UC Davis

A two-year experiment investigated the effects of compost application rate on soil chemical properties, vine nutrient status, vine performance, and grape juice characteristics in a degraded vineyard soil in northern California. The intent of the research was to identify vineyard management strategies to improve soil fertility and to identify optimal compost application rates. We applied composted steer manure at three rates (11.2, 22.4, and 33.6 t/ha) in a randomized complete block design before the 2012 growing season. Pruning and berry weight increased over the control at the highest application rate in both years, while vine yield significantly increased over the control in year two. Polynomial orthogonal contrasts suggest that pruning weight, vine yield, and berry weight increased linearly with increasing compost application rate in 2012, and that vine yield and berry weight increased linearly and quadratically with compost application rate in 2013. Measured soil properties increased from compost application, including nitrogen (N), carbon, pH, exchangeable potassium (K), manganese, and calcium and available phosphorus (P, Olsen-P), while phosphorus fixation decreased. Vine petiole nutrients (N, P, and K) significantly increased from compost application in both years. Juice characteristics (pH, total soluble solids, and titratable acidity) were unaffected by compost application. Similarly, vine balance was unaffected by compost application. All vine metrics improved at the highest application rate, and soil chemical properties increased with the two highest application rates. Therefore, significant benefits to soil fertility and vine performance can be achieved for at least two years in degraded vineyard soils following a single dose of compost at higher application rates (22.4 and 33.6 t/ha) without compromising juice characteristics or vine balance.