By Randy Weisz and Deanna Osmond
From year to year, and field to field, many factors influence both the wheat yield and the total amount of nitrogen that will be needed to maximize yield. No single nitrogen recommendation will be best for every field in every year. Wheat producers who want to maximize their economic return need to use a flexible approach to nitrogen fertilization that takes into account different soil characteristics and environmental variation that occurs from year to year. Methods for optimizing nitrogen applications based on planting date, Feekes Growth Stage 3 tiller density, and Feekes Growth Stage 5 tissue testing have been described in the previous chapter.
In some coastal plain watersheds, the state regulates how much nitrogen wheat producers may apply to their crops. Nitrogen recommendations made with a tissue test always supersede these regulations, but in the absence of a tissue test, growers in regulated areas must use the following guidelines.
Determine a Realistic Yield Expectation and Nitrogen-Use Factor
A realistic yield expectation (RYE) for each field must be determined. The best way to determine RYE is with field records. Take the average of the best three wheat yields out of five years. This will be the RYE for this particular field. If there are no yield records, use the RYE information (based the predominant soil in the field) available at http://www.soil.ncsu.edu/nmp/ncnmwg/yields/.
Different soil types require a different amount of nitrogen fertilizer to produce a bushel of grain. This is called the “nitrogen-use factor.” Nitrogen-use factors are also available for each soil type on the web at the address given above.
Computing a Regulated Nitrogen Rate
The final step is to compute the total amount of nitrogen fertilizer the regulations will allow for wheat production in a given field. This is done by multiplying the RYE by the nitrogen-use factor for the predominant soil type.
This file is a chapter from Small Grains Production Guide, 2004-05. Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the NC Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension Center.
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9/04—3M—JMG (Revised) AG-580
EO4-43980
Last Revised Sept. 2004