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“TRES FUENTES DE SILICIO EN LA PRODUCCIÓN DE BIOMASA DEL ARROZ (Oryza sativa L.) BAJO CONDICIONES CONTROLADAS” TESIS PARA OPTAR TÍTULO DE INGENIERO AGRÓNOMO CESAR FRANCO PADILLA CASTRO

A pot experiment was conducted in the campus of La Molina National Agrarian University in order to evaluate the effect of rice husk ash, steel slag and potassium silicate on the soil chemical properties an biomass of rice (Oryza sativa L.) cv. Fedearroz 60, using soil material from a commercial paddy field at Aucayacu, Huanuco, Peru. Doses were calculated taking into consideration each product extractable Si (SiA), for reaching concentrations of 100, 200 and 400 mg/kg (p/p) of SiA in soil before sowing. Control pots without any silicon amendment were considered as well. A completely randomized design with factorial arrangement (3x4) was used to assess the Si absorption by plant tissues, final SiA in soils, roots volume, tillering capacity, panicles per plant, spikelets per plant, nitrogen absorption and panicle tip degeneration due to cold stress. Salinity and pH of the growing media were registered weekly. Also were environmental temperature, relative humidity and light intensity on a daily basis. Results showed that potassium silicate sustainably increased SiA in soils and Si in plant tissue, however the yield components were not positively influenced. Steel slag increased those silicon parameters too, nonetheless for doses of 200 and 400 ppm, symptoms of severe toxicity appeared. Rice husk ash did not show statistical significance on SiA in soils and Si in plant tissue nor yield components. It was concluded that for soil and weather conditions involved in this experiment, silicon have no influence on yield components. In spite of this, steel slag exhibited an outstanding liming capacity and rice husk ash, a great amount of P, K and micronutrients.


Introduction
Rice (Oryza sativa L.) is one of the main food crops in the world (Food and Agriculture Organization of the United Nations [FAO], 2021). Not only is it important at a food security level, but it also represents a substantial source of income for farmers in the northern coast and rainforest areas of Peru (Ministerio de Desarrollo Agrario y Riego del Perú [MIDAGRI], 2021). Although the highest rice yields are obtained in the coast, this cereal's production should be encouraged mainly at the Amazon basin. There are two situations which back up this statement. In first place, Peruvian coastal valleys have constant threat of water shortage, due to their desert-like climate and a increasing expansion of farming land for export products (Drenkhan et al., 2015). Secondly, paddy fields tillage causes physical and chemical degradation which limits the use of these areas only to rice monoculture (Sione et al., 2017). This line of investigation involves silicon as part of a strategy for increasing yields at the Amazon basin, looking forward to making this crop more attractive for this area. This element, historically considered "non-essential" within the majority of nutritional programs, has gained importance in research which highlights its ability to indirectly increase yields, by alleviating conditions of biotic and abiotic stress (Meharg & Meharg, 2015). For this pot experiment, available silicon concentration in soil (SiA) was raised in order to verify whether or not %Si in tissue increased as well. Subsequently, this variable was correlated with some parameters associated with yield components, in order to check if higher silicon levels could have resulted in higher yields. For such purpose, three sources of silicon were used: potassium silicate, rice husk ash and ladle furnace slag. These last two amendments are materials considered as residues with potential to be used in agriculture. Rice husk is a residue obtained from rice mills. It has been used as a component of growing substrates in nurseries and different crops' plantations. According to (Della et al., 2002), its ashes contain up to 94.9% of SiO 2 . Ladle furnace slag is a by-product of steel plants. Encina (2017) studied its properties, finding good liming power in this material. Apart from that, its SiO 2 concentration varies from 10 % to 19 %. This amendment is a good candidate for Amazonian acidic soils, where it is known that high precipitation quickly leaches silicon.

Location
The experimental part of this research was conducted in the Soil Fertility Laboratory, belonging to the Soil Academic Department, at the campus of Universidad Nacional Agraria La Molina (UNALM), which is located at 12º 4' 46" S, 76º 56' 45" W and an altitude of 244 m.a.s.l. The experimental field part took place from February 16 th 2018 to August 17 th 2018.

Supplies, materials and tools
Topsoil samples from a commercial rice paddy field, located in river Huallaga's floodplain in Aucayacu (Leoncio Prado province, Huánuco region, Peru) was used for the experiment. This rainforest area has a tropical climate, with an annual mean temperature of 24.67 ℃ and precipitation of 2866 mm. The sources of available silicon (SiA) were ladle furnace slag (SiderPeru-Gerdau, Chimbote, Peru), rice husk ash (Feedcor EIRL, Lima, Peru) and potassium silicate (commercial name Klaida, Feedcor EIRL, Lima, Peru). Ammonium sulfate, potassium sulfate and diammonium phosphate were the regular soil fertilizers for the nutritional program. Irrigation water (pH 7.83; E.C. 0.5 dS / m; SAR 0.57) was classified C2-S1 according to Wilcox (1955), meaning low risk of sodium hazard, and medium salinity hazard. Rice seeds cv. 'Fedearroz 60' were brought from Aucayacu. Reagents for silicon analysis were considered following the reference of Parra et al. (2004) and Pereira et al. (2007). Regarding tools, 7.5 L plastic pots were used as growing containers. The equipment used for the measurements were scale, electric stove, potentiometer, conductivity meter, thermo-hygrometer with data logger (Elitech, California, USA), lux meter (Benetech, Guandong, China), thermal plate, muffle-type oven and a UV spectrophotometer (ThermoScientific, Massachusetts, USA).

Experimental design
A completely randomized design with factorial arrangement (3 × 4) was used. Factors under study were: (1) soluble silicon sources and (2) Initial SiA concentrations. Levels for factor one -(i) ladle furnace slag -"Slag", (ii) rice husk ash -"Ash" and (iii) potassium silicate -"KSi". Levels for factor two -(a) 0 ppm, (b) 100 ppm, (c) 200 ppm and (d) 400 ppm. The experimental unit was defined as a pot with a rice plant with 5.8 kg of air-dried soil previously sieved, homogenized and partially fertilized. Total: 72 experimental units. The experiment begun with six replicates per treatment, however due to the identification of other cultivars which were not 'Fedearroz 60', some experimental units had to be removed. As a consequence, all treatments suffered a reduction in the number of replicates and three of them had to be discarded from the experiment because were left with only two replicates (Slag 100ppm, KSi 400ppm, Ash 200ppm). Collected data was analyzed using the free software, R (RcoreTeam, 2014). A linear model was used to obtain the residuals for each quantitative variable and then were subjected to the Shapiro-Wilk test, in order to verify the assumption of residuals' normal distribution (). Breutsch-Pagan test was also carried out to corroborate the assumption of homogeneity of variances in the residuals (). In the event of non-compliance with any of the assumptions, specific mathematical transformations were carried out for each variable. They will be indicated individually in the tables. After verifying that data fit into the statistical assumptions, ANOVAs were carried out. Subsequently, Tukey tests were performed () in which all treatments were contrasted at the interaction level.

Variables
The evaluated variables were grouped into three groups: (1) Edaphoclimatic -electrical conductivity of the soil, soil reaction (pH), environmental temperature and light intensity.
(2) Morphological -tillers per plant, panicles per plant, average spikelets per panicle, whole plant's dry weight and root volume. (3) Analytical -Si concentration in tissues and available silicon in soils (SiA).

Experiment installation
The collected topsoil was air dried and passed through a 2 mm sieve. Three samples were taken to the laboratory in order to perform a soil characterization analysis (Table 1). The results indicated the textural class as Loam, with 40 % of sand and 41 % of silt, as expected for an area next to a river, where constant sediments are brought with water. Electrical conductivity was measured in 0.25 dS · m -1 , and pH in 5.14. The nature of river water, very low in salts caused low salinity levels. This soil can be considered as strongly acidic, which relates to the big annual precipitation and consequently, lacks calcium carbonate. Organic matter content remained at 1.98 %, which is considered high in relation to the 18 % of clay. This indicates that lack of oxygen is delaying processes of organic matter degradation, which correlates with a paddy field in constant state of saturation. This analysis was considered as the basis for designing the fertilization plan together with the nutrients' absorption curves provided by Bertsch (2009). The initial availability of silicon in the soil (Table 1) and amendments (Table 2) were also analyzed. This information was used to calculate how much of each amendment had to be mixed with the soil in the pots: Slag 100 ppm -92.82 g per pot. Slag 200 ppm -185.65 g per pot. Slag 400 ppm -371.3 g per pot. Ash 100 ppm -99.95 g per pot, Ash 200 ppm -199.92 g per pot, Ash 400 ppm -399.83 g per pot. KSi 100 ppm -16.05 g per pot, KSi 200 ppm -32.1 g per pot, KSi 400 ppm -64.21 g per pot. Additionally, a chemical profile analysis of these same amendments was carried out. ( Table 2). The seeds received a heat treatment at 40 ℃ for 48 hours to break the dormancy prior to sowing in order to ensure uniform germination. The pots' drainage holes were covered with duct tape. A total of 5.7 kg air-dried fine soil was separated for each pot in mixture with the diammonium phosphate and the correspondent treatment of rice husk ash and ladle furnace slag. One day before sowing, the pots were watered until saturation point. Potassium silicate treatments got their first doze with this first watering. Subsequently, sowing was carried out by placing 30 seeds per pot at a depth of approximately 1.5 cm. After ten days, only three plants per pot were left and after 20 days, only the most vigorous plant was left in the pot. The main agronomic activity was irrigation. A total of 57 L of water per pot was needed for finishing all crop cycle. Nitrogen fertilization was separated into five moments and potassium fertilization into one single application. Additionally, corrective measures had to be taken when some leaks appeared in the pots by placing patches with duct tape, plastic bags and paraffin wax. Apart from that, plastic cover was used as isolating material when temperatures went below of those recommended for rice development (18 ℃).

Assessment of variables
One pot per treatment was chosen for electrical conductivity and soil pH assessment. At the end of the experiment, all pots were evaluated for these variables. The first two weeks of the experiment, the samples were obtained using a spoon within the upper 2 cm from the surface. From week three onwards, a cylindrical sampler (15 cm x Ø 2.5 cm) was used to reach more depth in the pots' profile. Benchtop potentiometers and conductivity meters were used for sample analysis on a 1:1 (w / w) dilution rate methodology with deionized water (Mass & Hoffman, 1977). Temperature was measured every 15 minutes (from sowing until day 173 after sowing). Data was stored in the thermohygrometer memory for further processing. Light intensity was measured using the lux meter and data was manually registered in a data base. The daily light integral was calculated according to the methodology of Torres and Lopez (2012) with the support of the transformation constants from McCree (1981). Morphological parameter evaluations were performed after harvest, between day 171 and day 182 after sowing. Roots were separated from aerial organs using a band saw, in order to assess root volume, by the water displacement methodology using a beaker and a graduated cylinder. Samples were placed in labeled paper bags and placed in an electric stove at 65 ℃ for 72 hours. After this period, whole plant's dry weight was obtained. The number of tillers per plant, panicles per plant and spikelets per plant were manually counted. From these data, the average number of spikelets per panicle was calculated as well as the estimated grain yield per plant. Root samples and aerial parts samples were grounded separately in a laboratory mill and passed through a 1 mm sieve, in order to carry out the chemical analyzes. Silicon concentration in plant tissue was analyzed taking into consideration the NaOH fusion methodology detailed by Parra et al. (2004). Available silicon in soil (SiA) samples were measured according to the CaCl 2 0.01 M methodology, detailed by Pereira et al. (2007).

Effect of the silicon amendments in the chemical properties of the soil samples
It is necessary to clarify that, despite silicon is the second most abundant element in the earth's crust after oxygen -28.8 % (w / w) - (Wedepohl, 1995), most of this element is not available to plants. According to Matichenkov and Bocharnikova (2001), silicon is found in three fractions in soils: (a)the solution fraction, (b) weakly adsorbed fraction and (c) the solid phase. The solution fraction and the slightly adsorbed fraction involve monosilicic acids, polysilicic acids and organosilicate compounds. On the other hand, the solid fraction is composed of biogenic amorphous forms, such as phytoliths; or non-biogenic forms such as amorphous silica, as well as crystalline forms, which can be finely dispersed (micas, kaolinite, illite, smectite) or minerals dispersed in large pieces such as feldspars and quartz. The predominant form of silicon between pH 4.5 and 8 is H 4 SiO 4 (Elgawhary & Lindsay, 1972), which is also the available form to plants, according to Epstein (1994). It fluctuated from 0.1 mM to 0.6 mM (9.6 ppm to 57.6 pm) under conditions of pH range of 4.5 to 8. This is 375 times higher than the 0.0016 mM phosphorous concentration, according to the same author. Nonetheless, solubility depends on type of mineral, temperature, pH, texture, organic matter and land usage history (Struyf et al., 2010). For this experiment, the resulted initial SiA was 11.78 ppm ( Table 1), which is located very close to the lower limit stablished by Epstein (1994). In order to raise silicon availability to 100 ppm, 200 ppm and 400 ppm, it was necessary to analyze SiA for rice husk ash, ladle furnace slag and potassium silicate ( Table 2). Both two pieces of information were useful to calculate the amount of each silicon amendment for every treatment. Apart from that, all three silicon amendments were subjected to a complete chemical characterization (Table  2). It is necessary to clarify that such dozes were not commercial, therefore salinity and acidity variations were monitored for the entire crop's cycle. Figure 1, Figure 2 and Figure 3 show electrical conductivity changes taking into consideration the days after sowing and phenology. Salinity assessment took place for 14 weeks. It is possible to see that all control treatments (0 ppm) experienced increases since the first week of evaluation, because of pre-sowing fertilization and irrigation water. Within the treatments, all curves behaved similarly, corroborating that maintenance labors were the same for all. Higher dozes portrayed the higher values of electrical conductivity. Changes in the sampling method explained in the previous section tell why E.C. levels during first two weeks seems higher than the third one. Surface soil is always richer in salt content because of evaporation. Same material was used for keeping track of soil pH variations. Figure 4, Figure  5 and Figure 6 show pH behavior during the crop's cycle. Rice husk ash treatments remained almost invariable in relation to the control unit.
Potassium silicate treatments showed high values for first and second week because of the sampling methodology formerly explained, however all its dozes kept higher than the control. Ladle furnace slag showed a consistent rise in pH since the first week. At the end of the field stage, all experimental units were analyzed for electrical conductivity and pH.    40 development, as Yoshida (1981) explained that this crop tolerates up to 4.5 dS · m -1 . This indicates that even high dozes of those products will not rise salinity at dangerous levels for rice.  Table 5 summarizes root volume data. Its information corroborated the lack of plant growth with the poor root growth for 200 ppm and 400 ppm slag treatments, which were significantly smaller than the control units. The rest were statistically similar to the control units.      Liang et al. (2015). Table 7 summarizes Si% in roots. All potassium silicate and rice husk ash treatments were statistically similar to the control pots. Even KSi 200 ppm treatment, whose silicon availability was statistically higher than the control units (30.31 ppm SiA - Table 6) remained similar to control units for %Si in roots, showing that such availability did not impact this element's concentration in root tissue. Conversely, both slag treatments showed significant differences from the control units, being the Slag 400ppm treatment the one that portrayed the lowest Si content with 1.94 %. Table 8 summarizes Si% in aerial organs. In general, such concentrations are smaller than Si% in roots. Raven (2003) explains that H 4 SiO 4 is a neutral molecule and can defuse through the lipid components of cell membrane of roots. Thus, it is expected to find higher concentrations in roots than in stems and leaves, because aerial organs got their silicon supply from the xylem sap. In the xylem, the raw sap reaches silicic acid concentrations as high as 20 mM (1920 ppm), 36 times higher than the concentration in the soil solution (Nikolic et al., 2007), however this occurs for a very short period of time, due to the fact that, from 2 mM (192 ppm) the silicon begins to polymerize (Mitani et al., 2005). Much of those molecules are deposited in the xylem vessels where they help them to remain rigid when high transpiration rates take place (Balasta et al., 1989). Silicon leaves the xylem vessels through transporter, OsLsi-6. This transfers the H 4 SiO 4 via the symplastic pathway into the parenchyma associated to the xylem. This is an inflow transporter similar to OsLsi-1, but it is also expressed in leaves, stems and in the root tips (Yamaji et al., 2008). Silicon that follows this route ends up being deposited inside specialized cells that store silicon called phytoliths. Also, silicon can leave the xylem vessels by the apoplastic pathway, in which case, the silicon ends up deposited in the cell walls of the epidermis, binding with hemicellulose, as a hydrated amorphous polymer (opal), forming a silicate-cuticle association. The surplus can even escape out of the leaves by guttation (Ma et al., 2011). The reason why some rice varieties accumulate more silicon than others depend on the expression of the transporter genes (Ma et al., 2007b). Control units showed mean values of 2.87 %, 2.82 % and 2.76 % for Si concentration in aerial organs. All rice husk ash and ladle furnace slag treatments were statistically similar to control pots. Potassium silicate at 200 ppm doze was the treatment with the highest silicon absorption (significantly different from control units) with 4.75 %. Almost twice the amount found in the control pots. That treatment was the third in terms of silicon availability with 30.31 ppm SiA ( Table  6). The silicon content in plants varies in a very wide range that goes from 0.1% to 10% of the dry weight depending on the species (Epstein, 1994). Within the higher plant species, Poaceae family is the group with the highest relative content of silicon. (Hodson et al., 2005). The essentiality of this element according to the criteria of Arnon and Stout (1939), has not been proven (Ma et al., 2001). For Epstein (1999), silicon is considered a "quasi essential" element, which is defined by this author as an element which is present in plants and should be provided in determined quantities in order to avoid any strongly-enough deficiency to cause abnormalities in growth and development, otherwise in will be detrimental for agronomic performance. Rice is capable of accumulating up to 10 % of the dry weight in the aerial organs. This concentration is considered much higher than that of most macronutrients such as N, P or K. (Liang et al., 2015). This led to Savant et al. (1997) to deduce that large amounts of Si were required for sustainable rice production. According to Desplanques et al. (2006) the average silicon extraction is 270 kg • ha -1 • year -1 . Table 9 shows the silicon extraction for whole plants. Control units, extracted means of 5 482 mg, 5 220 mg and 4 917 mg, which were statistically similar to all treatments except for Slag 200 ppm and 400 ppm, which extracted only 26 mg and 11 mg respectively. Plants for such treatments did not grow nor developed because of the high pH levels ( Figure 5), therefore the biomass production was negatively affected. Apart from that, ladle furnace slag showed big concentrations of Fe, Cu, Zn, Mn, Pb and Cr (Table 2), hence any possible toxicity should not be discarded. There is extensive discussion on how silicon may relieve toxicity stress (Gu et al., 2011), however this beneficial effect depends on the easiness in which H 4 SiO 4 is absorbed. Ma et al. (2007a) mentions that high soil pH and low temperatures reduce the effectiveness of OsLsi-2 transporter, which partner OsLsi-1 (Ma et al., 2004) as the two transporters involved in the active silicon uptake by rice. This is the main route which is not influenced by transpiration flow (Nikolic et al., 2007). Further discussion on  this point will take place in the following section. Despite the fact that KSi 200 ppm treatment was the only one which had a significantly higher level of SiA (30.31ppm - Table 6), with suitable soil pH (5.59 - Table 4), silicon absorption was not statistically different from control treatments (Table 9). Similar increase in SiA was found by Yalda et al. (2020) for potassium silicate treatments. There is a possibility that control treatments could have received available silicon with the irrigation water, which was not measured. Other possibility is that the topsoil features and the environmental conditions of the experiment made it possible that the substrate could have solubilized enough silicon to satisfy plants' demand. This is supported by Paye et al. (2018), who argues that positive results on silicon fertilization can be seen only when soils have less than 11 ppm of SiA (using the CaCl 2 extraction methodology) and the initial available Si for our topsoil samples was 11.78 ppm, therefore they may have provided enough of this element.

The relation between silicon absorption and yield components
There are four components which determine yield in rice crop: (1) number of panicles per square meter, (2) number of spikelets per panicle, (3) % filled spikelets and (4)1000-grain weight (Yoshida,1981). The experimental unit consisted in a 7.5 L pot with one rice plant, therefore, the first yield component was related to the following morphological variables: number of tillers per plant (Figure 7) and number of panicles per plant (Figure 8). Figure 7 shows that all treatments were statistically similar to the control units, except for the Slag 200 ppm and 400 ppm treatments, which had considerably less tillers. This could be explained because of the detrimental soil pH conditions (Table 4) for those two treatments which made it impossible the normal growth of plants. Contrary to this, Das et al. (2020) found that slag treatments improved soil fertility as it enhanced microbiota activity, however dozes tested in that research work were smaller. According to Yoshida (1981) and Heros (2012), Nitrogen is the main element playing a role during the tillering stage, and all experimental units got the same Nitrogen fertilization. This explains why no enhancements were found in the potassium silicate treatments, despite having Si% increases in aerial organs (Table 8). Figure  8, portraying the number of panicles per plant, did not consider treatments of Slag 200 ppm and 400 ppm because none of them produced a single panicle. The rest of treatments were statistically similar to the control unit, except for the Ash 400 ppm treatment which was significantly superior. Rice husk ash, being an organic amendment, might have improved the physical properties in the pots by reducing the bulk density, helping the roots proliferate better, thus it might have helped to produce more panicles. Figure 9 summarizes whole plant's dry weight. This variable indicates   the total amount of photosynthates produced by each plant. It behaved similarly to the number of tillers per plant, however it is possible to see that Ash 400 ppm treatment had significantly lower values for this variable than the control units, despite having the highest amount of panicles ( Figure 8). This could be explained because rice husk ash provides large quantities of Ca, Mg and P (Table 2), therefore that reduction in dry weight in comparison with control units could have been attributed to a slight toxicity. Figure 10 summed up the second yield component, average number of spikelets per panicle. No significant differences were found in relation to the control units. Slag 200 ppm and 400 ppm treatments were not considered for this analysis because their experimental units did not produce any panicle. This yield component was not influenced by higher availability of silicon. The third yield component was 0 % because temperatures below 18 ℃ happened during the beginning of the stem elongation stage, which coincide with the transition to the reproductive stage (Figure 11), also pointed out by Hasanuzzaman et al. (2013), in which case, higher availability of silicon did not alleviate cold stress. The fourth yield component was estimated according to Abad (2017) who tested the same cultivar in the Amazonian region of San Martin and considering 90% of grain set per panicle. Thus, an estimated grain yield per plant was obtained portrayed in Figure 12. All treatments were statistically similar to the control units. Slag 200 ppm and 400 ppm treatments were excluded from this analysis for the reasons formerly explained. According to Table 2, potassium silicate provided mainly silicon and potassium, in contrast with the rice husk ash and ladle furnace slag, which also incorporated big amounts of P, Ca, Mg, Fe and Mn, as well as Pb and Cr. Such big quantities could have played a detrimental role in those treatments' yield components, however further tissue analysis must be executed to discard any toxicity or deficiency. Light intensity was also measured. Results are shown in Figure 13. According to Yoshida (1981), ideal levels of Photosynthetic Active Radiation (PAR) for rice is 300 cal • cm -2 • day -1 (57 mol • m -2 • day -1 ). It is possible to see that optimal levels were found until the beginning of the reproductive stage (May 10 th 2018). Camargo et al. (2007) and Pati et al. (2016) stated that high silicon concentration in rice tissues correlates  . Environmental temperature's fluctuation registered during the field stage of the experiment. Graphic was generated using the Elitech termohigrometer's software.
with yield increasing, however, this experiment did not reflect such findings. All current and past research highlights the benefits of silicon on yield enhancements; however, it focuses on tolerance to various forms of stress, both biotic and abiotic (Meharg & Meharg, 2015) Therefore, it would be incorrect to manage silicon nutrition as if it was nitrogen. Applying higher doses of this element did not improve rice yield components, under this experiment's-controlled conditions. There should be any unfavorable condition, such as presence of pests, diseases, water stress or deficit SiA, in order to see silicon fertilization's beneficial effects. Further research in other areas of Peru, where available silicon in soils is depleted, should be considered.  • Despite having two treatments with a significantly higher level of salinity, all of them remained within the tolerance limits for rice crops.
• Soil pH changed according to the treatment. Rice husk ash and potassium silicate treatments kept soil pH statistically similar to control units, however ladle furnace slag treatments significantly raised this variable. 200 ppm and 400 ppm ladle furnace slag treatments detrimentally affected growth and development of rice plants. Further tissue analysis should determine any deficiency or toxicity.
• Rice husk ash and ladle furnace slag have considerable amounts of other nutrients, nonetheless, ladle furnace slag demands further attention as it also contains some heavy metal elements such as Cr, Cd, Pb, Cu and Zn.
• Silicon availability did not keep the original concentration of 100 ppm, 200 ppm and 400 ppm. Possibly such high concentrations forced silicon polymerization. Control units variated varied from 11.78 ppm to 15 ppm at the end of the campaign.
• Potassium silicate treatments were considered as the base point for contrasting the silicon effects in the yield components, due to the fact that this amendment supplied predominantly silicon and potassium, while other elements' concentration were insignificant.
• Treatments which kept the higher levels of silicon availability without causing growing problems, were the potassium silicate treatments. In the same fashion, they had the higher silicon concentration in tissues.
• Higher silicon concentration in tissues did not correlate with any yield component's enhancement, for the given test conditions.