Technology and Biotechnology for Better Nitrogen Use Efficiency in Corn.

A better understanding of the N requirement, the different strategies for N use, and the degree of field spatial variability for N use is needed to devise technology and biotechnology strategies for improving N use efficiency (NUE) in corn (Zea mays L).  A series of on-farm N titrations conducted across the U.S. corn belt during the last four years showed an average N requirement of 17.2 kg N/Mg grain for modern hybrids with an average check plot yield of 6.2 Mg/ha and an average delta yield from fertilizer N of 3.5 Mg/ha. This research also showed that field spatial variability for N use was primarily a function of variation in the check plot yield, suggesting that variable rate application algorithms should target the low yield areas, and showing the value of the biotechnology product concept of lower N rates (25-30% less N) to achieve the same yield. Evaluation of an array of commercial hybrids, as well as hybrids with the intermated B73 x Mo17 recombinant inbred line population, showed the existence of two major N use strategies in corn: 1) a high yield at low N accompanied by a small delta yield response to fertilizer N; and 2) a low yield at low N accompanied by a large delta yield response to fertilizer N application. The check plot yield and delta yield were always negatively related among hybrids.  Comparison of rootworm bt hybrids with their non-rootworm counterparts showed that rootworm hybrids have a marked improvement in NUE and grain yield that is primarily the result of higher uptake efficiency (average of 55% in non-rootworm vs. 71% in rootworm hybrids), and a greater delta yield in response to N.  Combining biotechnology traits for better N use with technology for better application should result in considerable improvements in NUE.