We’re always learning methods to improve our soil health at the Duke Campus Farm. If our soil is healthy, our crops are correspondingly the healthier and more abundant. Moving to no-till is part of that effort, as is our crop rotation plan.
Crop rotation has been practiced since the Roman era. Until the mid-20th century, when industrial agriculture phased out crop rotation in favor of chemical inputs, farmers rotated crops from field to field.
Different crops take various nutrients from the soil—and some actually add nutrients back into the soil. Crop rotation plans vary from simple to highly complex, but the goal is the same: maximize soil fertility and minimize disease and pests.
Like many first-time farmers or gardeners, attempting to create a crop rotation plan daunted the DCF farmers. Our good friend and neighbor, Larry, gave us a simple and memorable plan that we’ve begun to put in place.
Our plan goes like this: leaves, fruits, roots, legumes, (flowers), cover crop.
This system is based on the nutritional requirements of each type of crop. (And to be sure to give credit where credit is due: this crop rotation comes from an article entitled “Yes, You Can Practice Crop Rotation” by Cynthia Hizer. Yes, we were encouraged by the title.)
Leaves are the first and last crop in a growing season, and their nutrient of choice is nitrogen. Leaf crops, such as lettuce, herbs, and mustard greens, are also first in the rotation because nitrogen is highly soluble—in other words, if nitrogen in fertilizer isn’t taken up by crops, it tends to react with water and wash away. (Nitrate pollution in drinking water is a big problem in major industrialized agricultural areas, like Iowa.)
Fruits are next up in the rotation, which include tomatoes, melons, squash, peppers, and eggplant. These plants need phosphorus to produce fruit and nitrogen less important.
After fruits are root crops, like carrots, beets, onions, and turnips. Roots need even less nitrogen than fruits; rather, they need abundance of potassium to develop their root structures.
Legumes are next, namely green beans and peas. These plants are technically fruits, but are capable of fixing atmospheric nitrogen. In layman’s terms, this means that legumes replenish nitrogen in the soil.
After legumes, the DCF plans to grow flowers, primarily because they’re pretty and we like them (thus the parenthetical around “flowers”). Finally, cover crops fill shorter rotations, replenish nutrients, and give the soil a chance to rest.
Furthermore, as I mentioned above, rotating crops also minimize pests. Imagine bug is drawn to a certain crop. If that crop is planted in the same space year after year, that bug can just hang out, make babies, and attack that crop. Crop rotation also reduces the risk of a crop contracting a disease that may have developed in that bed or field. In fact, certain crops can be planted that discourage pests and disease that may affect the next rotation.
Rotating crops takes advantage of inherent properties of a given plant to the collective advantage of the farm. Not only is this crop rotation easy to follow, but it improves yield through no additional inputs—so it’s sustainable too.
In summary: crop rotation is a great idea. Yes, it takes a bit of planning, but that’s a small price to pay for the benefits. When you’re out on the farm and see which crops are growing where, now you have a much better idea why.