Soil biological indicators associated with nitrogen mineralization patterns in rice soils under long-term integrated nutrient management

In long-term integrated nutrient management (INM) involving organic amendments with inorganic fertilizer application, understanding nitrogen (N) mineralization is key to assessing soil functioning. In this study, soil samples were collected following rice cropping from treatments consisting of various combinations of inorganic with organic fertilizers, including farm yard manure, wheat straw or Green Leaf Manuring, as well as 100% inorganic and a control (no fertilizer). The soil samples were incubated for 120 days at 30 & DEG;C for determining N mineralization potential, and the mineralization patterns were fitted to double first-order kinetic models to separate the potentially mineralizable nitrogen (PMN) into readily available N (PMN-I) and resistant N (PMN-II) fractions. The half-lives of PMN-I and PMN-II ranged from 1.2 to 3.3 days and 22.4 to 63.0 days, respectively. In the organically amended soils, we observed that microbial biomass carbon (MBC) and nitrogen (MBN) increased by 43% and 41%, respectively, compared to inorganic fertilizer application alone. Moreover, the soil enzyme activity increased, revealing enhanced biological activity (dehydrogenase-31.96 & mu;g TPF, Urease-35.69 & mu;g urea-N, glucosidase-57.78 & mu;g p-nitrophenol, fluorescein diacetate hydrolysis-45.84 & mu;g fluorescein, N-acetyl & beta;-glucosaminidase-46.47 & mu;g p-nitrophenol released g-1 dry soil h-1). We determined that PMN-I was affected by the soil urease activity; whereas, PMN-II was regulated by soil organic carbon, MBC, MBN, dehydrogenase activity and fluorescein diacetate hydrolysing capacity. These findings elucidate the soil biological indicators associated with nitrogen (N) mineralization, which can help optimize INM practice.