Short-term effects of organic amendments on properties of a Vertisol

Abstract

Application of organic waste products as amendments has been proposed as a management option whereby soil quality of Vertisols could be improved. An incubation experiment was, therefore, conducted for 4 weeks under controlled temperature conditions (30°C) to identify those potential organic amendments that might improve the quality of a Vertisol. Twelve organic amendments were investigated: cotton gin trash from three sources, cattle manure from two sources, green waste compost, chicken manure from three sources including a commercial product, biosolids and two commercial liquefied vermicomposts. Except for the biosolids, no other organic amendments had any effect on soil microbial biomass and respiration. Compared with NO₃₋N levels in the control, there was a 50% decrease in soil amended with 10 t ha⁻¹ green waste compost (65 μg g⁻¹). The three different types of chicken manures increased the NO₃₋N concentration from 75% (228 μg g⁻¹) to 226% (424 μg g⁻¹) over the control. Approximate recovery of P added by the amendment as resin-extractable soil P was 53% for cattle manure and 39% for chicken manure. Application of cattle manure resulted in a 22% increase in soil-exchangeable K over levels found in control. Organic amendments application also resulted in a significant increase in exchangeable Na concentration. Some of the organic wastes, viz. cotton gin trash (10 t ha⁻¹), cattle manure (10 t ha⁻¹), biosolids (10 t ha⁻¹) and composted chicken manure (3 t ha⁻¹) have value as a source of nutrients to soil and hence showed potential to improve Vertisol properties.