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This article in AJ

  1. Vol. 97 No. 2, p. 615-619
    Received: Aug 20, 2004

    * Corresponding author(s): jsawyer@iastate.edu


Nitrogen Application to Soybean at Early Reproductive Development

  1. Daniel W. Barker and
  2. John E. Sawyer *
  1. Dep. of Agron., Iowa State Univ., Ames, IA 50011-1010


Nitrogen application during soybean [Glycine max (L.) Merrill] reproductive stages has the potential to increase soybean productivity. The objective of this study was to determine the impact of N fertilizer applied to the soil at the beginning pod growth stage on soybean yield and grain quality. Additional objectives were to study alternative N fertilizer and application practices that might enhance soybean use of applied N. A field study was conducted at five locations in Iowa during 1999 and 2000. Nitrogen treatments were urea and polymer-coated urea broadcast and subsurface band placed between the rows at 45 and 90 kg N ha−1 and a no-N control. The study showed few, small, and inconsistent effects of N material, placement, and rate on grain yield and quality components at individual sites or when combined across individual sites. There were no significant effects on grain yield, with only a 39 kg ha−1 increase from applied N. Grain protein, oil, and fiber concentrations were the same with or without N application. Aboveground plant dry matter (DM) at the R6 growth stage was greater with the higher N rate, but plant DM with N application was lower than the no-N control. Nitrogen concentration in plant DM was significantly increased with applied N. In conclusion, N application increased N concentration in R6 soybean plants, but N rate and alternative application practices had no positive effect on plant DM, grain N concentration and removal, grain yield, or grain quality components. It was concluded that growers should not consider fertilizer N applied to soil during early reproductive stages as a method to increase soybean yield or grain quality.

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