In order to select the optimal concentration of dazomet for old apple orchard soil fumigation

a pot experiment was carried out. The pot experiment was designed to have 4 concentration treatments

i.e. Treatment CK(0

untreated old orchard soil)

Treatment T1(0.02‰)

Treantment T2(0.1‰)

Treatment T3(0.5‰). All the pots in the experiment were filled up with the same soil from a 25 years old apple orchard. And the dynamic change of soil culturable microorganisms number(bacteria

fungi)

community structure and diversity index under different concentrations dazomet fumigation was studied using microorganisms plate culture

a real-time quantitative PCR（qPCR）

biolog-Eco and terminal restriction fragment length polymorphism (T-RFLP) methods.The results showed that the soil microorganism number significantly decreased with the increase of applying dazomet content. At 30th day

compared with the control

the (T1

T2

T3) bacteria number reduced by 57%

81% and 87%

the fungi number reduced by 75%

81%

100%. The gene copy numbe of Fusarium proliferatum which analysised by Real-time PCR was reduced by 57%

80%

85%. Biolog-Eco showed microbial activity (using the average well development

AWCD) recovered gradually in the soil after fumigation

but the applied concentration was higher

the recovery speed was slower. At 30th day

AWCD of T1(0.02‰) significantly lower than that of CK

the processing AWCD had no difference with CK when 60 days

but AWCD of T3(0.5‰) was still significantly lower than that of CK until 90 days. T-RFLP principal component analysis showed that all treatments changed the soil microbial community structure in old apple orchard. Dazomet concentration was greater

the more significant change of microbial community

but community structure was not very stable under high concentration of dazomet fumigation. Cluster analysis showed that the community structure of T1 and T2 became more and more similar to that of CK over time

while the community structure of T3(0.5‰) always kept low similarity with CK. Microbial diversity analysis showed that Shannon index and Margalef index of T3(0.5‰) significantly reduced

Simpson index improved. In conclusion

0.5‰ dose of dazomet fumigation could significantly reduce microbial number and activity

change the microbial community and slow the recovery of microorganisms.