High-residue conservation-tillage systems, utilizing cover crops like black oat and wheat, could have potential in Georgia corn production, according to a continuing research project.
Research was conducted at Tifton and Plains in 1999 and 2000 comparing surface tillage and deep tillage in three cover crop situations — winter weeds, black oat and wheat. The study is looking at a ripper bedder or in-row subsoiling with a Paratill versus straight no-till.
“We didn't include rye in the study because we wanted to compare one of our favorite cover crops in corn and cotton — wheat — with black oat,” says Dewey Lee, University of Georgia Extension agronomist.
Black oat, says Lee, is used in Brazil as a primary cover crop. It is different from cultivated oats, he adds. “Black oat is a forage-type oat. It's a very poor seed producer, but it does produce a tremendous amount of forage. In this case, we wanted to see how black oat could influence corn. We wanted to know if we could produce enough residue to have an impact on moisture,” he says.
Pioneer 3163 was planted in the studies at 30,000 plants per acre. Phosphorus and potassium was applied according to soil test recommendations and 240 pounds of nitrogen per acre was applied to the corn.
“The first thing we looked at was the type of residue we were able to accumulate in producing a conservation-tillage environment. We saw very similar yields of black oat and wheat at Plains in the first year. Unfortunately, our planting was limited to the first part of December. “But in many growers' environments, that's when they're planting because they don't want too much cover, especially in a cotton/corn rotation. We were able to accomplish more than one ton of residue in Tifton, and that's where we really want to be — at about one ton to 3,000 pounds,” notes Lee.
Significantly more residue
In the Tifton trials, he says, there was significantly more residue from black oat than from wheat. “We get a little better root penetration with black oat. And there's research to suggest that black oats have a greater ability to grow through dense soils than wheat.”
The overall effect of tillage was as expected, he says, with no significant statistical difference between the cover crops of black oat and wheat.
“In our lighter soils, we expect a response to some type of deep tillage, whether we're subsoiling or using a Para-till. In the year 2000, we didn't pick up any additional yield with our no-till environment behind black oats.
“In no-till production in south Georgia, we've seen problems whenever we disturb the ground and then come back with no-till. The hardpan is easily reconstructed in our lighter soils, aided by winter rainfall.
“We would hope that as roots die and open up those root canals, that we wouldn't see such a rapid reconstruction of the hardpan. But that's exactly what we're seeing in these lighter soils. The soil moves with the water and reconstructs the hardpan.”
Another surprising find of the research, notes Lee, is the effect of surface tillage. “In most of these tests, we were not able to accumulate enough residue in the first two years. We saw a slight response to lightly disking that soil surface and incorporating the black oat, wheat and winter weeds.
“When we look at the amount of nitrogen being taken up, we really haven't seen much difference. We thought we might be picking up some nitrogen with that residue, but that wasn't the case. During the winter, when we get heavy rainfall, there's a slight crusting of the soil when there's not enough residue on the ground, and that might be the reason for our surface tillage response.”
In comparing wheat directly to black oat, there's less residue and less root penetration from a wheat cover, says Lee. “We're seeing a slight trend that tells us black oat is slightly better than wheat and only slightly better than winter weeds. So we'll be looking at black oat even further. This trend also has been seen in previous studies with peanuts and cotton.”
These high-residue and tillage experiments in corn production will continue in Georgia, says Lee. “We need to maintain a cover of 3,000 to 4,000 pounds of residue. You can do this in the second or third year. But when we go to a cotton-corn-cotton rotation, we begin to lose some of the accumulation effect.
“Also, you'll get a response to surface tillage whenever you don't have this type of residue. That somewhat defeats the purpose of a strip-till environment. If you're going to make a commitment to conservation-tillage, do it knowing full well that you may lose a little in the first couple of years until the residue accumulates.
“Carefully adjust your budget to fit that cost. Shifting to minimum-tillage will require better planning and careful attention to stand establishment. As you shift to conservation-tillage, you'll notice a shift in the populations and pressure of certain insects.”
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