Journal of the Indian Society of Soil Science

An appraisal was made in an ongoing long-term field experiment with a rice-rice cropping system followed for the last 17 years with 12 treatments and four replications having various combinations of inorganic fertilizers and organic manure. The 12 treatments were control, 100% N, 100% NP, 100% PK, 100% NPK, 150% NPK, 100% NPK + FYM@10 t ha^-1, 100% NPK + lime@1 t ha^-1, 100% NPK + lime@1 t ha^-1 + FYM@10 t ha^-1, 100% NPK + Zn, 100% NPK + B +Zn, 100% NPK + S + Zn. The present investigation was conducted during the year 2021-2022. After the harvest of kharif rice, the grain (42.4 q ha^-1) and straw (53.8 q ha^-1) yield were recorded as highest in plots receiving an integrated package of practices of both organic (FYM) and inorganic fertilizers along with ameliorant (100% NPK+FYM @ 10 t ha^-1 + lime @1 t ha^-1). The relative agronomic efficiency (RAE) was calculated as the highest (209%) in the same treatment followed by an optimal dose of NPK with organics. Various soil enzyme activities like dehydrogenase (DHA), urease, phosphatase, and β-glucosidase were also estimated the highest (72.62 μg TPF g soil^-1 day^-1, 106.40 μg NH₄⁺-N g^-1 soil 2 hr^-1, 432 μg p-nitrophenol g^-1 soil hr^-1 and 97.98 μg p-nitrophenol g^-1 soil hr^-1 respectively) in treatment where 100% NPK + FYM @ 10 t ha^-1 + lime @1 t ha^-1 was applied. A similar response was also noticed for microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorous (MBP) (182.86 μg C g soil^-1, 139.40 μg N g soil^-1, 19.78 μg P g soil^-1 respectively) in the same treatment followed by an optimal dose of NPK with organics. Interestingly SOC had a significant correlation with DHA (0.928^**), urease (0.925^**), phosphatase (0.950^**), β-glucosidase (0.853^**), MBC (0.789^**), MBN (0.732^**) and MBP (0.790^**). The soil enzymatic activities (DHA, urease, phosphatase, and β-glucosidase) were also positively correlated (R²=0.86, 0.93, 0.86, 0.77, respectively) with the total yield of rice and microbial biomass (C, N, P) was also positively correlated with SOC (R²=0.81, 0.83, 0.89, respectively).