Divergent Phenotypic Recurrent Selection for Nitrate Reductase Activity in Maize. II. Efficient Use of Fertilizer Nitrogen

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Abstract
Improving the efficiency of absorption and utilization of soil‐applied N by maize (Zea mays L.) cultivars should be an important goal of maize breeders. This study was conducted to determine the relationship between nitrate reductase activity (NRA) and reduced N, N harvest index, N uptake, N utilization, N‐use efficiency and grain N accumulation of maize. Eight cycles of divergent phenotypic recurrent selection for high and low levels of postanthesis leaf‐lamina NRA were completed in the maize synthetic Super Stiff Stalk (BSSS). Cycles 0, 3, and 6 of the high and low NRA strains were grown at N rates of 112, 224, and 336 kg ha−1 in 1983, 1984, and 1985 at Urbana, IL, and were evaluated for the above N traits. The 1985 experiment included Cycle 8 high and low NRA. Selection for high NRA had little effect on the N traits evaluated. In contrast, selection for low NRA resulted in significant reductions for many of the N traits examined. Reductions in grain N content for Cycle 8 low NRA were 9, 21, and 19% with 112, 224, 336 kg N ha−1, respectively, relative to Cycle 0, were observed. Nitrogen‐use efficiency of Cycle 8 low NRA decreased 21, 16, and 13%, relative to Cycle 0, at the three respective N rates. These results indicate selection for low NRA has adversely affected nitrate metabolism in this population, resulting in lower grain N production and less‐efficient use of soil‐applied N to produce grain.