The Study Of Mechanisation Of Continuous Cropping In Greenhouse

Soil fertility, bacterial community composition and phenolic acid autotoxicity in continuous cropping soil, was carried out in YangLing(E108°, N 34°), a unique high technical agricultural demonstration zone in Shaanxi Province, northwest China. In older to study the mechanism of continuous cropping in greenhouse, clarify the most sensitive limiting factors of soil nutrients, revelation which is the dominant species in the bacterial community composition, identification the maily phenolic acid and the effect of exogenous phenolic acid applicition on crop growth, In order to provid scientific bases for the mechanism on obstacle of continuous cropping. To evaluate these influences, were used to analyze the rhizosphere and non-rhizosphere soil of strawberry and tomatoes rotation, 2 years continuous strawberry cropping, 4 years continuous tomatoes cropping and 10 years continuous tomato cropping, respectively.The result showed that all the soil samples in our study were alkali at the beginning, but finally were seriously acidified (pH 7.8-7.5, Table1). All the chemical characteristics in rhizosphere soil of RST, CT4, CT10 and CS2 were higher than in non-rhizosphere. Compared with RST, the organic matter and nitrate were increased by 2.8%⁸.8% and in by 2.4%³1.1%, extractable P and extractable K were declined by 5.6%²5.5% and 1.1%¹5.3%. These led to some trace elements deficiency in soil (such as Cu²⁺ and Fe²⁺), which are essential for the plant growth after a long period of continuous cropping. The extractable Cu²⁺, Zn2+, Mn2+ and Fe²⁺ elements in CT10, appeared to be seriously deficient,while the extractable Cu²⁺ content in CT4 is about 43.0% and 34.8% lower, and the extractable Zn2+ content in CS2 is about 36.8% and 35.2% lower. The decline of extractable Mn2+ is not so significantly in CT4 and CS2. It has a significant correlation between trace elements and soil orgnic matter, but not significantly with soil nitrate and extractable P. The activtitys of catalase, phosphatase and urease in non-rhizosphere were higher in rhizosphere soil, while cellulase and saccharase showed a contrary.The number of bacteria, fungi, actinomycetes and 4 kinds microbial physiological groups in rhizosphere were higher than in non-rhizosphere, which shows a significantly rhizosphere effect. It showed a decrease-increase trends in both bacteria and fungi, but the actinomycetes showed linearity increased,CS2, CT4 and CT10 increased by 11.84% and 85.71%, 9.09% and 2.11%, 74.58% and 57.72% in rhizosphere and non-rhizosphere soil, respectively. The nitrobacteria and aerobic nitrogen- fixing bacteria were decreased, while the ammonifying bacteria and aerobic cellulose degrading bacteria shows increased-decreased trendence.The bacterial community composition is affected by continuous cropping and alternative ratation under protected cultivation. terminal restriction fragment length polymorphism (T-RFLP) and clonging of 16S rRNA genes. In ours study, Shannon–Weaver index and the Simpson index for continuous cropping soils were lower than rotational cropping in rhizosphere, however, there is a contradictory tendency in non-rhizosphere, which showed the continuous cropping had an decreasing effect on bacterial diversity in rhizosphere soil, but an increaseing effect in non-rhizosphere soil. The sequences of the clones in CT4-R were mainly belonged to Proteobacteria, Bacteroidetes, Acidobacteria, and Actinobacteria, which all accounted for about 73% of the clones examined in this study. Alphaproteobacteria were overwhelmingly dominant among the identified bacteria, The main genuses are Devosia, Bradyrhizobium and Sphingomonas, which had affinity with succession cropping obstacle.In some other divisions, the Planctomycetes, Firmlute, Gemmatimonadetes, Chloroflexi, Verrucomicrobia, FM7 and unclassified bacteria, which took up 5.88%, 4.41%, 2.94%, 1.47%, 1.47%, 1.47% and 1.47% of OTU, respectively.P-hydroxybenzoic Acid, Vanillic acid, Vanillin and Ferulic Acid were tested in rhizosphere soil of RST, CS2, CT4 and CT10, in which the P-hydroxybenzoic take account for more than 70%. The P-hydroxybenzoic Acid (increased by 48.31%, 93. 93% and 134.95%), Vanillic acid (by 26.94%, 3.11% and 57.52%) and Vanillin (by17.92%, 67.73% and 87.38%) were cumulated, while Ferulic Acid were decreased (by 9.55%, 6.55% and 2.52%), compared with RST, as continuous cropping years increasing. There were some significant correlation between allelochemicals and soil nutrients, allelochemicals and microorganism quantity. (eg. orgnic matter and P-hydroxybenzoic Acid, DTPA- Zn2+ and Vanillin, DTPA-Mn2+ and Vanillic acid, DTPA-Fe²⁺ and P-hydroxybenzoic Acid, bacteria and Vanillic acid, nitrobacteria and P-hydroxybenzoic Acid.)The growth of strawberry and tomatos were accelerated when the allelochemicals consistency were low, but inhibits growth while high consistency. The activity of SOD and POD showed an increased tendency, CAT,MAD showed decreased-increased tendency, with time prolonging. The activity of SOD, POD and CAT showed an parabolic shape relativity after Vanillic acid and Vanillin were applied, but showes much fluctuation after P-hydroxybenzoic Acid and Ferulic Acid were applied, with the allelochemicals consistency increased. In less than 30 days the survival of starwberry about 16.7%, appears to leaf fall off and death, after high P-hydroxybenzoic Acid consistency (eg. D2, D3 and D4). The allelochemicals will do less damage, as it is far from death consistency, with time prolonging(eg. after 30days), becaused of resistance improved of plant.The bacteria, fungi and actinomycetes in soil takes account for 85.50%～98.27%, 1.72%～14.49% and 0.002%～0.067%, after allelochemicals were applied, respectivly.When the Vanillic acid, P-hydroxybenzoic Acid and Ferulic Acid consistency is lower, bacteria and fungi were increasd, but decreased when higher. Decreasing effect was also showed in actinomycetes after Vanillin treatment.