By Lyndon Kelley and Angie Gradiz
Irrigated small grains for forage or grain, as well as alfalfa hay, play a key role in many dairy and vegetable operations. These early-season crops provide valuable rotation opportunities for vegetable growers and serve as an important source of spring forage for dairy producers. Small grains and forages are among the first crops of the season that can benefit from irrigation. Providing adequate water to meet the crop water needs allows you to maximize yield and quality while also maintaining adequate soil moisture to start the second crop. While May and June rainfall is often enough to support moderate yields, dry spells can reduce productivity and leave the soil moisture depleted for the next crop.
To achieve high yields in both forages and small grains, strategic irrigation is essential, especially when rainfall does not meet the crop water demand. Careful planning must take place early in the season to determine how much irrigation water to add and at what times to reduce the incidence of disease, produce high yields and create an environment conducive for the second crop to be established.
Irrigation scheduling is the process of deciding how much and when to apply water. The core principle is to replace the water used by the crop through evapotranspiration (ET), which is the combination of water lost from the soil surface and plant transpiration. For more information, refer to “What is evapotranspiration and why is it important in irrigation?” from Michigan State University Extension.
During the grain-fill stage, wheat can use up to 0.19 inches of water per day at an average temperature of 75 degrees Fahrenheit (or 0.25 inches per day at 85 F). This means that a 1-inch rainfall or irrigation event may only meet the crop's needs for about five days during this critical period. Maintaining adequate moisture during grain-fill is crucial for maximizing yield potential in both wheat and forage crops.
The following chart shows how wheat ET increases, peaks and declines as the crop matures and how crop water use increases as average daily temperatures increase. For irrigation scheduling purposes, the spring green-up of winter wheat and rye is equivalent to emergence. The two charts estimate daily water removal by wheat and alfalfa. These charts may also be used as a reference for forage crops in all small grains by looking for the equivalent stage of growth provided in the chart.
Source : msu.edu