One tool to boost irrigation efficiency
With such a dry start to spring, the prospect of keeping crops watered on irrigated ground may seem daunting...and pricey. But, there's one simple tool that you can use to get more out of your irrigation water.
The atmometer, or ETgauge, measures evapotranspiration in a field. The cylindrical device -- similar to a rain gauge -- shows how much water your crops are using by comparing the amount of water applied on a field and the amount of evaporation. The distance the water level in an ETgauge drops is that which the crop is using.
"It acts as a mini weather station to provide reference evapotranpiration (ET) information for nearby fields. Information is displayed on a site tube mounted in front of a ruler on the instrument. Reading the site tube is like reading a rain gauge in reverse as you watch to see how much the water level drops each week," according to a report from University of Nebraska (UNL) Extension specialists Chuck Burr, Aaron Nygren, and Gary Zoubek. "A grower or crop consultant can use an atmometer to quantitatively gauge how crop water use varies from week to week and season to season with changing weather conditions. This is more accurate than using an average number for a given season or growth stage."
An ETgauge is usually mounted near the irrigated field it's monitoring in an area that represents "average field conditions," the UNL specialists say. That way, it's getting a representative sample of moisture that's best extrapolated across a field.
"Do not install near farm buildings, trees, or tall crops that may block the wind," Burr, Nygren and Zoubek say in a university report. "Don’t install an atmometer under the throw of an irrigation system, as evaporated irrigation water will leave minerals...that can inhibit water flow."
Want to build one? The materials cost about $250 per unit. "Atmometers consist of a wet, porous ceramic cup (Bellani plate) mounted on top of a cylindrical water reservoir. The ceramic cup is covered with a green canvas (Gor-Tex) that simulates the canopy of a crop," the UNL specialists say.
"The reservoir is filled with distilled water that evaporates out of the ceramic cup and is pulled through a suction tube that extends to the bottom of the reservoir. Underneath the fabric, the ceramic cup is covered by a special membrane that keeps rain water from seeping into the ceramic cup. A rigid wire extending from the top keeps birds from perching on top of the gauge."
Image courtesy UNL Extension.