Effect of fertilizers and INM on soil properties under long term rice-wheat cropping system in Mollisols

To evaluate the effects of inorganic fertilization and integrated nutrient management on soil organic carbon (SOC), soil carbon storage, soil chemical properties (pH, electrical conductivity) and bulk density, replicated soil samples were collected in May 2015 from a 32 year old long term field experiment at Norman E. Borlaug Crop Research Centre of the Govind Ballabh Pant University of Agriculture and Technology, Pantnagar, (Uttarakhand). Continuous application of fertilizers either alone or in combination with organic nutrient sources (farmyard manure, wheat straw and mungstraw) decreased the soil pH with lowest pH value of 7.01 in the treatments where 25% of recommended dose of N-fertilizers was substituted by mung straw. But, a reverse trend was obtained in case of EC of soil with maximum increase of 46% in treatment where integration of fertilizers and FYM was done in 50: 50 ratio. However no significant difference was observed in values of soil bulk density among different treatments upto 30 cm depth. Under continuous cultivation of rice-wheat cropping system for 32 years the initial level of organic carbon could not be sustained. However in both surface and sub-surface soil organic carbon content was increased significantly in treatments receiving either fertilizers alone or in combination with organic manures over control. Similar trend was followed in soil organic carbon stock. In surface soil highest values of soil organic carbon (1.19%) and soil organic carbon stock (22.49 t ha-1) were observed in treatments where 50% of N-fertilizer was substituted through mung straw. So, it can be concluded that farmyard manure and green gram straw were best organic sources with respect to soil fertility and can be used as partial substitute of chemical fertilizers.