Predicting the Nitrogen Needs of Wheat Using Stem Nitrate Analysis

The high yielding spring wheats grown in Arizona usually require applications of fertilizer nitrogen (N) to achieve optimum yields and acceptable quality. The University of Arizona's currently recommended procedure of preplant soil plus periodic stem tissue analysis for NO₃-N to predict the N needs of wheat is not widely used by Arizona growers. A nitrogen fertility trial was conducted at the Maricopa Agricultural Center during the 1985-86 crop year to evaluate the accuracy and practicality of the currently recommended procedure for predicting the optimum N rate for 'Aldura' durum wheat grown on a sandy soil low in residual N. Five rates of N from 0 to 500 lbs N/a were applied in four split applications. Three additional N treatments were made using equivalent amounts of three different N sources (urea, ammonium nitrate, and calcium nitrate) as indicated by the current UA procedure. Maximum grain yields of over 6500 lbs/a and protein levels above 13% were attained with the application of 215 to 250 lbs Nia. The amount of N predicted by the UA procedure (215 lbs N/a) did attain maximum grain yield and resulted in the most favorable adjusted economic return of all the fertilizer treatments used in the trial. Though additional work is needed, the stem NO₃-N tissue test was practical to use and proved quite accurate in predicting the N needs of durum wheat