Minnesota Farm Guide: Leading Farm Newspaper

You've seen it. Warm weather and high humidities can affect pasture growth. During the summer of 2006, hot and dry weather stopped pasture growth dead in some places.

Most of Minnesota's pastures consist of cool season grasses which are particularly vulnerable to lower growth in periods of hot weather as a result of their metabolism. Pasture management can either reduce or exacerbate the effects of hot weather.

Rotational grazing, leaving a 3-4 inch stubble height after grazing promotes root growth, reduces soil compaction, reduces soil temperature, encourages water infiltration and retention, which results in more yield of the growing species in a particular pasture over time.

Without management, animals will continuously defoliate the most desirable species, weakening and shrinking their root system, making them susceptible to disease, drought stress, and even death. Short occupancy periods by livestock and longer rest periods for the forages allow for the survival of more desirable plants with a deeper, healthier root system which are able to withstand drought and warm weather stress.

Under heavy continuous grazing pressure, less desirable species and weeds such as thistles, leafy spurge, and other unpalatable or even poisonous species increase in the pasture because their root systems are fully developed as a result of a lack of grazing.

Desirable pasture plants benefit if they are grazed for periods of no more than 6 days at a time and then allowed to rest for 30 days or until the forage has regrown to a height of 8-10 inches tall.

Actually, the highest utilization rates of pastures and the best regrowth potential in warm weather from cool season grasses occurs when the pastures are stocked heavily with very short durations of grazing, sometimes as little as 12 hours, followed by a long rest period.

Another strategy to improve summer growth and combat “summer slump” is to allow a small portion of a pasture each year to head out, which will strengthen the roots of the desirable species. This should be done only if the pasture is not infested with weeds.

Even if there is a small concentration of weeds, care should be taken to clip or spot spray any weeds present before they go to seed. Multiple weed clippings or spot sprayings may be necessary to weaken them.

Many legumes possess a deep taproot that can utilize deep soil moisture. Adding legumes to an existing cool season grass sod can improve production. Overgrazing the sod to reduce competition prior to seeding is best.

Several seeding methods may be used. The most common is frost seeding in which legume seeds are broadcast on top of the ground utilizing the cracks in the soil caused by alternate freezing and thawing. The best time of the year for this is late winter and early spring when the ground may go through a number of freeze thaw cycles.

The most common type of legume used is red clover which has high seedling viability and good yield potential once established. Soil type does influence the results with sandy soils less desirable for frost seeding due to less potential for crack formation during the freezing and thawing cycle.

If your soil types tend to be loamy or sandy, using a no-till drill early in the spring would be a better option. Work with someone to get a specific recommendation for your site. Red clover does not respond well to poorly drained or somewhat poorly drained soil conditions. Whatever legume you choose to use, be sure to inoculate it with the specific type of nitrogen fixing bacteria for that species.

Another option that is not often used, but would help overcome the shortage of pasture forage that producers often experience in the months of July and August, is having warm season native grasses in their pasture. Species such as Big Bluestem, Indiangrass, and Switchgrass produce when the cool season species are dormant or nearly so.

Only 10-20 percent of the pasture acreage needs to be devoted to the warm season perennial grasses to supplement the cool season species. Warm season native grasses require much different management than cool season forages so they should be located in separate paddocks.

For the taller warm season native species a 6-8 inch minimum stubble height needs to be maintained to allow them to compete with invasive introduced cool season grasses.

The downside to utilizing warm season grasses is that they take 2-3 years to establish. In other words, no grazing during that establishment period and the seed is relatively expensive compared to cool season grasses.

Another strategy that has been used to add summer pasture is planting summer annual forages such as sorghum-sudan hybrid, pearlmillet and even corn. These furnish forage in the July-September period. Sorghum/sudan hybrids, if damaged by frost, may produce enough prussic acid, a poisonous cyanide containing compound, to be dangerous to livestock.

Summer slump can be reduced by careful management of cool season species, addition of legumes to an existing cool season grass stand, and by giving extended rest to a small part of the pasture each year.

Some producers decide to devote 10-20 percent of their pasture to warm season native grasses such as Big Bluestem, Indiangrass, and Switchgrass to be sure they have enough forage during the hot summer months. Others rely on warm season annual grasses to overcome forage shortfalls.