Effect of active silicon forms on phosphorous plant-availability in growing wheat (greenhouse experiment)

Abstract

Modern agriculture faces the problem of declining phosphorus fertilizer efficiency in chernozem soils. The increased Ca and Mg content facilitates rapid fixation of phosphorus supplied by fertilizers. Several studies show that the application of silicon-containing chemicals may increase phosphorus bioavailability in the soil and provide additional phosphorus nutrition to plants. The goal of the greenhouse experiment was to study the effect of natural silicon-containing minerals (zeolite and marl) and their thermally activated forms on the transformation of phosphorus compounds in the soil and phosphorus uptake by wheat plants grown on carbonate chernozem soil. Thermal activation of the natural minerals was carried out at 700°C for 15 minutes which significantly increased their content of active silicon forms. With separate or combined application of double superphosphate and silicon-containing minerals, increase of aboveground and underground biomass was observed. This effect may be explained by improved plant phosphorus nutrition, as the total phosphorus content in wheat roots and leaves increased in all variants of the experiment compared to the control. The greatest increase of phosphorus content in plant tissues was observed with the combined application of superphosphate and thermally activated marl. The data of the fractional analysis of phosphorus in the soil indicated that in the variant with the application of double superphosphate alone, a significant portion of the applied phosphorus was transformed into poorly soluble compounds, whereas the application of silicon-containing minerals, either separately or in combination with phosphorus fertilizer, resulted in decreased content of poorly soluble phosphates and increase of the content of plant-available phosphorus fractions. Thermodynamic calculations indicate the possibility of a substitution reaction of phosphate anions in calcium and magnesium phosphates by silicate anions. Thus, silicon-containing compounds may be used to increase the effectiveness of phosphorus fertilizers and improve the phosphorus nutrition of plants grown on carbonate chernozems.