Garlic (Allium Sativum L.) Continuous Cropping Influence On Soil Microflora, Physical And Chemical Characteristics And Root Exudates

Continuous cropping is one of the main reasons for the destruction of farmland ecological environment; it influences the agricultural production seriously. Continuous cropping obstacle was affected by many factors in the system of soil-pathogens-plant. In this paper, the soil microflora, soil physical and chemical properties, the composition of soil organic compounds and the allelopathy of root exudates were studied to explore the reasons of continuous cropping obstacle. From this paper, some conclusions are acquired as follows:1.In the five main producing areas, the number of soil fungi was lager after continuous cropping, and the number of soil bacterium was reduced. The influence of continuous cropping on the number of soil actinomycetes was different in different areas. This showed that the impact on soil actinomycetes was complicated, may be resulted by the soil environment, microbial flora and other factors.2. In the five main producing ares, only Pizhou’s continuous cropping soil pH slightly higher than the non-continuous cropping soil samples, in the other four ares, the continuous cropping soil pH were lower than the non-continuous cropping soil samples. Continuous cropping of garlic lead to the soil pH decreased. But the soil pH was obviously also affected by other factors.Combined with the conditions of five main producing areas of garlic, continuous cropping caused the contents of available N, P and K decreased, nutrients deficient in soil, affected the normal growth of the garlic.3. In the soil which planted garlic, the main organic compounds are alkenes, alcohols, esters, phenols, benzene and so on. There were some different between the four soil samples, but no regular pattern were found. There were2,6-Di-tert-butylphenol and diisobutyl phthalate in the four soil samples, they are allelochemicals. Studies have shown that garlic root exudates contain these two allelochemicals. It showed that the accumulation of garlic root exudates in soil may affect the normal growth of Garlic, resulted in continuous cropping obstacles.4. Garlic root exudates not only inhibited the germination of Cabbage seed, but also inhibited Shallot and Chinese chive, which belong to the same genera with Garlic. The low concentration of Garlic root exudates played a catalytic role on the germination of onion, may be related to some of the nutrients in the root exudates provide an effective energy to seeds.