The practice of rotating cotton with other crops is generally believed to have a wide variety of benefits. Numerous SSP studies have focused on understanding and documenting the specific benefits on reducing disease, nematode, weed, and insect pressure, supplying nutrients, increasing organic matter, and decreasing erosion.
We first asked growers whether they typically rotate cotton with other crops. We then presented growers with a list of factors and asked them to indicate the extent to which each one influenced their decision about crop rotation. Growers responded by selecting a number from 1 (not at all) to 4 (very important). We also presented a list of winter cover crops and asked how frequently they plant each one. Growers responded by selecting a number from 1 (never) to 4 (always).
The overwhelming majority (77.7%) of Southeastern cotton growers use crop rotation. Grower responses regarding the importance of different factors in influencing decisions about crop rotation are shown in Figure I. The figure shows the proportion who indicate each factor influences their decision either moderately or very much.
Figure I - Factors Influencing Decisions About Crop Rotation
There was limited variation in the factors that influence grower decisions about crop rotation. Reducing nematodes was the most important factor, with 80.8% saying this influences their decision either moderately or very much. The importance of reducing diseases was slightly lower (79.1%). The remaining factors (reducing weed pressure, increasing the supply of nutrients, increasing organic matter and decreasing erosion) were of approximately equal importance, with about 70% of growers indicating those factors influenced their decisions. The only exception was for "reducing insect pressure," for which slightly more than half (55.6%) said this influenced their decisions.
Winter wheat, rye, and winter weeds were the only winter cover crops that a substantial proportion of growers report planting. Winter wheat was the most common, with 50.4% indicating they plant this crop often or always. Forty-three percent indicate they plant rye and 15.1% said that winter weeds are the cover.
Frequent use of crop rotation is not unexpected. Current production guides include rotation as a suggested Best Management Practice. In Louisiana, fields with nematode, weed, or disease problems typically experience a large yield increase after rotation39. Cotton-peanut and cotton-corn rotations in Alabama were found to increase lint yield between 9 percent and 24 percent39. In addition to soil conservation value, reports have described additional positive yield benefits from rotations including improved farm profitability67. Researchers have noted that positive effects may not be due to plant nutrition factors: instead positive effects may result from pest population dynamics and the differences in pest control costs associated with either rotations or mono-cropping, factors which are often omitted in comparative economic assessment. Finally, a long term study in the Tennessee Valley determined that rotation increased cotton yields, particularly after conversion to a no-till system.15
There is however some contrary evidence regarding the value of rotation across the entire cotton belt. In Georgia, while corn-cotton or soybean-cotton rotations reduced nematode pressure and increased cotton yields, net returns were reduced compared to continuous cotton 86 due to inadequate yields of the rotated crops. Additional research in Mississippi found increases in cotton yield, but the observed increase did not overcome the cost of establishing the cover crops. 35
Our results indicate that winter wheat and rye are the cover crops used most often. Researchers employed a mathematical model and found specifically that a using a rye cover crop prior to cotton increased profitability. 67 In addition, one study found that Heliothis virescens (F.) and Helicoverpa zea (Boddie) reached economically damaging levels less often in cotton preceded by rye or crimson clover covers.98 Finally, there is anecdotal evidence that a family of Georgia cotton farmers 67 reduced their insecticide and fertilizer use by growing a lupine cover crop ahead of their spring-planted cotton.
The high degree of crop rotation indicates that a majority of growers believe it can benefit their bottom line in a number of ways. Further research on this topic may be needed as prices change for commodities typically used in rotations (e.g., peanuts, corn). We agree with the assertion that more growers would probably use cover crops in conservation tillage systems if more consistent supporting evidence were available.40
Although the literature suggests that frequently-used cover crops are beneficial to cotton grower profitability, at this point we can not say with any degree of confidence whether SSP research into less-used cover crops has affected profitability.