Date of Award
Doctor of Philosophy
Critical %N is defined as the concentration associated with maximum yield with respect to N. Objectives of this research were to determine: (1) the extent to which various maize single crosses differ in their critical %N; (2) the constancy of these values in different crop seasons; (3) the relationship between the critical %N of single crosses and their parental lines; and (4) the N use efficiency of different single crosses. The study involved N-rate experiments in 4 site-years, and commonly used genotypes selected for a wide range in %N in the grain. Maximum yields and critical %N values were predicted from the separate regressions of yield and of %N on the quadratic functions of N fertilizer rates;Maize single crosses differed significantly in critical %N, and ranged from an average of 1.33 to 1.71. Critical %N values for different site-years were highly correlated, as shown by coefficients ranging from 0.83 to 0.90 and averaging 0.87 for 21 single crosses used in 3 site-years. The critical %N and associated %P values were highly correlated, with r-values of 0.76 and 0.83 in two experiments;The critical %N values of the single cross progeny were highly correlated with the mean critical %N values of the parental inbreds, indicating that an estimate of the critical %N of single crosses could be obtained from a knowledge of the critical %N values of their parental inbreds;Maize single crosses differed in their efficiency of N use. Hybrids containing B73 (a low-N inbred) produced the most grain with no applied N and with sufficient applied N to maximize yields. However, based on yield response per unit of applied N, hybrids containing B14A (a high-N inbred) were at least as efficient. The B73 hybrids contained more total N than B14A hybrids at the no-N level, but the reverse was true with sufficient N applied to maximize yields. Hybrids containing B14A were the most efficient of the 3 groups of hybrids studied in recovery of the N applied to maximize yields;A knowledge of the critical %N in the grain of maize will be useful in diagnosing N sufficiency, in characterizing hybrids for protein feeding value, and in improving hybrids for protein content.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Cloyce Gene Coffman
Coffman, Cloyce Gene, "The critical nitrogen percentage in the grain of maize single crosses and their parental lines, and the efficiency of nitrogen utilization by different single crosses " (1981). Retrospective Theses and Dissertations. 6898.