It’s still winter outside, which means farmers are carefully planning how they plan to manage their crops starting in the spring. One thing that farmers carefully plan is what crops they want to plant in what fields.
Though you may not notice by driving by farm fields every year, most farmers plant different crops on their fields year after year. For example, one specific field in 2016 might have been planted in corn and another field might have been planted in soybeans. Then in 2017, the first field may have been planted in soybeans, and the second field may have been planted in corn. This is called a crop rotation. But why do they do that?
There are multiple reasons and multiple ways to rotate crops. The first, and likely the most prevalent reason, is nutrient uptake in plants. Compared to other crops, corn needs lots of nutrients, especially nitrogen. This makes soybeans a good crop to alternate with corn, because soybeans have nodules on their roots that host bacteria that fix atmospheric nitrogen. Thus, soybeans require less nitrogen to be applied to the field and they deposit more nitrogen into the soil. Other legume crops, like alfalfa, offer similar benefits.
Another reason farmers rotate crops is to break fungus, disease, or insect life cycles. By changing up the type of crop grown in a specific location, you can disturb certain pests that rely on that environment. However, if this is a large concern, the field would likely require more than one year of an alternate crop. For example, soybeans are often affected by nematodes. Nematodes won’t feed on corn like they do with soybeans. By rotating corn and soybean fields, farmers can minimize the nematode population that might affect their soybean yield.
Planting various crops year after year can also benefit soil tilth. Different crops have different root structures, which can help aerate the soil in different ways, as well as provide different amounts of organic material to the soil.
In Iowa, many farmers do a corn-soybean crop rotation, meaning one year they will plant corn on the field, and the next year they will plant soybeans before returning to corn the following year. They are able to do this because Iowa has relatively healthy soils, and both of these crops offer farmers here the most financial gain at the end of the season. However, lots of research is being done on extended crop rotations, which add in other components, like small grains (like oats) and forages (like alfalfa).
According to Soil Fertility and Fertilizers by Havlin, Beaton, Tisdale, and Nelson, “Numerous long-term experiments have demonstrated that, in general, rotations increase long-term crop and soil productivity compared with continuous cropping.” Extended crop rotations could also play a role in mitigating nitrate losses.
However, these extended crop rotations are not always an easy sell. Because the markets in Iowa tend to favor corn and soybeans, small grains and forages might not be valuable if the farmer doesn’t also raise livestock. That said, even if extended crop rotations aren’t the best option for a specific farmer, two-year crop rotations, conservation tillage systems, and responsible nutrient management are all tools that can help to meet similar objectives.
In summary, crop rotations are good for many things, but mostly help to keep the soil healthy. Iowa’s main crops are corn and soybeans, and when alternated, they can help each other grow the best they can.