Perhaps the most well-known tool a farmer can use to introduce diversity into their growing system is the crop rotation. A simple crop rotation used widely in the midwestern United States is the two-year, soybean and corn rotation implemented by many large-scale farmers. Each farm is different and may benefit from a crop rotation designed specifically to fit the needs of the land and the stewards who tend it.
Our farm has produced a wide-range of food crops for nearly twenty years, and we continue to make adjustments to our rotation plan. We believe that our growing system becomes more resilient as we introduce more, rather than less, complexity and diversity onto our farm’s landscape.
What is crop rotation?
Crop rotation is a technique that is typically used with annual crops (plants that grow for only one season), though some plans can include perennial crops. In the simplest terms, the grower changes the crop each season so that plants from the same family are not grown in the same location each year. On our farm, we create multi-year growing plans that prevent us from growing vine crops (squash, melons and cucumbers) in the same plot. We might arrange to grow other crops, like broccoli and beans, in the intervening years.
A crop rotation plan can be very simple, like the corn-soybean rotation, or very complex, like our seven-year rotation. A common five-year rotation used by many organic row-crop growers in Iowa might include corn, soybeans, alfalfa and oats – alfalfa is a perennial and often occupies two years of this growing plan.
What does a crop rotation do for the grower?
A carefully developed crop rotation is one of many useful tools that can be a part of a healthy growing plan based on the principles of agroecology. The benefits are numerous and the explanations can be complex, but here are some simple arguments to encourage the use of crop rotation practices.
Pest and disease control
Perhaps the easiest benefit to recognize is that crop rotation makes it more difficult for pests and diseases to persist from one season to the next. For example, the disease called black rot infects plants in the cabbage family and can persist on the residue (old leaves and other plant material) left behind by the prior year’s crop. Planting more of the same crop in that location the following year simply makes it likely that black rot will infect those plants again during the new season.
Each crop type has different cultivation preferences and required growing conditions. This diversity makes it more difficult for weeds to become established and persist from year to year. The introduction of alfalfa provides cover for the soil for more than one year, which can suppress many problem weeds for annual crops that would follow. On our farm, we might use buckwheat as a cover crop to choke out Canadian Thistle, one of our problem weeds.
Different crops interact with the soil in different ways. Some crops are known to be greedy for nutrients while others, like those in the legume family, can actually return nutrients to the soil. For example, beans, peas and lentils can collect nitrogen and improve future fertility.
Improved crop yields
Research continues to show that the introduction of diversity through crop rotations results in better production in individual crops. Corn yield can be increased by 28%, regardless of the growing conditions for the year. The improvement is even greater during poor growing seasons, such as those experienced during drought.
Diversified crop income
One of the benefits I have seen on our own farm over time is the home grown “crop insurance” that comes with diversification in our growing system. More diversity makes it likely that at least some of our cash crops will provide sufficient income for our farm to keep doing what it does from year to year.
More ways to add diversity in crop rotations
It is easy to simply assign one year to each annual crop in a rotation. While this is certainly better than growing the same crop in the same place year after year, a farm can do better than this.
Part of a crop rotation could include a perennial crop that is foraged for two to three years by animals. Our farm has included poultry on some of our production fields as part of our rotation. This makes perfect sense because we can ask our laying hens to spread their own manure for fertility in future years; it saves some labor and provides necessary nutrients.
Many farms also include cover crops in their rotations. These are crops that are introduced to cover the soil, but are not intended to be harvested. For example, we have planted tillage radish in the fall to help loosen the soil for the following season. The radish crop is terminated by the cold weather and we don’t need to do any additional work other than adjust our rotation so we don’t grow other crops from that family in the same location.
Why is this important?
The simplest crop rotation is no rotation at all. Many row crop farms in the United States grow the same crop in the same location year after year. The only way this can happen is to rely heavily on synthetic fertilizers and pesticides to prop up soils that are being abused by this approach and to keep diseases and pests at bay.
The introduction of diversity through methods such as crop rotation and intercropping helps us to break this cycle of dependence. Diversity and complexity in our growing systems are natural ways to maintain the health of our soils and increase the resilience of our crops. These are techniques that require the ingenuity of those who would be stewards of the land, and they do not require purchased inputs from the pesticide industry.