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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 Ρ often at the beginning of reproductive growth. Few studies have addressed the potential use of tissue phosphate (PO4-P) tests to characterize the Ρ status of grain crops during early vegetative growth which could allow for correction of Ρ 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 Ρ applications, and residual soil Ρ on tissue phosphate (PO4-P) concentrations and yield of irrigated durum wheat (Triticum turgidum L. var durum cv. Aldura). Fertilizer Ρ additions resulted in significant increases in basal stem and leaf tissue PO4-P concentrations at GS 2, 6 and 10. Fertilizer Ρ applications of up to 40 kg P/ha increased extractable Ρ 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 Ρ 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 Ρ availability, routine use of basal stems for nitrate testing and significantly higher PO4-P levels in basal stems at GS 2053

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