NITRATE LEACHING UNDER IRRIGATION ON COASTAL-PLAIN SOIL

The effect of irrigation and nitrogen management on ground-water quality was evaluated for four years on a Sassafras sandy loam Coastal Plain soil. Applying the greatest portion of the nitrogen by side-dressing and by fertigation were compared. Maintaining optimum soil moisture and partial irrigation (applying one half the water as optimum irrigation) were the water management practices investigated. Nitrate concentrations increased in the ground water for all nitrogen and irrigation-management practices. The mass of the nitrate leached was related to the drainage volume. In all but one year the largest mass of nitrate was leached during the fall and winter months, when the largest amount of recharge occurs. Very little nitrate was leached during the growing season for any nitrogen or irrigation management practice except for one year when 30 cm of rainfall occurred in August. The mass of nitrate leached during that growing season ranged from 33.9 kg/ha for partial irrigation to 139.0 kg/ha for full irrigation.