Predicting grassland productivity is a major challenge for ranchers and other land managers with grazing livestock, but this productivity is key each spring when they are trying to decide how many cattle to turn out to pasture, how long to graze an area or where forage might be abundant, according to the U.S. Department of Agriculture's Agricultural Research Service (ARS).
ARS announced that an online tool designed to help make such decisions is once again available this spring — with some new upgrades to ensure that it serves a wider audience and provides more helpful and detailed information.
The Grassland Productivity Forecast or "Grass-Cast" was developed in 2018 by ARS scientists, along with other federal agencies and several universities. It was originally designed for ranchers and grassland managers in the northern Plains and was expanded in 2019 to cover the southern Plains. Later this spring, it will be expanded again to cover much of New Mexico and Arizona, ARS said.
Additionally, ARS said Grass-Cast will now be providing forecasts for individual 6-mile x 6-mile areas rather than the county-by-county results available in previous years.
"It's increasingly popular with ranchers and other land managers, who are hearing about it from our partners with the Natural Resources Conservation Service (NRCS), Forest Service, Farm Service Agency and university extension [services]. Still, we are always looking for ways to make it more useful, so we welcome any suggestions," said ARS economist Dannele Peck, who oversees Grass-Cast as director of the USDA Northern Plains Climate Hub.
During the 2019 season, the Grass-Cast website was visited nearly 3,000 times by more than 1,800 different users, ARS said.
Grass-Cast uses more than 30 years of historical data about weather and vegetation growth — combined with seasonal precipitation forecasts — to indicate whether grasslands are likely to produce above-normal, near-normal or below-normal amounts of vegetation. It is the result of a partnership among ARS, NRCS, Colorado State University, University of Arizona and the National Drought Mitigation Center (NDMC) at the University of Nebraska-Lincoln.
The first Grass-Cast maps for the 2020 season were released in mid-April and will be updated every two weeks until the end of August to incorporate newly observed weather data, ARS noted. Grass-Cast becomes more accurate as the growing season progresses, so it should be consulted more than once.
According to ARS, land managers typically start paying close attention to the forecasts in May and June, when the risk of drought might prompt them to sell yearlings or older cows, wean calves early, buy feed or move livestock to areas where grass is more plentiful.
Grass-Cast has some limitations, though. It cannot tell the difference between desirable and undesirable forage species, so land managers need to know what proportion of their pastures are weedy and how those weeds will respond to rain or a lack of it. They should also combine the forecasts with their knowledge of local soils, plant communities, topography, management history and other conditions that affect vulnerability to drought, Peck said.
The Grass-Cast website provides tutorial videos, printable handouts, scientific papers and other features.