There are a number of advantages for rotating corn with soybeans rather than planting continuous corn.
Agronomists have talked for years about the advantages of crop rotations, but recent market prices and the relative productivity of soybeans compared corn often come out in favor of farmers planting more acres of corn than of soybeans. Still, there are known advantages to keeping soybeans in the crop rotation, points out Tristan Mueller, program manager for the Iowa Soybean Association’s On-Farm Research Network. These include:
1. Ability to better manage weeds
2. Better management of insects and crop disease
3. Less net use of nitrogen fertilizer
4. Reduced use of energy in both the production and in the handling, drying and conditioning of stored grain
5. Spreading spring and summer fieldwork and harvest over a longer time period
A number of university studies comparing continuous corn, with a three-year corn-corn-soybean rotation and/or a two-year corn-soybean rotation have generally concluded that having beans in the rotation can have both economic and environmental benefits.
Traditionally, production costs for soybeans have been well under the per acre costs of producing corn. The yield relationship in recent years between corn and soybeans has been roughly 3 to 3.5:1. That is, fields that produce 50 to 55 bushel beans will produce 150 to 175 bushel corn. Per bushel soybean market prices have generally been 2.5 to 3 times those of corn. All of these factors vary from field to field, farm to farm, and year to year.
Weed resistance to certain herbicides and insect resistance to corn rootworm traits
The point is, however, this all makes for a rather complicated equation for determining which crop generates the most profit. “We won’t get into that in more detail here, except to say that when corn prices are more than half of soybean prices, it’s hard for corn to not come out on top,” says Mueller.
However, looking back to the herbicide resistance management discussion and the corn insect resistance problem that is becoming more widespread each year both problems that have increased along with the increase in continuous corn acres — there’s no denying that there is value in a crop rotation that creates a system requiring rotation of pesticides, herbicides, genetic traits and even fertilizer inputs.
(Source – http://farmprogress.com/story-keeping-soybeans-crop-rotation-9-96711)