Effect of inorganic and integrated nutrient management on soil carbon and nutrient status in Mollisols

From an ongoing long term field experiment at Norman E. Borlaug Crop Research Centre of the Govind Ballabh Pant University of Agriculture and Technology, Pantnagar, (Uttarakhand) soil samples were collected in 2015 to study the effect of sole application of fertilizers and their integration with different organic sources (farmyard manure, wheat straw and mungstraw) on soil nutrient status, organic carbon status and total carbon. The study revealed that under continuous cultivation of rice-wheat cropping system for 32 years all the nutrient management treatments failed to sustain the initial level of N (392 Kg ha-1), however soil phosphorus level was increased in all the treatments over initial value (18 Kg ha-1). In surface soil layer highest value of available nitrogen (316.46 Kg ha-1) and available phosphorus (26.64 Kg ha-1) was recorded in treatment where recommended dose of nitrogen was applied through both fertilizers and moong straw. The level of available potassium was decreased with sole application of fertilizers but increased slightly with integration of fertilizers with either FYM or moong straw. Although in both surface and sub-surface layers soil organic carbon content was increased significantly over control in all treatments receiving either fertilizers alone or in combination with organic manures but all these nutrient managements failed to sustain initial level (1.48%) of soil organic carbon. Integrated nutrient management raised organic carbon content to a higher level as compared to fertilizers alone. Similar trend was followed in soil total carbon. In surface soil highest values of soil organic carbon (1.19%) and total carbon (1.57%) were observed in treatments where 50% of N-fertilizer was substituted through moong straw followed by treatment where 50% of N-fertilizer was substituted through farmyard manure. So, it can be concluded that farmyard manure and green gram straw were better organic sources of plant nutrients and thus can be used as partial substitute of chemical fertilizers to maintain soil fertility and to sustain crop productivity.