Nitrogen fertilizer management based on site-specific management zones reduces potential for nitrate leaching

ABSTRACT:

Although nitrogen (N) is an essential nutrient that is a key component of intensive irrigated agricultural systems, its management to maximize yields and reduce losses to the environment is difficult. One reason is due to the spatial and temporal variability that affect residual soil nitrate-N (NO₃-N) and NO₃-N leaching potential. The objective of this study was to evaluate the potential of N fertilization prescriptions based on site-specific management zones to reduce NO₃-N leaching losses. We mapped site-specific management zones based on soil color from aerial photographs, topography, and the producer's past management experiences that reflect spatial soil variability. We used the Nitrate Leaching and Economic Analysis Package (NLEAP) model to assess the benefits of N management based on site-specific management zones. Nitrate leaching was variable across management zones with the highest leaching occurring in the low productivity zone. This study found that productivity zone is an important spatial factor in determining NO₃-N leaching potential since site-specific management zones characterized the variability of factors that affect NO₃-N leaching. As the N fertilizer rate is increased by productivity zone the rate of NO₃-N leaching increased faster for the low productivity zone creating a “higher leaky zone.” Since we found that a factor other than N is limiting yields, a better N management practice is to apply N accounting by realistic maximum yields to avoid over-fertilization, to reduce NO₃-N leaching losses during the growing season and residual soil NO₃-N that is available to leach during the non-growing season. Furthermore, this study demonstrates that spatially variable N management based on productivity zones produces less NO₃-N leaching than uniform strategies while maintaining maximum yield. We estimated that by using a Site Specific Management Zone we cut NO₃-N leaching losses by 25 percent during the first year after a site-specific management zones nutrient management plan.