Compost Application on Degraded Vineyard Soils: Impact on Vine Nutrient Status, Grape Quality, Yield Parameters and Soil Fertility.

A two-year study was undertaken to investigate compost (CSM) as a method to enhance productivity and improve soil quality of a cabernet sauvignon vineyard in a degraded volcanic soil in the Red Hills American Viticulture Area of Lake County, California. The intent of the research was to i) identify a dose response relationship between the application rate of compost, and vine nutrient status, biomass and yield, ii) identify vineyard nutrient management strategies for remediating degraded vineyards, and iii) assess the sustained response of a single dose of compost over two years. A randomized complete block field study was designed to investigate the response of CSM additions at rates of 5, 10 and 15 tons/acre applied in December 2011, on cabernet sauvignon vines on 3309-C rootstock. Vine nutrient status was measured in petioles at bloom, veraison and postharvest in 2012 and 2013. Juice chemistry, berry weight, vine yield and pruning weights were measured in 2012 and 2013. Petiole nitrogen and phosphorus at bloom displayed a significant linear response to CSM application rate in both years. Yields, pruning weights and berry weights were significantly increased with increasing application rates. Average per vine yields improved 50% in the first year and 59% in the second year. Yields, pruning weights, cluster weights and berry weights significantly increased with application rate. Vine balance (yield/pruning weight) and juice chemistry were not significantly affected by application. Soil (0 – 10 cm) C and N were significantly increased and P sorption significantly reduced at the end of the first year. This study demonstrates that compost application can provide a sustained 2-year benefit to vineyard soils, significantly improving vine nutrient status, yields, pruning weights, berry weights and cluster weights without changing vine balance or juice chemistry on degraded volcanic soils in Northern California.