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Abstract
During the past decades, science and new technology have helped to improve food production and productivity by the use of increasing rates of N fertilizer, although excessive N in soil has resulted in ground water contamination. Several agronomic approaches to reduce N use have been tried; however, economic approaches also need to be considered in order to practice reasonable of fertilization. The general objective of this study was to determine if nitrogen use efficiency (NUE) expressed as dry matter per unit N uptake $\rm (NUE\sb1)$ and total grain per N unit uptake $\rm (NUE\sb2)$ can be used to determine the greatest net returns for corn hybrids. A split-plot experiment was used with N treatments as main plots and genotypes as split-plots. Five commercial hybrids (P-3379, C-7177, H-2628, J-8210, F-4673) and one open pedigree hybrid (B73 x Mo17) were compared for their response to six N treatments of 0, 80, 160, 240, 80/80, 80/160 kg N $\rm ha\sp{-1}.$ The results showed that hybrid P-3379 had the greatest grain yield in 1992 and 1993 of 7337 and 8870 kg $\rm ha\sp{-1},$ respectively. Hybrids C-7177 and P-3379 had the maximum $\rm NUE\sb1$ values of 103 g $\rm g\sp{-1}$ in 1992 and 1993. Hybrid C-7177 and H-2628 had the greatest $\rm NUE\sb2$ value of 61 g $\rm g\sp{-1}$ in 1992 and 58 g $\rm g\sp{-1}$ in 1993. To facilitate the economic analysis, grain yield and total biomass production net, gross return and return per unit N uptake were calculated by year. Hybrid P-3379 had the greatest returns for grain of $459.40 $ha sp-1$ and \$640.25 $\rm ha\sp{-1}$ in 1992 and 1993. Hybrids F-4673 and P-3379 had returns for total biomass production of $674.23 $ha sp-1$ in 1992 and \$580.69 $\rm ha\sp{-1}$ in 1993, and removed more N from the soil than the N applied. This study indicated that corn hybrids vary markedly in net return for grain or grain plus forage when based solely on the amount of N taken up (greater NUE). Additional research is needed to provide a better explanation of the relationships among NUE responses, N applied and levels of N uptake among hybrids. This information will be useful for hybrid development in corn based on economic terms.
