Crop rotation refers to a cultivation method in which different crops are planted sequentially in rotation on the same field.
Through crop rotation, soil quality can be improved, diseases, pests, and weeds can be reduced. Increasing crop yield is called the crop rotation effect. As an important agricultural technical measure, crop rotation is widely adopted by countries all over the world, and it occupies an important position in the world’s agricultural development.
1. Reduce the Number of Pathogenic Bacteria
One of the reasons for the serious occurrence of diseases in continuous cropping obstacles is that certain specific pathogens have become the dominant flora in the soil microflora, which ultimately increases the probability of plant diseases.
Through crop rotation, the living environment of pathogens can be changed, causing them to lose their original host or change their living environment, thereby reducing disease.
Wheat rot disease is a global wheat root disease, which can lose 33% of spring wheat production during the high-incidence period. Early and timely removal of plant residues carrying pathogens,
Planting wheat every other year or planting two other crops and then planting wheat is one of the effective measures to control wheat rot. When the barley-ryegrass-potato rotation is combined with beneficial microbial fertilizers and aerobic fermented fertilizers, the incidence of potato canker and scabs can be reduced by 18.0%-33.0%.
Studies have found that when corn is the previous crop, the number of actinomycetes and Trichoderma in the rhizosphere soil increases, which inhibits soil-borne diseases of the subsequent peanuts.
2. Improve Soil Microbial Population Structure
Crop rotation can increase the diversity of microbial groups, reduce the number of harmful microorganisms in the soil, and significantly change the number and composition of soil microorganisms.
The continuous cropping years increase, the number of bacteria and actinomycetes in the soil of American ginseng increases, the number of fungi decreases, and the bacterial diversity increases.
The natural recovery period of the microbial community in the American ginseng soil is at least 2 years. After the rotation of American ginseng and amorpha. Bacteria, actinomycetes, nitrogen-fixing bacteria, and cellulolytic bacteria showed a gradual increase, the number of fungi decreased, and the total number of microorganisms increased.
3. Improve Soil Nutrients
Crop rotation can increase soil nutrients and improve soil quality. Research on crops has found that with the rotation system of legume crops, soil nutrient status can be significantly improved.
Compared with monocropping, the yield of cereals and legumes increased after rotation and the soil nitrogen content increased. In addition to the main contribution of rotation legumes to biological nitrogen fixation, cereal crops can also obtain nitrogen from the rotation soil or legume residues to reduce the application of mineral nitrogen in the soil;
Crop rotation also has a certain effect on improving the status of phosphorus in the soil and increasing the content of organic matter. Some legumes such as chickpeas can activate the fixed phosphorus in the soil through organic acids such as citric acid and malic acid secreted from the roots.
Through the differences in plant root distribution and nutrient absorption and utilization, crop rotation can not only adjust and improve the soil structure but also solve the nutrient imbalance caused by continuous cropping.
4. Avoid Autotoxicity
The substances secreted by the rhizosphere of some plants are toxic to the growth of themselves or other plants, and crop rotation can reduce their harm. For example, American ginseng and perilla rotation can effectively overcome the influence of phenolic acid self-toxic substances in the continuous cropping obstacle of American ginseng. Compared with the soil without rotation, the survival rate and root weight of American ginseng increased by 26.8% and 11.5%.
Utilizing the bactericidal properties of allelochemicals secreted by some plant roots, using them as the front crop can reduce the occurrence of crop diseases in the subsequent crops.
Garlic can obviously inhibit the germination of melon wilt spores, mycelial growth, biomass, and spore formation. In the field, the rotation of garlic and melon significantly reduced the damage of fusarium wilt, the incidence was reduced from 50% to 10% during continuous cropping, and the number of spores of pathogenic bacteria that survived in the soil was also significantly reduced.
Allelochemicals and environmental factors play an important role in the growth and development of subsequent crops. Giving full play to or avoiding the role of allelochemicals secreted by plant roots can not only save production costs but also reduce environmental pollution caused by the use of chemical agents.