Author(s):
Lars Pierce* - California State University Montery Bay
Andy Michaelis - California State University Monterey Bay
Ramakrishna Nemani - NASA Ames Research Center
Abstract:
In 2006, California agricultural receipts topped $31 billion while using 80% of the state's developed freshwater resources. However, this water must be shared with a growing population while warming trends and recent drought threaten to reduce the supply of water. In wine grapes, targeted deficit-irrigation scheduling not only reduces water use, it also improves berry quality and color, and reduces energy costs and agricultural runoff. Spatial and/or temporal variations in weather, soils, and the canopy lead to variations in vine water requirements across vineyards, making it a challenge to precisely estimate vine water needs. Growers need accurate information on crop, soil, and weather variations, and a way to consolidate all of this information, to precisely define targeted irrigation strategies that save water yet minimize the risk of crop loss. We combine aircraft-based imagery, soils maps, and weather data within a spatially-based 'crop-coefficient' model to estimate daily irrigation needs across a 550-acre Napa Valley vineyard split into 100 management blocks. For 2008, we found that model-based estimates of soil moisture and vine water potential compare favorably with measurements taken at specific locations within the vineyard. Annual variations in spring weather, and its corresponding effect on timing of budbreak and canopy development, significantly influence the date of first irrigation. Spatial variations in vine spacing and soil properties had the greatest influence on block-to-block variations in irrigation requirements. Soil heterogeneity, particularly rooting depth, remains our greatest uncertainty and we briefly discuss ways to improve these maps.
