The occurrence of phosphorus (P) deficiencies in small grain crops are normally predicted through the use of preplant soil analysis and verified by tissue analysis for total ? often at the beginning of reproductive growth. Few studies have addressed the potential use of tissue phosphate (PO4‐P) tests to characterize the ? status of grain crops during early vegetative growth which could allow for correction of ? deficiency in irrigated production systems during the current season. Three field experiments were conducted in southeastern Arizona from 1986–89 to examine the effects of ? applications, and residual soil ? on tissue phosphate (PO4‐P) concentrations and yield of irrigated durum wheat (Triticum turgidumL. var durum cv. Aldura). Fertilizer ? additions resulted in significant increases in basal stem and leaf tissue PO4‐P concentrations at GS 2, 6 and 10. Fertilizer ? applications of up to 40 kg P/ha increased extractable ? levels in the soil by 82% at the beginning of the next growing season but had no significant effect on grain yields or tissue PO4‐P concentrations of the succeeding wheat crop. Band applications of ? resulted in higher tissue PO4‐P concentrations versus broadcast applications. While both basal stem and upper leaf tissue PO4‐P concentrations were responsive to differences in ? availability, routine use of basal stems for nitrate testing and significantly higher PO4‐P levels in basal stems at GS 2 and GS 6 favor its use in diagnosing ? deficiency. Basal stem tissue PO4‐P analysis seemed to accurately reflect ? nutrition of durum wheat from GS 2 to 10. Preliminary critical levels of PO4‐P in basal stem tissue of irrigated durum wheat were 2000, 1200 and 500 mg/kg at GS 2, 6 and 10, respectively.