Implementing a Well-Designed Nutrient Management Plan in a Semi-Arid Environment.

            The Environmental Protection Agency currently requires that application of manure and lagoon water from concentrated animal feeding operations (CAFOs) to agricultural lands follow an approved Nutrient Management Plan (NMP).  Field experiments were conducted to investigate the transport and fate of nutrients, indicator microorganisms and salts under a well-designed and implemented NMP in a semi-arid environment.  The NMP was developed and implemented based on measured information for water and nitrogen mass balance in the root zone during each irrigation event.  Several different irrigation methods (sprinklers, drip, and furrow) and dairy lagoon water application strategies (cyclic and blended) were considered.  The field site was heavily instrumented to monitor evapotranspiration and precipitation rates, irrigation amount and uniformity, and soil water status and composition with depth and time.  The nutrients composition of the lagoon water, the uptake rate of nitrogen by the plants, nitrogen losses to the atmosphere and by leaching, nitrogen transformation rates, and the transport and fate of salts and indicator microorganisms in the root zone were also measured.  While nitrate was mainly removed by plant roots and microorganisms were retained by the upper soil layers, salts accumulated in the root zone and affected the soil fertility. Moreover, the transport and fate of nitrate and salts were affected by the irrigation method and lagoon water application strategy that induce different water and nutrient status and flow patterns in the root zone.