Cumulative forage reduction index values assist ranchers in drought planning

With drought potential looming for 2013, another tool for ranchers to utilize is the Cumulative Forage Reduction (CFR) index. 

“The CFR index came out of working with ranchers and agency folks in Nebraska, Colorado and Wyoming,” commented Pat Reece, the principle consultant and owner of Prairie and Montane Enterprises, LLC. 

Reece educated ranchers on what the CFR index does and how to use it in the third webinar in the Managing Drought Risk on the Ranch series, presented by the University of Nebraska – Lincoln and National Drought Mitigation Center.

Benefits and assumptions

The CFR index offers two benefits to producers said Reece, mentioning that that tool allows an assessment of drought impacts and planning of grazing strategies. 

“The first expected benefit is to avoid drought-induced declines in livestock market value,” Reece commented. 

Noting examples where waiting two weeks to move cattle to markets could cost losses of $40,000, he emphasized the necessity of selling cattle before ranges are over-grazed.

“The other expectation is that this system will allow you to optimize the resilience of your rangeland vegetation,” Reece noted. “We are going to do everything possible with the CFR Index to help ranchers avoid overgrazing and drought stress.”

The combination of overgrazing and drought stress drives range conditions down most rapidly. 

At the same time, he commented that the method will allow ranchers to leave optimal amounts of litter to influence the infiltration of water into the soil and minimize the negative impacts of temperature extremes on the soil. 

Necessary data

In using the CFR Index, Reece also emphasized that it is important to utilize the best, most specific information available. 

“It is critically important for you to be specific with information as close to home as you can possibly get,” he commented. 

Data for total monthly precipitation and long term precipitation averages are also necessary.

“The numbers are cumulative in this index,” Reece said.

He also mentioned that data for monthly percentage of herbage production is necessary.

“Producers can go to the web soil survey website to get the information, but it would be a big time savings for them to work directly with the local NRCS folks,” Reece explained. “They can provide long-term herbage production numbers and monthly percentages, often referred to growth curve data.”

The data differs among range sites and with range conditions, so he commented that working with local NRCS personnel can help producers to get more accurate data.

“The last category of data that we need is the monthly percentage of local livestock forage use,” said Reece. 

Assumptions

In using the index, Reece said there are several assumptions that producers must make. 

“In order to do this, we must assume that expected herbage production is going to be directly related to precipitation,” said Reece. “The second assumption, in terms of the calculations, is that all drought-induced herbage deficits are billed directly to the livestock enterprise.”

The herbage category of the formulas utilize in the index only account for current plant growth, or the non-woody, above ground plant growth, so drought losses are accounted for in the livestock category.

“The third major assumption is the total estimate of livestock forage use is based on moderate stocking rates determine in years with near average precipitation,” said Reece, noting that the stocking rate is the same rate that is the moderate stocking rate used by NRCS.

Calculating data

Utilizing the index involves some calculations by producers. Calculations should be done on a month-by-month basis.

Among the first calculations, it is necessary to figure the monthly deficit of cumulative precipitation.

Deficit is calculated by subtracting current year precipitation from the long-term average precipitation. The deficit should also be calculated as a percent of the normal precipitation by dividing the deficit by long-term precipitation.

In the herbage production category, producers can calculate their expected herbage production. First, divide the current year’s precipitation by long term precipitation to obtain the percentage of precipitation obtained. Then, multiply that figure by the long-term herbage production percentage data obtained from NRCS.

The deficit of herbage can be calculated by subtracting expected herbage production from long term data.

In calculating drought-induced forage losses, Reece noted that producers should take the number calculated for herbage deficit and multiply it by 3.125.

“On average, if we look at nothing but grasses and sedges – the primary species used by cattle – they are going to be consuming about 32 percent of all grass and sedge herbage,” explained Reece. “Multiplying the deficit by 3.125 is the same as dividing by the 0.32 percent consumed by cattle.” 

The sum of the drought deficit should also be calculated by adding the total drought-induced deficit.

As a final calculation before obtaining the CFR Index value, producers should sum the total livestock use from month to month. 

The CFR Index value is obtained by adding drought induce forage use to livestock use.

If the value exceeds 100, that means that producers are utilizing more forage than is available and should take action in selling or moving animals. 

“This year, we are starting out plant year with a deficit,” said Reece. “That is a point that should be emphasized.”

Using the CFR Index, he said, should help producers decide how much forage they have available in making decisions to sell cattle and to help make them at the right time.

To view this webinar or other webinars presented in the series, visit drought.unl.edu/ranchplan/Overview.aspx.

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at saige@wylr.net.