Principles for managing nitrogen leaching

ABSTRACT:

Managing leaching presents a challenge to nutrient managers who must develop nitrogen (N) management plans that consider rate and application strategies that account for soil properties, hydrology, and crop-tillage systems of specific sites. Nitrogen-leaching losses from common grain-production systems typically range from 10% to 30% of the total N input. Major leaching events occur when soil N concentrations are high and water is moving through the soil profile. The universal tools for managing N leaching include understanding the soil-crop-hydrologic cycle, avoiding excess N applications, and applying N in phase with crop demand. Specific cropping system tools for managing leaching include use of grass cover crops, adding a legume to a rotation, and adding crops that more fully utilize the soil-water resources. The primary water-management tool to reduce N leaching is irrigation scheduling. Other watershed approaches to reduce leaching losses include use of riparian zones and conservation reserve program areas. Site monitoring tools such as the pre-sidedress soil-nitrate test, the leaf chlorophyll meter, and tissue-nitrate tests are useful in identifying N-sufficient sites and avoiding excess N rates. Real-time monitoring techniques, such as the N Reflectance Index, can be combined with global positioning systems and geographic information systems to produce maps of the crop N status. Crop simulation models can also be used to integrate N and water dynamics during a growing season, and they can provide guidance in designing practices for reducing N leaching. The application of the above N management tools to fields, or to specific management areas within fields, will improve crop N recoveries with subsequent reductions in N leaching.