Divergent phenotypic recurrent selection for nitrate reductase activity in maize. II. efficient use of fertilizer Nitrogen

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.