Changes in Vertisol properties as affected by organic amendments application rates S. Ghosh 1,2 , P. L ockwood 2 , H. D aniel 2 , N. H ulugalle 3 , K. K ing 2 & P. K ristiansen 2 1 Centre for Urban Greenery and Ecology, National Parks Board, Singapore 259569, 2 Agronomy and Soil Science, University of New England, Armidale, NSW 2351, Australia, and 3 NSW Department of Primary Industries and Cotton Catchment Communities CRC, Australian Cotton Research Institute, Narrabri, NSW 2390, Australia Abstract There is considerable global interest in using recycled organic materials because of perceived benefits to soil health and environment. However, information on the effects of organic waste products and their optimal application rates on the quality of heavy clay soils such as Vertisols is sparse. An incubation experiment was therefore conducted using five organic amendments at various rates to identify their optimal application rates, which could improve the quality of the Vertisol. Cotton gin trash, cattle manure, biosolids (dry weight basis 7.5–120 t ⁄ ha), chicken manure (dry weight basis 2.25–36 t ⁄ ha) and a liquefied vermicast (60–960 L ⁄ ha, volumetric basis) changed the soil chemical, physical and microbiological properties compared with a control where no amendments were applied, viz. higher light fraction of organic matter, nutrient content (N and P) and soil microbial activity. Higher application of chicken manure resulted in an increase in dry-sieved mean weight diameter. Increasing rates of cattle manure increased exchangeable Na concentration and ESP. Although vermicast itself did not contribute a significant amount of N into the soil, when applied at higher rates (60–960 L ⁄ ha), its application resulted in increased concentration of NO 3 -N in soil by amounts ranging from 43 to 429%. Optimal application rates for cattle manure and cotton gin trash were 30 t ⁄ ha, whereas for biosolids and chicken manure, the optimum rate was 60–18 t ⁄ ha, respectively. Keywords: Vertisol, manure, compost, biosolids, vermicast, light fraction OM Introduction Continuous cultivation, which involves soil disturbance and vegetation removal, results in losses of soil nutrients, particularly soil organic matter, indicative of widespread soil degradation. Conservative land use practices are of growing interest, particularly with regard to replenishing soil nutrient losses. These practices include greater cropping frequency, reduced tillage and application of organic amendments (Sommerfeldt et al., 1988). Application of farmyard manure (FYM) onto agricultural soil has been a global practice for many years as a means of disposing waste and as a fertilizer for plant growth (Unger & Stewart, 1974). Numerous studies have shown that application of manure can improve the nutrient status of the soil, improve soil physical properties and also increase soil organic carbon levels (Chang et al., 1991; Aoyama et al., 1999; Eghball, 2002). Meek et al. (1982) reported that high rates (180 t ⁄ ha every 2 yr over a 9-yr period) of cattle manure applications to a silty clay soil led to increased availability of phosphorus (P) and potassium (K) in soil. Chang et al. (1991) observed that application of cattle feedlot manure resulted in an increase in total soil nitrogen (N) from about 6–8.2 Mg ⁄ ha with 90 Mg ⁄ ha manure application to the non-irrigated soil, and from 6 to 12 Mg ⁄ ha with the 180 Mg ⁄ ha manure application to the irrigated soil. Three annual applications of dairy cattle manure at varying rates of 22.5, 45, 90, 180 and 270 Mg ⁄ ha increased the total N and NO 3 -N in the surface soil (Mugwira, 1979). Substantial quantities of cotton processing waste, previously used as a cattle-feed substitute during drought, is presently dumped and left to degrade in stockpiles around the gins in cotton growing regions of southeastern Australia. Cotton-producers have recognized this waste as a potential Correspondence: S. Ghosh. E-mail: subhadip00@rediffmail.com Received June 2010; accepted after revision January 2011 Soil Use and Management, June 2011, 27, 195–204 doi: 10.1111/j.1475-2743.2011.00333.x ª 2011 The Authors. Journal compilation ª 2011 British Society of Soil Science 195 Soil Use and Management