Not All Crop Rotations Are Created Equal
Crop rotation and crop diversity are being touted as particularly beneficial components of a “new” approach to agriculture production–e.g. ”smart” production systems. However, not all crop rotations are beneficial, and not all diversified cropping systems provide all the benefits they are projected to have. The following are two examples of this.
According to recent surveys,, nematodes are the no. 1 pest that negatively affects midsouthern U.S. soybean producers, and crop rotation is touted as one of the primary management options to control them. However, producers must be sure of the nematode species that is present in their fields so that the appropriate rotation crop can be chosen, and collecting soil samples from infested fields is the best way to determine this. Click here to access a White Paper that provides guidelines for nematode sampling.
Following are rotations that are promoted to be used by soybean producers, depending on whether the culprit is Soybean Cyst Nematode [SCN] or Root Knot Nematode [RKN].
• For fields that are infested with SCN, a resistant soybean variety should be rotated with a non-host crop such as corn, cotton, grain sorghum, peanuts, and rice. Doublecropping with wheat is not considered a rotation to a non-host crop, even though wheat is a non-host for SCN. Do not rotate with host crops such as common vetch, lespedeza, or snap bean.
• For fields that are infested with RKN, a resistant soybean variety should be rotated with a non-host or poor host crop such as peanuts or vetch. Do not rotate with host crops such as alfalfa, corn, cotton, or wheat.
• In fields that are infested with either SCN or RKN, there are common host weeds that must be controlled. Thus, rotating a soybean variety with a non-host crop will be less effective if host weeds are not eliminated.
• The take-away message is this–to use crop rotation as a control measure for both SCN and RKN, a resistant variety should be grown in rotation with a non-host crop.
• Click here to access a White Paper that provides further details about the management of nematode pests in soybean fields.
An article titled Diversified cropping systems with limited carbon accrual but increased nitrogen supply provides results from an Iowa study that examined soil organic carbon [SOC] stocks and nitrogen [N] dynamics in a conventional soybean-corn rotation and in diversified systems that included oats, alfalfa or clover, and the addition of livestock manure to replace N fertilizer. Following are important points from that article.
• Over the 20 years of field experiments and lab studies, there were no differences in profile SOC and N stocks.
• Diversified systems used in this study increased N mineralization rates and decomposition of old corn stalks.
• These findings highlight a trade-off between C storage and N supply in the diversified systems used in this study.
• The authors concluded that their findings demonstrate that the key climate benefits from using diversified cropping systems and livestock manure such as in this study may be a decrease in synthetic N fertilizer use, but not a contribution to increased C sequestration in the soil. Thus, more diverse rotations of crops that are fertilized with livestock manure may be environmentally beneficial because of decreased synthetic N fertilizer use and subsequent reduced nitrous oxide emissions, but increased C sequestration in the soil apparently will not be a benefit.
• Click here and here for summaries of this research compiled by Iowa State Univ. personnel.
The above are two examples of how using “crop rotation” must consider the crops being included in the rotation, the reason for rotating crops, and what is/can be expected from diverse rotations vs. those that are currently being used. In other words, simply rotating crops or increasing crop diversity in a rotational cropping system may not accomplish the intended result if crop and/or input selection is not properly chosen.
Composed by Larry G. Heatherly, Apr. 2025, larryh91746@gmail.com