| Due to the long-term continuous crop in Ningxia area,the Brassica campestris L.growth is slow,the yield decreases,the quality deteriorates,and there is a serious continuous crop disorder.To investigate the causes of continuous crop barriers in Ningxia,this study was conducted in five areas of Ningxia,Pingluo County,Helan County,Yongning County,Wuzhong City and Guyuan City,where one-year-old Brassica campestris L.and their soils were used as controls,and those with 2-5,6-9 and 10-13 years of continuous crop and their soils were studied.Determination of physicochemical properties,enzyme activity and microbial community changes in inter-root soils of Brassica campestris L.,as well as agronomic traits and quality of Brassica campestris L.,and a comprehensive risk health evaluation of continuous cropping soils of Brassica campestris L..(1)Effect of continuous crop on the physicochemical properties of Ningxia’s Brassica campestris L.for Hong KongIn this study,the physical properties,soil nutrients,and soil elements of a continuous crop of Brassica campestris L.were analyzed,and the results showed that long-term continuous cropping led to a significant increase in soil bulk weight and a significant decrease in total soil porosity(p<0.05).With the increase of continuous crop years,the soil showed an acidification trend and the soil conductivity was inconsistent in different places,while long-term continuous crop in Pingluo and Wuzhong led to an increase of soil conductivity in Brassica campestris L.,while long-term continuous crop caused a significant decrease of soil conductivity in Helan,Yongning and Wuzhong(p<0.05).Soil organic matter,total nitrogen and alkaline nitrogen decreased significantly(p<0.05),while effective potassium increased significantly(p<0.05)after long-term continuous crop of Brassica campestris L.soil in all regions.upward trend,while in Wuzhong and Guzheng showed a downward trend.With the increase in the number of years of continuous crop,the total carbon and total organic carbon of rapeseed soil showed a significant decreasing trend(p<0.05).Through the study of soil elements,it was found that long-term continuous cropping significantly increased the contents of As,Cd,Cr,Mn,Zn,Cu,Tl,Ni and Co in the soil of Brassica campestris L.,and continuous cropping led to the accumulation of these heavy metals.(2)Effect of continuous crop on soil enzyme activity of Ningxia’s supplying Brassica campestris L.to Hong KongThe study of soil enzyme activity in different years of continuous crop in different places revealed that continuous crop had a large effect on soil enzyme activity in all places.The long-term continuous crop caused a significant increase in the soil urease activity(p<0.05),while alkaline phosphatase activity,catalase activity and cellulase activity showed a decreasing trend with the increase of continuous crop years,while sucrase showed different performance in different places,with the increase of continuous crop years,in which Pingluo showed a downward trend and then an upward trend,while Helan,Yongning and Gu-principle showed an upward trend and then a downward trend.Wuzhong,on the other hand,showed a continuous decreasing trend.(3)Effect of continuous crop on soil microorganisms of Ningxia Brassica campestris L.for Hong KongAccording to the changes of physicochemical properties and enzyme activities in the soil of Brassica campestris L.,the soil of Wuzhong area,which was most obviously affected by the continuous crop barrier,was selected as the research object to determine the changes of microbial community structure diversity and richness,and the results showed that long-term continuous crop changed the richness and diversity of microbial community in the soil of Brassica campestris L.inter-root,and the richness of bacterial community decreased and the diversity increased,while the fungal community The abundance and diversity of fungal communities decreased,and the abundance of harmful pathogenic bacteria increased while the abundance of beneficial bacteria such as Nitrospirae and Ascomycota decreased in the soil.Correlation analysis of soil microbial communities and environmental factors revealed that total phosphorus,effective phosphorus,fast-acting potassium,sucrase,urease and alkaline phosphatase activities had highly significant(p<0.01)effects on changes in the communities of Acidobacteriota and Nitrospirae,and pH,total phosphorus,effective phosphorus,fast-acting potassium,sucrase,urease and alkaline phosphatase activities had highly significant(p<0.01)effects on changes in the communities of Basidiomycota.(4)Effect of continuous crop on the yield and quality of Ningxia Brassica campestris L.for Hong KongA study on the yield and quality of cabbage in different years of continuous crop in various Brassica campestris L.growing areas found that continuous crop significantly reduced the yield and quality of Brassica campestris L..The length,thickness,above-ground dry and fresh weight,below-ground dry and fresh weight,and mu yield of Brassica campestris L.shoots showed a decreasing trend as the number of years of continuous crop increased;the soluble sugar content,soluble protein content,and vitamin C content also showed a decreasing trend as the number of years of continuous crop increased,while the nitrate content showed a significant increasing trend at 10-13 years of continuous crop.(5)Comprehensive risk evaluation of Ningxia’s soil for continuous crop of Brassica campestris L.for Hong KongThe results of the comprehensive health evaluation of the soil showed that As,Cr,Cd,Mn,Tl,Zn and Cu appeared to accumulate to a certain extent in the soil of Brassica campestris L.with more than 10 years of continuous crop,but did not exceed the risk control value of soil contamination of agricultural land and appeared to be mildly polluted,and only Cd appeared to be a medium potential ecological risk of 32%,with no non-carcinogenic risk and carcinogenic risk.In summary,long-term continuous crop leads to the deterioration of soil environmental changes in Brassica campestris L.,causing a decrease in yield and deterioration in quality;in a comprehensive view,there is no higher grade ecological risk in the soil of Ningxia Brassica campestris L.growing area,and the environmental conditions of farmland soil production are good;continuous crop increases the accumulation of soil heavy metals and ecological risk. |
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