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ISHS Acta Horticulturae 852: IV International Symposium on Ecologically Sound Fertilization Strategies for Field Vegetable Production

REGULATION OF NUTRIENT MANAGEMENT IN VEGETABLE PRODUCTION: THE CALIFORNIA EXPERIENCE

Author:   T.K. Hartz
Keywords:   water quality, nitrate, fertility management, irrigation management
Abstract:
More than 160,000 ha of cool-season vegetables are produced annually in the coastal valleys of central California. In these valleys vegetable production dominates the landscape, and since most fields produce two or more crops per year the mean annual fertilizer input is very high. Not surprisingly, environmentally problematic levels of soluble phosphorus in surface waters, and nitrate-nitrogen (NO3-N) in both surface- and groundwater, are common. The Central Coast Regional Water Quality Control Board (WQCB) is struggling to develop effective regulatory measures to improve water quality without damaging the viability and competitiveness of the commercial vegetable industry. Recognizing the dynamic nature of a system in which dozens of vegetable commodities are produced year around on a range of soils and in varying rotational schemes, the WQCB has been reluctant to impose numerical limits on fertilizer application, or to mandate the use of specific management practices. To date, regulatory efforts have been tied to the discharge of irrigation tailwater or storm runoff from agricultural land. In 2004 the WQCB granted a 5-year waiver from the requirement to obtain a permit for such discharge to all growers who agreed to: a) attend an extensive water quality training course; b) develop a written farm water quality protection plan outlining practices to be undertaken to reduce nutrient losses; and c) participate in a watershed-scale water quality monitoring program. In the initial years of this program the majority of vegetable growers met these requirements, yet the monitoring data have shown no substantive improvement in water quality parameters related to nutrients. The WQCB is currently planning additional grower educational activities to encourage wider adoption of efficient nutrient and irrigation management practices, and is considering additional grower requirements for extending the discharge waivers.
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