Improvement of soil health and nutrient transformations under balanced fertilization with integrated nutrient management in a rice-wheat system in Indo-Gangetic Plains - A 34-year Research outcomes

The impact of integrated nutrient management seems crucial for the sustainability of crop production as revealed by studies on long -term experiments. It provided the opportunity to monitor long -term variations in crop yields and associated factors. The impacts of various nutrient management strategies on yields and soil attributes in a rice-wheat system have been researched under a long -term experiment that has been running since 1983 at Punjab Agricultural University, Ludhiana. Further, a positive correlation has been observed between crop yields and soil properties such as soil organic carbon (SOC), nitrogen (N), phosphorus (P), potassium (K) and zinc (Zn). The negative correlation with K could be attributed to soil becoming deficient in K and necessitating the application of potassium fertilizer. The treatments receiving organic manures (green manure, farmyard manure and wheat cut straw) showed a better population of soil microorganisms in comparison to the treatments receiving chemical fertilizers, thereby proving as precursors of sustaining soil health. The best soil characteristics (water-soluble aggregates, exchangeable and non-exchangeable K, fixed and total K) after rice and wheat harvesting were found where 50 % of the recommended NPK was supplemented with farmyard manure (FYM). The build-up of trace elements particularly for Fe and Zn was also noticed. In crystalline Fe oxide bound fraction (CFeOX), Fe increased between 717.1 and 984.8 mg kg -1, while Zn increased between 2.64 and 3.08 mg kg -1. Furthermore, amorphous iron oxide (AFeOX), CFeOX, carbonate (CARB), organic matter (OM) bound and exchangeable (EXCH) Fe and Zn were higher in treatments where organic manures were supplemented with 50 and 25 % N. Farmyard manure showed an incremental trend, followed by wheat cut straw and green manure (GM). The incre- mental trend in soil quality was noticed with FYM followed by wheat cut straw and GM.