ARS | Publication request: California Nitrogen Index

Submitted to: Government Publication/Report
Publication Type: Government Publication
Publication Acceptance Date: March 11, 2009
Publication Date: April 10, 2009
Citation: Delgado, J.A., Gagliardi, P., Rau, E.J., Fry, R., Figueroa, U., Gross, C., Cueto-Wong, J., Shaffer, M.J. 2009. California Nitrogen Index. Government Publication/Report. (USDA-ARS-SPNR and NRCS User Manual).

Interpretive Summary: The following pages explain how to use the stand-alone California Nitrogen Index included with NLEAP-GIS 4.2. Both the N and P indices are included in this California N Index. For related information not included in this manual, as well as additional applications for the N Index, please review Delgado et al. (2006 and 2008) and De Paz et al. (2009). This tool is designed to help nutrient managers quickly assess N loss risk related to agricultural N management. For detailed descriptions of the advantages and disadvantages of previous indices, please review Shaffer and Delgado (2002). This manual will use an example scenario to demonstrate how to use the N Index. The assumptions presented in the training example are used simply to assess the N loss risk from liquid N manure inputs while introducing you to N Index functionality. This manual walks you through N management for a forage system receiving manure applications. The six provided case scenarios for this cropping system consist of very high, high and low manure inputs for irrigated forage systems grown on both clay and sandy soils. We have also included an irrigated vegetable system. The four provided scenarios for this cropping system are back-to-back lettuce with and without cover crops grown on both clay and sandy soils. This manual is currently being tested in California by multiple users, and an N index version adapted for Mexico was transferred to scientists from Mexico’s INIFAP. A more advanced version of the Index that integrates the N and P indices with GIS databases is currently in development.

Technical Abstract: The California N Index User Manual is designed to help you become accustomed to the software environment in which the N Index runs. This manual will use an example scenario to demonstrate how to use the N Index to assess nitrogen losses. The objective of this theoretical example is to guide you toward other potential applications of the N Index. The Assessment of Risk screen displays the final qualitative scores for the 3 subcategories: Nitrate Leaching, Surface Transport and Atmospheric, as well as the Total N-Index score. We suggest that those fields with very high and high risk rankings necessitate re-evaluation of N management practices by farmers/managers. We suggest that those fields with medium risk for nitrogen losses are being managed adequately, perhaps using current Best Management Practices. A medium risk assessment suggests the potential for reactive N losses to the environment is of minor concern. We also suggest that those fields with low and very low risk for nitrogen management are being managed very well, probably using current Best Management Practices.