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Regulations

FARMING IN WESTLANDS

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Each year District farmers are surveyed to determine the types of irrigation systems used during the crop year as part of the annual crop production report survey. Several trends become apparent when this information is compared to a similar survey conducted in 1985, as shown in the table below. In 1985, 63 percent of the District was irrigated exclusively by surface irrigation (furrow or border strip). In 1990 this figure decreased to 43 percent and by 1996 it decreased to 34 percent. The acreage irrigated only by sprinkler systems decreased from 21 to 16 to 15 percent. The acreage irrigated by a combination of sprinkler and furrow almost tripled, from 15 to 43 percent. The drip/trickle acreage increased from 1 to 6 percent.

Various factors may account for these trends. The District has experienced a decrease in its water supply during the drought which began in 1986. Project water supplies declined by over 100,000 AF annually for the five-year period ending in 1990 when compared to the previous five-year period. In 1990 the District received only 50 percent of its Contract allocation. To cope with these reductions and to continue farming their land, the farmers had to reduce field applications or pump additional groundwater. The pumped groundwater is more expensive than the surface water, and in most cases is of poorer quality.

The IIP data indicates sprinkler preirrigations followed by regular season furrow irrigations produce the highest irrigation efficiencies. Also, tailwater reuse systems, when used with furrow irrigation, increased distribution uniformity, thus facilitating better irrigation efficiencies. These findings were shared with the Program participants through their program advisors and with the rest of the District water users through workshops and Profitable Practices. Undoubtedly, some farmers adopted recommendations from the IIP to stretch their supplies in response to supply cutbacks.

Shallow-rooted vegetable crops are difficult to irrigate efficiently with surface systems and are best irrigated by sprinklers during the early portion of the growing season when small applications of water are desirable. Well-managed furrow irrigation will suffice during the remainder of the season, especially on those crops which are susceptible to mildew caused by mid-to-late season sprinkler irrigations.

The irrigation systems used on the major crops grown in the District are shown in the table below. High-value, shallow rooted crops such as tomato, garlic, and onion are most likely irrigated by a combination of sprinklers and furrow during the season. Lower-valued, deeper rooted crops such as alfalfa and wheat are more likely to be surface irrigated. Moderate valued crops such as cotton have about one-half the fields irrigated by sprinklers for at least a portion of the season. Trees and vines such as almonds and grapes tend to be irrigated by pressurized systems and new plantings are almost exclusively drip/trickle irrigated.

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On-Farm Irrigation Systems
Type of System                       Percentage of Land Irrigated

The 1987 through 1989 Irrigation Improvement Program (IIP) data were analyzed to determine the use of on-farm tailwater reuse systems in the District. The analysis shows that 62 percent of the 451 fields irrigated by surface irrigation had tailwater systems. This is an increase from 54 percent in the 1985 survey. The 1989 Program data show 16 percent of those fields utilizing tailwater systems returned the water to the same field while only 11 percent of the fields with tailwater systems returned the water to the same field as reported in the 1985 survey.