Grape response to phosphorus fertilizer: Petiole to blade P ratio as a guide for fertilizer application

Abstract A two‐year fertilizer study on a mature vineyard of grapes (Vitis vinifera L., cv. ‘Cabernet Sauvignon’ and ‘Sauvignon blanc') was conducted on a White House sandy loam (fine, mixed, thermic Ustollic Haplargid) soil at the University of Arizona Oracle Agricultural Center. Two cultivars were grown and treated with different levels of N and P fertilizer and tested for total P and NO3‐N content of plant tissues. Available P was evaluated with two extracting methods (Olsen and Bray P1). Relationships between soil pH, extractable Al, Fe, Mn, and Zn with the availability indexes of soil P were also examined. Furthermore, the effects of P rates and placement on the P content of plant tissue, grape yield, and petiole to blade P ratios were investigated. Three fertilizer placements (0, 25, and 50 cm depths) at rates of 88 g P and 80 g N per vine were used for both cultivars in 1987, whereas, in 1988, three P rates (0, 88, and 176 g P per vine) and 207 g of N per vine were applied. The results of this inve...