Calibration and Categorization of Plant Available Silicon in Louisiana Soils

Abstract

A survey was conducted to document the silicon (Si) content of soils from 27 (selected) agrarian parishes of Louisiana using different extraction procedures. For 0.01 M calcium chloride (CaCl©ü) extraction procedure, all surveyed soils (n=212) fell below 56 mg Si kg⁻©ö. For five of the procedures, about 50% of surveyed soils in Louisiana had Si level below the critical Si level that thus far established in other regions. Calcium silicate slag and wollastonite were compared through chemical extractions after laboratory incubation with six different soil types, and then an assessment of quantity of monosilicic acid (H©þSiO©þ) sorbed and the quantity in solution was made. It was concluded that the addition of large quantities of slag or any Si rich fertilizer with high rate of dissolution will lead to the greater polymerization of the H©þSiO©þ. A greenhouse study was also conducted with six soil series of Louisiana with distinct physico-chemical properties, to evaluate different soil test methods and estimate the critical soil Si level for rice. At harvest, dry matter yield and Si uptake by straw and panicles, and soil Si levels using seven different extractants were evaluated. The soil Si extracted by 0.5 M acetic acid (24 hours rest, 2 hours shaking) and 0.01 M CaCl©ü showed maximum linear positive correlation (r ©÷ > 0.45) with shoot biomass yield, and Si uptake. The soil Si critical level determined using quadratic regression model (P < 0.03) for Sharkey clay soil was 110 mg kg⁻©ö but for Crowley silt loam and Commerce silt loam were 37 and 43 mg kg⁻©ö. It is very likely that certain regions in Louisiana would benefit from Si fertilization in rice and sugarcane production. Also, there is a need to establish the soil or site specific extraction procedure because it is unlikely that there is a single universal extraction procedure for all soils.