Evaluating Fertilization Effects on Soil Physical Properties Using a Soil Quality Index in an Intensive Rice-Wheat Cropping System

Soil quality assessment has been suggested as an effective tool for evaluating sustainability of soil and crop management practices. The objective of this study was to develop a sensitive soil quality index (SQI) based on bulk density (BD), water-holding capacity (WHC), water-stable aggregates (WSA), aggregate mean weight diameter (AMWD), total organic C (TOC) and C input to evaluate the important rice-wheat cropping system on an Inceptisol in India. A long-term experiment has been conducted for 18 years at the Indian Council of Agricultural Research-Indian Institute of Farming Systems Research, Modipuram, India. The treatments selected for this study were comprised of a no-fertilizer control and N, P and K fertilizers (NPK) combined with Zn and S fertilizers (NPK Zn S), farmyard manure (NPK FYM), green gram residues (NPK GR) and cereal residues (NPK + CR), laid out in a randomized complete block design with three replications. Soil samples were collected and analyzed for BD, WHC, WSA and TOC. Correlation analysis revealed that both rice and wheat yields significantly increased with the increases in AMWD, TOC and C input, but decreased with the increase in BD. The SQI values were then generated based on regression analysis of BD, WSA, AMWD, TOC and C input with rice and wheat yields for the 0-15 and 15-30 cm soil layers, respectively. Regression analyses between crop yields and SQI values showed a quadratic type of relation with the coefficient of determination (R-2) varying from 0.78 to 0.89. With regard to soil sustainability, applying crop residues to both rice and wheat could maintain soil quality for a longer period, whereas the highest yields of both the crops were recorded in the NPK Zn S treatment. The regression equations developed in this study could be used to monitor soil quality in a subhumid tropical rice-wheat cropping system.