Effects of P Applications on Wheat Tissue Phosphate Levels and Grain Production in Graham County

Abstract

Collecting additional data to calibrate and refine current guidelines for interpreting soil and plant test values for P is an ongoing need in Arizona. An experiment was conducted at the Safford Agricultural Center during the 1987 -88 crop year to evaluate the response of 'Aldura' durum wheat to P fertilizer applications on a clay loam soil testing low in available P. Maximum grain yields of more than 5,500 lbs. /A were obtained by banding 40 lbs. P₂O₅/A as triple super phosphate with the seed at planting. A December 9 planting date subjected plants to cold soil temperatures early in the season (up to 80 days after planting), rendering soil P less available for plant utilization. Preplant soil P analyses predicted the yield increase observed with P fertilization (11.2 %);however, economic returns were not sufficient to offset the cost of P fertilizer. The recommended preplant soil test for P proved accurate in predicting P status and stem PO₄⁻P tissue analyses seemed reliable in monitoring P nutrition of durum wheat. A critical nutrient range of 1200 - 2000 ppm PO₄⁻P is proposed for basal stem tissue sampled prior to the joint growth stage, and 1500 - 1706 ppm PO₄⁻P is suggested for flag leaf tissue sampled at the boot stage.