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UCCE Tulare County, Best Management Practices for Nitrogen Fertilization of Grapes Page 1 of Tulare County Disclaimer: This article is geared towards a Tulare County audience and may not be applicable to other geographicai areas. Reprint freely with credit to: The University of California Cooperative Extension, Tulare County. UCCE Tulare County Graue Program Page Tulare County Home Page Grape Publications For more information contact: Bill Peacock, Farm Advisor, wlpeacock@.ucdavis.edu Publ. # NG4-91 Best Management Practices for Nitrogen Fertilization of Grapevines Bill Peacock, Pete Christensen, and Donna Hirschfelt University of California Cooperative Extension Introduction Nitrate contamination of California's groundwater is widespread, and according to the State Water Resources Control Board is a more serious problem than water pollution with pesticide (2). It is important, therefore, when using nitrogen (N) fertilizer to apply best management practices that optimize N use efficiency. Nitrogen should be applied when —vine uptake is rapid, and N rates should not exceed vine requirements. Nitrogen inputs from irrigation water, crop residues, and mineralization of soil organic matter must be considered when determining N fertilizer requirements. Irrigations must be accurately scheduled and applied to minimize leaching losses of nitrate from the root system. The —potential for increasing N fertilizer efficiency in vineyards has greatly improved in recent years with new information on N fertilizer timing, the grapevine's N demand, and maximizing irrigation efficiency. —When to Apply Nitrogen Nitrogen should be applied during the growing season,preferably after budbreak through fruit set, or postharvest —(September). When fertilizing postharvest, the canopy should be healthy and functional; applications should be made before October in the San Joaquin Valley. In some viticultural areas or with late varieties, the season may be too short after harvest for effective uptake to occur. On soils highly susceptible to leaching, a split application of N (fruit set+ —postharvest)will minimize leaching losses. Nitrogen should not be applied during the dormant period or early spring especially on sandy, rapidly drained soils. Timing of N application does not vary with method of irrigation. —Supporting Research Nitrogen is most critically needed by grapevines during the period of rapid shoot growth in the spring through bloom and early berry development. The need for N declines from midsummer to senescence (4,28). Grapevines and deciduous fruit trees depend heavily on redistribution of N previously stored in roots, trunk, and canes or limbs to http://cetulare.ucdavis.edu/pubgrape/n2496.htm 10/11/200