The fertile ground of the U.S. Midwest is ample proof that a sod-based rotation can be beneficial, says David Wright, University of Florida Extension agronomist.
“There’s a lot of data out of the Midwest, and long-term rotation studies have shown the value of perennial grasses in these rotations,” says Wright.
Sod-based rotations could be a fit in the Deep South, he says, in areas like north Florida where producers typically grow two years of cotton followed by a year of peanuts. “A sod-based rotation is good for reducing nematodes in peanuts and cotton. We also encourage our growers to use conservation-tillage or strip tillage. Essentially, what we see is a year of peanuts followed by an oat cover crop followed by cotton followed by an oat cover crop. We strip-till into it, and it’s a three-year rotation. We are trying to encourage growers to use a four-year rotation,” says Wright.
Some producers, he adds, have cattle and other livestock, and they’re looking for a way to utilize the land year-round.
“We’re growing two years of bahiagrass followed by an oat cover crop. We kill off the bahiagrass in the second year, plant oats into it, and then strip-till peanuts into that. We go back into an oats cover crop and then into cotton before going back into bahiagrass,” he says.
Perennial cover crops, says Wright, have been shown to be more beneficial than annual ones. “That is why the entire Midwest is covered in fertile soils,” says Wright.
Peanuts are strip-tilled using a strip-till rig with a ripper-bedder. “When we go into a perennial cover like bahiagrass, there are about 20,000 pounds of bahiagrass roots underneath there. With an annual cover crop, there are 3,000 to 4,000 pounds of root mass — it makes a tremendous difference in many things you do,” he says.
Researchers looking at the sod-based rotation are in their third rotation or ninth year in small plots, says Wright.
“We have been increasing organic matter by about one tenth percent per year. That doesn’t sound like much, but after nine years, we have almost 1 percent higher organic matter in the sod-based rotation than in the conventional-tillage system,” he says.
This system also has been taken from the small plot to a 135-acre pivot, says Wright. “We have a rotation that turns counter-clockwise one-quarter of a turn each year. We have exclusion cages where cattle are never allowed to graze either the bahiagrass or the oats cover crop. Therefore, we can determine the cattle impact not only on the winter grazing, but also on the bahiagrass and on the cotton and peanut crops, as well,” he says.
On small-plot replicated trials, there were irrigated and non-irrigated strip-till experiments, he says. “The main problem we’ve had is stand establishment without irrigation. But later on, at the end of the season, it doesn’t make much difference. In those plots, we’ve also looked at nitrogen — above ground with the biomass and nitrogen rates. We looked at no nitrogen being applied and at 95 pounds of nitrogen applied. Again, because we are increasing organic matter in the sod system, we have more nitrogen available in that system. The above-ground biomass is much greater in the sod systems than in the other systems,” says Wright.
The leaf area index of the cotton plant was larger in the plots, and the cumulative nitrogen uptake showed a similar trend, he says. Looking at cotton yields from 2007, Wright says there was no significant difference where no nitrogen was applied and where 95 pounds of nitrogen was applied in the sod-based system.
“We’ve also had other trials where we looked at nitrogen, and we’re about to the point where 30 pounds of nitrogen in the system will give us three-bale cotton, year in and year out. Two years after bahiagrass was in the system, you could still see an impact on cotton yields.”
The sod-based research also is looking at what, if any, impact the cattle are having in each of the systems, says. “We’ve found that with winter grazing after bahiagrass, we have much higher yields from the winter grazing if you have perennial grass in that system compared to the conventional system of just cropping each year. We were very concerned about the impact of compaction since we were strip-tilling.
“When we plant bahiagrass, we do it with a no-till drill. We do have increased soil compaction where cattle were grazing. But most of the compaction we see from cattle is in the top 6 inches of the soil.”
Research also has looked at cotton plant height and main stem nodes, says Wright, and no significant difference has been seen between sod-based and conventional systems. “Whether it was irrigated and grazed, or whether it wasn’t grazed, there wasn’t a great deal of difference in plant height and main stem nodes.”
Little difference also was seen in cotton turnout, he adds. “We looked at grazed and non-grazed, irrigated and non-irrigated. Generally, lint yields were higher where we had cattle. This was probably due to nitrogen cycling in that system. There was a significant difference between the irrigated grazed and the non-grazed, with about four-bale yields from the grazed, irrigated cotton. So there’s some potential there.”
Lint yields, says Wright, were impressive in the sod-based system. “We thought the compaction might be a deterrent, but cattle do add to the system.”
In conclusion, he says, the highest lint yields were in cotton that followed grazed cover crops.
“They were numerically higher in the grazed, non-irrigated plots than in the non-grazed, irrigated plots, probably due to nitrogen cycles. Total nitrogen uptake was higher in the sod versus the conventional rotation, in the four years versus the three years, with or without nitrogen applications. Cotton yields were higher in the bahiagrass versus the conventional rotation.”
The bottom line, says Wright, is that if you can graze winter cover crops and have bahiagrass in the rotation, it will increase yields.
“We saw a particular advantage recently when a hurricane came through our area during harvest, and only half of our farm was in row crops. Cattle don’t mind hurricane winds and high amounts of rainfall nearly as much as cotton and peanuts.”