NITROGEN ACCUMULATION IN SHOOTS AS A FUNCTION OF GROWTH STAGE OF CORN AND WINTER WHEAT

Midseason fertilizer nitrogen (N) rates based on predicted yields can be projected if the quantity of N accumulated in winter wheat (Triticum aestivum L.) and corn (Zea mays L.) is known especially early in the growing season. This study was conducted in 2006 and 2007 to establish the amount of N accumulated in corn and winter wheat over the entire growing season. Plots representing three N fertilization rates 0, 45, and 90 kg ha-1 at Stillwater and 0, 67, and 112 kg ha-1 at Lahoma were selected from two long-term wheat experiments located at research stations in Stillwater and Lahoma, Oklahoma. For corn, three N fertilization rates 0, 112 and 224 kg ha-1 at Lake Carl Blackwell and 0, 56 and 112 kg ha-1 at Perkins were selected from N studies, located at research stations near Lake Carl Blackwell and Perkins, Oklahoma. Sequential aboveground biomass samples were collected from 1 m2 area of wheat and 1.5 m long row (0.76 cm spacing) for corn throughout their respective growing seasons. In general, this work showed that more than 45% of the maximum total N accumulated could be found in corn plants by growth stage V8 (8th leaf collar fully unfolded). For winter wheat, more than 61% of the maximum total N accumulated at later stages of growth could be accounted for by Feekes growth stage 5 (F5, leaf strongly erected). Our findings are consistent with those of others showing that yield potential can be predicted at mid-season since such a large percentage of the total N accumulated was accounted for early on in the growing cycle of either wheat or corn.