Estimating potential nitrate leaching in nitrogen fertilized and irrigated tomato using the computer model NLEAP

Groundwater pollution caused by leaching of NO3-N from agricultural systems has caused public concern for decades. To preserve the groundwater and reduce economic losses for the farmers, a rapid and accurate estimation of NO3-N moving below the root zone is crucial. In this study, the value of the computer program NLEAP (Nitrate Leaching and Economic Analysis Package) to simulate nitrate leaching was evaluated using data from an experiment conducted with 12 lysimeters (1.25 m i.d. and 2 m deep) in 1996 and 1997. Three tomato (H2274 variety) seedlings were planted in each lysimeter and nitrogen rates of 0, 80, 160, and 240 kg N ha−1, as ammonium nitrate and ammonium sulphate, were applied to the lysimeters under a fixed irrigation program. Effluent was collected from the outlets of the lysimeters and analyzed for NO3. The model adequately simulated nitrogen leaching for each year (R2=0.93 and P<0.03 for 1996, and R2=0.87 and P<0.06 for 1997). The high coefficients of determination, between observed and simulated values, revealed that the model can be successfully used to estimate the amount of the NO3 leaching under the experimental conditions. The results also showed that the NO3 available for leaching (NAL) values were important background information for determining an optimum N rate for groundwater quality and maximum gain, and NO3 available for leaching (NAL), amount of NO3 leached (NL), movement risk index (MRI), and annual leaching risk potential (ALRP) parameters should be considered together to estimate the nitrogen pollution risk.