Genetic variability in nitrogen utilization at four growth stages in soft red winter wheat

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Abstract
Studies were conducted to determine relationships among nitrate reductase activity (NRA), dry weight (DW), nitrogen (N) uptake, and N concentration in soft red winter wheat (Triticum aestivwn L.). Data were collected for three growing seasons from field plots grown on a silt loam and one growing season on a sandy loam. Ten cultivars were measured under field conditions with plant samples taken at Feekes Growth Stages 6, 10, 10.5, and 11.1. NRA was measured using an in vivo assay method on fully expanded leaves representing the upper most part of the canopy. Results indicated that N uptake was highest during Stages 10.5 to 11.1, although not significantly different for all cultivars. Few differences were found among cultivars for N concentration. The NRA measured under field conditions was more stable at Growth Stage 6. Path coefficients between NRA and DW, N uptake, and N concentration varied considerably depending on the growth stage, indicating that selection for N utilization using one or more of the measurements evaluated in this study should consider the stage of growth.