Update on Hay and Pasture Crop Irrigation

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

Many of our hay and pasture species are just beginning the rapid growth phase that occurs each spring. More and more hay and pasture fields are set up to receive irrigation. The limited rainfall the southern half of the state has received so far this spring means that the soil water supply will be rapidly depleted as the cool-season hay and pasture grasses enter the rapid growth phase. Orchardgrass, in particular, since it matures earlier than many of the other species we grow, will be using large quantities of water during the next few weeks. If you are set up to irrigate hay and pasture fields, now is the time to begin the irrigation system. Try not to let the soil moisture levels be lowered to the point that water stress symptoms actually show up on the crop. As the species enter the rapid growth phase of spring, water use will increase from about a tenth of an inch of water per day to a quarter inch or more water per day. To keep fields actively growing, be sure to replace that quantity of water each week. When warmer temperatures occur in June, water use can increase to that approaching corn (about a third of an inch per day) so your irrigation regime will need to increase as summer approaches. Keep in mind that you will need to stop irrigation long enough for the soil to dry enough to support haying and baling equipment without causing significant compaction. It’s also usually best to wait until the crop begins regrowth before resuming irrigation so that you do not encourage weeds.

It also is time to get nitrogen (N) out on irrigated and non-irrigated hay and pasture fields. For hay, the latest research from Pennsylvania State University and Dr. Marvin Hall’s team shows that you should be applying about 50 lbs of N per acre per ton of expected yield. This is a good compromise between maximum economic yield from the hay and the risk of high nitrate levels in the hay if the crop becomes very drought stressed. For pastures, our N recommendations still vary based on the amount of legume in the pasture. If pastures contain a one to one ratio of legume to grass (50 percent of the biomass-forage-comes from the legume), additional N fertilizer will not be needed. If the legume component makes up between 25 and 50 percent of the forage, then apply about 25 lbs N/acre and if there is less than 25 percent legume in the forage, you may need as much as 50 lbs N/acre to maximize productivity of the pasture.

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