Studies On Mechanism Of Garlic (Allium Sativum L.) Replanting Problem And Ameliorative Effect Of EM

With rapid population growth and socio-economic development, a raise in demand for some specific crop has brought modern agriculture characteristic with single-crop large-scale cultivation. As a widespread agriculture phenomenon, continuous cropping has caused great harm to agriculture and sideline many countries. Garlic is not only internationall loved health vegetables, but also an important seasoning and pharmaceutical raw materials. In china, it is an important raw material and export vegetables. Along with the continuous development of the production, continuous cropping phenomenon in the main production areas of garlic is a growing problem.In this test, in order to investigate the mechanism of continuous cropping of garlic and provide the scientific basis for easing garlic cropping obstacles, we have studied continuously cropped garlic from three aspects. In this test, in order to investigate the mechanism of continuous cropping of garlic and provide the scientific basis for easing garlic cropping obstacles, we have studied continuously cropped garlic from three aspects: first, allelopathy of root exudates and straw aqueous extracts of garlic; second, influence of continuous cropping garlic on rhizosphere microbial environment, yield and quality; and last, EM help relieve cropping obstacles of garlic. The main research results were summarized as follows:1. In short-term (5 years and 10 years), the number of bacteria, actinomycetes and various physiological groups from garlic rhizosphere soil rose dramatically; fungi'increased slowly; and soil enzyme activity increased gradually; soil microenvironment obtained improved; Garlic yield and quality were increased significantly. But in long-term (15 years and 20 years), the number of bacteria, actinomycetes and various physiological groups from garlic rhizosphere soil decreased; soil enzyme activity reduced; but the number of fungi raised; soil microenvironment turned to deterioration; garlic yield and quality were decreased significantly, continuous cropping obstacles was obvious.2. Garlic root exudates obtained by tissue culture method inhibited the germination and growth of genus allium crop seed such as welsh onion, onions and leek, and inhibition increased with increasing concentration of garlic root exudates. The main substances of garlic root exudates were identified by GC-MS as follows: 2,2'-methylenebis[6-(1,1-dimethylethyl) -4-methyl]-Phenol, dioctyl phthalate, 5-octanoyl-pyrimidine-2,4,6(1H,3H,5H)-trione, eicosanoic acid, ferulic acid, 9-hexade- cenoic acid, tetradecanoic acid and diallyl disulphide.3. In this study, the high concentration of garlic straw aqueous extracts inhibited the germination (embryo and radicle) of tomato, pepper and cucumber, but the low concentrations displayed promoter action. All concentration designed in this experiment restrained the germination rates of tomato and pepper, but had no obvious effect on cucumber'germination rate; garlic straw aqueous extracts showed inhibition on the germination of onion and welsh onion.4. Five spots were observed on TLC plates under UV light, with Rf values of 0.12(spot 1),0.43(spot 2),0.64(spot 3),0.74(spot 4) and 0.88(spot 5). Of these, only three spots suppressed lettuce emergence, with spot 2, spot 3 and spot 5, respectively; and spot 1 and spot 4 promoted lettuce emergence. Several compounds were detected in the five spots collected by TLC as shown. The first spot consisted of 9-octa- decenoic acid, methyl este, diacetone alcohol, caprolactam, N,N-dibutyl- formamide. The second spot contained diethyl phthalate and a derivative of phenol (2,2'-methylenebis[6-(1,1-dimethylethyl) -4-methyl]-Phenol). 1,8-diazacyclotetradecane-2, 9-dione, biphenyl and 1-methyl- naphthalene were detected in the third spot. Several esters were observed in the fourth spot, including 8-octadecenoic acid methyl ester, hexadecanoic acid methyl ester and 7,10-octadecadienoic acid methyl ester. In the fifth spot, aromatic compounds and aliphatic ester were identified.5. EM (Effective Microorganisms) helped improve structure of rhizosphere microbial of continuously cropped garlic, promote beneficial microbial activities and normal reproduction and inhibit harmful pathogens growth and reproduction. Compared with the control, EM enhanced enzyme activities in garlic rhizosphere soil, reduced the accumulation of harmful substances, improved soil fertility. regulation of physiological metabolic functions crops, improve crop yields and improve crop quality. And the physiological metabolism of garlic was regulated, yields and quality were improved by use of EM.