Overton, Texas
March 2, 2005
It's common knowledge that the
high price of crude oil has driven up fertilizer prices. But
studies here have shown cattle can gain 3 pounds per day grazing
spring pastures of a new disease-tolerant clover.
"That's with no added nitrogen, as you'd have to do with
ryegrass pastures," said Dr. Ray Smith, legume breeder with the
Texas Agricultural
Experiment Station.
Commercial nitrogen fertilizer costs have increased to 40 cents
per pound from about 35 cents a pound last year. Natural gas is
used in nitrogen fertilizer production, and natural gas price is
linked to other fuel costs, including crude oil, Smith said.
Luckily for farmers and ranchers, Smith has developed Apache, an
arrowleaf clover that is tolerant to bean yellow mosaic virus,
has great seedling vigor, gives early forage production, a long
grazing season, and offers high nutritive value, he said.
"This new clover is tolerant to the bean yellow mosaic virus
that has plagued arrowleaf for the last 20 years," said Smith,
who is based at the Texas A&M University System Agricultural
Research and Extension Center at Overton.
Smith would say that science had more to do with the development
of the clover than luck, however.
Older arrowleaf clovers varieties such as Yuchi, Meeche and
Amclo, are affected by bean yellow mosaic virus in several ways.
Some plants are killed outright by lethal wilt. Others go on to
survive but suffer a variety of symptoms, including misshapen
leaves, yellowed leaves or leaves spotted in a yellow mosaic
pattern. Of the surviving plants, yields are reduced by as much
as 50 percent. But worse, the productive lifespan of the
survivors is shortened and that leaves months during the spring
without forage production, Smith said.
Ryegrass is one way to fill the production gap, but unlike
clovers, it needs supplemental nitrogen to be highly productive.
Smith began work on arrowleaf clover disease resistance in the
late 1980s. He started with the conventional method of growing
arrowleaf cultivars in the field and selecting those plants that
appeared healthy while rejecting those that were prone to
disease infection.
"This conventional breeding method just wasn't working," Smith
said.
Why? Because, he said, the bean yellow mosaic is spread by
aphids, and the insect's haphazard habits meant that some plants
would become infected while those nearby might not.
"So we were selecting those plants that both had tolerance to
bean yellow mosaic virus and those which just happened to dodge
the bullet, so to speak," Smith said.
With this realization, Smith moved to greenhouse trials where he
could control the spread of virus. He inoculated plants by hand
with a slurry of tissue from infected plants. At the same time,
he continued field trials, but mechanically inoculated those
plants with the virus as well.
After years of crossing plants from both the greenhouse and
field selections, Smith released the result, Apache clover, in
2001. Seed production made the new clover available to farmers
in 2002.
Dr. Monte Rouquette, another forage scientist also based at the
Overton center, did a grazing study with Apache that lasted from
early March 2003 to the first of June 2003. The test showed
calves' average daily gains ranged from 1.7 to 3.5 pounds,
depending upon the stocking rate.
For consistency between studies, forage scientists typically use
poundage to define stocking rates instead of head counts. In the
study, one animal unit was defined as 1,000 pounds of animal per
acre. Low-, medium- and high-stocking rates were defined as 1.2,
2.0 and 2.8 animal units, respectively.
As might be expected, the low stocking rates showed the highest
rate of daily gain, 3.5 pounds per day. And the highest stocking
rate of 2,800 pounds of animal per acre showed the lowest daily
gain. But the medium stocking rate of 2,000 pounds of animal per
acre resulted in nearly 3 pounds gain per acre per day. To put
stocking rate in perspective, figure the average beef cow will
weigh in about 1,200 pounds, her calf 300 pounds and young
stocker animal 600.
As early as the 1960s, common practice was to mix arrowleaf seed
with crimson clover seed and grow it throughout many southern
states, from East Texas to Georgia. By mixing the early-maturing
crimson clover and late-maturing arrowleaf, ranchers and farmers
could have forage from February through early June.
Multiple disease problems, including plant viruses and fungal
disease, effectively put a stop to this practice more than a
decade ago. Of the diseases, bean yellow mosaic virus was the
most prevalent and damaging.
Bean yellow mosaic virus didn't affect crimson clover, but it
killed arrowleaf clover, stunted it, or caused it to mature
early.
"It left a production gap from when the crimson matured to when
warm season grasses came on in June that was not filled until
the release of Apache," Smith said. |