Assessing Crop Rotational Nitrogen Use Efficiency.

In annual cropping systems, nitrogen use efficiency (NUE) is typically estimated on a single crop basis.  However, this approach ignores the dynamic nature of nitrogen cycling within multi-year crop rotations featuring a diverse set of crops. Our objective is to develop a component analysis of NUE of an entire crop rotation.  This approach will also provide insight into the propensity of cropping systems to retain and recycle N within a rotation.  The rotational NUE analysis will factor in crop yields, grain and residue N, fertilizer N, N mineralization estimates, and changes in soil residual inorganic N.  The analysis will be applied to two-and three-year rotation studies in the low, intermediate, and high rainfall zones of Eastern WA.  There is evidence that fertilizer carry over contributes to overall rotational NUE. By tracking changes in soil N supply between crops, the rotational NUE will help us evaluate and adopt alternative cropping systems with the propensity to retain and recycle N within a rotation.