Nitrogen Fertilization Timing Effect on Wheat Production, Nitrogen Uptake Efficiency, and Residual Soil Nitrogen

Abstract Split fertilizer N application has been proposed for improving N uptake efficiency in wheat ( Triticum aestivum L.) production systems, but results have been inconsistent. In this field study, 75 and 150 kg N ha −1 was applied either all preplant or in two, three, or four split applications based on wheat growth stage (GS) to determine N timing effect on wheat yield and apparent fertilizer N recovery. Vegetative samples were also collected at Feekes GS 4, 6, and 10 to determine treatment effects on tissue N concentration during the growing season. Soil samples were collected after harvest to evaluate residual N quantity and movement in soil relative to N rate and time of application. The soil used was a Fluventic Ustochrept‐Udic Chromustert intergrade. Nitrogen rate and application timing appeared to have less effect than year on yield and N parameters. Significant grain yield increases were achieved with split applications of N fertilizer when N was topdressed at GS 4 or 6 in 1989 as compared with all preplant or application at GS 10. Split N application at GS 10 produced greater grain yield than application at GS 4 or 6 in 1990. Nitrogen uptake efficiency was greatest with 75 kg N ha −1 and split application. Soil NO ‐ 3 –N concentration was significantly higher at 150 kg N ha −1 than at 75 kg N ha −1 . Significantly lower residual NO ‐ 3 ‐N with the preplant treatment was not accounted for by greater grain or straw N content.