Tuesday, November 6, 2007 - 2:15 PM
191-5

Solving Severe Phophorous Deficiency in Grapevines Grown in very Acidic Soils.

Daniel Roberts, Integrated Winegrowing LLC, Integrated WineGrowing, LLC, 8207 Candy Apple Lane, Sebastopol, CA 95472

Vines growing in soils derived from volcanic ash or marine sandstones by first crop year are often phosphorous deficient. The soils derive from volcanic ash have soil pH often less than 4.5 with high levels of aluminum (500 to 2000 mg/kg), potassium and low levels of calcium, magnesium and phosphorous. Soils derived from marine sandstones have soil pH ranging from 4.5 to 5.2 with soil aluminum levels moderate to high. These soils are low in calcium, magnesium, and potassium and phosphorous. The two years prior to first crop, an aggressive phosphorous fertilizer program is essential to avoid severe deficiency during first crop year. The fertilizers of choice must contain nitrogen to get sufficient phosphorous into the vines. It is critical during this time period to not only ensure adequate phosphorous nutrition but to avoid excessive growth which may cause other nutritional issues such as potassium and/or magnesium deficiencies.