First Hollow Stem Advisor benefits cattle-wheat producers

Thursday, January 26, 2017

Timing is everything when trying to get as much bang for your buck as possible in the wheat fields. Wheat producers in Oklahoma have historically circled March 15 on their calendars to remember to pull cattle from the fields. Waiting much longer than that would result in a drastic decrease in yield.

However, rather than using a fixed calendar date, past research at Oklahoma State University has shown the optimal time to pull cattle off wheat is when ungrazed wheat reaches a particular growth stage called First Hollow Stem. Leaving cattle on wheat past this growth stage can result in grain yield losses of anywhere from 1-5 percent per day, so grazing one week past FHS could reduce grain yield by as much as 35 percent.

Economic analysis has shown the added cattle weight gains associated with grazing past FHS are insufficient to offset the lost grain yield, said J.D. Carlson, agricultural and fire meteorologist in OSU’s Department of Biosystems and Agricultural Engineering.

Using Mesonet weather and soil data, as well as FHS observations from 1995-2012, researchers at OSU developed a tool for producers to consult when deciding how long to leave cattle on their wheat fields.

Available on the Mesonet website, mesonet.org, the FHS Advisor is located in the Agriculture section, under both the “Crop/Wheat” and “Livestock/Cattle” tabs. A detailed video on how to use the Advisor is located in the “Learn More” section.

The tool utilizes soil temperature-based models to predict when FHS will occur.

“Looking at a variety of weather and soil variables, we found that 4-inch soil temperatures under vegetative cover were best correlated to FHS dates,” said Carlson, who developed the models used in the tool. “The Advisor includes separate models for three different FHS categories of wheat varieties – early, middle and late.”

Within the Advisor, producers can select their wheat variety to determine its category. Then, maps can be accessed to provide information on the probability of FHS occurrence. Charts and tables for individual Mesonet sites also are available.

“Three maps are available for each FHS category,” Carlson said. “They include a current map of observed soil heat unit accumulations since model start date, projected one-week soil heat unit totals and projected two-week soil heat unit totals.”

The projected maps employ soil heat units based on 14-year daily averages of observed Mesonet soil temperatures over the next seven or 14 days from the current date. To arrive at these projections, the soil heat units over the next seven and 14 days are then added to the current heat totals.

In addition to soil heat unit totals, probabilities for FHS are shown. A color scheme is used to show these levels of probability – blues for FHS probabilities less than 5 percent, greens for 5 percent to 10 percent, yellows for 10 percent to 25 percent, oranges for 25 percent to 50 percent, reds for 50 percent to 75 percent and browns for more than 75 percent.

“We recommend scouting for FHS in ungrazed fields once the 5 percent probability levels (greens) start occurring in the grower’s area, as FHS development starts to speed up at that point,” Carlson said. “For those who don’t scout, we recommend removing cattle by the date the 50 percent level is reached.”

A 50 percent probability level means that over an extended multi-year period (e.g., 100 years) FHS would have occurred by that date in 50 percent of those years. The same interpretation applies for other percentage values.

The FHS Advisor is currently indicating wheat varieties in the “early” category will be approaching or at FHS by the end of January in parts of southeast and south central Oklahoma, so dual-purpose wheat producers in these areas should take notice.