Development of Geographic Nutrient Management Regions for Winegrapes Based On Soil-Landscape Characteristics.

The Lodi Winegrape District is one of the largest wine districts in California and encompasses a wide range of winegrape varieties, production systems, and soils. Winegrape nutrient management is especially complicated by this soil diversity. We developed a conceptual soil landscape model based on digital soil survey information (SSURGO) to identify regions within the District that have similar potassium management needs. The model uses degree of soil development and parent material to explain the ability of soils to retain K on cation exchange sites, supply K through weathering, and/or fix K in unavailable forms. Our current model identifies five regions with presumed relationships between soil properties and potassium supplying ability: Region 1 weakly developed, smectite clay-rich soils in basin alluvium; Region 2 weakly developed coarser textured soils on recent alluvial fans, flood plains, and stream terraces, Region 3 moderately developed soils on low terraces derived from granitic alluvium, Region 4 highly developed soils on high terraces derived from mixed alluvium (granitic, metamorphosed sedimentary and metamorphosed volcanic rock), and, Region 5 weakly developed soils formed on undulating volcanic terrain. Field and lab studies of soils in these regions show that our model is reasonable in concept, but that it must be fine-tuned to account for differing degrees of soil variability within each region in order to make realistic nutrient management predictions.