we depend on it for our food, for clean water and clean air. But for a lot of our land, the responsibility to maintain it falls on farmers who use it to plant crops, grow food and livestock. They are our land managers; and so responsibility for our land falls inevitably on their shoulders even though for them a primary concern is earning an income from that land. But are the two incompatible? The answer is no, so long as the farmer is encouraged to invest in agricultural methods that are environmentally-friendly. Most of these methods can also secure a better yield which translates into higher profits for the farmers.
A great example of such a method is crop rotation. For example, a recent study found that modified three- and four-crop farming systems could be scaled up and adopted widely in the US Corn Belt states, generating benefits to farmers and taxpayers worth hundreds of millions of dollars. The analysis, “Rotating Crops, Turning Profits: How Diversified Farming Systems Can Help Farmers While Protecting Soil and Preventing Pollution,” builds on a long-term study at Iowa State University, known as the Marsden Farm study¹.
Crop rotation is one of the oldest and most effective agricultural control strategies.
It is based on growing a series of different types of crops in the same crop rotation area in sequential seasons. The planned rotation may vary from 2 or 3 year or longer period. What this practice allows for is the replenishment of nutrients in the soil and the control of pests. For example, rice stem borer feeds mostly on rice. If you don’t rotate rice with other crops belonging to a different family, the problem continues as food is always available to the pest. However, if you plant legume as the next crop, then corn, then beans, then bulbs, the insect pest will likely die due to absence of food.
But crop rotation is appealing for more reasons which are worth highlighting. Here are the top ten benefits of crop rotation:
#1 Nitrogen management
Over the past 50 years, nitrogen has been used in large amounts in order to maximize farming production. Too much nitrogen though entails risk for our water supplies and aquatic ecosystems. And this is where crop rotation can play a key role in reducing this risk by improving the availability of soil nitrogen and reducing the nitrogen fertilizer used².
Crop rotation may impact the rate of nitrogen mineralization or conversion of organic nitrogen to mineral nitrogen because of differences in soil temperature, moisture, plant residue, pH and tillage practices. Indeed, research on the impact of long-term crop rotation on soil nitrogen availability shows that planting alfalfa, corn, oat, and soybean significantly increased the mineralized net nitrogen in soil compared with planting continuous corn. Because soil nitrogen mineralization can affect yield, crop rotation thus can be used as a management system to enhance the soil nutrient pool, thereby reducing the use of fertilizers and minimizing the risk of leaching of excess nitrogen³.
#2 Improved soil structure
What we plant in our soil and how we plant it affects the quality of our soil in the greatest of ways. Monocultures are known for depleting soil nutrients but in contrast, annual crop rotations enable a drastic difference in the root structure over a period of time. For crops having either tap or fibrous roots, the diversity in the root structure will enhance the chemical, physical and biological structure of the soil.
Over time, improved soil structure can help increase soil water-holding capacity and development of macro pores in the soil that promote new root growth in following crops. Rotating crops with a high carbon to nitrogen ratio (corn, small grains) with low carbon to nitrogen ratio crops (soybeans) helps establish a diverse population of soil micro-organisms. This improvement in soil microbial populations can lead to more stable soil structure and a decrease in the potential for soil erosion⁴.
#3 Reduced soil erosion
Improvement in soil structure means not only healthier soils, but is also reduces the chances of soil erosion which is very important for farming.
#4 Improved pest and weed control
Rotating different crops allows you to diversify the use of herbicides by selecting chemistries with different modes of action. Alternating herbicide products for several years can lead to better overall weed control and reduce the risk of developing weed resistance. The same applies to some insects²,³.
#5 Improved disease control
When it comes to disease control, the diversification of cropping sequences takes away the host organism and causes a disruption in the annual life cycle of the disease. Brown stem rot, northern corn leaf blight, and Diplodia ear rot are examples of diseases for which crop rotation can be an effective management tool.
#6 Reduced greenhouse gas emissions
By implementing crop rotation, the use of nitrogen fertilizer is drastically reduced which in turn considerably lowers greenhouse gas emissions. The global warming potential of nitrous oxide is much higher than that of carbon dioxide. Reduced synthetic fertilizer also means reduced greenhouse gas emissions from manufacture and transportation².
#7 Reduced water pollution
Given the reduced levels of nitrogen due to the more limited use of fertilizers as well as the increased ability of soil to metabolise natural nitrogen, crop rotation helps reduce water pollution. Diversified rotations with high share of crops and lesser dependence on pesticides bring down the use of pesticides as well as run off into groundwater².
#8 Increased ability to store carbon
Crop rotation practices also help increase soil carbon content through high crop cover periods, reduced frequency and tillage intensity.
#9 Enables the use of green manure cover crops
Green manures are fast-growing plants sown to cover bare soil. They are often used in vegetable gardens as their foliage smothers weeds and their roots prevent soil erosion. When dug into the ground while still green, they return valuable nutrients to the soil and improve soil structure. The main aim of planting green manure cover crops is the purpose of providing nitrogen, cover and for smothering weeds. They are normally cut down before they reach maturity.
#10 The yield bump!
Farmer observations and studies have shown a 10% or greater yield bump for both corn and soybeans, when they are grown in a rotation, compared to either continuous corn or continuous soybeans. Recent research at the University of Wisconsin indicates that the yield bump for these crops may be closer to 19% and that this rotation effect lasts for two years. This is likely due in part to the pest management benefits and soil improvements associated with crop rotation as well as the decrease of typical problems associated with monoculture. Research has also shown that crop rotation is more important for maximizing yield potential in stressful environments³!