What Does Planting the Same Crops on the Same Soil for Many Years Cause?

Crop rotation, or the act of swapping out one crop for another on the same plot in varying years, plays an important part in agriculture. Whether you’re a backyard gardener or a commercial farmer, crop rotation provides notable benefits when practiced on a yearly or seasonal basis. Failing to rotate crops has notable detrimental effects not only on the plants and their productivity, but on the soil itself.

Different plants require different amounts of varying nutrients. Wheat (Triticum aestivum), for example, requires a large amount of nitrogen for optimum fertility. If wheat is planted in the same space for many years, the amount of available nitrogen in the soil becomes suboptimal. By varying crops from year to year in the same space, the soil can regain the nutrients depleted by the previous years’ plant needs. When the same crops are planted on the same space year after year, the nutrients needed by that crop are used up and can lead to decreased fertility for the crops and a decrease in production.

Certain pests are very particular about the crops they eat. When you plant the same crop on the same soil for many years, you support these crop-specific pests and allow them to continue abiding in your fields. Varying crops over a period of years keeps the pest population down by rendering the food source for these crop-specific pests unacceptable, and they die off or leave the site. Similarly, bacteria and fungi specific to certain crops or crop families increases year after year. When the same crops are planted on the same site for many years in a row, crop health decreases from insufficient nutrient intake and pesticide resistance increases.

Each type of plant has a different root structure. Some have knots or balls for root systems while others have fibrous networks of tendrils for roots. By failing to rotate crops on a regular basis, soil erosion becomes much more likely. The soil becomes compact and loses aeration, allowing it to wash away in periods of flooding or heavy rain. Varying out a crop with a compact root system with a crop that has an intensive root system can help the soil maintain quality and aeration, allowing for reduced soil erosion over the years.

By planting the same crops on the same soil for many years, you risk an increase in the weed population. Crops with dense foliage choke out the light, reducing weeds. Even if the plant does not have dense foliage, crops compete directly with weeds for the same nutrients, soil space and light, choking them out of the competition. As the years go on, there are fewer nutrients to compete for and the plants that are native to the area and require fewer nutrients and lesser soil quality -- weeds -- proliferate. Still other plants, like alfalfa (Medicago sativa), produce chemicals that inhibit the growth of other plants in the same family. By planting these allelopathic crops year after year, the plants become weaker and weaker and cannot compete with weeds for the same plot.