Effect of chemical composition of plant residues on nitrogen mineralization

The successful use of plant residues as sources of nitrogen for crops requires an understanding of the process of N mineralization from the residues, which is primarily dependent on the chemical composition or quality of the residues. In this study, 7 crop residues and 13 tree residues were characterized for important quality parameters, viz., C, N, lignin and polyphenol concentrations. Nitrogen concentration in the residues ranged from 0.51% in sugarcane trash to 3.59% in Leucaena leucocephala; lignin concentration from 5.19% in paddy straw to 10.50% in Annona squamosa; and polyphenol concentration from 0.37% in sugarcane trash to 7.04% in Calliandra calothyrsus. Crop residues had lower concentrations of N, lignin and polyphenols than tree residues. A laboratory incubation experiment was conducted to study N mineralization from the residues and to examine the effect of residue quality on N mineralization. The residues were incubated with soil at 25°C and 9% (w/w) soil water and the release of N was monitored. There were considerable variations in the N mineralization patterns of the 20 residues. All the residues caused immobilization of N immediately after addition to soil, but with the progress of time, net mineralization occurred from most of the residues. The proportion of residue N mineralized at the end of 100 days of incubation ranged from −20.67% in sugarcane trash to 81.89% in Glyricidia sepium. Correlations between residue quality parameters and % N mineralized at different intervals showed that while N mineralization was strongly influenced by N concentration of the residues and lignin whereas polyphenol concentrations had little or no effect. There were no temporal patterns in the degree of relationship of various residue quality parameters with per cent N mineralized.