Pasture X-Competitive Rotational Grazing on Smut Grass - Field Trial

August, 2018
Aaron Stam, UF/IFAS Extension Seminole Tribe of Florida, Okeechobee

Background-Smutgrass (sporobolus indicus) is an invasive, bunch type grass that has created significant financial and grazing loss across ranches in South Florida. Many ranches in South Florida are now 80-100 percent covered in smut grass. For many of these ranches combatting smut grass through chemical means is unlikely due to cost and the persistence of the smut grass. Several south Florida ranches have traditionally weaned very heavy calves utilizing smut grass as their primary forage. This lead to Aaron Stam, UF/IFAS agent for the Seminole Tribe and Lindsey Wiggins (Multi-county agent) to begin looking at smut grass nutritive values.

The 2016-2017 field studies analyzed smut grass on the Big Cypress Seminole Reservation. Exclusion cages were placed in pastures in the early spring. Cages were set in three specific test areas for the first field trial. The first test section was a section of ground that had been fertilized with 50 pounds of nitrogen per acre with a 20-0-6 fertilizer. The second area was a control, where no fertilizer had been applied. The third area was treated with fifty pounds of nitrogen only, in a liquid based fertilizer.

After fertilization, samples were taken at 14, 21, 28 and 42 days. The section receiving the balanced fertilizer tested highest for crude protein (CP) and total digestible nutrients (TDN). The average CP of the dry fertilizer samples was 15.0%CP and TDN 57%. The samples fertilized with liquid fertilizer, consisting of nitrogen only, had an average value of 13.32% CP and TDN of 55.4%. The control area, with no fertilization had an average CP of 10.7% and a TDN of 56.25%.

After reviewing the nutritive values of our field trials we decided we needed to dig deeper into whether or not smut grass could be utilized as viable forage in South Florida. The Seminole Tribe of Florida contributed 40, two year old, commercial type Brangus heifers for a grazing study. A typical stocking rate of 1 cow unit per 2.75 acres is the norm in many southern Florida pastures. It is commonly believed this low density stocking was one of the reasons smut grass has spread so quickly across parts of south Florida. As Bahia stays palatable for greater periods of time, many ranchers were allowing cattle to stay on large, Bahia based pastures for 20-30+ days before rotating their herds. In this time, smut grass was becoming non-palatable and gaining a competitive advantage over the Bahia grass. The goal of the smut grass grazing trial was to take advantage of the grass’s nutritive qualities, by increase the stocking rate to 2 cows per acre, reducing the smut grass’s opportunity to go to seed and gain a competitive advantage over the Bahia or other improved species of forage.

 The 20 acres, known as Pasture X, was divided into (4) 5 acre paddocks. Based on the results from the nutritive study of the smut grass, we elected to rotate cattle onto paddocks that had 21 day old growth of smut grass. This seemed like the best combination of quantity of grass and quality of the forage. After the smut grass is matured, it lost much of its nutritive value. Keeping cattle on young, tender smut grass would be a critical component to this feeding trial. Cattle are moved every seven days into a new paddock, with 21 day old growth. The heifers were turned out in early September of 2017. The average body condition score of the heifers when they were turned out was 3.9.

Initially the heifers received 1 ton of field cubes over the first 60- days. This amounted to 50 pounds of field cubes per animal. The herd was given approximately 1 bag per day to “gentle down” and make rotation easier. The heifers were worked in late November and their average BCS had increased to 4.4, an improvement of .5 BCS in a short period of time. The field cubes assisted in that performance, but the cubes’ effects were only part of the cattle’s increased BCS. The two year old heifers were also supplemented with a commercial feed for 60 days prior to bulls being introduced to the herd, and for 30 days while the bulls remained in the herd. The feed was removed after a total of 90 days. The feeding period saw improved BCS to 5.5-6.0 across the herd. On average, each animal had feed costs at $100 per head over the 90 day feeding period, not uncommon for heifer development protocols. Heifers also had access to molasses on a year round supplement plan. The cost per cow for molasses and mineral supplementation was $133.52 per head. The pasture was also mowed twice, bringing the cost per head for mowing to $22.50. The pasture was fertilized with a 20-0-6 fertilizer at a rate of 250 lbs of fertilizer per acre, giving a nitrogen rate of 50 pounds per acre.

Summary of costs on per head basis
90 day commercial heifer feed $100.00
Molasses/mineral supplement $133.52
Mowing $ 22.50
Fertilizer $ 20.50
Total of feed/supplement/mowing/fertilzer per head $276.52


The costs associated with carrying the heifers on smut grass seem to be in line with typical costs associated with breeding two year old heifers. The biggest difference is the stocking rate of 2 cows per acre help lower the per head cost.

 In the summer, the cattle could not keep up with the smut grass. They typically could manage to eat about half of the total available forage and the uneaten portion of the grass went to seed. The cattle continually selected the new and tender growth. The grazing and selection of smut grass diminished the canopy of the smut grass, allowing the ground to open up. We have seen the open ground begin to fill in with Argentine bahia grass as well as common Bermuda. As winter came, the smut grass continued to grow, but at a slower rate. The cattle then began to eat much of the older, stockpiled grass, consuming smut grass that we had believed to be non-palatable. Their winter time consumption of molasses did increase, as was expected.

Results: The heifers had bulls placed in with them on January 15th 2018. The bulls were half-bloods (angus and Brahman). The heifers were pregnancy tested on May 21st, 2018. The conception rate of the heifers was 93 percent, 37 of the 40 heifers were bred. The three open heifers had other issues that prevented them from conceiving.  One was found to have Ovarian Follicular Dysplasia, and the other two heifers had immature reproductive tracts. The three open heifers had an average BCS score of 5.75.

The open heifers were culled and new, open heifers were added to Pasture X to bring the herd size back up to 40. As of August 1st of 2018, their current body condition scores range from 5.5-6.5 with the average BCS of the cattle being a 6.0. We have also seen having a stocking rate of two cows per acre has allowed for Bahia grass and other grass species to reemerge in the pasture. At the beginning of the trial very little Bahia, common Bermuda or other species of grass could be found in the pasture, as the overgrown smut grass canopy had out-competed the improved species of grass. This spring it was documented that white clover, common Bermuda, and Bahia (mostly Argentine) had all taken advantage of the reduced clump sizes and reduced canopies of the smut grass and were now growing in Pasture X.

As the cattle begin to calve this fall, I will give the herd access to two paddocks- 10 acres so they can spread out while calving. The current plan is to continue this competitive rotational grazing trial for at least the next two years to see if the pasture can continue to support two cow units per acre, and to monitor the effects of competitive rotational grazing on the types of grass found in the pasture.

Please feel free to email Aaron Stam at if you have any questions regarding competitive rotational grazing strategies, or are interested in talking smut grass.


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