Evapo-transpiration during this period
|Crop||Total inches||Average use|
|spring wheat or barley||2.55||0.17|
How to use this tool
This chart represents water use by a well watered crop. The table under the graph indicates how much total water was used by the crop and estimates average water use for the period. This provides an estimate of expected water use over the next few days.
The ideal way to utilize this information is to select the last date that you were confident you had a soil profile full of water. By knowing your soil's water holding capacity you can estimate when the next irrigation will be necessary. It's best to keep your soil available water above 50% (60% for dry beans) during the growing season.
If you don't know your soil's water holding capacity, you can get an estimate from your county soil survey as conducted by NRCS. Click on Web Soil Survey to open a second tab. In addition open this Tutorial in a third tab to guide you through WSS if it's your first time at this site.
As an example, assume that your soil profile is estimated to hold 7 inches of available water. If the graph above was made using the date of your last flood irrigation, and the total water use for this period is at or above 3.5 inches, then you need to make another application. If water use since the last flood is less than 3.5 inches, you can use the daily water use value to estimate when the field will reach 50% depletion.
Toward the end of the season, care must be used to apply enough water to finish the crop without applying so much that the field is at a full profile at harvest time. Knowing when the crop is expected to mature, and using this tool to estimate water use, you should be better able to choose a proper time for that last irrigation.
Proper irrigation scheduling can help increase profits while decreasing negative effects to the environment such as off-site movement of agricultural chemicals, leaching of fertilizer below the root zone, and overly wet conditions that can lead to increased disease incidence. This ET estimation tool has been developed to help irrigators make more informed decisions as to when to apply the 'next' irrigation.
Evapo-transipiration (ET) is an estimate of the amount of water that is transpired by the crop AND evaporated from the soil surface. Early in the season when the crop is just established, evaporation is the primary loss. As the crop canopy develops, and the crop enters a phase of rapid growth, transpiration becomes the dominant use of water. Early attempts at estimating ET primarily used devices such as evaporative pans. These provide a reasonable estimate of the energy driving evaporation, but they lack the ability to model how plants transpire. By measuring inputs such as temperature, humidity, wind speed, and net radiation, coupled with a crop growth model, a better estimate of ET can be obtained.
At the Southern Agricultural Research Center, we use an automated weather station that tracks these parameters on a minute by minute basis. The above graph is produced using these inputs generating a real-time estimate of ET specific to each crop.
This website generates water use estimates using estimates of evapotranspiration (ETo) as described in "Crop Evapotranspiration - guidelines for computing crop requirements - FAO Irrigation and drainage paper 56".
Crop water use curves for the upper Yellowstone River valley are being developed. The crop water use curves currently used are based on research conducted at the Northwest Irrigation & Soils Research Lab, and are adjusted to growing conditions here at the Southern Ag Research Center. We will adjust these curves for this environment over the next couple of years. In the meantime please use the data on this page as general guidelines.