Abstract

Oliver R. Khama, Kaiser Cedric and Lule E. Nelson

The role of organic matter (OM) in soil aggregation and saturated hydraulic conductivity (Ksat) has long been recognised but their depedence on the intensity of decay is less studied. The objective of this study was to determine the effect of decomposition intensity of incorporated chickpea manure on soil aggregate stability and Ksat. Samples of a clay loam and clay soil were collected from the top 15 cm layer and amended with chickpea green or mature dry manure and incubated at 30°C and ~60% water holding capacity. Decomposition intensity was determined by measuring CO 2 evolution using NaOH traps, aggregate stability by wet sieving and Ksat by the constant head method. All determinations were made 3, 7 and 30 days after incubation and the data analysed following the general linear model for a 2 × 3 × 3 factorial in randomised complete block design. Evolution of CO 2 in both soils and manure was highest on day 7 compared to day 3 and 30. In both soils >60% of the soil aggregates were macroaggregates >0.5 mm but the relative proportion of microaggregates <0.5 mm increased from ~10 to ~20% in the control and to ~15% in the amended cay loam soil in the day 30 treatments. Decomposition intensity was increased by incorporating chickpea manure which resulted in improved soil aggregate stability and Ksat especially in soil with low clay content. CO2 which is a simple product of decomposition may be used as a rapid indicator of soil aggregate stability and water movement in agricultural soils.