Nitrogen Dynamics in Dryland Cropping Systems.

Effective nitrogen management is critical to ensure optimum crop yield and quality while avoiding negative environmental effects.  Nitrogen not used by the crop will remain in the soil where it is subject to losses by immobilization, leaching, denitrification, and ammonia volatilization.  In dry environments, denitrification and leaching losses may be small, so residual N may persist though several cropping cycles, allowing the balance between N supply and crop demand to be viewed over multiple years.  In contrast, under wetter conditions, persistence of inorganic N is limited, as it may be lost rapidly from the soil-crop system when soils are warm and moist. An understanding of the relationship among environmental conditions, patterns of N accumulation by the crop, and soil N dynamics must be used to develop nutrient management systems that optimize crop yield and quality and economics of production, while minimizing N losses to the air and water. Considering N reactions over the long-term rather than on an annual basis may improve our understanding of overall N dynamics and nitrogen use efficiency.