For high yields, small grains need 14 to 17 inches of water, depending on weather conditions and length of growing season. The water used for optimum growth is a combination of stored soil moisture, rain and sometimes irrigation. Small grains require about six inches of water as a threshold for grain yield. Each additional inch of water will provide four to five bushels per acre. In deep, well-drained soils, the roots of small grains will extract water to a depth of 3 to 3.5 feet. Small grains are most sensitive to water stress in the boot to flowering stage of growth.

During the peak water use period, small grains can use up to 0.30 inches per day depending on air temperature and cloud cover (Tables 1, 2 and 3). Daily crop water use -- often called evapotranspiration or ET -- depends on plant development and local weather conditions. Small grain water use will generally peak between heading and early dough stage. Daily ET estimates in the following table are based on long-term average solar radiation and cloud cover. Daily ET estimates in northwestern Minnesota may be 5 percent to 10 percent greater than estimates found in Table 1 for central Minnesota because there is a greater chance for a clear and cloud-free sky.

Table 1. Avg water use/day by wheat in Central Minnesota.

Table 2. Avg water use/day by wheat in North Dakota.

Table 3. Avg water use/day by barley in North Dakota.

Real-time daily crop ET estimations during the growing season can be obtained from the Internet.

Minnesota:
http://www.soils.wisc.edu/wimnext

North Dakota:
http://ndawn.ndsu.nodak.edu/index.html