Long term effect of fertilizer, manure and lime on yield sustainability and soil or-ganic carbon status under maize (Zea mays)–wheat (Triticum aestivum) cropping system in Alfisols

A field experiment was conducted on permanent manurial trial (PMT), initiated in 1956 to evaluate the long-term impact of fertilizer, manure and lime application on yield trends, soil organic carbon status, soil quality parameters and their inter-relationship with sustainable yield index (SYI) under maize (Zea mays L.)–wheat {Triticum aestivum (L.) emend. Fiori & Paol.} cropping system at Ranchi. The treatments were control, 100% N, 100% NP, 100% NPK, 100% NPK + lime, FYM alone and ½ [(N + FYM) + P (A-X/2) + K (B-Y/2)]. The result indicated that continuous application of 100% NPK along with lime recorded increasing yield of maize (46 kg/ha/yr) and wheat (43 kg/ha/yr), while imbalanced use of fertilizers like 100% N, 100% NP showed decline in yield trend. The application of 100% NPK + lime recorded highest value of SYI for maize (43.87) and wheat (36.39), respectively followed by integrated use of organics and inorganics and FYM alone. However, the value of SYI was negative due to application of N alone. Continuous addition of organic manure alone or in combination with inorganic fertilizers significantly influenced the total organic carbon, CO₂ evolution, microbial biomass, water soluble carbon, water soluble carbohydrates. The relationships between sustainable yield index (SYI) and soil quality parameters revealed that the total and active fractions of SOC ultimately support the productivity and in contrast, their losses reduce the nutrient supplying capacity of soil. Thus, continuous application of 100% NPK along with lime, FYM and integrated management practices had beneficial impact on restoration of SOC, maintaining soil fertility and yield sustainability of maize–wheat cropping system in Alfisol.