Effect of Nitrogen on Root Growth of Two Corn Genotypes in the Field¹

Corn ( Zea mays L.) genotypes vary in their response to applied N fertilizer. Nitrogen uptake by the plant is controlled by N influx at the root surface and the size and morphology of the root system. The objective of this study was to investigate the effect of applied N on mean N influx and root growth of two genotypes that differed in their response to N. Nitrogen rates were 0 and 227 kg ha −1 for ‘Pioneer 3732’ and ‘B73✕Mo17’ grown on Raub silt loam (Aquic Argiudolls) and 227 kg N ha −1 on Chalmers silt loam (Typic Haplaquolls). Root growth, plant weight, and N content were measured 31,47,61,75,91 and 109 days after planting. Apart from an initial difference at 31 days, mean N influx of roots of both genotypes were similar. Root length and root surface area of Pioneer 3732 were not increased by the application of N. In contrast, applied N increased root growth of B73✕Mo17. By midsilk (75 days) root length of B73✕Mo17 was 36 and 39% greater than that of Pioneer 3732 on the Raub and Chalmers soils, respectively, to which N was applied. The greater root growth of B73✕Mo17 and the continued root growth of this hybrid after midsilk appears to be one possible mechanism to explain the greater growth of this hybrid under a high‐N fertilizer regime. This requires further verification under a wider range of environmental conditions. A lack of moisture limited the grain yields of both hybrids in this study.