Elizabeth Gillispie, Devin A. Rippner,* Julie Tarara, and Paul Schreiner
*USDA-ARS Horticultural Crops Production and Genetic Improvement Research Unit, 24106 N Bunn Road, Prosser, WA, 99350 (devin.rippner@usda.gov)

The critical phosphorus (P) level for winegrape whole leaves at veraison is thought to be 0.15% of dry weight for eastern Washington (WA) winegrape vineyards, but other research suggests that this may be too high. Therefore, more P is likely being applied to soil than is necessary, leading to excess P in soil and possible alteration of other nutrients in soil and in vine tissues. This study tested the impact and/or limitations of P application to a vineyard soil (via fertigation) on i) soil-P concentrations and bioavailability, ii) leaf-P concentrations, and iii) vine productivity and physiology. Approximately 20 acres of Cabernet Sauvignon grown near Paterson, WA was split into four replicates, where all replicates contained three treatments (four rows each). Three rates of P were evaluated: a 10 lb/ac application of P (as H3PO4), 20 lb/ac application of P, and a zero-P control. Soil, leaf, and root samples were collected at multiple stages over the annual growth cycle of the grapevine: initial treatment application, prebloom, bloom, fruit set, lag phase, veraison, harvest, and postharvest. Micro-x-ray adsorption near-edge spectroscopy (µ-XANES) was performed on select soil samples to assess changes in P-speciation and mineralization over a growing season and across treatments. Results were compared with soil and leaf nutrient analyses, such as total soil- and leaf-P, soil-P sequential extraction, colonization of roots by arbuscular mycorrhiza fungi, and vine productivity. Results will be used to provide better P management recommendations and assess current tissue-P standards for Cabernet Sauvignon vineyards in eastern Washington.

Funding Support: United States Department of Agriculture - Agricultural Research Service – CRIS Project No. 2072-21000-057-000-D, and in part Project No. 2072-21000-055-000-D