Soils in the Southeast typically are sandy, acidic, poorly buffered and low in organic matter, making it a wonder that farmers here can grow anything at all. But there are a few advantages, and growers can compensate for the disadvantages, says Glen Harris, University of Georgia soil scientist.
“There actually are advantages to our soils,” said Harris, speaking at the recent National Agronomy Meeting in Auburn, Ala. “For example, our soils are well drained, sometimes too well drained. But we don't have the drainage problems as farmers do in the Midwest.
“And we can lime for pH and fertilize for our other needs. The only thing left after doing all that is working on our organic matter, which is where conservation-tillage comes in.”
One of the biggest challenges in converting growers to conservation-tillage systems is that they are so different from conventional systems, says Harris. “Some growers want to go ahead and fertilize just as they do in a conventional-tillage system, but it's important that we realize the difference,” he says.
While preventing erosion is an important reason for converting to conservation-tillage, many farmers are making the switch due to simple economics, he adds. “It doesn't really matter why they're doing it, as long as they're doing it,” says Harris.
It's important, he says, that farmers get off to a get start with conservation-tillage. “Once you switch from conventional-tillage, if you don't have good pH and nutrients in the plow layer, you're asking for trouble from the start. There are some challenges there that we don't always think about.
“For instance, some farmers clear out new ground for conservation-tillage, and some who make the switch sell all of their tillage equipment. If you have to plow in the nutrients, you might have to borrow some equipment. Other farmers might make the decision to switch at the last minute. A conventional farmer may be going out of business, and you pick up their land. You might not want to plow, and you might not have time to plow. But it's important to take that last opportunity to incorporate lime and fertilizer before you begin strip-tilling,” says Harris.
Farmers who switch to a conservation-tillage system also have to think differently about soil sampling, he says. “You've heard about soil sampling a million times, and you might think there's nothing new and you can continue as you have with conventional-tillage, but there are a couple of issues. One is how deep or shallow the soil sample should be, and the other issue is where the sample should be taken from,” he says.
University of Georgia recommendations call for a deep and shallow soil sample, although it doesn't have to be done every year, says Harris. It's especially important, however, if you're switching from conventional to strip-tillage, or if you're planting into new ground.
“It requires more work and time — you'll have to take two buckets to the field. Take a sample down to 2 to 3 inches, put it in one bucket, and then go back to the same hole and go down 6 or 7 inches, putting this sample in another bucket. These two samples should be analyzed separately.”
One farmer, says Harris, asked if you should lime by the top recommendation and fertilize by the bottom one. “One of the main reasons for taking the shallow sample is to catch pH problems before they get too deep. Does it make sense agronomically? We need to do more research and get into these stratified situations where we have higher phosphorus levels at the top. We need to fertilize at different rates and see if we're both agronomically and environmentally sound. The challenge of two samples is that it takes more time and money.”
Many growers who have never used conservation-tillage aren't convinced that it'll work, says Harris. They believe they have to incorporate lime, and they're not convinced that fertilizer will ever get down into the root system.
“We're pretty confident that as long as you start off right, you can maintain fertility levels with surface applications. Many times, those nutrients are carried better in conservation-tillage systems.”
As far as timing, he says, it may be good to go in earlier with fertilization in conservation-tillage systems. “It might be good to give that lime a chance to get in earlier. But we have not had any problems with surface-applied P and K not getting to the root systems of our crops.”
When growers first began switching to conservation-tillage, there was debate over whether or not you could have too much residue in a field, says Harris.
“What it comes down to is if you can't plant into it, then you probably have too much residue. As long as you can plant into it, you probably can't have too much residue. Many of our growers have developed a great deal of expertise and determination as far as strip-tilling into a lot of cover.”
Another issue in conservation-tillage is nitrogen management, says Harris. “We recommend that you use a cover crop, and it makes a difference if you're using a small grain or a legume. About 95 percent of our people who use a cover crop are using a small grain. Rye seems to be the most popular because it makes good residue. I'm surprised we don't use more legumes, especially considering nitrogen prices. The problem with using legumes in the Southeast, especially in cotton production, is the threat of nematodes.
“We also need more research in this area. We've had studies with crimson clover that showed no problems with nematodes in strip-tilled cotton. The cotton made good yields, and the crimson clover re-seeded itself after four or five years. But I wouldn't recommend that if you already have nematode problems.”
Nitrogen recommendations for a conservation-tillage system with a small grain cover crop followed by cotton call for increasing the nitrogen rate by 25 percent if you don't use nitrogen on small grains, says Harris. If you put 30 pounds of nitrogen on a rye cover crop in February, you still can't cut back much on the nitrogen applied on cotton, he says.
“Our research shows that by applying nitrogen, you produce more residue, and you have a greater potential to tie it up. You can talk about N ratios all you want, but you can't cut back. The questions only become more difficult as far as nitrogen rates go. What if you have a small grain cover crop, fertilized with poultry litter, followed by grazing, followed by cotton? How much nitrogen should you use?”
Many farmers who switch to strip-tillage are afraid of using poultry litter because they think they'll lose all of their nitrogen if it's lying on top of the ground, says Harris. “They may lose some, but we don't think they lose that much. They also fertilize forages, pastures and hay with it. If you look at the availability co-efficient and application methods, it's 50 to 60-percent available if you incorporate it. And if you don't incorporate it, they usually knock off about 10 percent. I usually tell growers to use about 10 percent more in conservation-tillage systems compared with conventional-tillage systems. You'll incorporate some if you apply it before strip-tilling.”
Growers who plant a legume cover crop get a nitrogen credit of about 30 pounds of N, says Harris, although there's probably about 200 pounds of nitrogen in a cover crop of clover.
Using starter fertilizer in a conservation-tillage system is a debatable issue, he says. “Personally, I like to see starter fertilizer used in conservation-tillage. If you plant strip-till cotton early, like in April, I want to see you use a starter. We've had some farmers who've learned tough lessons from starter fertilizers because there's always the potential for burning.”
Turning to strip-till peanuts, Harris says a good start is just as important as in cotton production.
“We still want to soil sample by depth. We do have fixed nitrogen on peanuts, and don't recommend that you use a starter. We have a liming method for bringing up pH in the pegging zone. Either that or our growers are using gypsum. This probably works even better in strip-till than in conventional because by the time we put out our gypsum, the strip-till soils, hopefully, will be more mellow, and we'll have better water infiltration to get it down into the pegging zone.”