Many producers believe rotating cotton and corn will help them increase cotton yields. Is that the stuff of “rural” legend, or can growers really expect to boost cotton yields when they return to cotton following corn?

Multiple years of studies at the Delta Research and Extension Center at Stoneville, Miss., indicate that the yield increases are real. But the amounts can vary by location and by year, according to agronomists with Mississippi State University.

The researchers have compared rotation systems on two different soil types around Stoneville to examine the interaction of nitrogen and potassium rates and the benefits and problems associated with cotton/corn rotations on different soil types in the Mississippi Delta.

“Changes in farm legislation have allowed producers the flexibility to shift from continuous mono-crop cotton production to alternative crops and cropping sequences to replace some of their traditional cotton acreage,” says Wayne Ebelhar, research professor and agronomist at Mississippi State University. “Using a rotation allows them to improve soil productivity and yield.”

Ebelhar says he began conducting research on corn production at Stoneville because, being a native of Illinois, he was considered the most likely candidate for those studies.

“They thought I knew something about corn, so I was elected,” says Ebelhar, one of a number of scientists from Mississippi State who spoke at the National Conservation Systems Cotton & Rice Conference in Marksville, La.

The response to the three-year rotation studies — one year of corn followed by two years of cotton — has been variable with differences ranging from a decrease of 14.1 percent to an increase of 51.7 percent on a Bosket very fine sandy loam at the DREC.

“Total lint yield has averaged 889 pounds of lint per acre per year where cotton followed cotton and 988 pounds of lint per acre where cotton followed corn,” Ebelhar said. “This translates to an 11.1 percent increase or 98 pounds per acre where cotton followed corn in rotation.”

A similar test on a Forestdale/Dundee silty clay loam at the DREC's Tribbett, Miss., Satellite Farm produced an average lint yield of 939 pounds per acre per year where cotton followed cotton and 1,047 pounds per acre for cotton after corn. Over seven years, the response to rotation ranged from -5.1 percent to +50.1 percent with an average of 11.4 percent or 108 pounds per acre.

Ebelhar said researchers found no significant interaction between nitrogen rates and potassium rates for the cotton and corn. “Both corn and cotton have shown significant responses to increasing N rates in most years while neither has shown significant increases with increasing K rates in the presence of adequate potassium levels.”

(In the tests, nitrogen was applied at a uniform rate of 60 pounds per acre for cotton and 120 pounds per acre for corn prior to or near planting with various rates of additional nitrogen determined at the time of sidedress N application. Potassium was applied at the same time as the sidedress N with the same equipment.)

“Several factors have affected the rotational benefits with the primary influence coming from climate/weather phenomenon,” says Ebelhar. “During the times of these studies, rainfall in August has set all-time records for the least (0.0 in 2000) and most (8.47 inches in 2001) in back-to-back years.

“Total rainfall has ranged from more than 18 inches above normal to more than 13 inches below normal for the region. There has also been as much as 10 inches difference between the locations in the same year leading to a different response in the same year.”

One factor in the yield differences between the two sites is that the DREC location has had more problems with timely irrigation and severe insect infestations compared to the Tribbett Satellite Farm, which is a few miles south of the DREC.

“The largest rotational responses have been in years where severe droughts occurred and where irrigation was not timely or sufficient,” he said. “In other years, excessive rainfall and the associated cloudy days resulted in photosynthetic stress and subsequent fruit shed.

“Heavy vegetative growth has also resulted in severe boll rot that was more pronounced in cotton following corn compared to cotton following cotton. Production-related problems such as delayed planting (related to harvest windows), weed competition in rotation system, antagonistic pesticides and pesticide drift have also contributed to variations from year to year.”

In the rotations, some residual herbicides cannot be used due to the potential for carryover in the succeeding crops, and increased pressure from perennial grasses such as bermudagrass and Johnsongrass has resulted in lower yields for cotton following corn compared to cotton following cotton.