Effect of Temperature and Soil Moisture Regime on Green Manure N Mineralization in Clay Loam Soil

The effect of environmental factors on green manure (Sesbania aculeata) N mineralization during 12 weeks of incubation period was investigated in clay loam soil. This study included three incubation temperature (25, 35 and 45°C) and constant water regime (1 cm floodwater depth over the soil surface) or four moisture regimes (25, 50, 75 and 100% WHC) and constant temperature (35°C). Mineralization of Sesbania N under flooded conditions increased significantly with increase in incubation temperature from 25 to 45°C at each incubation period. The mineralized N reached its peak on 4th week at 35 and 45°C and on 5th week at 25°C and decreased thereafter. The apparent rates of N mineralization were 1.42 and 0.75 at 25°C, 1.94 and 0.80 at 35°C and 2.4 and 0.84 mg N kg⁻¹ soil day⁻¹ at 45°C between 0–7 and 7–28 days of incubation, respectively. At 100% WHC, N mineralization increased up to the 4th week and decreased thereafter. Cumulative N mineralization of plant materials incubated at 35°C and at 25,50 and 75% WHC, (but not at 100% WHC) increased with the increase in incubation period. Nitrogen mineralization patterns observed at all moisture regimes except 100% WHC were similar and followed first order kinetics. The nitrogen mineralization potential (N₀) at all moisture regimes (25, 50 and 75% WHC) differed significantly and ranged from 20.5 mg kg⁻¹ green manure unamended soil at 52% WHC to 73.8 mg kg⁻¹ green manure amended soil at 50% WHC. The nitrogen mineralization rate constant (k) varied from 0.2742 week⁻¹ at 25% WHC in control to 0.4206 week⁻¹ at 75% WHC in soil amended with green manure. Irrespective of green manure treatment, the nitrogen mineralization rate constants (k) did not differ significantly between 50 and 75% WHC moisture regimes but were significantly higher than those at 25% WHC moisture regime. The maximum N mineralization occurred at 50% WHC followed by 75 and 25% WHC. Most of the N mineralization at these moisture regimes occurred during the first 4 weeks of incubation which represented about 85% of the total N mineralized during 12 weeks of incubation period.