Balancing forage resources to ensure supplies aren’t being overdrawn is critical to the long-term profitability of a ranch. The key is ensuring that the stocking rate doesn’t exceed pasture carrying capacity.
Overgrazing can cause long-term reductions in forage production, leading to decreased livestock production, says Miranda Meehan with North Dakota State University.
The stocking rate is the number of specific kinds and classes of animals grazing, or using a unit of land for a specific time period, Meehan says in a news release. When setting the stocking rate, knowing the carrying capacity of the pasture is critical.
Carrying capacity is a measure of how much forage a grazing unit has and is able to produce in an average year.
It’s well into the growing season. As it progresses, the potential for timely precipitation and forage growth decreases. By July 1 cool-season-dominated grasslands will have produced 90% of their forage. That’s delayed to Sept. 1 for warm-season-dominated grasslands.
Now is the time to evaluate potential for forage production for the current grazing season. To accurately do that, it’s important to understand the relationship between precipitation and forage production in the area.
April-June precipitation is usually a good predictor of annual forage production in mixed-grass prairies. The best predictor in warm-season prairie is May-July precipitation.
Due to the relationship between precipitation and forage production, precipitation during those months can be used to predict potential deficits in forage production. If precipitation during that period is 75% of normal, producers can expect forage production to be 25% less than normal.
Those predictions of production then can be used to make forage- and grazing-management decisions earlier in the grazing season. Those decisions will balance resources and reduce risk.
Ranchers can use precipitation records for their locations to predict the potential for forage production. That can be done by comparing the current year’s precipitation during a time period to the median precipitation for the past 30 years at a location. Producers can use that information to calculate the probability of receiving adequate precipitation for forage growth.
If a location typically receives 6.88 inches of precipitation in April-June and a producer received 2.5 inches in April and May, the producer will need to receive 4.38 inches in June to achieve normal forage production.
Producers can determine the probability they will receive adequate precipitation to achieve normal forage production levels by assessing the number of times they have received 4.38 inches in June in the past 30 years. If producers have received 4.38 inches 12 times in the past 30 years, there’s a 40% chance of receiving adequate precipitation.
Other tools that can aid in predicting forage-production potential include weather-prediction models and Grass-Cast. Grass-Cast is a forage-production-prediction tool developed by the U.S. Department of Agriculture’s Agricultural Research Service, Colorado State University, the National Drought Mitigation Center, the University of Arizona and the USDA Northern Plains Climate Hub. It can be found at https://bit.ly/2ITmYrh.
The tool compares seasonal estimates to a 34-year average to develop county-level forage-production maps which are updated every two weeks.
But those are just estimates. There are several other factors that influence carrying capacity, including growing conditions for the past year, grazing history and, of course, stocking rate.