The Rotation Effect - It's For Real

Jane Sooby, NSAS Western Organizer

How can you reduce erosion, control weeds, improve the soil, and increase yields?

Use a crop rotation. Farmers have been using rotations for centuries; researchers have been studying the "rotation effect" for decades. The rotation effect is the increase in yield that crops grown in rotation show compared with crops grown in monoculture.

A classical rotation involves alternating a legume like alfalfa or clover with a grass crop like corn or wheat. In a study done in Minnesota, continuous corn yielded 103 bu/acre while corn in rotation with alfalfa yielded 150 bu/acre. This rotation adds N to the soil (from the nitrogen-fixing legume), disrupts weed cycles, breaks pest and disease cycles by introducing a non-host species, and reduces erosion during fallow.

Despite extensive studies that have attempted to isolate what causes the rotation effect, no one factor (like soil nutrient levels or disease persistence) can definitively be held responsible for it. Instead, the rotation effect seems to result from a synergistic interrelationship of many factors, including improved soil structure and increased water-holding capacity.

Farmers who have experimented with rotations in western Nebraska have a lot to say about them. Scott Easterly, who farms west of Lorenzo, uses a 3-year dryland rotation of winter wheat-millet-fallow, a winter crop-spring crop-fallow rotation. He gets 2 crops in 3 years instead of the 1 crop in 2 years that wheat-fallow brings in. Using this rotation, he is successful in controlling winter annual weeds like downy brome and jointed goatgrass that become serious problems in the winter wheat-fallow system. Says Easterly, "If I vary my crops, I get rid of the weeds that have the same cycle." Growing millet allows him to control the winter annuals with tillage, while growing winter wheat similarly enables him to control late-season weeds.

Ken Disney, an organic farmer in Lodgepole, says, "Rotations are probably the most important thing we're doing." Disney elaborates on the winter wheat-millet-fallow rotation that Easterly uses by varying the spring crop, and using a legume cover crop during fallow. Millet, oats, amaranth, sunflower (both confectionery and oil), barley, and a current experiment with fall-planted peas are some of the spring crops Disney has grown. He has interseeded yellow clover and red crimson clover into the wheat stubble and then incorporated it the following year, with long-term benefits to soil fertility. His successful use of a legume cover during fallow contradicts popular opinion that there isn't enough precipitation in the region to support clover or other legume growth.

Disney feels that rotation is his best strategy for getting rid of grassy weeds like cheat, downy brome, and jointed goatgrass without the use of chemicals. He has also noticed that his ground is mellower and less hard than before he started rotating.

Dennis Demmel farms south of Ogallala and has experimented with rotations on his irrigated and dryland ground for a number of years. Demmel has made a number of observations about his rotations.

On his irrigated land, Demmel has considered a winter wheat-corn-sunflower-soybean rotation, but his experience indicates that winter wheat-sunflower-corn soybeans may be a better sequence for a number of reasons:

1. Wheat stubble is wet in early spring when corn needs to be planted. Sunflower is planted later, giving the ground more time to dry out. Also, he has more time to control volunteer winter wheat before planting sunflowers into wheat stubble.

2. Sclerotinia mold is a problem on sunflower and soybean back-to-back, especially on his low areas that tend to hold water.

3. The typical corn-soybean rotation, which Demmel started out using, required him to irrigate most of the summer. His lower ground never dried out. Sunflower uses a lot less water and wheat is only irrigated until July, so "using these two crops helps bring the ground out of an anaerobic state."

On Demmel's dryland acres, he uses a 4-year rotation of winter wheat-corn-sunflower-fallow with legume cover, as Disney does. Demmel plants the legume into the sunflowers during the last cultivation, then allows it to grow until the following June, when he destroys it by tillage (discing or sweeps).

Demmel has gotten higher wheat yields from wheat after sunflower-fallow than from wheat after wheat-fallow.

Demmel observed that there were fewer early weeds in ground that was going through a second round of rotation compared to an adjacent field that had just undergone its first round. He feels that "with successive series of rotations, weed problems become successively less." He also thinks that two years of row crops, like wheat-corn-sunflower-fallow, help to reduce weed problems more than a single year of row crops like wheat-corn-sunflower-fallow. The former rotation helps eliminate annual grasses much better than the latter.

With a rotation, Demmel gets better weed control and improved yields, and increases his total cropped acres by 50% (by reducing total winter wheat-fallow acres by 50%). He also feels that it reduces erosion because the ground is covered with a crop more of the time. Accompanying the reduction of acres in summer fallow, Demmel noticed a significant reduction in fuel consumption.

Rotations can be as simple as the two-year wheat-fallow rotation, or as complex as 8- or 10-year rotations. Many factors need to be considered in designing a rotation for a farm. Neighbors who have tried different rotations may be the best source of information you can get. Extension educators can make a number of suggestions, too, The literature is crowded with information on rotations. If you would like to try it out, ask around and think about what crops would fit best on your farm.

If you have developed a rotation that works for you, we'd like to hear about it. Call Jane Sooby, NSAS western organizer, to let us know. The number is 308-254-3918.

Nebraska Sustainable Agriculture Society: Home        Features