The mineralization of N from legume residues may vary considerably depending upon their chemical composition. The N mineralization of seven legumes (45-day old) in Hisar sandy loam (Typic Camborthid) and Karnal loam (Typic Ustochrept) soils were studied under constant temperature (35°C) and water (−0.03 MPa) conditions. Patterns of N mineralization in both the soils from different legumes were almost similar and followed the first order kinetics. The nitrogen mineralization potential (N0) of legumes differed significantly and ranged from 59.8 mg kg−1 for clusterbeanto 96.9 mg kg−1 for green gram. The rate of N mineralization (k) was highest for green gram (0.199 week−1) and lowest for clusterbean (0.149 week−1). The k values were significantly affected by lignin to N ratio, lignin plus polyphenol to N ratio and C:N ratio of legumes. The net amounts of N mineralized at the end of 56 days of incubation was lowest from clusterbean amounting to 53 and 55 mg kg−1 and highest from green gram amounting to 96 and 99 mg kg−1 in Hisar and Karnal soils, respectively. The order of N mineralization (%) from different legumes was same in both the soils and followed the sequence: green gram > black gram > soybean > cowpea > sesbania > sunnhemp > clusterbean. The percentage of N mineralized was positively correlated with total N content and negatively with C: N ratio, lignin to N ratio, polyphenol to N ratio. However, the best chemical index of N mineralization was found to be lignin + polyphenol to N ratio which accounted for 84 per cen~ of the variation in the percentage of legume N mineralized.
Green manures, lignin, N mineralization potential, polyphenol
