ROOT DISTRIBUTION OF CORN - THE EFFECT OF NITROGEN-FERTILIZATION

Root growth and development can affect N uptake. In turn, N additions may affect corn (Zea mays L.) root growth. Prolific (multiple ear) hybrids may need a more active root system to satisfy ear demand. To determine the extent of the effect of N fertilization on root growth in the field, three corn hybrids (Pioneer 3320, and prolific hybrids I202 x Mo17 and I117 x B73) were grown under fertilizer application rates of 56, 140, and 223 kg N ha(-1) to determine (i) whether application of N fertilizer stimulated root growth of corn in the zone of application in the field 20 d before silking, at silking, and at physiological maturity and (ii) whether prolific hybrids have enhanced root development before silking compared with nonprolific hybrids. Ah three hybrids were grown at a uniformly low plant-population density Root length density to a depth of 60 cm, averaged ol er hybrids, was 1302, 2238, and 1184 m plant(-1) in 1987, and 2195, 2833, and 3317 m plant(-1) in 1988 for the three sampling dates. There were few genotypic differences in root length density. Root weight averaged over hybrids was 20.4, 40.5, and 21.5 g plant(-1) in 1987, and 44.6, 61.7, and 58.9 g plant(-1) in 1988 for the three sampling times, respectively: Root weight at harvest declined as N application increased, but increased in response to N at two earlier sampling times. The second year of the study when rainfall was more plentiful than in the first year, root growth continued after silking for all hybrids. This coincided with higher yields. The data suggest that N stimulated root length in the area of application, without affecting total root length.