Stratification of mineral-N, P, K and organic C in the vertisols as affected by tillage systems

摘要

Field experiments were conducted from 1996 through 2001 with a fixed layout. Cotton was sown within 2-5 cm of the previous years (60 cm row spacing). At the end of six years, soil was sampled from different depths (0-7.5, 7.5-15 and 15-30 cm) and positions (within planted row and between rows) of the three tillage systems namely, conventional tillage (CT), reduced tillage-1 (RT_1) and reduced tillage-2 (RT_2). The soil samples were analyzed for mineral-N, available P. exchangeable K and soil organic C (SOC). Continuous application of fertilizers within a planted row resulted in horizontal and vertical stratification of nutrients. Tillage effect was not significant but depth effect was highly significant for exchangeable NH_4~+, available P. exchangeable K and SOC. The nutrient content declined with increasing depth. Nitrate content was almost uniform through out the soil depth (0-30 cm) indicating its mobile nature. In general, fertilizer nutrient content was more within a planted row (WR) thanthe between row (BR) sampling position. The differences were significant for NO_3~-, NH_4~+ and exchangeable K~+. Tillage X position, tillage X depth X position interactions were highly significant for nitrate, ammonium, available P and exchangeable K. Within row surface layer (0-7.5 cm) of the RT plots, generally, had greater amount of exchangeable NH_4~+, available P and exchangeable K compared to the CT plots. SOC declined with depth, however, it was not affected by tillage and sampling position. Although no change in soil lest rating was evident after six years, positional application of fertilizers may affect the nutrient status and may warrant a change in the fertilizer recommendation to cotton.