Analysis and Interpretation of Factors Which Contribute to Efficiency of Nitrogen Utilizatilon'

Differences in 3 response among corn (Zea mays L.) genotypes reflect variation in numerous processes involved in N use efficiency. In order to facilitate the study of such variation, we develop and demonstrate a concept for evaluating the contribution of N uptake and utilization processes to variation in N use efficiency. Eight hybrids were grown in a replicated field experiment at two levels of N fertilizer on a Dothan loamy sand (Typic Plinthic Paleudult). Differences among the hybrids for components of N use efficiency were evaluated from measurements of grain yield, N accumulation in the plant at silking, and N accumulation in the grain and stover at harvest. Significant differences were found among hybrids and between N levels for all traits. Interactions among hybrids and N levels were significant for all traits except grain yield. At low N supply, differences among hybrids for N use efficiency were due largely to variation in utilization of accumulated N, but with high N they were due largely to variation in uptake efficiency. Variation in proportion of N translocated to grain was also important at the low N supply. Variation in N accumulated after silking was not important at either level of N supply. Variation in N remohilization from vegetative tissue to grain was moderately important at the low N supply. Hybrids with similar levels of N use efficiency showed marked differences in component traits which contribute to efficiency. Aa'ditional index words: N uptake, N translocation, Zea mays L. HE effectiveness with which N is used by corn T (Zea mays L.) and other non-legume crop plants has become increasingly important because of increased costs of manufacture and distribution of N fertilizer. Differences in N utilization among corn genotypes have been demonstrated, not only in differential responses to N fertilizer (Smith, 1934; Stringfield and Salter, 1934), but also in differences in absorption and in utilization of absorbed N (Beauchamp et al., 1976; Chevalier and Schrader, 1977; Moll and Kamprath, 1977; Pollmer et al., 1979; Reed et al., 1980). Thus, the potential for developing superior, Nefficient hybrids appears to exist. Efficiency in uptake and utilization of N in the production of grain requires that those processes associated with absorption, translocation, assimilation, and redistribution of N operate effectively. The relative contribution of these processes to genotypic differences in N use efficiency is unknown and may vary among genetic populations and among environments, including N supply. It therefore is important to characterize efficiency of N use in terms related to variation in the major processes involved. However, a severe constraint in doing so is that direct measurements are not feasible in large field studies involving both genotypic and fertilizer variables because of high costs in terms of land, labor, and time. As a consequence, most studies to date have been limited to estimates of N accumulation in certain plant parts at certain stages of growth. We contend herein that judicious use of such data can afford appreciable insight about genotypic variation in response to N Supply. ' Paper N o x 8 4 2 of the Journal Series of the North Carolina Professor of genetics and professors of soil science, North CarAqric. Res. Service, Raleigh, NC 27650. Received 30 Mar. 1981. olina State University. Our objective is to develop and to demonstra1.e a concept for using data on N accumulation to evaluate the relative contribution of various N acquisition and distribution processes to variation in overall efficie.ncy of N use.