Effect of silicate on nutrition and yield of wheat

Universidade Estadual do Oeste do Paraná – UNIOESTE. Campus Marechal Cândido Rondon/PR, Pernambuco Street No. 1777, Zip Code 85960-000, Parana state, Brazil. Universidade Estadual do Oeste do Paraná/ Centro de Ciências Agrárias. Rua Pernambuco, 1777, CEP: 85960-000. Marechal Cândido Rondon, Paraná, Brazil. Master's Energy in Agriculture, Rua Universitária, 2069, ... (UNIOESTE), in the city of Cascavel, Paraná, Brazil.


INTRODUCTION
Wheat (Triticum aestivum L.) is an important winter cereal crops from Brazil.In 2012/2013 season, the wheat production area was of 2.0 million ha, producing 4.2 million tons of grains (Conab, 2013).Wheat production, mostly concentrated in the three southern-most states of Paraná, Santa Catarina and Rio Grande do Sul, is shifting further south.Paraná is the largest wheat producing state.
The calcium and magnesium silicate can be used as corrective of soil acidity and as silicon (Si) source (Ribeiro et al., 2011;Crusciol et al., 2009).Silicon is not considered an essential element for plant growth.Several studies have shown that Si application is beneficial to crops such as rice (Zanão Júnior et al., 2010), sugar cane (Demattê et al., 2011), maize (Zargar and Agnihotri et al., 2013) and wheat (Soratto et al., 2012), which are considered Si-accumulating species.However, Si is still relatively unknown and rarely applied in agriculture.Silicon uptake can occur actively, in an energy-spending process, even when roots are exposed to high concentrations of this nutrient (Malavolta, 2006).In plants take up Si exclusively as monosilicic acid, also known as orthosilicic acid [Si(OH) 4 ] (Elawad and Green Junior, 1979).In many cases, increasing Si availability has increased crop development and yield, once this nutrient can indirectly influence some photosynthetic and biochemical aspects, especially in plants under biotic or abiotic stress conditions (Ma and Yamaji, 2006).The largest growth and biomass accumulation of plants grown with the Si application is associated to the changes in plant architectures, making them more erect, improving the angle of leaves and light interception, avoiding the excessive self-shading, delaying senescence, increasing the structural rigidity of the tissues and improving photosynthesis and reducing lodging (Gong and Chen, 2012;Ma and Yamaji, 2008).These beneficial effects are attributed to Si deposited in the cell wall of various plant organs (Ma and Yamaji, 2006) and by other mechanisms.High deposition of Si in tissues forms a physical barrier that enhances the strength and rigidity of the tissues.
There are few studies on the effect of Si on plant nutrition, with the majority of publications reporting aspects of wheat growth and the beneficial role of this element in resistance to biotic and abiotic stress (Rizwan et al., 2012).In addition to this aspect, the beneficial effects of Si are not always observed (Dann and Muir, 2002).There is evidence that Si has no effect on dry matter yield in Brachiaria grasses under water stress conditions (Melo et al., 2003).
Considering that the use of silicate tends to be and most common agricultural practice in Brazil, an improved understanding of the effect of Si on wheat crop is essential in order to adopt management strategies for improving crop production.In this context, the purpose of this study was to investigate the effects of Si on nutrition and yield of wheat (T.aestivum L.) subjected to high rates of calcium silicate in the soil under controlled conditions.
The experiment was arranged in a completely randomized design, with five treatments, and four replicates.The treatments consisted of growing wheat plants with 0 (control), 1.2, 2.4, 4.8 and 9.6 Mg ha -1 of calcium silicate (Ca 2 SiO 4 ).The calcium silicate source used was AgroSilício ® (10.5% Si; 25% Ca and 6% Mg).The fertilized soil was kept for 15 days with water content near the field capacity.The basic fertilization was carried out with applying 30 mg kg -1 of N (urea), 60 mg kg -1 of P (simple superphosphate), 45 mg kg -1 of K (potassium chloride).At 30 days after plant emergence, the application of 45 mg kg -1 N was applied as a urea solution.
Five seeds of wheat (T.aestivum L., cv.BRS Pardela) were sown, and 9 days after seedling emergence, they were thinned to three plants per pot.The soil water content was monitored daily and maintained near at the field capacity.
At maturity (115 days after plant emergence), soil samples were collected for evaluation of pH CaCl 2 (1:2.5 suspension solo/CaCl 2 0.01 Mol L -1 ), the crop yield was evaluated in terms of shoot dry matter production (SDM, g pot -1 ), grain yield (g pot -1 ) and the harvest index.The shoot length was measured (cm plant -1 ) using meter scale.Plants of all treatments were harvested separately, dried for 4 days at 65 ± 2°C, and then weighed.The number of spikes per pot was also measured.Wheat flag leaves were also collected for foliar diagnosis.The collected leaves were dried in a forced-air oven for 3 days at 65 ± 2°C, grounded to smaller size and analyzed.Concentrations of K, Ca, Mg, Cu, Fe, Mn, and Zn were determined by flame atomic absorption spectrophotometry, P was determined by colorimetry, N by sulfuric acid digestion and vapor distillation, and Si by hydrogen peroxide and sodium hydroxide digestion and determined by colorimetry, as previously described (Embrapa, 2009), and Si by digestion with hydrogen peroxide and sodium hydroxide and then by colorimetry (Korndorfer et al., 2004).Original data were analyzed by analysis of variance (ANOVA) and regression analysis, and significant equations with the highest coefficients of determination (F-test, P ≤ 0.05) were adjusted.All analyses were performed using Saeg 8.0 software for Windows (Statistical Analysis Software, UFV, Viçosa, MG, BRA).

RESULTS AND DISCUSSION
The application of silicate significantly increased the concentration of Si in the shoots of wheat in both the stem and leaves (Figure 1), the concentrations of Si in the leaves increased from 26.7 g kg -1 in the control to 36.2 g kg -1 with a maximum dose of Si (9.6 Mg ha -1 ).The Si concentration in leaves was on average higher than the stem.In the initial values stem 12.29 g kg -1 in control, increasing to 17.27 g kg -1 at a dose of 9.6 t ha -1 (Figure 1).The increased concentration of Si in the shoots indicated that the source of Si used is reactive and very effective in providing Si in the soil and the plant.
Corroborating the results of Korndörfer et al. (2010), this reported that the application of Si in soil caused concentration of this nutrient in the leaves, but did not alter the production of dry matter.The differences in the concentration of Si were not enough to affect the vegetative growth of forage.
Lima Filho and Tsai (2007) also observed absorption exponentially in three cultivars of wheat and two of oats with Si added to the nutrient solution until the dose of 100 mg l -1 , and concluded that the two grasses, wheat and Table 1.Effect of calcium silicate rates on concentrations of N, P, K, Ca, Mg, S, Cu, Zn, Fe and Mn in the flag leaf of wheat (T.aestivum L.) plants.oats, have high absorption capacity of silicon, indicating the possibility of absorbing larger amounts if there were an increase in the availability of the substrate element.

Calcium
The use of calcium silicate positively increased linearly CaCl 2 pH values, with threshold values of 4.6 increasing to 6.6 at the highest dose (Figure 2).Similar results with the effect of silicates in neutralizing soil acidity were also obtained by several authors (Korndörfer et al., 2010).This effect of the slag ground reaction occurred primarily by the presence of the base SiO 3 2-silicate generated by the reaction of compounds in the soil (Alcarde, 1992), which positively affects the pH.Ramos et al. (2006) studied different ways of correcting the pH in a Quartzipsament and observe that the silicates were more efficient than gypsum and limestone.Prates et al. (2011) observed that the application of calcium silicate and magnesium to the soil increased the pH and did not affect the growth and development of physic nut.
Application of calcium silicate did not affect the N, P, Mg, S, Cu, and Fe concentrations in the wheat flag leaves (Table 1).These results agree to report by Soratto et al. (2012), who found that the N, P, Ca, Mg and S concentrations in the wheat flag leaves were not affected by silicon leaf application.Potassium and Ca concentrations in the wheat flag leaves were increased by the application of calcium silicate rates and the Zn and Mn concentrations were reduced (Table 1 and Figure 3).Soratto et al. (2012) also found that the silicon leaf application increased K concentration in the wheat flag leaves.Despite the effects of silicate treatments, only N, P, K, Mg and Cu concentrations were within the ranges considered appropriate by Cantarella et al. (1997), which are 20 to 34 g kg -1 , 2.1 to 3.5 g kg -1 , 15 to 30 g kg -1 , 1.5 to 4.0 g kg -1 and 5 to 25 mg kg -1 , respectively.Calcium, Fe, and Mn concentrations were above the optimum ranges, which are of 2.5 to 10 g kg -1 , 10 to 300 mg kg -1 , and 25 to 150 mg kg -1 , respectively.Sulfur and Zn concentrations were below the optimum ranges, which are of 1.5 to 3.0 g kg -1 and 20 to 70 mg kg -1 , respectively.
These results confirm those obtained by Moraes et al. ( 2009) except for Mn, in which to assess the effect of calcium and copper sulfate on the nutritional content of bean silicate, found that doses of calcium silicate had no significant effect on the concentration of Cu, Fe and Mn in shoots, however, observed a reduction of the levels of Zn.
The application of 9.6 Mg ha -1 calcium silicate increased the K and Ca concentrations in the wheat flag leaves in 29 and 38%, respectively as compared to control (Figure 3a and b).The results presented here are similar to those reported by Rocha et al. (2011), who found that the residual effect of silicate tended to enhance the K concentration in sorghum leaves.This result can be a consequence of improved root growth, once Si application enhances root structures, as reported by Carvalho-Pupatto et al. (2003).In addition this increase in Ca concentration in the wheat leaves (Figure 3b) is due to supply of this nutrient with calcium silicate rates.
Zinc and Mn concentrations in the wheat flag leaves decreased progressively with increasing rates of calcium silicate.The percentage reduction of Zn and Mn concentrations was 29 and 68%, respectively, when comparing the growing wheat plants with 0 (control) and 9.6 Mg ha -1 (Figure 3c) and 7.0 Mg ha -1 of calcium silicate (Figure 3d).Lower concentrations of Zn and Mn in wheat leaves with calcium silicate rates occurred because the silicate use may rates the soil pH (Figure 2), thereby reducing the bioavailability of these micronutrients in the soil.
The Mn was higher rated for culture (Raij, 2011) range.A comprehensive range of Mn in the nutrient suitable range is between 25 to 150 mg kg -1 , and the plants showed mean values of 162.3 to 430.3 mg kg -1 .The Sarto et al. 959 deposition of Si on the leaves helps to improve the distribution and avoid toxicity, reducing the mean concentration of Mn in the tissues of wheat (Figure 3d).According to Zanão Junior et al. ( 2010), the addition of Si to the solution increased the content of Mn in roots and decreased in leaves and sheaths, showing a lower translocation of Mn to leaves which indicates that Si reduces the toxicity caused by Mn, what may be an alternative to alleviate such adversity.In areas where excess Mn is a problem, studies to establish rates and sources in order to increase the Si availability to plants must be implemented to supplement information for fertilizer recommendations for this crop.
Lima Filho and Tsai ( 2007) also observed a decrease in the Mn and Zn in wheat with the supply of Si in nutrient solution; this was attributed to the fact that the accumulation of dry matter increased faster than the rate of accumulation of nutrients, resulting in a dilution effect for most nutrients studied.
Calcium silicate provided better balance in the absorption of Mn to the grain, reducing excessive amount absorbed while maintaining the appropriate concentration range (25 to 150 mg kg -1 ) according to Raij (2011).According to Okuda and Takahashi (1964), the Si may provide better nutritional balance in the rice plant due to its ability to reduce the absorption of Mn.When rice plants are fertilized with Si, increased oxidation of Mn 2+ is the surface of the roots, and as a result, these precipitated nutrients not being absorbed by the plant.Rogalla and Römheld (2002) worked with cucumber plants grown with Si supply, found less than 10% of Mn in the symplast and more than 90% bound to the cell wall.Regarding plants that did not receive Si, the distribution of Mn was similar in the two compartments.These authors claim that tolerance of cucumber plants to Mn toxicity is also due to its attachment to the cell wall, which lowers its concentration in the symplast.
The application of calcium silicate rates did not affect plant height and shoot dry matter, number of spikes per pot, grain yield and harvest index of wheat (Table 2).The results presented here are similar to those reported by Melo et al. (2003) and Tokura et al. (2007); these authors found that the Si application did no effect dry matter production of Brachiaria grasses and rice, respectively.However, a beneficial effect of silicate application on wheat growth and yield was expected as reported by Soratto et al. (2012).Silicon positively influences plant growth and biomass production, especially monocotyledons, as a consequence of improved tissue rigidity, better angle of leaves and light interception, improving photosynthetic rate (Gong and Chen, 2012;Ma and Yamaji, 2006).According to Elawad et al. (1982), Si is involved in cell elongation and division processes as well as in hormone balance.
Studies indicated that there is an increased on number of a wheat spike per area with Si foliar application compared to the control (Soratto et al., 2012).Takahashi  (1995) had also confirmed the effects of Si on the number of rice panicles per area.These authors attributed higher number of spikes or panicles per area to a better Si nutrition of plants.Soratto et al. (2012) found that grain yield was significantly increased by Si leaf application compared to the control (without Si application), as a result of the higher photosynthetic area, due to the higher dry matter production and higher number of spikes per area.In this study, the numbers of spikes per pot and grain yield were not increased by silicate application (Table 2).The lack of response to Si fertilization can be seen when the initial Si content available soil is above the critical level, as in the work of Mauad et al. (2003).
According to Korndörfer et al. (1999), the Si content available soil (extracted with CaCl 2 0.05 mol L -1 ) at least 6 to 8 mg dm -3 , in general, indicates a high probability of response to Si application, but the Si contents in the soil studied were high, with 18.9 mg dm -3 Si may be one reason for the lack of response of wheat.
Studies have demonstrated that Si is involved in a number of structural, physiological and biochemical aspects of the plant cycle, with diverse functions.As pests and diseases were controlled during the experiment and irrigation ensured the water supply, it is believed the absence of Si effects may be correlated to the lack of biotic or abiotic stress.Beneficial effects of Si on plant metabolism has been attributed to the fact that this element activate genes involved in phenol production and enzyme activity related to defense mechanisms, especially in plants under biotic or abiotic stress conditions (Buck et al., 2008;Ma and Yamaji, 2006).The results presented here report that a larger number of studies must be conducted because the beneficial effects of silicate on wheat, Si-accumulating specie, are not always observed.

Conclusions
Calcium silicate increased the pH of the soil, and the silicon concentration in leaves and stems of the wheat.Application of calcium silicate increased K and Ca concentrations in the flag leaves of wheat and reduced Zn and Mn concentrations, whereas the treatments did not influence the concentrations of all other nutrients.Application of calcium silicate did not affect development, yield components and grain yield of wheat crop.

Figure 1 .
Figure 1.Effect of dose of calcium silicate on foliar concentrations of silicon on leaf and stem in wheat (T.aestivum L.) plats.

Figure 2 .
Figure 2. Mean values of pH CaCl 2 at the end of the experiment, after cultivation with wheat (T.aestivum L.), depending on the doses of calcium silicate.

Figure 3 .
Figure 3.Effect of calcium silicate rates on potassium (A), calcium (B), zinc (C) and manganese (D) concentration in the flag leaf of wheat (T.aestivum L.) plants

Table 2 .
Effect of calcium silicate rates on plant height, shoot dry matter, number of spikes per pot, grain yield and harvest index of wheat (T.aestivum L.) plants.

Calcium silicate Plant height Shoot dry matter Number of spikes per pot Grain yield Harvest index Mg ha
ns, not significant; CV, coefficient of variation.