By Len Wilcox
California’s consistent sunshine makes for long growing seasons and allows tremendous varieties of foods to be grown, but it isn’t a perfect environment. Chronic water shortages create challenges for everything except cactus grown for tequila or jelly — but not many growers specialize in that. The rest of them, including citrus growers, have to deal with water shortages by buying ditch water or paying even more to pump it out of the ground. And, as was seen during the most recent drought, there are times when and places where water is not available at any price.
California State University, Fresno (CSUF) has been dealing with water issues since its inception. CSUF formalized its research and training in irrigation in 1980 when it created the Center for Irrigation Technology. Since that time, the school has become a leading independent testing laboratory and applied research facility for the irrigation industry. CSUF has built state-of-the-art indoor and outdoor testing facilities and works with the public and private sector to advance irrigation technology, water management practices and equipment standards.
Ditch water is considerably less costly than paying to pump it out of the ground. However, not every tract is served by an irrigation canal, and allocations are often cut to the point that supplemental pumping is necessary.
IRRIGATION SCHEDULING
The goal of the research and educational activity is to assist growers with getting the most value possible from every drop of water that runs through their irrigation systems, whether it is a drip, flood or sprinkler system. The key to effective, efficient water use is irrigation scheduling — knowing when, how much and how to irrigate.
Irrigation scheduling basically tries to model the physical process of water movement into the soil, through the soil and through the plant. The “water budget” method of irrigation scheduling is the day-by-day accounting of the amounts of water coming into and going out of the effective root zone. The graphical/sensor-based (also called bottom-line) method of irrigation scheduling monitors the quantity of water that is in the root zone.
For either method, the grower has to know a lot about the specific conditions, including the crop being grown, depth of the root zone, type of soil, and the amount of water that soil can hold. Weather is also a factor, as it affects the crop evapotranspiration rate.
EVAPOTRANSPIRATION RATE
Figuring out the crop evapotranspiration rate is a complicated matter that depends upon the weather in the field as well as the type of crop being grown there. The first step in finding this rate is to obtain weather data from the California Irrigation Management Information System (CIMIS).
CIMIS was developed by the state Department of Water Resources and University of California, Davis to help irrigators save water. It is a network of more than 145 weather stations in growing regions around the state that reports weather data hourly. The stations use this data to calculate ETo, which is a reference point for evaporative demand for that micro-region.
Although CIMIS was initially designed to help growers determine when to irrigate and how much water to apply, the user base has expanded over the years. Current CIMIS data users number about 40,000 and include landscapers, local water agencies, firefighters, air pollution control boards, pest control managers, construction engineers, consultants, hydrologists, government agencies and many more.
The ETo number is useful for measuring the effect of the weather on crop water demand. After obtaining the ETo from a nearby CIMIS station, the grower multiplies that number by a crop coefficient (determined by the type of crop being grown) to determine the crop’s evapotranspiration rate.
With all this information — type of crop and its evapotranspiration rate, type of soil and the amount of water it can hold, and the quantity of water in the soil — growers can estimate how much water to put in the field. A grower will be able to maintain the water quantity at a level the plant can use, but will avoid putting so much water in the ground that it is wasted. Throughout the growing season, the grower replenishes that water when it draws down close to the “wilt point,” the point at which there isn’t enough water in the soil to maintain a healthy plant. It is not a simple plan, but it is one that will save water and money.
GROWER RESOURCES
Collecting, monitoring and using all this data begs for computerization. Sensors are available that monitor the amount of moisture in the root zone, and computer-controlled switches can be programmed to operate irrigation systems as needed. It is a significant investment in equipment, but some have reported savings of up to 50 percent of water use as well as improved crop production due to better watering habits.
CSUF provides tutorials and much more information at the Center for Irrigation Technology website (www.fresnostate.edu/jcast/cit). Many tutorials are also on the Wateright website (www.wateright.org). Wateright is designed to be a multi-function, educational resource for irrigation water management. Visit www.cimis.water.ca.gov for more information about CIMIS and to sign up for its free service.
Len Wilcox is a freelance writer in Sanger, California.
Share this Post
About the Author
