximum tillering stage) with 120 kg N ha -1 in combination with recommended rates of TSP, MoP and Gypsum fertilizers to ensure optimum requirement of nutrients for commercial wheat cultivation. Further study should be undertaken on a priority basis because the fertility status of Bangladesh soils may vary from place to place or region to region. In dry winter season in Bangladesh, farmers may be advised to apply two times irrigation (at Crown Root Initiation + Maximum tillering stage) with 120 kg N ha -1 , respectively for proper utilization of water regime and nitrogen fertilizers to obtain higher grain yield of wheat. Before making final conclusion, further trails with the same treatment combinations on different Agro Ecological Zones (AEZ) of Bangladesh will be useful.