Uniformity means applying water evenly. Efficiency measures how well the amount of water you supply matches the needs of the plant.
Measuring uniformity is simple and can be done by the grower.
With a drip system, measure flow rates and times from different discharge points. With a pivot system, you can simply capture water in cans and compare the volumes.
For more specific information, Zazueta suggests consulting any of a number of publications listed on the IFAS Web site—http://www.ifas.ufl.edu.
Some drawbacks to achieving uniform application are pressure variations along pipes, manufacturer variations, using non-matching sprinklers and poor system design, he says.
Unlike uniformity, efficiency can be difficult to measure.
An estimate of water use must be established by measuring the amount of water needed by the plant over a long period, maybe a full season.
“Then you have to look at how much water you used,” Zazueta says. “If you had a crop that required 20 inches, based on weather, and you applied 40 inches, that means your efficiency is around 50 percent.”
Several methods of determining how much water is adequate have been devised over the years, Trout says.
One is climatic irrigation scheduling, which involves measuring weather parameters, such as temperature and sunlight, to predict how much water a crop is using.
Another method is to monitor the soil with instruments to find out how much water is in the ground and adjusting your water use to an appropriate level.
Trout advises using both methods simultaneously.
One way to ensure accurate weather-related data is through agencies such as CIMIS—or California Irrigation Management Information System. The free, Web-based service comprises 140 stations that constantly gather weather-related information including temperature, humidity, radiation and wind direction, says Baryohay Davidoff, chief of agriculture, water management and financial assistance for the California Department of Water Resources in Sacramento.
This information provides a reference evapotranspiration number that can be used to calculate a crop coefficient, which can help a grower determine how much water to apply.
The site can be accessed by visiting http://www.cimis.water.ca.gov. Some other states, such as Washington, Oregon and Arizona, have similar but less sophisticated systems, he says.
Two factors should be considered when implementing an efficient irrigation system, Trout says—the system itself and management of the system.