Fall Pasture and Hay Fertilization

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

I had a question this week from a hay producer about whether it was best to apply the soil test recommended fertilizer the first thing in the spring or not. Since his crop was an alfalfa orchardgrass mix, he was not thinking about nitrogen (N) which is the first thing most people think of in the spring. He was asking about potash (K) and phosphorus (P). The answer really lies in the function of these nutrients.

Phosphorus really helps plants establish or grow a better root system and we’ve discovered that root development really goes on for quite some time in the fall for two reasons. First, we generally get more rain in the fall; and, when that is combined with the lower air temperatures and shorter days, it means that soil moisture levels are usually higher in the fall than in the summer months. Secondly in the fall, we’ve found that the soil temperatures stay warm until fairly late in the year unlike spring time when soils start off very cold from winter and tend to warm up slowly throughout the spring. The combination of available moisture and warm soil temperatures and the accumulation of fixed carbohydrates (sugars) and translocation of the sugars down to the roots means that fall applied P will further help plants establish a vigorous root system for better growth during the next spring growing season.

Potash has a number of functions in the plant ranging from enzyme activation to stress reduction to the control of transpiration and water use in the plant. For us, fall K fertilization helps plants lower the freezing point of the cell sap so there will be less winterkill or winter freeze damage to the plant crowns. In addition, fall K helps plants fight off disease problems and other pest injury. For K, I prefer that growers split their application with half going on the pasture or hay field in late May or early June and the other half going on in late August or September.

Finally thanks to research in the turfgrass industry, the forage industry is beginning to discover the benefits of adding at least some N in late summer or early fall to help grasses regrow after summer grazing or summer drought. Some recommendations even suggest a second application in mid-October that the previously N stimulated grass can pick up and store for early green-up growth the next spring. This second application negates the need for an early spring N application and seems to help prevent excessive forage growth the next spring. Too many people apply much of the nitrogen forages need in the spring causing such excessive growth that their grazing plan can’t keep up with it or causing so much yield in the first hay cutting that there is a significant delay in being able to dry and cure the hay. This can lead to poor quality first cut hay or to hay that retains too much moisture so that it either spoils or is at risk for spontaneous combustion.

In conclusion, think about changing your fertilization timing from the early spring to early fall. There are many potential benefits from this change as outlined above.

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