Sub-soil Properties as Influenced by Long-Term Manuring and their Relationship with Yield and Sustainability of a Rice-Rice Production System in Eastern India

Investigation was made to study the impact of long-term fertilizer and manure application on the sub-soil properties of an acidic Inceptisol under continuous rice-rice cropping system. For this purpose, a long-term fertilizer experiment commenced from 2005-06, rabi season in the Central Farm of Odisha University of Agriculture and Technology (OUAT), Bhubaneswar under aegis of ICAR, New Delhi was used. The experiment had 12 manurial treatments whose impact has been assessed after 20 cropping cycles. The initial soil was acidic (pH 5.8) with low soil organic carbon (4.3 g kg -1) and CEC of 3.75 cmol (p+) kg-1. After 20 cropping cycles there was decrease in surface soil pH in all the fertilized treatments by 0.16 - 0.96 units except high yielding FYM amended treatments (NPK+FYM and NPK+FYM+lime) that resisted the drop. The pH, however increased to alkaline level (7.72-8.44) down the layers irrespective of treatments. More accumulation of salt was found at 60-75 cm layer with highest (0.418 dSm-1) recorded in 100% NPK + FYM+lime treatment. The soil organic carbon (SOC) content increased in all the fertilized treatments in the surface layer and with depth it decreased sharply from 15-30 cm to 30-45 cm layer. The high yielding NPK+FYM treatment had highest content of SOC in all the layers. Among the parameters studied, SOC of all the layers, pH & EC of 15-30 cm layer could explain maximum variation in both yield and sustainability. Lower layer properties particularly of 15-30 cm layer had strong correlation with the surface layer. The SOC of layers up to 75 cm could explain 64.1 - 85.8% variation in productivity and 53.0 to 78.7 % variation in sustainability. The pH and EC of 15-30 cm layer also explained 75.6 and 47.9 % variation in productivity and 75.4 and 62.3 % in sustainability, respectively. Thus, lower layers also contribute to soil fertility of surface layer and in turn the productivity and sustainability of wet land rice-rice cropping system in sub -tropical ecosystem.