|
Rotational Benefits
Dr. Gene Stevens, cropping systems specialist at the University of Missouri Fisher Delta Center at Portageville, discussed the topic of research & soybean rotations with grain crops.
Photo by John LaRose, Jr.
Secondary Crops Benefit Most From Crop Rotation
BETTY VALLE GEGG-NAEGER
MidAmerica Farmer Grower
PORTAGEVILLE, MO.
Soybean rotations with grain crops is a topic under research by Dr. Gene Stevens, cropping systems specialist at the University of Missouri Fisher Delta Center at Portageville.
He spoke about crop rotation recently and with emphasis on profitability and pest control.
“Mid-South farmers typically have the flexibility to select from several crop options to plant in a field. Crop rotation plans often change in response to the current prices of commodities. The question is, ‘How much of a yield hit will occur?’ Benefits of crop rotation include better control of insects by disrupting their reproduction cycles. Rotations also give farmers an opportunity to change herbicide chemistries. For example, atrazine is available for corn but not soybeans,” he said.
“In recent years, we have seen weeds such as Palmer pigweed and mare’s tail become resistant to herbicides. Using the same class of herbicides every year in a field increases your chances for new resistance,” Stevens said. “ There are also other reasons for rotating. Including legumes in a crop rotation helps reduce nitrogen fertilizer rates and speeds up the decomposition of crop residues. Decomposition is a good thing because the chemicals from microbes improve soil structure but we need to retain some soil organic matter for soil water holding capacity.”
In past years, Stevens has studied rice straw burning and its impacts on the following year of soybeans.
“When we burned straw about 37 percent of the nitrogen was lost from the residue. In plots without burning, 211 pounds of nitrogen per acre was measured in the residue versus 131 in burned plots. We lost between 6 percent and 7 percent of the P&K from burning,” he explained.
Stevens also reported on a grant funded by Cotton Incorporated and the Missouri State Support Committee. He is surveying Missouri cotton fields for soil health. There were 11 fields being monitored in the second year of the trial. This test focuses on evaluating active carbon and phospholipid fatty acid (PLFA) which is a fingerprint of the microbes in the soil.
“The poorest soil health was found in a cotton field that was land graded this May. Apparently, the cutting and earth moving devastated the microbes in the topsoil,” he said. “A cotton field near New Madrid had the best soil health. The field was rotated with corn and part of the corn residue was still on the surface.”
He compared the distribution of microbial biomass levels in the fields based on phospholipids.
“Freshly tilled fields give off a pleasant ‘earthy’ aroma from chemical produced by actinomycete bacteria,” he explained. “Bacteria can be separated into gram positive and gram negative groups. Microbiologists test samples by using a purple (gram) stain. If a bacteria appears purple under a microscope they are classified positive. If they are mainly clear, they are negative. Chicken manure contains a lot of E. coli which is a gram negative bacteria. E coli makes people sick in food and water but helps build soil structure. We also measured eukaryotic biomass from critters such as earthworms. I was surprised to see live earthworms in cotton fields. The benefits of crop rotation and wheat cover crops were noticeable in the samples from the fields.”
Stevens said he started his career at Mississippi State University at Holly Springs and conducted soybean/grain sorghum rotations there. Johnsongrass was a real problem at that time.
“In plots, where we grew continuous grain sorghum, johnsongrass density was high; but where we rotated with soybeans the levels were much lower,” Stevens explained. “Also, we found a large increase in yield from grain sorghum rotated with soybeans. We also soil sampled the fields for nematodes. We measured more nematodes in the sorghum plots than the soybeans. Yields from the continuous soybeans were lower than the rotation but only by three or four bushels. So, in this case, it was the grain sorghum that benefited more than soybeans.
“To understand the impact of rotation on soybeans we began new research at the Delta Center funded by the Mid-South Soybean Board in association with the United Soybean Board. Most of the research on corn and soybeans has been done in the Midwest. Purdue University summarized a long term experiment with Iowa, Illinois, Indiana, Nebraska, Minnesota, Wisconsin, and South Dakota. Each one of these tests ran at least six years or more and they found, averaged across locations and years, that continuous corn produced 142 bushels an acre versus the corn rotated with soybeans 154 bushels, so there is about an 8 1/2 percent yield increase. If a farmer has his normal corn-soybean rotation system, he may decide to deviate and grow corn two years in a row and accept the yield loss, if corn prices were higher than soybeans.”
The University of Nebraska researched it a step farther, and determined that one of the main benefits of soybean in the rotation was 60 pounds of N per acre benefit to the corn. When they took soil samples in the beginning of spring you couldn’t find that nitrogen but it slowly mineralized over the season.
“I’m only aware of two studies with soybeans in the southeast United States,” he reported. “Don Howard at the University of Tennessee at the Ames Plantation and Jim Edwards at Auburn did rotation research. Edwards found an 8 1/2 bushel corn yield benefit from rotation. Howard found a 10 percent yield increase in the corn from rotating with soybeans.”
Dr. Edwards at Auburn used Essex variety soybeans which were cyst nematode susceptible. He found that every year where there was corn-soybean rotation versus continuous soybeans, a soybean yield benefit from rotating with corn was found.
“Thankfully breeders, like Dr. Grover Shannon, have done a good job of coming up with new nematode resistant varieties, but the races are constantly changing,” Stevens said. “A farmer may have a field that has the right match of nematode resistance, but the nematode race changes. Rotation adds another layer of protection.
“We’re in the first years of a six-year soybean rotation study with Louisiana, Mississippi, Missouri, Arkansas, Tennessee and Texas,” he said. “We’re planting plots with corn, soybeans and wheat based on treatments of annual rotations with one to one year rotations, two and one, and one and two soybean corn rotations. Plots are split with irrigation and rain fed or dryland treatments. Also some corn plots are burned in the fall. Dr. Bobby Golden, at Mississippi State University is coordinated the work at the six states.”
Stevens’ take home message is that you never know when you might have a field with a cyst nematode or disease problem that is cutting yields. “Rotating soybean with corn gives you an added layer of protection,” he summed. ∆
BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower
|
|