Sweet potato has been planted in Guancun village, Dazhai town, Yangling, Shaanxi Province for three consecutive years, with high annual output and good benefits in the first year. The second year's output decreased, and the harm of sweet potato stem nematode disease was found one after another, with less rot and little influence on the overall benefit; In the third year, sweet potato stem nematode disease broke out, rotted seriously and suffered heavy losses, and finally gave up planting.
Why does the same sweet potato produce such a huge difference? A piece of land can be planted for eight years in a row: if it is planted for only three years in a row, the yield will be reduced, the pests and diseases will be aggravated, and the rotten potatoes will fail. So what is the reason for continuous cropping? Can sweet potatoes be repeated?
The technical term of continuous cropping is called "continuous cropping obstacle" It refers to planting the same crop on the same plot for many years, which leads to poor crop growth, aggravated pests and diseases, and decreased yield and quality.
There are four theories about the causes of continuous cropping obstacles at home and abroad: pathogen accumulation, autotoxicity, salinization and nutritional deficiency.
After years of research, Liu Cunshou of Northwest A&F University showed that among the four reasons of continuous cropping obstacle, nutrient deficiency, especially organic nutrient deficiency, is the fundamental reason of continuous cropping obstacle, autotoxicity is the result of trace element nutrient deficiency stress, and disease aggravation is due to the decline of crop immunity.
Different crops have different physiological characteristics, and the continuous cropping performance of different crops is not the same. Plants with secondary metabolites, such as ginseng, have more prominent autotoxicity; The disease aggravation of watermelon and sweet potato, which are mainly primary metabolites, has become the main reason.
Continuous cropping is a systematic damage to the rhizosphere environment of plants, which comes from the imbalance of nutrient elements, the accumulation of a large number of bacteria, the accumulation of toxins discharged by crops in the roots, the abnormal soil microbial flora, the imbalance of soil nutrients and the proliferation of nematodes, thus destroying the growth environment of roots, thus causing some diseases and a large number of yield reductions.
The effects of continuous cropping on rhizosphere soil microorganisms of sweet potato and the control measures of continuous cropping obstacles were studied in the long-term location experimental area of sweet potato. The results showed that after continuous cropping of sweet potato, the total number of soil microorganisms decreased, the number of bacteria and actinomycetes decreased and the number of fungi increased, and the soil changed from "bacterial type" with high fertilizer to "fungal type" with low fertilizer. Continuous cropping aggravated the occurrence of sweet potato diseases and insect pests, which led to the reduction of sweet potato production. After the application of anti-continuous cropping agent, the number of bacteria in rhizosphere soil of sweet potato continuous cropping increased and the number of fungi decreased. However, compared with continuous cropping, the overall soil microbial flora is still quite different. Anti-continuous cropping agent can improve the overall yield of sweet potato, but it can't effectively inhibit the occurrence of pests and diseases, so it can't significantly improve the effective yield of sweet potato.
In the case of no disease in sweet potato field, sweet potato is barren-tolerant, and sweet potato is not afraid of continuous cropping. Of course, if a piece of land is planted with sweet potatoes for the first time, the first yield will definitely be the highest.
Disease is the most important reason for continuous cropping of sweet potato. If diseases occurred last year, such as sweet potato stem nematode, root rot, root rot and black spot, continuous cropping should be considered.
The most economical and effective measure to reduce the yield of sweet potato in continuous cropping land is to carry out reasonable rotation and stubble replacement. If crop rotation and stubble cleaning cannot be carried out, stubble cleaning agent can be applied, and then combined with chemical agents to control pests and diseases.
To solve the problem of continuous cropping of sweet potato, we should not rely solely on formula fertilization and chemical agents, but should control it from the following aspects:
1, select seedlings
The selection of high generation virus-free seedlings requires clean seedlings, clean water and pure ground.
2. Choose disease-resistant varieties.
According to the cause of the disease, select the corresponding disease-resistant varieties. The main diseases of continuous cropping are root rot, root rot and nematode disease, and the application of corresponding disease-resistant varieties is the most effective technical measure.