Dryland Winter Wheat: Eastern Washington Nutrient Management Guide

Dryland Winter Wheat: Eastern Washington Nutrient Management Guide

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Richard Koenig, Extension Soil Fertility Specialist, Department of Crop and Soil Sciences, Washington State University, Pullman
This publication provides detailed information on nutrient needs of dryland winter wheat for eastern Washington and includes a 1-page worksheet
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Nutrient management is essential to the economical production of high-yielding, high-quality crops, and to preserving soil, air, and water quality. As the term implies, nutrient management includes activities such as sampling to monitor soil nutrient levels and adjust application rates; altering practices such as the placement, application timing, and source of nutrients to maximize plant availability and uptake; and conducting a post-harvest assess­ment of yield, grain protein levels, and nutrient use efficiency.

Eastern Washington is unique in that diverse envi­ronment, soil, and topography result in variations in crop yield across the region as well as across farms and individual fields within farms. Due to the inherent variability associated with eastern Washington dryland crop production, a one-size-fits-all recommendation for the management of any one nutrient is of little value. Recommenda­tions must be based on individual grower practices, achievable yields, and current soil test data. This document presents guidelines for managing major nutrients in eastern Washington dryland winter wheat and emphasizes how producers can tailor rec­ommendations to their own production systems. It also identifies opportunities where information such as crop yield and protein and soil test nutrient levels can help refine and improve nutrient management practices.

Nutrient uptake and removal by dryland wheat

High-yielding wheat absorbs large quantities of nu­trients from soil. Box A shows average values for nutrient uptake and removal in the grain and straw of wheat. This table can be used as a guide to forecast nutrient removal from the field with the grain and straw portions of the crop. Note that the majority of nitrogen and sulfur in straw is lost if a field is burned; other nutrients generally remain in the ash.

Nitrogen (N) recommendations

Nitrogen recommendations are based on the potential yield for a site, the amount of N required to achieve yield and protein goals for a desired wheat class, and an inventory of soil N contribu­tions. A worksheet is included in this guide to aid in developing an N recommendation and as a record-keeping tool. The following paragraphs refer to specific sections of the worksheet. A separate Mi­crosoft Excel® spreadsheet is also available to make these calculations electronically.

Yield potential and N supply needed (Block A of the worksheet). The amount of N required to achieve yield and protein goals is a function of the yield potential of the site and class of wheat grown.

A1. An accurate yield goal is essential to develop an accurate N recommendation; however, yield varies within a field and from year to year in response to weather, and rotation, seeding date, and other man­agement variables. Acceptable methods of estimat­ing potential yield for a site are based on: 1) grower practices and experience with the field; 2) measured historic averages; and 3) pre-plant soil moisture and rainfall expected during the growing season.

A2. Different wheat classes require different amounts of N to achieve quality goals. The number of pounds of N required per bushel (lb N/bu) for different wheat classes is summarized in a footnote on Block A2 as a single value +/- 0.2 to reflect varia­tions in N use efficiency among years and landscape positions. Actual values may vary by more than +/- 0.2 lb N/bu. Methods of calculating the actual lb N/bu required to produce wheat in the field are included in Block E. Note that



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