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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
astam@ufl.edu if you have any questions
regarding competitive rotational grazing strategies, or are interested in
talking smut grass.