Grass-Cast can help livestock producers with stocking rates and drought management plans
for The Fence Post
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This year, ranchers have some exciting key upgrades to their forage planning through Grass-Cast, a website tool for ranchers planning on grazing cattle.
Grass-Cast has now been expanded to include all of the Plains states. When it was launched last year, officials only specifically selected eastern Colorado, eastern Wyoming, eastern Montana, western North Dakota, western South Dakota, and western Nebraska.
Grass-Cast in 2019 also now covers grassland areas of the Southern Plains, including western Kansas, western Oklahoma, north Texas, and eastern New Mexico. So, it now provides forecasts of grassland plant production for ranchers in the entire middle one-third of the U.S., beginning in spring and updating the forecasts every two weeks.
“The Grass-Cast team focused on the Great Plains region for two reasons. First, this region is where much of the nation’s rangeland cattle graze during the summer. Second, this region’s weather is highly variable, especially precipitation, so it has a big impact on year-to-year changes in grassland plant production,” said Bill Parton, senior research scientist in the Natural Resource Ecology Lab and professor emeritus at Colorado State University.
Grass-Cast offers three different “what if” scenarios through maps, which may help livestock producers make stocking rate decisions, drought management plans, and triggers for implementing those plans. The maps show the potential range of grassland production (relative to an area’s long-term average production) which depends on whether rainfall over the remaining growing season is either below-normal, near-normal or above-normal.
“Grass-Cast helps farmers and ranchers plan, for example, if they get ‘this much’ rain at ‘this time,’ what might their grass production be for their livestock,” said Laura Edwards, South Dakota State University Extension state climatologist, who was instrumental in providing guidance to help make Grass-Cast a significant tool for ranchers.
The website features a webinar, as well as frequently asked questions to explain Grass-Cast, which caught a lot of attention when it was drier last year.
Focusing on pounds per acre of vegetation at the peak of the growing season, also called above-ground net primary productivity or ANPP, it all depends on evapotranspiration (ET), which relates to how much water is moving through the soil and plants.
“We estimate how much ANPP during the upcoming growing season might differ from the long-term average for a given area. Our estimates are based on current weather (up to the date the forecast is made) and seasonal precipitation outlooks for the upcoming summer,” Parton said.
Low levels of ET are a sign that vegetation might be struggling to grow. Higher levels of ET are a sign that vegetation is likely greener and growing more vigorously.
“So if we have daily weather data (observed or forecast) we can use it to estimate ET, to tell how green and vigorously the grassland plants should grow,” said Dannele Peck, director of the U.S. Department of Agriculture’s Northern Plains Climate Hub in Fort Collins, Colo.
Peck and Parton developed Grass-Cast with colleagues from USDA, and through partnering with several different land-grant universities. Parton has spent the last 40 years studying primarily how weather, climate, and human activities like grazing influence grassland ecosystems.
“The hope is that Grass-Cast can reduce some of the uncertainty that ranchers face every spring when they have to guess about how much grass will be available for their livestock to graze during the upcoming growing season,” Peck said. She said they also improved how readers read the Grass-Cast visuals. Last year they used a county-level scale. This year, they have a finer, sub-county scale.
Grass-Cast is supported by the USDA’s Agricultural Research Service, Natural Resources Conservation Service and Northern Plains Climate Hub, in addition to the National Drought Mitigation Center. Scientific collaborators for the development of Grass-Cast include Colorado State University, University of Arizona and the University of Nebraska-Lincoln.
“Grass-Cast has some important limitations, so ranchers should not rely on Grass-Cast as a sole source for making management decisions. First, it cannot tell the difference between desirable forage species and undesirable plant species, so producers need to know what proportion of a pasture is occupied by weeds and how well those weeds respond to rain (or lack of rain) compared to the desirable species. Ranchers and other rangeland managers should combine insights from Grass-Cast with their knowledge of local soils, plant communities, topography and other conditions,” Peck said
Interestingly, comparing last year to this year so far, much of the Southern Plains in 2018 experienced moderate-to-extreme drought (see archived Drought Monitor maps for 2018 at https://droughtmonitor.unl.edu/Maps/MapArchive.aspx), while much of the Northern Plains saw near-average or above-average precipitation and grassland production. “These very different outcomes for the Northern and Southern Plains are shown in last year’s Grass-Cast map for July 31 (http://grasscast.agsci.colostate.edu/archive). In contrast, the spring of 2019 has been abnormally wet and cold across much of the Great Plains. Above-normal precipitation is a good thing for grassland vegetation growth in our region,” Peck said. However, abnormally cold temperatures may have caused some delays in growth. “Despite this, the most recent Grass-Cast maps suggest above-average or near-average grassland production is still possible for many areas — as long as precipitation over the rest of the growing season doesn’t drop suddenly to below-normal levels.”
Last year, the Grass-Cast team heard from ranchers in the Southern Plains who were experiencing drought, and were eager to expand Grass-Cast into their area. “Even though drought isn’t on the minds of many producers this year in these regions, Grass-Cast can still provide valuable information about just how abundant grass might be, given all the rain they have received so far,” noted Peck, adding, “Yet, if the rain suddenly ceases and the rest of summer is drier than normal, Grass-Cast also gives them a sense for how much of a decrease in pounds per acre they should expect.” ❖
— Hadachek is a freelance writer who lives on a farm with her husband in north central Kansas and is also a meteorologist and storm chaser. She can be reached at firstname.lastname@example.org.