Simulation processes for the nitrogen loss and environmental assessment package (NLEAP).

Authors: SHAFFER, MARVIN - USDA-ARS, RETIRED; Delgado, Jorge; CROSS, C - USDA-NRCS, MARYLAND; Follett, Ronald

Submitted to: Soil and Water Conservation Society
Publication Type: Book / Chapter
Publication Acceptance Date: 12/7/2007
Publication Date: 12/10/2010
Citation: Shaffer, M.J., Delgado, J.A., Cross, C., Follett, R.F. 2010. Simulation Processes for the processes for the nitrogen loss and environmental assessment package (NLEAP). Soil and Water Conservation Society. p. 361-372. In Delgado, J.A. and R.F. Follett (eds) Advances in Nitrogen Management for Water Quality, SWCS, Ankeny, IA.

Interpretive Summary: The identification of potential problems with N losses quickly leads to a list of potential solutions in terms of Best Management Practices (BMPs). Local Extension and NRCS have identified practices shown to be of value in each local region. This list should be used as a starting place and potential BMPs evaluated for the site-specific conditions. Some common practices for control of NO3-N leaching include multiple fertilizer applications, the use of fall cover crops to recover residual soil NO3-N, adjustment of fertilizer and manure rates to account for other sources of N, precision application of fertilizers across a field, use of management zones, crop rotations with deeper rooted crops and legumes, and avoidance of off-season fertilizer applications. The relative effectiveness of each method will depend on site-specific conditions and can be evaluated by comparing simulated N loss results with corresponding results using the historical data. There is potential to use NLEAP-GIS as a management tool to assess the effect of BMPs. The NLEAP-GIS model uses national database resources from soils, climate, and management, which allows for the potential application of the model without any ground-truthing. We caution the users to be aware that application of the model without a previous evaluation of local conditions and management are often wrong, leading to a poor application of the model and questionable results. We emphasize that the users and staff should visit the site; talk to local producers, NRCS, and extension; and take some samples if possible. Users need to remember, N losses (especially their magnitudes) are often determined by local effects, as opposed to regional or national generalizations. Users need to review Shaffer and Delgado (2001) and their recommendation for a Tier approach to management. If more detailed and accurate results are needed, users should move to a tier 3 approach, supported by research at the local site. The model will use adequate databases, accurate information, and realistic management scenarios that have been calibrated and evaluated only when examples can be reported by multiple national and international users across hundreds of simulations. Application examples with analyses are included from a dairy farm (manure inputs) in the mid-west United States; a minimum tillage system from the North Atlantic United States; and an irrigated system in the dry, western United States, where cover crops and rotations with deeper rooted crops are used to minimize NO3-N leaching. Additional examples on how to use NLEAP-GIS to assess the effects of BMPs on N pools dynamics and N losses and how to credit N changes due to the effects of implementations of better BMPs vs a traditional practice with a base line case scenario is also discussed in this book. These examples should be of special interest to practitioners looking for improved methods to reduce N losses from agricultural fields.

Technical Abstract: The Nitrogen Loss and Environmental Assessment Package model with Geographic Information System (GIS) (NLEAP-GIS) has been updated to include a MS Windows© user interface and simulation code refinements for surface residue decay, N2O soil gas emissions, crop rooting, multiple simultaneous simulations, and long-term analyses. The current NLEAP-GIS model is more advanced, versatile and powerful. GIS compatibility has been added along with a management database and connectivity to current NRCS soil (NASIS and SSURGO) and NRCS climate databases. This new NLEAP-GIS model has the capability of conducting a large number of simulations simultaneously to allow analysis on how implementation of Best Management Practices (BMPs) impact a field with spatial variability or to conduct multiple analysis of several fields with similar or different BMPs. This flexibility will allow nitrogen managers to conduct quick assessments of BMPs across risky landscape scenarios. Additionally, this new NLEAP-GIS is directly connected to the new Nitrogen Index (NI) tool version 1.1, allowing users to make both Tier 1 (spreadsheet) and Tier 2 (application model) soil N loss analyses from the same spreadsheet tool (Delgado et al., 2006). The revised NLEAP-GIS model provides a faster and more efficient means of integrating management effects with soil and climate information to estimate nitrogen (N) losses from multiple agricultural fields, which include NO3-N leached, N2O and N2 soil gas emissions, ammonia (NH3) volatilization, and surface wash-off of N. The NLEAP-GIS simulation algorithms are described in detail, and a discussion is included regarding the status of international testing and validation. Application examples with analyses are included from a dairy farm (manure inputs) in the mid-west United States; a minimum tillage system from the North Atlantic United States; and an irrigated system in the dry, western United States, where cover crops and rotations with deeper rooted crops are used to minimize NO3-N leaching. Additional examples on how to use NLEAP-GIS to assess the effects of BMPs on N pools dynamics and N losses and how to credit N changes due to the effects of implementations of better BMPs vs a traditional practice with a base line case scenario is also discussed in this book. These examples should be of special interest to practitioners looking for improved methods to reduce N losses from agricultural fields