Silicon Dynamics in Soils Under Different Cropping Systems in Louisiana.

Silicon (Si) is classified as a beneficial nutrient taken up by several plant species at levels even higher than nitrogen (N) and potassium (K). With continuous cropping, the amount of plant-available Si may likely become yield-limiting especially for Si-accumulator plants. The concentration of plant-available Si in the soil is controlled by several reactions, commonly influence by soil type and management practices. The objective of this study was to investigate the adsorption and desorption of Si onto soil particles of soils under different cropping systems in Louisiana. In addition using the same soil types, the influence of silica (CaSiO3) fertilization on ryegrass biomass accumulation, and concentration of extractable Si and plant-essential nutrients was also evaluated. Bulk soil samples collected across Louisiana were air-dried and processed to pass a 5-mm size sieve. Pots were filled with approximately 2 kg of processed soils and applied with different rates of CaSiO3 slag (0, 1, 2, 4 and 8Mt ha-1) and two check pots, with (2 Mt CaCO3 ha-1, calcium carbonate equivalent – 81%) and without lime. All treatments for each soil were replicated four times and arranged in a split plot in randomized complete block design. The positive effect of CaSiO3 fertilization on the amount of biomass samples at 30 days after sowing was not consistent across the soil types. The amount of extractable Ca and soil pH of all soil types increased with increasing rates of CaSiO3 slag. The adsorption studies by Batch method showed moderate to high adsorption of plant available monosilicic acid in all the soils. The highest adsorption was observed on the 7th day of incubation of Norwood fine sandy loam soil from Rapides Parish. The trend in adsorption was  attributed to the chemical nature of monosilicic acid and the physicochemical properties of the soil. Across all soil types, the amount of adsorbed monosilicic acid increased with the amount of initial soil Si content and total time of incubation.