46-16 Impact of Long Term Management Practices on Soil Chemical Properties Under Cotton Based Organic and Conventional Farming Systems.
However, the process of changes in soil chemistry and how it affects the soil fertility during transition from conventional to organic farming is not well explained in tropical environments. A long-term farming systems comparison trial consisting of a two year crop rotation with Cotton-Soybean-Wheat was set up in 2007 on Vertisols of Madhya Pradesh, Central India. Replicated field plots under continuous organic (Organic and bio-dynamic) and conventional (with and without Bt-cotton) management provides a unique opportunity to examine the process of changes in soil chemical properties over time. The results show a significant increase of soil organic carbon (SOC) in top-soil under bio-dynamic management compared to conventional and Bt-conventional system (0.69 v. 0.59 and 0.57). Over a period of seven years, SOC in the top-soil increased by 0.25 ± 0.02 percent points and 0.21 ± 0.03 percent points under bio-dynamic and organic systems management compared to 0.11 ± 0.02 percent points and 0.16 ± 0.02 percent points under conventional and Bt-conventional systems, respectively. However, SOC in sub-soil did not differ among the systems. Organic management slightly increased alkalinity of soil (8.54 to 8.56) whereas Bt-conventional management reduced the alkalinity of soil (8.52 to 8.39). Organic systems had more total N in top-soil compared to conventional systems, while all systems depleted N in subsoil. A vertical stratification was also measured for P: All systems reflected the addition of P in top-soil and depletion in sub-soil. Fe (EDTA) content of soil increased under all systems with significantly higher additions in top-soil than sub-soil. In all systems, the macronutrients K and Mg, and the micronutrients Zn, Cu and Mn showed an increase in top-soil and depletion in sub-soil. It is evident that fertility of top-soil can be improved with organic managements, however none of the tested systems is replenishing the nutrient pool of sub-soil.