Fall is often a welcome time of the year. It evokes images of shorter days, cooler temperatures, maturing crops and weaning calves. Fall is also an important time in the life of perennial cool-season grasses. While it is commonly thought that dormant plants can be grazed short without hurting anything, perception is far from the truth. Leaving sufficient residual plant material (leaves, lower stem bases and crowns) is essential to maximize next year’s production for perennial grasses.
Fall is considered the beginning of the perennial cool-season grass cycle. This is the time of year when grasses produce the first generation of roots and most of their apical meristems (growing points) for the next growing season. For this process to begin, grasses must retain sufficient basal leaf material to “recognize” that days are getting shorter.
Additionally, new roots and apical meristems need a steady supply of nutrients and protection from stress. In the fall, nutrients are supplied from the previous season's tillers, which have stored carbohydrates in the bottom 3 to 4 inches of their bases. Often, these older tillers are dormant and brown in the late fall, giving the impression that they are dead and of little value. Reality is that they are very much alive and performing the critical function of carbohydrate (energy) storage. These older tillers also provide physical protection to the new tillers.
Plants that are grazed short during the fall are less likely to overwinter and will be slower to “green up” in the spring. With limited leaf area, they lack the stomata and chloroplasts to efficiently capture solar energy through the process of photosynthesis that is required for plant growth. Instead, they must rely on the limited energy reserves in the roots in order to initiate growth. The result is that these plants/pastures will require more time in the spring before they are ready to graze. Overall, their seasonal production potential will be reduced.
It is good practice to ensure that adequate phosphorus and potassium are available in the fall. These nutrients help to stimulate apical meristem development. Appropriate irrigation during this time is also important to maximize development. A fall application of nitrogen is generally not recommended, as it can encourage additional plant growth and inhibit the natural plant process of preparing for dormancy and the coming growing season. Additionally, nitrogen is very mobile in the soil and winter precipitation could push it beyond the root zone or completely off the pasture in any runoff.
Similar to all other times of year, good grazing management is important in the fall. Livestock grazing should be controlled in order to avoid excessive defoliation of the pasture. For the majority of cool-season grass species, a 3- to 4-inch residual plant height (after grazing) is appropriate for the winter. This will maintain sufficient plant energy reserves for the development of new roots and apical meristems. It will also provide the energy for the plants to initiate earlier growth in the spring.
Take-home message
Fall is an important time for perennial pasture plants. Livestock grazing should be managed to leave sufficient residual for cool-season grasses to develop the framework for the next season’s growth. This will promote improved plant vigor and help to maximize production potential for the next growing season. For additional information, please refer to the Inland Pacific Northwest Pasture Calendar.
