NITROGEN EFFICIENCY COMPONENT ANALYSIS - AN EVALUATION OF CROPPING SYSTEM DIFFERENCES IN PRODUCTIVITY

The development of cropping systems that use N efficiently requires me thods that evaluate system differences in N use. A procedure, based co nceptually on soil and plant processes that affect N use, was develope d to evaluate differences in N use efficiency among cropping systems. The method uses measurements of yield, grain N, above ground plant N, applied N, and postharvest inorganic soil N to partition cropping syst em differences in yield and grain N into N efficiency components. The components consist of N supply, available N efficiency, available N up take efficiency, N utilization efficiency, grain N accumulation effici ency, and N harvest index. The N efficiency component analysis was dem onstrated for a field study with bard red spring wheat (Triticum aesti vum L. 'WB 906R') where conventional tillage had a greater yield and g rain N than no-tillage. At low N rates, 78% of the difference in yield between the two was attributed to N supply and available N efficiency components. At high levels of applied N, 88% of the yield difference was attributed to the N utilization efficiency component. Differences in grain N were attributed to N supply and available N efficiency comp onents, whereas components of grain N accumulation efficiency, availab le N uptake efficiency, and N harvest index were nonsignificant. Overa ll, this new approach transcends empirical analyses and provides insig ht into underlying mechanisms of cropping system differences in N use.