Grazing During the Summer Slump

By Sjoerd Willem Duiker and Justin Brackenrich

Many grazers and agricultural professionals will refer to the hot, dry part of summer, as the summer slump. The summer slump is when cool-season grasses, which compose the majority of Pennsylvania hay and pasture fields, slow in growth or essentially go dormant. The optimum temperature for cool-season grasses is between 60°F to 80°F, anything above this and growth dramatically declines. Since regrowth slows during this period, it is critical to avoid grazing too low during the summer months. Ignore this and serious soil degradation, nutrient loss, and weed invasion is usually the result. This article will outline a few practices that will promote stand health, and encourage regrowth when temperatures drop, and grasses begin to regrow.

First, maintaining 3-4 inches is the general rule of thumb for grazing practices, but it is especially important during this time for various reasons. Above ground biomass is so important to grazing systems because what you see above ground is reflected belowground. Research has shown that if grass is grazed very short repeatedly, the root system dies back significantly, and the stand declines. This is critical during the summer months as grasses try to scavenge for limited water sources. Most problematic pasture weeds have taproots, which makes them excellent water scavengers because that taproot grows deeper than the fibrous root system of grasses. Research shows, that grazing too short during the summer slump, as would occur in a continuous grazing system, results in increased weed populations and exposed soil which results in increased soil erosion and nutrient runoff. Further, soil health degrades because it depends in great degree on vigorous root systems. Grazing too aggressively negatively impacts the grass's ability to regrow as temperatures cool in the fall.

Second, just like tall, thick forage stands can help to protect crowns and tillers from freezing, these kinds of stands can also shade them from high temperatures. If grazed too low, tillers could be exposed to temperatures as high as 95°F compared to temperatures in the mid-70s°F under a well-developed canopy. Those high temperatures could cause tillers to die and result in thin stands.

Third, many grasses store energy in the lower portion of their stem. They need that 3-4 inches of stem left behind so that they can use the excess nutrients stored there and grow new leaves. Once there is enough leaf material, they can photosynthesize more efficiently and begin storing extra energy before the next grazing cycle. That energy is also used to maintain a hardy root system that is able to scavenge for water. If the grasses are grazed too short, then they use up all their stored nutrients to grow new leaves and they don't have enough energy left over to maintain a dense root system so the roots will die off. Eventually, they will regrow new roots once enough leaves are present to photosynthesize and begin storing excess nutrients again. However, if this happens during the peak of summer, the grasses will be slow growing and struggle to get a long enough root system that can scavenge for water.

Implementing a rotational grazing system is one of the best ways to maintain sufficient grass height. Separate a large pasture into smaller sections with permanent or temporary fencing and rotate animals out when grasses reach that 3-4 inch height. They can then be rotated back into an already grazed paddock when forage height reaches 6-8 inches or more. As temperatures continue to climb and rainfall becomes less prevalent, there may come a time when grazing animals should be taken off cool season pasture to help maintain its quality and resiliency. To supply summer forage, it is ideal to have a portion of the farm in warm season annuals and/or perennials. These forages are adapted to high temperatures and dry soils. Examples are millets, sudan- and sorghum sudangrass, teff, sunn hemp, cowpea, forage soybean, switchgrass, big bluestem, Indiangrass, etc. If you only have cool season pastures, bringing animals into a dry lot and feeding hay for a few weeks can allow the grasses to regrow, which will help to increase stand longevity and reduce the need to reseed a stand that has become thin from overgrazing. If a dry lot isn’t an option, consider using a section of pasture that is in poor condition and needs some Tender-Loving-Care as a sacrifice lot. The extra nutrients provided from the animals and imported hay material can supply nutrients and, if necessary, the pasture can be reseeded in the fall once the animals are removed. Be sure to use an area with adequate fencing, whether it is permanent or temporary, as animals will be prone to push fence and try to get to "greener" pasture. It is also important to ensure the area is adequate distance from surface and groundwater and to consult your local Conservation District as to any local runoff and erosion regulations.

Check out Extending the Grazing Season with Plant Diversity  , for alternative forage options during the summer slump or Alternative Forages for Spring and Summer Planting  , to review some summer planting options or Harvesting and Feeding Warm-Season Annuals for Forage  , to find more details on utilizing warm-season annuals.