Effects of Continuous Cropping on Soil Microbial Flora and Research Progress of Continuous Cropping Obstacle Reduction Techniques

Continuous cropping can bring economic benefits in a short time and meet the growing demand of agricultural products such as grain,but long-term continuous cropping will accelerate soil degradation,lead to the reduction of crop yield and the increase of disease rate,and destroy the balance of soil microbial structure.Therefore,it is not conducive to the sustainable development of soil ecosystem.In this paper,the problems caused by continuous cropping,such as imbalance of soil microbial flora,decrease of biodiversity,accumulation of root exudates and their effects on soil fertility and crop growth,were summarized,and some measures were suggested to alleviate the obstacles of continuous cropping,such as reasonable rotation,adjustment of intercropping planting mode and application of biological fertilizers.Moreover,the paper also looked forward to the development trend of continuous cropping obstacle reduction techniques,including the integration and application of biological techniques,the promotion of green ecological techniques and the application of intelligent management system.This study provides theoretical basis and technical support for the research of continuous cropping obstacle reduction techniques and promote the healthy and sustainable development of modern agriculture.

Research Progress on Effects of Continuous Cropping on Soil Microbial Florae and Its Restoration

Continuous cropping has become a common form of agricultural production at present, but with the increase of continuous cropping years, continuous cropping obstacles such as soil-borne diseases and plant growth potential decline are becoming more and more common. At present, the causes of continuous cropping obstacles and continuous cropping restoration have become a hot issue in agricultural research. This paper summarized the effects of continuous cropping obstacles on soil microbial community structure and main technical methods to repair continuous cropping obstacles, such as agricultural measure management, microbial balance adjustment and soil improvement, aiming to provide theoretical reference for protecting the sustainable utilization of soil ecosystem and ensuring the stability of crop production.

Impact of Continuous Cropping on Soil Phenolic Acid Substances and Research Progress on Continuous Cropping Obstacle Reduction Techniques

At present,long-term continuous cropping in agricultural production has formed a relatively common development trend.With the increase of continuous cropping years,soil phenolic acids are also affected to varying degrees.This paper summarized the effects of continuous cropping on soil phenolic acids and the research progress of continuous cropping obstacle reduction techniques,aiming at providing theoretical basis and technical support for the research of continuous cropping obstacle reduction techniques and promoting the healthy and sustainable development of modern agriculture.

Effects of Allelochemicals on Root Growth and Pod Yield in Response to Continuous Cropping Obstacle of Peanut

Continuous cropping(CC)obstacle is a major threat in legume crops production;however,the underlying mechanisms concerning the roles allelochemicals play in CC obstacle are poorly understood.The current 2-year study was conducted to investigate the effects of different kinds and concentrations of allelochemicals,p-hydroxybenzoic acid(H),cinnamic acid(C),phthalic acid(P),and their mixtures(M)on peanut root growth and productivity in response to CC obstacle.Treatment with H,C,P,and M significantly decreased the plant height,dry weight of the leaves and stems,number of branches,and length of the lateral stem compared with control.Exogenous application of H,C,P,and M inhibited the peanut root growth as indicated by the decreased root morphological characters.The allelochemicals also induced the cell membrane oxidation even though the antioxidant enzymes activities were significantly increased in peanut roots.Meanwhile,treatment with H,C,P,and M reduced the contents of total soluble sugar and total soluble protein.Analysis of ATPase activity,nitrate reductase activity,and root system activity revealed that the inhibition effects of allelochemicals on peanut roots might be due to the decrease in activities of ATPase and NR,and the inhibition of root system.Consequently,allelochemicals significantly decreased the pod yield of peanut compared with control.Our results demonstrate that allelochemicals play a dominant role in CC obstacle-induced peanut growth inhibition and yield reduction through damaging the root antioxidant system,unbalancing the osmolytes accumulation,and decreasing the activities of root-related enzymes.

Effects of Different Agricultural Managements on Characteristics of Soil Microbial Community under Continuous Cropped Strawberry(Fragaria ananassa Duchesne)

[Objective] The objective of this study was to investigate the effects of different agricultural managements on soil microbial population,activity,functional diversity and soil enzyme activity in continuous mono-cropping field of strawberry.[Method]A field plot experiment was carried out to evaluate characteristics of soil microbial community by soil enzyme analysis,microbial cultivation and Biolog analysis.[Result]The results showed that bacteria population proportion,the ration of bacteria to fungi,microorganism amount,AWCD,soil dehydrogenase activity,the Shannon,Simpson,and Mcintosh indices of soil microbial communities were obviously increased under strawberry-rice rotation,soil solarization with rice bran,and calcium cyanamide（CaCN2）treatments,in addition,soil urease activity was significantly increased under strawberry-rice rotation and soil solarization with rice bran treatment,when compared with no fertilization.When compared with conventional fertilization treatment,strawberry-rice rotation and soil solarization with rice bran both significantly increased AWCD and Mcintosh index of soil microbial communities,meanwhile respectively increased soil urease and dehydrogenase activity.PCA analyses suggested that carbon utilization of soil microbial communities under strawberry-rice rotation,soil solarization with rice bran,and calcium cyanamide treatment was obviously different from that of conventional fertilization and no fertilization treatment.[Conclusion] strawberry-rice rotation and soil solarization with rice bran were effective agricultural managements to control soil biological degradation under Continuous Cropped Strawberry.

Analysis of the Causes of Continuous Cropping Obstacles for Atractylodes macrocephala Koidz in Pingjiang County and Its Control Methods

First at all, it introduced the concept and the damages of continuous cropping obstacle. Then, it analyzed the causes of continuous cropping obstacles for Atractylodes macrocephala Koidz. In the end, in order to provide guidance for pro- moting sustainable development of Atractylodes macrocephala Koidz industry in Pingjiang County, it put forward some control methods for eliminating continuous cropping obstacles of Atractylodes macrocephala Koidz, including breeding varieties with high resistance; applying rotation cropping and intercropping reasonable; rational fertilization and soil disinfection; introducing antagonistic bacterial and eliminating au- tointoxication.

Effects of Tobacco-rice Continuous Cropping Years on Soil Physicochemical Properties and Tobacco Yield and Quality

To investigate the effects of long term tobacco-rice continuous cropping on soil nutrients and flue-cured tobacco leaf yield and quality, the soils of different con- tinuous cropping years were selected in tobacco-rice multiple system of Hengyang. Some important indexes, including pH, contents of organic matter and available nu- trients of N P K, contents of medium trace elements of soil samples, and contents of main chemical components of flue-cured tobacco samples were detected for fur- ther analyzing. The results showed that pH value of moderate continuous cropping soil（≤7 years） was more coordinated, in addition, leaf yield and quality of flue-cured tobacco were contained, and the sugar-nicotine ratio and potassium-chlorine ratio were proper. However, under long-term continuous cropping （≥10 years） condition, the soil became acidification, and yield and output value of flue-cured tobacco de- clined. It was suggested that improving soil quality by planting green manure or keeping fallow after continuous cropping 7 years in tobacco-rice system.

Investigation and Analysis of Continuous Cropping of Flue-cured Tobacco in Henan Province

The continuous cropping of flue-cured tobacco in the major producing areas of Henan Province by designing questionnaire, fieldwork, enquiry and phone calls, mails, and other forms, the data were obtained then classified and analyzed. The results showed that the main planting areas of flue-cured tobacco were in Nanyang, Xuchang, Luoyang, Sanmenxia, Pingdingshan, and Luohe where were the major producing areas of succession cropping of flue-cured tobacco with percentage of 20%-40% for three years and over three years, and a few places up to 50%. Morbidity was common with wide distribution, and the main diseases were black shank, viral disease, and black rot. It proved that tobacco was not suitable for continuous cropping. Both of tobacco disease and pest rate and mortality significantly increased by more than 40% under continuous cropping for three years and over three years, and the yield and quality of flue-cured tobacco also decreased after continuous cropping. For many places, the tobacco yield started to decrease in the second year of continuous cropping, and after three-year cropping, the yield decreased in the range of 9%-24%. Continuous cropping for a long time would make a serious decline in the quality of tobacco, resulting in non-economic benefits. Therefore, in order to reduce the occurrence of diseases and economic loss in tobacco production, it is recommended to avoid continuous cropping, or to adopt appropriate measures to control tobacco continuous cropping obstacles in the unavoidable case.

A comprehensive analysis of the response of the fungal community structure to long-term continuous cropping in three typical upland crops

Certain agricultural management practices are known to affect the soil microbial community structure;however,knowledge of the response of the fungal community structure to the long-term continuous cropping and rotation of soybean,maize and wheat in the same agroecosystem is limited.We assessed the fungal abundance,composition and diversity among soybean rotation,maize rotation and wheat rotation systems and among long-term continuous cropping systems of soybean,maize and wheat as the effect of crop types on fungal community structure.We compared these fungal parameters of same crop between long-term crop rotation and continuous cropping systems as the effect of cropping systems on fungal community structure.The fungal abundance and composition were measured by quantitative real-time PCR and Illumina MiSeq sequencing.The results revealed that long-term continuous soybean cropping increased the soil fungal abundance compared with soybean rotation,and the fungal abundance was decreased in long-term continuous maize cropping compared with maize rotation.The long-term continuous soybean cropping also exhibited increased soil fungal diversity.The variation in the fungal community structure among the three crops was greater than that between long-term continuous cropping and rotation cropping.Mortierella,Guehomyces and Alternaria were the most important contributors to the dissimilarity of the fungal communities between the continuous cropping and rotation cropping of soybean,maize and wheat.There were 11 potential pathogen and 11 potential biocontrol fungi identified,and the relative abundance of most of the potential pathogenic fungi increased during the long-term continuous cropping of all three crops.The relative abundance of most biocontrol fungi increased in long-term continuous soybean cropping but decreased in long-term continuous maize and wheat cropping.Our results indicate that the response of the soil fungal community structure to long-term continuous cropping varies based upon crop types.

Effects of Continuous Cropping of Panax notoginseng on the Properties of Rhizosphere Soil

[Objective] This experiment aimed to investigate the effects of continuous cropping of Panax notoginseng on the properties of rhizosphere soil. [Method] A total of 12 rhizospheres oil samples were collected in the fields continuously cropped with P. notoginseng for different years and the soil properties including pH value, contents of available N, available K, available P,total N, total K, total P and organic matter were determined. [Result] With the increase in the number of years of continuous cropping, seven soli indices: soil pH value, organic matter content, total N, total P, total K, available P and available K gradually increased, while available N showed a gradual downward trend. The contents of organic matter content, total N, total P, total K,available P, available K and available N after three years of continuous cropping were increased by 74.93%, 65.85%, 123.82%,18.78%, 341.67%, 120.16% and-32.16%, respectively, indicating that continuous cropping of P. notoginseng resulted in nutrient enrichment in rhizosphere soils. The pH value and available N in IBC(soil inside the border check) and UBC(soil under the border check) were higher than that in BBC(soil beside the border check), suggesting that the soil was gradually alkalized due to the continuous cropping of P. notoginseng. [Conclusion] These results suggest that pH change and nutrient imbalance may be the obstacles to the continuous cropping of P. notoginseng.

Effects of Se on Reducing Membrane Lipid Peroxidation of Soybean under Continuous Cropping Stress

Reports the effects of selenium on lipid peroxidation of soybean under continuous cropping stress.Results of pot culture and plot experiment showed that appropriate amount of Se addition increased the activity of glutathione peroxidase (GSH-Px) significantly,and cleared away the excessive free radicals existing in soybean plant under continuous cropping stress,decreased the concentration of malonaldehyde(MDA),which is the end product of lipid peroxidation,maintained the perfection of chloroplast and mitochondrion structure,enhanced the resistance of continuous cropped soybean,and therefore increased the dry weight of seedlong and yield.

Changes in Soil Enzyme Activity and Nutrient Content in Different Years of Continuous Cropping Tobacco Fields

In order to find out changes in the main fertility indicators of continuous cropping tobacco fields in Henan Province with years of continuous cropping,5 typical tobacco fields( Jia County,Shaoling District,Fangcheng County,Xiangcheng County,and Song County) were studied. Indicators in question included activity of main enzymes( sucrase,urease,catalase,and acid phosphatase),p H value,organic matters,total nitrogen,available phosphorus and available potassium. The results indicate that in most tobacco fields,the activity of sucrase and urease increased in two years of continuous cropping,later,it showed a declining trend with increase in years of continuous cropping; in some fields,it directly declined with increase in years of continuous cropping; the activity of catalase increased in two years of continuous cropping,later,it showed a declining trend with increase in years of continuous cropping,and it became stable after three years of continuous cropping;generally,the activity of acid phosphatase declined with increase in the years of continuous cropping within 3 years continuous cropping,later,it became stable. Except Fangcheng County,the soil p H value of other districts( counties) generally declined with increase in years of continuous cropping,and it was in the range of 5. 6-6. 8. With the increase in continuous cropping,the soil organic matters( SOM) in tobacco fields of Jia County and Song County declined,changes of SOM in tobacco fields of Fangcheng County and Xiangcheng County were not obvious,and SOM showed the trend of first decline then rise in Shaoling District. In most tobacco fields( Jia County,Xiangcheng County,and Song County),the total nitrogen showed a declining trend; in Shaoling District,it showed a trend of first decline then rise; in Fangcheng County,it showed a rising trend. The available phosphorus firstly slightly declined then rose in tobacco fields of Shaoling District and Song County; it showed a trend of first rise then decline in Jia County; there were no obvious changes in Fangcheng County and Xiangcheng County. Changes in the available potassium were different in tobacco fields. In sum,there are certain rules for changes in soil enzyme activity and nutrient content in tobacco fields in Henan Province,but changes are not completely the same. It is concluded that the site conditions and farming activities exert a certain influence on soil enzyme activity,p H value,organic matters,and nitrogen,phosphorus and potassium content. Therefore,to solve obstacles in continuous cropping of tobacco fields,different regions should take different measures.

Effects and Mechanisms of Oil Cakes on the Growth of Cucumber (Cucumis sativus L.) Under Continuous Cropping System

Fxperiments on the effect of soil amendment with rape (Brassica chinensis L.) seed cake, cotton (Gossypium hirsutum L.) seed or sesame (Sesamum indicum L.) seed cake on the growth of cucumber seedlings under a continuous cropping system were conducted in a greenhouse environment. The results indicated that two applications of sesame seed cake (0.1 and 0.5 %, w/w) increased the growth of cucumber, but the rape oil cake showed a negative effect at a rate of 1.5% (w/w). The sesame seed cake was separated into four fractions (Ⅰ, Ⅱ, Ⅲ and Ⅳ) according to the polarity, and all four fractions had a positive effect on the growth of cucumbers under a continuous cropping system. Fraction number Ⅲ was isolated into 25 proportions by silicon column, and only oleic acid, palmitic acid and octadecanoic acid were identified in proportion 10 by GC-MS in which 93.3% was oleic acid and palmitic acid. The oleic acid had a significant and positive effect on cucumber growth under salt stress at the level 30 mmol and showed slight resistance to several pathogenic fungi.

Variation and Dynamics of Soil Nematode Communities in Greenhouses with Different Continuous Cropping Periods

Continuous cropping in greenhouses can result in root-knot nematode outbreaks resulting from imbalances in the soil nematode community.However,the changes in soil nematode communities in greenhouses with continuous crop production are unclear.We compared soil nematode communities in greenhouses after 2 years(2-yr)and 10 years(10-yr)of continuous crop production by 18S rDNA high-throughput sequencing.Compared with the 2-yr greenhouse,soil in the 10-yr greenhouse showed acidification,nutrient accumulation and salinization.Bacterial-feeding nematodes(BF)were dominant in the 2-yr greenhouse over the whole growing season,but plant-parasitic nematodes(PP)were the dominant group in the 10-yr greenhouse during the late growing season.Meloidogyne gradually became the dominant group and had a relative abundance of 70.9%(maximum)in the 10-yr greenhouse.Rhabditidae,with relative abundance ranging from 99.8%to 26.8%,was the predominant group in the 2-year greenhouse.Forβ-diversity,hierarchical clustering analysis,unweighted UniFrac principal component analysis(PCA)and principal co-ordinates analysis(PCoA)all revealed that soil nematode communities in the two types of greenhouses were significantly different.Redundancy analysis(RDA)showed that soil nematode communities in the 10-yr greenhouse were related to high soil organic material,total nitrogen,electrical conductivity and disease index of root-knot nematodes.Fisher’s exact test and Pearson’s correlation coefficients revealed that Meloidogyne contributed to themain differences in soil nematode communities between the two types of greenhouses.Population dynamics of Meloidogyne were divided into dormant phase,low-level increasing phase and exponential phase during the whole season.The soil nematode communities within the 2-yr and 10-yr greenhouses had significant variation and different dynamics.This work contributes to a deeper understanding of changes in the soil nematode community in greenhouses with different continuous cropping duration.

Effects of Dongshengbao Liquid Organic Fertilizer on Soil Improvement of Continuous Cropping Cucumber

[Objective] The effects of Dongshengbao liquid organic fertilizer on soil im- provement of continuous cropping cucumber and the growth conditions of the cu- cumber were studied to provide the scientific basis for solving the problem of con- tinuous cropping of vegetable soil. [Method] The soil of continuous cropping was sampled. The soil EC, pH, nutrient contents and cucumber height, dry weight of aboveground part and leaf area etc were studied with the method of potted cucum- ber test. [Result] Soil EC applied by Dongshengbao liquid organic fertilizer reached 0.93 mS/cm, and decreased by 27.91% compared with the contrast. Soil pH reached 5.89, and increased with 0.86% compared with the contrast. Dry weight of aboveground part, plant height and leaf area of cucumber were increased by 283.08%, 242.12% and 254.02% compared with the contrast. The incidence rank of cucumber Didymella bryoniae was below grade 2. Soil EC applied by compound fertilizer reached 1.53 mS/cm, and increased by 18.6% compared with the contrast. Soil pH reached 5.09, and decreased by 12.84% compared with the contrast. Dry weight of aboveground part, plant height and leaf area of cucumber were increased by 32.31%,-37.24% and 26.20% compared with the contrast. The incidence rank of cucumber Didymella bryoniae was above grade 2. [Conclusion] The organic fertilizer could solve the problems of soil salinization and soil acidification of continuous crop- ping, improve the resistance ability of Didymella bryoniae and promote the plant growth.

Microecological Prevention and Control Technology of Facility Strawberry Continuous Cropping Diseases and Its Application Effects

In order to actively develop green ecological strawberry, the authors have studied integrated microecological prevention and control technologies of strawberry continuous cropping diseases, including increasing soil biomass and solar high temperature disinfection during strawberry greenhouse leisure period in summer, biological fertilizer (agent) treatment before colonization, root irrigation treatment with biocontrol agent, as well as appropriate amount of fulvic acid and cytex after colonization, forming a supporting technical system for the microecological prevention and control of soil-borne diseases in facilities. The demonstration application in production shows that the technology has the functions of restoring and enhancing soil biological fertility, enriching beneficial microbial flora, antagonizing harmful bacteria, significantly promoting the growth and development of strawberry, reducing the incidence of soil-borne diseases, reducing the use of chemical fertilizers and pesticides, promoting the early ripening and high yield of strawberry, significantly improving the quality and flavor of strawberry, reducing the risk of pesticide residues, and boosting consumer confidence, which further improves the economic benefit, social benefit and ecological benefit, with good application prospect in production.

Physical-biological Collaborative Prevention and Control of Facility Strawberry Continuous Cropping Diseases

The aim was to develop green strawberry varieties,control soil-borne diseases from facility strawberry continuous cropping,improve the safety and quality of strawberries and promote the healthy and stable development of the strawberry industry. Based on the production practices in recent years,we summarized the physical-biological collaborative prevention and control technology for the disease of facility strawberry continuous cropping facilities,established the technical goals,the main types of soil-borne diseases,and the physical-biological collaborative control prevention and control technologies,mainly including the specific methods and technical points of solar high temperature disinfection technology and biological bacterial fertilizer（ agent） treatment technology.

A review of research progress on continuous cropping obstacles

Due to the increasing global population and limited land resources, continuous cropping has become common. However, after a few years of continuous cropping, obstacles often arise that cause soil degeneration, decreased crop yield and quality, and increased disease incidence, resulting in significant economic losses. It is essential to understand the causes and mitigation mechanisms of continuous cropping obstacles(CCOs) and then develop appropriate methods to overcome them. This review systematically summarizes the causes and mitigation measures of soil degradation in continuous cropping through a meta-analysis. It was concluded that not all continuous cropping systems are prone to CCOs. Therefore, it is necessary to grasp the principles governing the occurrence of diseases caused by soilborne pathogens in different cropping systems, consider plant–soil-organisms interactions as a system, scientifically regulate the physical and chemical properties of soils from a systems perspective, and then regulate the structure of microbial food webs in the soil to achieve a reduction in diseases caused by soilborne pathogens and increase crop yield ultimately. This review provides reference data and guidance for addressing this fundamental problem.

Impact of Anaerobic Soil Disinfestation Treatment on the Properties of Tomato Continuous Cropping Soil

To investigate the impact of anaerobic soil disinfestation(ASD)treatment with different processing duration on tomato continuous cropping soil,a total of eight treatments were designed,which included two treatment temperatures of 10℃ and 30℃,and four treatment times of 3,4,5 and 7 weeks(w).The results showed that whether the temperature was 10℃ or 30℃,the pH values,TOC and available K contents in the soil treated by the ASD method were significantly increased(P<0.05),while the EC values and NO_(3)^(-)contents in soils treated by ASD were significantly reduced compared with the untreated group(P<0.05).The Fusarium oxysporum population in soils treated by ASD decreased with the extension of the treatment time.When the treatment temperature was 30℃,the effect on the removal of the NO_(3)^(-)that had accumulated in soils treated by ASD was significantly better than the treatment temperature of 10℃(P<0.05).When soil was treated by ASD for more than 5 w at 30℃,the NH4+content in soil was significantly increased(P<0.05)compared with the untreated soil.In conclusion,NO_(3)^(-)accumulation in soils could not be completely eliminated with treatment by ASD,even when the treatment time at 10℃ was prolonged.Whether the treatment temperature was 10℃ or 30℃,the F.oxysporum population in soils treated by ASD decreased significantly with the extension of the treatment time to more than 5 w compared with treatment only for only 3 w.

Effect of Autotoxicity and Soil Microbes in Continuous Cropping Soil on Angelica sinensis Seedling Growth and Rhizosphere Soil Microbial Population

Objective To study the effect of autotoxicity and the co-effect of autotoxicity and soil microbes from continuous cropping soil on Angelica sinensis growth, root yield and content of essential oils, and soilmicrobalpopulation. Methods The pot experiments were conducted upon A. sinensis seedlings in continuous cropping soil. At the different growth stages, we determined the seedlings in growth parameters, root yield, content of essential oils, ethanol extract, and cultivable microbial populations in rhizosphere soil. Results A. sinensis seedlings were significantly inhibited in growth, root yield and quality. Compared with the control, the composition and structure of soil microbes were changed and the diversity indexes of bacteria functional groups were reduced in rhizosphere soil ofA. sinensis. A. sinensiscropping problems were more seriously after the treatment with combination of autotoxicity and soil microbes than with autotoxicity alone. Conclusion The autotoxicityand soil microbes from continuous cropping soil of A. sinensis could cause the continuous cropping obstacle together.