Effect of Integrated Use of Inorganic and Organic Materials on the Distribution of Different Forms of Nitrogen in Soil and their Influence on Sugarcane Yield and Nutrient Uptake

A study was undertaken to evaluate the effect of fertilizers and organic manures (biogas slurry, green manure, sulphitation pressmud and sugarcane trash) on the amount and distribution of nitrogen (N) fractions in soil. After 17^th crop cycles of sugarcane based cropping system, application of fertilizers alone and in combination with organic manures significantly increased all the forms of N except NO₃⁻-N over control (N₅₀P₁₀₀K₁₀₀). Among the various N fractions non-hydrolysable N was the dominant N fraction. The highest values of these fractions were found in T₄ (100% NPK + 20 t ha⁻¹ biogas slurry). The relative contents of these fractions were in order: non-hydrolysable N > amino acid-N > unidentified-N > hydrolysable NH₄⁺-N > exchangeable NH₄⁺-N > hexoseamine-N > NO₃^–-N. All the fractions except NO₃^–-N were in dynamic equilibrium as indicated by significant and positive correlation (r = 0.861** to 0.977**) among them. The per cent distribution of soil N into different N fractions varied from 2.15 to 3.24 per cent as NO₃^–-N, 11.4 to 15.6 per cent exchangeable NH₄⁺-N, 4.54 to 5.37 per cent hexoseamine-N, 18.6 to 20.8 per cent amino acid-N and 13.3 to 14.3 per cent in unidentified form of N. Correlation studies between plant parameters of sugarcane and soil N fractions indicated that the yield of sugarcane as well as sugar yield and uptake of N, P, K, S and Zn by sugarcane were significantly and positively correlated with all N fractions except NO₃^–-N.