Application of Soil Conditioner Solutions to Soil Columns to Increase Water Stability of Aggregates1

Abstract

Soil aggregate stabilization by water-soluble anionic polymers (soil conditioners) applied by drip irrigation was studied in columns containing silt loam and clay aggregates. Soil conditioners moved during irrigation to depths similar to the wetting front depth (30 cm) and increased aggregate water stability. Conditioning depth was controlled mainly by convective flow through the soil profile. Distribution of conditioner macromolecules, which affects the size of water-stable aggregates, was controlled by both convective flow into aggregates and molecular diffusion. Conditioning depth and mean diameter of water-stable aggregates were found to depend on initial aggregate size, initial soil moisture content, application flux rate, polymer molecular weight, solution concentration, and total applied volume. Conditioning effect was more apparent in silt loam than in clay loam. Best conditioning results were obtained for silt loam aggregates at a moisture content somewhat lower than field capacity, treated with polymers of molecular weight >75 000 at concentrations >4 g L−1 applied at a small flux rate of 1.5 × 10−3 cm s−1 (50 mm h−1). Conditioners of molecular weight <75 000 acted better than those of molecular weight >75 000 in increasing water stability of aggregates in the surface layer.