Phosphorus Requirements of Wine Grapes: Extractable Phosphate of Leaves Indicates Phosphorus Status

Abstract

Abstract Although premium wine grapes (Vitis vinifera L.) are planted in soils of low P availability, there is little knowledge of P requirements and of the appropriate methods of P analysis in grapevines. Therefore, acetic acid extractable P was investigated as a method for determining grapevine P status. Analysis of absorption spectra established that absorbance peaks at 710 or 882 nm of the phosphomolybdate complex formed in acetic acid extracts of grapevine tissues can be used for analysis of P status. Acetic acid-extractable P was independent of sample size and extraction time and was linearly related (r2 = 0.96) to total P in four premium wine grape varieties. Lamina indicated whole plant P status better than petioles, since extractable P accumulated more in lamina than in petioles. Total and extractable P of basal lamina decreased significantly after anthesis, which diminished the differences between P-sufficient and P-deficient vines. Therefore, the best time to assess vine P status using leaves is at anthesis. When P fertilizer was applied, lamina-extractable P was positively correlated with berry weight, yield, and pruning weight in Chenin blanc vines growing under P-deficient conditions. The results indicate that acetic acid extractable P in lamina sampled at anthesis is a sensitive measure of grapevine P status.