UC Delivers

3 Year Study Examines Most Efficient Sprinkler Spacing

The Issue

Questions about water and fertilizer use efficiency are major economic and environmental issues for California agriculture. Excess nitrate is an important concern for San Joaquin Valley communities that depend on groundwater for drinking. Vegetable crops such as carrots, onions and potatoes typically require high amounts of nitrogen fertilizer and frequent irrigation, usually by sprinkler. Although sprinkler lateral spacings vary from 30 to 50 feet, no season-long field study had determined the impact of these different spacings on efficiency of water and nitrogen use.

What Has ANR Done?

A three year study funded by the statewide Fertilizer Research and Education Program compared seven different sprinkler lateral spacings from 33 to 48 feet for impacts on irrigation uniformity, nitrogen leaching and yield. Yield and quality were statistically unaffected by spacing. With set times of 12 hours, more traditional lateral spacings (42 to 46 feet) achieved the same seasonal uniformities and carrot yields as 33 to 40 foot spacings. However, the 40-foot spacing was the most consistent over the season for water and nitrogen use efficiency. When wind speed is greater than 12 mph the 40 to 42 foot spacing has a definite advantage over wider spacings. Narrower spacings did not give additional improvement. A full "season-long average" sprinkler uniformity was found to be about 10% higher than the reported statewide average. Sprinkler age made no difference in uniformity, except when set duration dropped below six hours. Short sets decreased uniformity by 10 to 20%. Carrot yields were statistically the same where sprinkler precipitation was from 80 to 120% of crop ET.

The Payoff

40 Foot Sprinkler Spacing Now Standard for Kern County Carrots

Most carrots, onions and potatoes in Kern County are now irrigated at 40 or 42-foot lateral spacings with six to 12 hour sets. With this system, this study shows that water use effiency in the 50,000 acres of carrots grown in Kern County is closer to 90% than the 75-80% estimate normally used for hand-move sprinkler irrigation. This high level of efficiency also means that less water is available through "ag conservation savings" than is typically estimated by California water policy makers for these types of systems.

Contact

Supporting Unit: Kern County Soils, Irrigation, and Agronomy

Blake Sanden, Irrigation & Agronomy Farm Advisor
UC Cooperative Extension
1031 S. Mt Vernon Ave., Bakersfield, CA 93307
(661) 868-6218 (661) 868-6208 (fax)
blsanden@ucdavis.edu