Soil Nitrogen Fractions in Relation to Rice-Wheat Productivity: Effects of Long-Term Application of Mineral Fertilizers and Organic Manures

ABSTRACTMajor portion of soil N, present as organic fractions (SON), plays an indirect but vital role in N nutrition of plants. The SON fractions are sensitive to management practices, including fertilization. The nature and distribution of different forms of soil N were studied under long-term use of mineral fertilizers and organic manures in a rice (Oryza sativa)-wheat (Triticum aestivum) cropping system. Long-term fertilizer treatments included control (T1), 100% N (T2), 100% NP (T3), 100% NPK (T4), 150% NPK (T5), 100% NPK plus straw (T6), 100% NPK plus green manure (T7), and 100% NPK plus farmyard manure (T8). Prolonged application of fertilizers and organic manures differentially influenced mineral N (NO3–-N and NH4+-N), organic N fractions, and total N in soils. Organic N fractions constituted about 94.2% of total N as compared with 5.8% share of mineral N. Nitrate N was the dominant mineral N fraction in the soil, which was 4.4 times higher than NH4+-N fractions. Application of fertilizers improved...