Effect of Organic Matter Amendment on Hydraulic and Pore Characteristics of a Clay Loam Soil

Abstract

The objective of this study was to examine the effect of compost, rice straw and sawdust amendment on hydraulic and pore characteristics of a clay loam soil. Amendments were applied at an application rate of0.2 m3/m3 (apparent soil volume) in three rectangular plots each comprising an area of3.0 m2. Water retention characteristics were measured by hanging water column and centrifuge method. Hydraulic conductivity was measured by disc permeameter at -15.0, -6.0, -3.0 and0 cmof water pressure heads. Volumetric water content increased in all amended soils, compared with the control. Unsaturated hydraulic conductivity was almost identical for straw and sawdust at all pressure heads, although that for compost amended soils were much higher. Field saturated hydraulic conductivity (Kfs) was higher in organic matter amended soils as were number of macropores (14.7% - 29.2%). Contribution of each pore class to the total saturated flux was evaluated from the hydraulic conductivity and water retention measurement. A new alternative weighed factor (We) was proposed to estimate the actual contribution of macro- and mesopores to the total saturated water flux. The Wg was found to be more representative for calculating pores contribution to saturated water flux than that of hydraulic conductivity measurement. Although there is only a small fraction of the total porosity, amendment increased effective macro- and meso-porosity (qe). Pores in the amended soils were hydraulically active and water movement was dominated by gravity. Collectively, our results demonstrated that organic matter generated as agricultural by-product could effectively be used to improve soil quality