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United States Department of Agriculture

Agricultural Research Service

Research Project: WATER MANAGEMENT TO IMPROVE PRODUCTIVITY AND PROTECT WATER QUALITY Title: Adapting irrigated agriculture to drought in the San Joaquin Valley of California

Author
item Ayars, James

Submitted to: Agricultural Drought Monitoring Strategies in the World
Publication Type: Proceedings
Publication Acceptance Date: April 1, 2011
Publication Date: May 5, 2013
Citation: Ayars, J.E. 2013. Adapting Irrigated Agriculture to Drought in the San Joaquin Valley of California. Agricultural Drought Monitoring Strategies in the World. p. 25-39.

Interpretive Summary: Drought refers to a continuous state of dryness without identifying a cause for that dryness. Irrigated agriculture is in a continuous state of drought by definition because water is supplied from stored surface or groundwater supplies. Thus agriculture is in a constant competition for that supply with municipal, industrial, and environmental uses. Any one of these may have a higher right to the water supply than agriculture. Therefore even in times of plentiful water supply, a drought condition still can exist in irrigated agriculture. Agriculture’s challenge is how to improve water productivity to compensate for potential losses to competing demands. The options available to agriculture for improved water productivity include; changing irrigation systems to improve irrigation efficiency, improving use of water and fertilizer, and improving irrigation water management through irrigation scheduling. Additional water management strategies discussed include; defining production goals based on the available water supply, integrated water management of irrigation and drainage systems, alternative crops, deficit irrigation, and physical management of crops e.g. pruning and thinning. The San Joaquin Valley of California is one area that has been significantly affected by the drought. Crop and water data from the Westlands Water District, which is located on the westside of the San Joaquin Valley, demonstrate how farmers by changing cropping patterns, increasing ground water pumping and increasing the area of fallowed land have had approximately the same depth of water per unit area available for crop production during the drought period from 2006 to 2009.

Technical Abstract: Webster’s dictionary defines drought as a continuous state of dryness but does not identify a cause for that dryness, just the existence. Irrigated agriculture is in a continuous state of drought by definition, simply because water is supplied by stored surface or groundwater supplies. This results in agriculture being in constant competition for that supply with municipal, industrial, and environmental uses, any one of which may have a higher right to the water supply than agriculture. Thus, even in times of plentiful water supply, a drought condition still can exist in irrigated agriculture. The challenge for agriculture is how to improve water productivity to compensate for any potential losses to competing demands. This manuscript discusses options for improved water productivity; including changing irrigation systems from surface to pressurized systems to improve distribution uniformity and better regulate depth of applied water. The impact of improved use of water and fertilizer on yield is discussed. Irrigation water management strategies including deficit irrigation and partial root zone drying are highlight as current practices to reduce total applied water. Alternative water management strategies are discussed that include defining production goals based on the available water supply, integrated water management of irrigation and drainage systems, cropping alternatives, and physical management of crops e.g. pruning and thinning. Westlands Water District data for cropping and applied water in 2006 and 2008 and 2009 are used to demonstrate how farmers have adapted to a reduce water allocation from the Central Valley project. The data demonstrate that there was the same duty of water in each year analyzed even though the allocation was reduced from 100% in 2006 to 40% in 2008 and 10% in 2009. This was accomplished by increased fallowing of land and increased groundwater pumping of poor quality water. Groundwater pumping increased by 20 fold and the fallowed land increased by 300%.

Last Modified: 11/28/2014
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