Tissue nitrogen (N) content in Virginia wheat at GS 30 can be directly related to final grain yield. This information can be used to adjust the second application of spring N to bring the crop to high yield levels. The first requirement for obtaining a good plant tissue sample for use in estimating N fertilizer requirement at GS 30 is to be certain that the wheat is in growth stage 30.
Growth stage 30 is when the leaf sheaths of the wheat are strongly erected and splitting the stem shows a hollow internode area about 1/2 inch in length.
A representative tissue sample from the field is essential for accurately predicting fertilizer N requirement at GS 30. The sample is taken by cutting a handful of wheat tissue at 20 representative areas in the field. The plants should be cut at approximately 1/2 inch above ground; soil particles brushed from the tissue; and dead leaf tissue removed from the sample. The individual samples should be placed in a paper bag large enough to allow good mixing of the tissue.
After thorough mixing of the tissue sample, take approximately three handfuls of tissue from the mixed sample and place in the sample bag provided by the laboratory, or in a clean paper bag. Samples should go directly to the laboratory. If samples cannot be analyzed within 24 hours from the time they are taken, they must be dried to prevent spoilage. Tissue samples should never be packaged in plastic bags due to condensation that can initiate sample decay.
Nitrogen Rate Determination
Use the graph below to obtain a rate recommendation from tissue test results. Up to 120 lbs. N/acre may be applied at growth stage 30 if no N was applied at growth stage 25 (due to high tiller density) and tissue N measured at growth stage 30 is low. Total spring N applications (growth stage 25 plus growth stage 30) should not exceed a total of 120 lbs. N/acre in order to avoid problems with lodging and yield loss. For example, if 40 lbs. N/acre was applied at growth stage 25, and tissue test results give a recommendation from the figure of 100 lbs. N/acre at growth stage 30, only 80 lbs. N/acre should be applied at growth stage 30.
Many agricultural testing laboratories can provide this analysis. Consult your Virginia Cooperative Extension agent or professional crop consultant for more information.
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