Modification of Infiltration Rates in an Organic-Amended Irrigated

Slow water infiltration in some California soils results in considerable irrigation water loss through increased runoff and evaporation. This 25-1110 study was conducted to evaluate the effects of different organic amendments on soil physical parameters and water infiltration rates on an irrigated soil. Incorporation of three loadings (25 Mg ha⁻ each) of poultry manure, sewage sludge, barley straw (Hordeum vulgare L.), and alfalfa (Medicago sativa L.) to an Arlington soil (coarseloamy, mixed, thermic Haplic Durixeralf) for 2 yr increased soil respiration rates (139-290%), soil aggregate stability (22-59%0), organic C content (13-84%), soil saccharide content (25-41%), soil moisture content (3-25%), and decreased soil bulk density (7-11%). The change in soil physical properties resulted in significantly increased cumulative water infiltration rates (18-25%) in the organic-amended plots as compared with the unamended plots. Although additions of poultry manure and sewage sludge contributed to higher soil organic matter compared with straw and alfalfa, the straw amendment was statistically more effective in increasing soil aggregate stability, total saccharide content, infiltration rates, and soil respiration rates and in decreasing bulk density in the tillage zone. The increase in cumulative infiltration rates measured with the first organic addition (April 1987–January 1988) were significantly correlated with increased soil aggregation (P ≤ 0.01). Cumulative infiltration rates during the second (February 1988–September 1988) and third (October 1988–May 1989) organic incorporation were signficantly correlated with decreased bulk density (P ≤ 0.01), but not with aggregate stability. Multiple linear regression analyses indicated that water infiltration rates in the organic-amended soils were initially increased by stimulation of microbial activity, which increased the stabmty of soil aggregates. Cumulative infiltration rates were further increased by a decrease in soil bulk density with additional organic treatments to the tillage zone.