Crop rotation is based on growing a series of different types of crops in the same area in sequential seasons. The planned rotation may vary from a growing season to a few years or even longer periods. Farmers usually do not follow one specific crop rotation plan. They choose to alternate crops based on their individual requirements, possibilities, environmental conditions and budget.
For example, one farmer might follow a seven-year crop rotation scheme as follows:
- First year: Corn
- Second year: Oats
- Third to fifth year: Alfalfa or clover
- Sixth to seventh year: Fallow or use as a pasture for livestock
Another farmer might choose a simpler scheme:
- First year: Carrots
- Second year: Wheat
- Third to seventh year: strawberry
Even though these two plans differ, they both stick to the general rule of crop rotation. The basic principle is to plant leguminous crops (e.g. pulses, alfalfa, clover) after the cereal crops (e.g. wheat, oats, maize, rice), and then leave the land undisturbed for at least one season.
- Weed control and improvement in crop yields
Integrating both broadleaf and grass crops into a rotation will help in utilizing various herbicides with different modes of action at different times of the year, which will better control some of the problem weeds. Rotations using only Roundup Ready crops may not be an option, as regular use of Roundup can cause some Roundup-resistant weed problems.
Introducing crops that are not Roundup Ready will play an important role in the control of weeds.
Yields are higher when a crop different than the preceding crop is grown. Research has shown that, even with the same fertility levels, significant positive yield differences can be achieved through rotation.
- Prevention of soil erosion
Soil erosion has become a widespread problem around the world today. Extensive erosion causes many problems in modern agriculture, including the loss of topsoil, harmful agricultural runoff, and an increased risk of flooding and landslides due to restricted capacity of soils to retain water.
While soil erosion wreaks havoc on intensively-cultivated farmlands, rotation planting helps to prevent all these negative impacts. According to a 13-year period research of a crop rotation system in Iowa, crop rotation reduces erosion by almost 90 percent compared to traditional maize and soy monoculture farming.
Amongst the reasons why crop rotation reduces erosion are:
- Reduced soil disturbance: Longer periods of reduced disturbance to soils. When the land is left fallow, the soil is not tilled at all. This is the complete opposite to intensive monoculture crop farming, where the land is often tilled every year.
- Cover crops: Cover crops are planted on the land for most of the rotation cycle. Plants hold soil in place and minimize its direct exposure to rain and wind – the main factors causing erosion.
- Diverse root systems: Combination of crops with different length and shapes of root systems ensures that soil particles hold better together.
- Spacing: Each crop has different space demands. Some crops grow when rows have larger spaces in between; other crops require smaller or no rows at all. The period of leaving some parts of soil directly exposed is shorter in crop rotation planting, because the subsequent crop will most likely need shorter spacing or none at all.
- Healthy soils: Improved soil structure and water holding capacity prevents the damage done by heavy rainfall or flooding – the common triggers of erosion.
- Control of soil borne pests and diseases
When rotation is practiced by farmers it ensures that the various types of pests that affect the produce are controlled as they are not able to survive and attack certain types of plants in the field. Rotating therefore is the most suitable way of controlling the spread of diseases. Leaf Blight is a good example of a disease that has increased over the last several years, and can be reduced by rotating corn and soybeans.
Similar plants tend to have the same pathogens, therefore, crop rotation intercepts the pest life cycle and their habitat. A cycle entails similar events that happen in constant rotation, meaning that the infestation of pests and diseases happens in season.
- Reduces pollution
The constant application of fertilizers to soils causes soil leaching, which is the excessive buildup of nutrients in the soil to a toxic and harmful level that do not allow plants to grow well. Crop rotation increases the nutrients in the soil, thus allows the farmer to plant crops successfully without the need of applying fertilizers.
Crop rotation also reduces the constant infestation of crops by pests and diseases, stopping the need of spraying the crops with pesticides. Although pesticides work very well on crops, they contain dangerous chemicals that can build up in the soil to harmful levels. The chemicals may also find their way in water ways when the rain water washes them off from the farms and the buildup results in the rise in levels of toxicity in the water.
Increase in the use of forages in crop rotations as a residue management while higher carbon the soil content helps combat climate change.
- Better Soil Structure
Annual crop rotations affect the root structure over a period. 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.
Better soil structure creates several macrospores and enables new root growth of next crops. Improving the soil organic matter and nutrient pools is also a benefit of crop rotation that results in increasing water-holding capacity of the soil.
A certain research shows that many of these organisms decompose organic matter, resulting in nutrient release to the crop.
- Water conservation
In combination with improved soil structure, crop rotation enhances water holding capacity of soils. Soils with good structure allow fast and thorough absorption of water. Some of this water is readily taken by crops, while the additional water is retained deeper in pores to be drawn by plants during a drier season.
In this situation, crop rotation helps conserve water in the farms, because the need of irrigation is decreased.
Some additional benefits of better water holding capacity are:
- Reduction of runoff and loss of nutrients from soils
- Lower risk of flooding because soils act as a sponge
- Prevention of erosion
- Groundwater reservoir replenishment
- Striving crops
Based on these results, it is clear that crop rotation could help tackle the widespread chemical contamination of the environment we live in. The practice is, therefore, beneficial to our health and could be one of the ways to maintain our food security while minimizing negative effects of agriculture on ecosystems. This only highlights the importance of crop rotation in creating a sustainable future.