Date of this Version



University of Nebraska Extension Circular EC195 (Revised August 2012)



Copyright © 2012 University of Nebraska


This publication provides the basis and procedure for using a phosphorus (P) index to assess risk of P delivery from agricultural land to surface waters. The P index is intended for planning as well as regulatory and educational purposes.

Phosphorus is an essential nutrient for the growth of both crops and aquatic vegetation. Phosphorus, either in inorganic form such as with fertilizer or in organic form as with animal manures, often needs to be applied to the land for optimal crop growth. An important byproduct of animal feeding is manure that contains P. Land application of manure can be beneficial to crop production but can result in increased risk of P loss to surface waters. Fortunately, P is easily managed compared with nitrogen which can be easily lost to the environment through several pathways including leaching, volatilization, denitrification, emission of nitrous oxide, and runoff and erosion, while P loss to the environment is through transport by runoff and erosion with generally negligible losses through sub-surface drainage.

Phosphorus indexes are tools for the assessment of the potential for P delivery from agricultural lands to surface waters. Therefore, operators of large concentrated animal feeding operations (CAFOs) in Nebraska need to assess the risk of P delivery to surface waters from each field before manure can be applied by using a P index. This assessment needs to be done once every five years. The Nebraska P Index (2012) is a tool for risk assessment, land management planning, education of factors contributing to P loss, and regulation of P application to agricultural land. The Nebraska P Index was developed using the Iowa P index as a base (Iowa NRCS, 2004) with adaptation to Nebraska conditions and with revisions in consideration of current information.