The Potential of Wine-Grape Production in the San Joaquin Delta Area of California

¹ Agricultural Extension Service, San Joaquin County, Stockton, California 95202
² Department of Soils and Plant Nutrition, University of California, Davis 95616.

The San Joaquin Delta of California is a new area for wine-grape production. Climate, soils, and fruit quality were investigated from 1965 through 1967.

The climate as measured by degree-days was found to be essentially the same as in the Lodi (California) district and varies from year to year between Temperature Regions III and IV. Although only 15 to 20 miles from the Lodi district, the Delta has cooler days and warmer nights during the growing season. There is evidence that in hot years the Delta climate is cooler than the Lodi climate.

The vineyards are on Ryde series soils, which are unique in a number of ways. They are medium-textured alluvial soils that occur as narrow, meandering bodies standing higher than the surrounding peat soils. The surface is highly acid, varies in organic-matter content from 10% to 20%, and is generally very loose and friable. The soils are irregularly stratified with respect to such properties as pH, organic matter, salinity, texture, and nutrient status. The soils are usually well drained, because of their higher position. Subsoil pH's can run as low as 3.4, but no adverse vine nutritional problems have been observed.

Analysis of the expressed juice from berries sampled from 10 varieties showed the balling-acid ratio for some varieties to be satisfactory for table wines. Varieties tested that may have a potential in the Delta are: 'Chenin blanc,' 'Grey Riesling,' 'Petite Sirah,' 'Helena,' and 'White Riesling.' Vines were vigorous and produced good yields.