Influence of garlic continuous cropping on rhizosphere soil microorganisms and enzyme activities.

Objective The objective of the experiment is to study the effect of garlic continuous cropping on rhizosphere soil microbial and enzyme activities.Method With the soils cropped garlic for 0(control),5,10,15 and 20 years as test materials,a pot experiment was conducted to investigate the influence of garlic continuous cropping on rhizosphere soil microbial and enzyme activities.Result With the increasing of continuous cropping years,fungi number in rhizosphere soil increased gradually,the number of 20 years continuous cropping was 2.88 times higher,but the number of other microorganisms and the enzyme activities in the garlic rhizosphere soil were increased at the short-term (5-10 years) continuous cropping.The quantities of bacteria and actinomycetes were increased by 8.72% and 25.81%,respectively,and in the meantime,the ammonifier,nitrifying bacteria,and aromatic compounds-degrading bacteria increased by 5.63,11.60 and 3.35 times.The root exudates of successively cropped garlic for 10 years increased the activities of catalase,polyhenoloxidase,urease,phosphatase and sucrase in rhizosphere soil by 26.67%,41.67%,203.13%,23.73% and 43.65%,respectively,but long-term (15-20 years) continuous cropping showed a downward trend.Correlation coefficients between ammonifying bacteria and urease,polyphenol oxidase,bacteria and phosphatase,total microbe quantity were significant at 0.05 levels,and correlation coefficients between aromatic decomposing bacteria and urease,catalase,phosphatase and total microbe quantity were significant at 0.01 levels.Conclusion The balance of rhizosphere soil microbial flora was destroyed and the enzyme activities of rhizosphere soil decreased in a long period of time (from 15 to 20 years),the obstacles of continuous cropping were obvious.