Forage Considerations For Fall Grazing

Forage Considerations For Fall Grazing

From “Pastures for Profit: A guide to rotational grazing”. University of Wisconsin
Extension. 2014.

By Dr. Emily Glunk, MSU Extension Forage Specialist and Assistant Professor

There are a lot of questions regarding whether or not it is safe to graze your fall pasture, and to what extent. Fall is a tricky time to manage grazing on pastures, as there is a lot going on with the plants below-ground, which we can’t always see. Grazing too hard in the fall has the potential to be very detrimental to forages, and should be managed accordingly.

So what all is happening right now in our forages? Cool-season grasses are trying to grow more new roots to replenish those that had been shed earlier in the summer. Right around June 21, the summer solstice, a lot of our introduced cool-season grasses shed their roots and begin to grow new ones, contributing to what is known as the “summer slump”. If you trek out to your pasture and dig up a couple plants, you should see quite a few new white roots and tillers forming, indicating a healthy plant and a healthy stand. Our legumes don’t shed their roots, as they have one well-defined taproot, but they are trying to store up enough carbohydrates to serve as any energy source for regrowth in the spring.

It is important that we don’t graze our pastures too heavily in the fall, as we can significantly impair the plants ability to store carbohydrates, or energy, which will help in the regrowth and recovery process. Plants go through a process called photosynthesis, which transforms sunlight into a usable energy source. The plants ultimately convert the sunlight (in the form of photons) to carbohydrates, which are stored in the roots or lower parts of the stem in some grasses. By grazing heavily, and removing most of the leaf area which is required for photosynthesis, we are limiting the plants ability to capture sunlight, and therefore create and store energy. This will be evidenced by slow growth in the spring, creating an opening for weed invasion, or if bad enough, winter kill over the winter.

So what can we do to manage these plants and prevent this from happening? Number one is to not graze very heavily in the fall. Allow those plants enough leaf area to continue photosynthesis, while not trying to use too much of their carbohydrate reserves for regrowth prior to winter. That is not to say don’t graze at all, but try to maintain an adequate stubble height for those forage species. You can contact myself or your local county agent to get species-specific recommendations. Number two, you can wait until after the plant has gone dormant to graze it down lower, because at this point the plant is no longer going through photosynthesis and accumulating carbohydrates, and it will no longer be using its energy reserves for regrowth before spring. You still should take care and be mindful of the impacts of hoof traffic on plant roots, especially in muddy conditions. While the plant may be healthy and have plenty of carbohydrates, if the animal physically injures the plant or its roots, this too can have a negative impact on regrowth ability and plant survival.

From the figure below, we see that carbohydrate reserves are at their lowest around internode elongation phase, a time when we have to be very careful in our management. This is when reserves are being used for primarily for plant regrowth and leaf production. Once there are enough leaves present, and the plant has begun the stem elongation phase, we see an accumulation of carbohydrates. The plant will be able to start storing carbohydrates at this point for regrowth in the spring. We want to make sure that the plant has the ability to store enough carbohydrates before a killing frost, so that we don’t see a problem in the spring.

Another thing that we see happening in the fall is the development of growing points for next spring’s growth. Those are the tillers that we can hopefully see when we dig up some plants. Old tillers may appear brown and dead, but they still serve an important role to the plant. They are a form of stored nutrients, as well as provide protection to the new, developing tillers. We also want to avoid allowing animals the ability to graze off these new tillers, which will be helped by leaving adequate stubble height. Another benefit of leaving some stubble in the field is that it increases the amount of snow that is caught, insulating the soil, and decreases the potential for ice sheeting. This too will help increase plant survivability over the winter.

For any questions or forage recommendations, contact Dr. Emily Glunk at [email protected] or 406-994-5688. or contact your local county extension agent.