How does crop rotation work? By alternating crops to give the soil a rest and to replace nutrients that are removed.
People transitioned from a hunter-gatherer culture to an agricultural culture in about 12000 BC. First, they domesticated animals. This happened in different places on Earth within a few thousand years. In about 9500 BC, people started to grow crops, such as wheat, barley, peas, lentils, and flax. By 8000 BC, farming was common around the world, which brought a huge change in the way people lived and caused a growth in population. There is evidence that people were rotating crops from about 6000 BC in the Ancient Near East. They didn’t know why, but they knew from experience that rotating crops allowed them to use the same field for longer.
The Egyptians used a system of crop rotation that the Romans may have picked up. The Romans called it “food, feed, fallow”. Farmers divided their farming land into three parts. In the “food” part, they would plant grain, such as wheat. In the “feed” part, they would plant barley or oats that would be used to feed the livestock. And the “fallow” part would be left empty.
In most countries after the time of the Romans, a two-field system was used. One field would be used to grow crops while a second field was left empty. This would be reversed the following year. From the Middle Ages onwards in Europe, a three-field system was introduced. This was basically the same as the Roman system. In the early 16th century, a four-field system was invented in what is now Belgium. This system was picked up and introduced to the UK in the early 18th century. It is one of the biggest reasons why the British Agricultural Revolution was able to happen, which was, in turn, one of the reasons why the Industrial Revolution was able to happen.
So, how does crop rotation work and why is it good? How crop rotation works is very simple. Farmers alternate the crops that they grow on a field. They may alternate them yearly or they may have a three or four-year cycle that uses different kinds of crops. What benefits does crop rotation have? There are six clear advantages of rotating crops.
The first two are pests and diseases. Insects and other pests tend to have evolved to feed on a particular kind of crop. If you change the type of crop at the end of the year, their food source is removed, and they die. They also usually live in the crop, so their habitat is also removed, and they die. Crop rotation spares crops from diseases in a similar way. Diseases that blight crops tend to be species specific and they can live in the soil. If the same crops are planted year after year, the diseases will come back. If different crops are planted, the diseases often die out.
The third reason is weed control. If the same crops are planted in a field for consecutive years, or if a field is left fallow, weeds can become a problem. To prevent this, farmers use cover crops in their crop rotation cycle. Cover crops are plants that can stop weeds from growing by out competing them for resources. There are many different types of cover crops, but beans and peas would be a good example. They are crops that might not necessarily bring in a big profit for the farmer, but they are invaluable in what they do for the land. When they kill the weeds, those weeds are usually gone for most of the rest of the crop rotation cycle.
The fourth reason is erosion. A field that doesn’t have crop rotation will lose the consistency in its soil and it will be very easy for the wind and rain to erode the soil. Cover crops also help to bind the soil and prevent erosion.
And the fifth reason is probably the most important. Different crops require different nutrients. Crops such as corn need a lot of nitrogen to grow. Corn uses about 20 kg of nitrogen per acre. They take this nitrogen out of the soil and use it. By the end of the season, the nitrogen in the soil is greatly depleted. If the farmer plants corn again the following year, there isn’t enough nitrogen and the crop won’t be very successful, if they grow at all. To fix this, farmers use our friend the cover crop again. Cover crops, such as beans, take nitrogen out of the atmosphere and store it in the soil. If a farmer alternates corn and beans, the soil will be replenished on each rotation.
In the 1950s, farmers discovered that they didn’t have to rotate crops if they used pesticides, fertilizers, and other chemicals. Financially, it is much easier for a farm if they only grow one crop. However, the concern over health and the environment pressured farmers to move back to the rotation system. Some farmers might rotate two or three crops, and some farmers might have far more complex rotations.
So, how does crop rotation work? By reducing the damage to the soil and allowing crops to be grown in the same place for longer.
Sources
https://education.nationalgeographic.org/resource/development-agriculture
https://science.jrank.org/pages/1870/Crop-Rotation-History.html
https://en.wikipedia.org/wiki/History_of_agriculture
https://en.wikipedia.org/wiki/Crop_rotation
https://agsci.oregonstate.edu/sites/agscid7/files/coarec/attachments/may_2013_article.pdf
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