Soil Moisture Control of Nitrogen Fixation Activity in Dry Tropical Casuarina Plantation Forest

Nitrogenase activity nitrogen accretion to soil in two age groups of Casuarina equisetifolia plantation forest have been assessed. Our findings show that, in the summer months, the nitrogenase activity is at a minimum but, with the onset of rain even though it continues to be very warm, new nodulation starts and the peak of N2-fixing activity is soon reached. Multiple regression analysis showed soil moisture in the warm temperature condition as the major factor controlling the nitrogenase. Based on our finding, we are tempted to suggest that if adequate moisture through judicious irrigation management is made available in summer, the nodulation could be hastened and N2 fixation activity could be prolonged at a high level during 4 months of summer and 4 months of rains.