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With hay supplies tight and pasture growth limited in many areas across northeast Nebraska, producers with irrigated acres available may be considering an annual forage crop to help fill the feed gap. Millet, sorghumsudangrass or even corn silage can produce a lot of forage quickly under a center pivot, but irrigation timing is critical — especially during stand establishment and early vegetative growth.
Before starting the pivot, check how much moisture is already in the soil profile. Even during a dry year, fields irrigated late last season may have more stored water than expected. Off-season precipitation may have also rewetted the upper portion of the profile.
Use a soil probe or shovel to determine where the soil is moist and where it is dry. A silt loam soil may hold more than six inches of plant-available water in the root zone, while a sandy soil may hold only about half that amount. Depending on what is already stored, it may take only about one inch of water to refill a sandy profile or around two inches for a silt loam.
For stand establishment, pre-irrigate only when the soil is too hard or dry for the drill to penetrate and place seed at the proper depth. If the drill can place the seed correctly in dry soil, planting first and irrigating immediately afterward is usually more waterefficient. It can also improve seed-to-soil contact.
When irrigating for emergence, avoid applying just enough water to wet the top inch or two. Seedlings may germinate, but their roots cannot grow through a dry soil layer to reach moisture below. When possible, apply enough water to connect surface moisture with moist soil deeper in the profile, or wet the soil to at least 12 inches.
Sandy soils can be an exception. Because the surface dries quickly, smaller and more frequent applications may be needed while seedlings are becoming established. Once the crop develops a root system, return to larger applications—ideally eight-tenths to one inch at a time, or as much as can be applied without runoff.
Producers should also expect annual forage water use to increase rapidly. Corn may be planted at 30,000 to 34,000 seeds per acre, while some annual forages are planted at one to two million seeds per acre. That dense stand can reach full canopy while plants are still only a few inches tall.
Full canopy occurs when leaves capture about 90 percent of the sunlight at noon.
Once that happens, millet, sorghum-sudangrass, corn, soybean and other full-canopy crops use roughly similar amounts of water.
Depending on weather, that could range from three-quarters of an inch to two-and-a-half inches per week.
Finally, if forage tonnage is the goal, prioritize irrigation during vegetative growth.
Water stress during this stage reduces plant height, leaf area, tillering and ultimately total biomass. Irrigation after seedheads begin emerging may increase grain production, but it generally has less effect on total forage yield.
For producers with irrigation available, annual forages can be a productive way to turn water and open acres into additional feed.
— Ben Beckman is a beef systems Extension Educator serving northeast Nebraska. He is based out of the Cedar County Extension office in Hartington.
You can reach him by phone: (402) 254-6821 or email: ben.beckman@unl.
