Characterization of Nitrogen Use Strategies in Commercial Maize Hybrids.

Determining the best strategies for improving maize N use necessitates a thorough understanding of how modern hybrids use N, and the degree of variation that exists among commercial hybrids for N use traits. In 2006-2009, we measured N use parameters for 47 representative commercial hybrids. There was a wide range among the commercial hybrids in both grain yield at low N and maximum yield with fertilizer N, and the average N response for the commercial hybrids (3.5 Mg ha^-1) was the same as the average N response obtained in concurrent on-farm studies. Associated with a hybrid’s yield at low N was its genetic utilization which accounts for the plant’s ability to acquire N from the soil when it is limiting, and the plant’s ability to efficiently use limiting tissue N for growth and yield. Differences in N uptake at low N could be due to variation in root architecture or root metabolism, while differences in N utilization at low N are almost always related to an increase in kernel number due to less kernel abortion. Considerable hybrid variation was observed for all NUE parameters. The NUE of commercial hybrids averaged 23 kg_grain kg_N^-1 (range of 10-38), with an average uptake efficiency of 0.54 kg_plantN kg_N^-1 (range 0.36-0.78), and an average utilization efficiency of 41 kg_grain kg_plantN^-1 (range 27-97). No hybrid was optimized for both N uptake and N utilization suggesting room for improvement in overall NUE.

One N use strategy observed in the commercial hybrids involves producing a high yield at low N accompanied by a small response to fertilizer N, while another involves a low yield at low N and a large response to fertilizer N. Hybrids with high check plots yields could presumably be used to reduce N inputs for maize production. Conversely, hybrids with large fertilizer responses should be more suited to situations where N can be intensively managed. Few hybrids exhibited relatively high yields under low N and large fertilizer responses, which is the most desired strategy, as these hybrids would produce good yields when N was limiting, but even higher yields with adequate N. Because the absolute values for check plot yields (average of 6.9 Mg ha^-1) are twice as high as the average fertilizer response (3.5 Mg ha^-1), research efforts targeting N use for high-yield potential, high input production systems will have to focus on increasing the magnitude of response to fertilizer N, while maintaining high yields under low N.