Nutrient transformation in soil due to addition of organic manure and growing crops

Abstract

Maintaining organic pools of nitrogen (N) in soil is important for providing a steady flux of N in soil solution. Bioslurry, which is the product obtained from anaerobically digested (methanised) farm yard manure (FYM), is an efficient source of organic manure with capability to supply nutrients, particularly N to crops. A study was conducted to see the equilibrium relationship between the inorganic and organic N fractions as affected by application of bioslurry and fertilizer N in a maize (Zea mays L.) — mustard (Brassica campestris) crop sequence. Results obtained revealed that 75.7 percent of the total soil N was in the hydrolyzable N fraction. Among the hydrolyzable fractions, aminoacid N, unidentified N and hydrolyzable NH 4 + constituted 25.8, 25.7 and 18.6 percent of the total N, respectively. Ammonium fixed in clay lattice constituted 19.1 percent of the total N. Application of bioslurry @ 13.32 t ha−1 under N-unfertilized conditions increased NO3-N, fixed NH 4 + , aminoacid N, hexosamine N and hydrolyzable NH 4 + . The magnitude of increase in total hydrolyzable and inorganic N fractions was 31.4 and 15.2 percent, respectively. Growing crops decreased N in the inorganic fractions. Transformation reaction of organic N to inorganic N was evident after second crop in the sequence. Fertilizer N application encouraged build-up of N in organic fractions, particularly in aminoacid, hydrolyzable NH 4 + and unidentified N fractions. Application of bioslurry maintained higher status of N in both organic and inorganic N fractions. Linear regression relationship between N content in different fractions and bioslurry applied both under fertilized and unfertilized conditions assisted in developing prediction models on the rate of bioslurry to be applied to arrive at the desired N content in different fractions. Significant intercorrelation coefficients (r2) between different fractions indicated free mobility between the N fractions under limited N conditions suggesting a dynamic equilibrium between them. Path coefficient analysis showed that exchangeable NH 4 + and NO3-N had substantial direct positive effect on N uptake by mustard with bioslurry application. Under untreated conditions exchangeable NH 4 + , hexosamine and hydrolyzable NH 4 + fractions had higher direct contribution to meet mustard N requirement. Most of the hydrolyzable N fractions contributed to N uptake by mustard by first transforming to exchangeable NH 4 + and NO3—N and thus setting an equilibrium condition for maintaining the steady flux of N to plants.