| In this study,the greenhouse vegetable planting demonstration area of rugao agricultural science research institute was used as the research platform.Because of the poorly physichemical properties,unbalanced nutrient content,secondary salinization,defective aeration,acidification,disturbance of enzyme activity and decline of cucumber yield,the biological organic fertilizer was applied only once in the first quarter of the cucumber plant to study the effects of biological organic fertilizer on soil physical characteristics,fertility,enzyme activity,organic carbon mineralization,plant nutrient absorption and utilization and cucumber yield in four seasons.The correlation analysis and path analysis were used to study the index changes of the soil properties in the process of continuous cropping cucumber.Principal component analysis was used to clarify the difference of soil quality level among different treatments.The mechanism of biological fertilizer on alleviating the occurrence of soil continuous cropping obstacles,balancing soil nutrients and regulating soil enzyme activities under high-intensity continuous cropping system was explored,which provided some scientific basis for biological fertilizer in improving soil fertility and promoting sustainable agricultural development.At the same time,this experiment explored the nutrient utilization rate of NPK under different soil fertility levels,studied the effect of applying bio-organic fertilizer to prevent and control continuous cropping obstacles and the soil non-biological influencing factors of vegetable crop nutrient utilization,proposing new measures to regulate the obstacles of continuous cropping.The main results were as follows:(1)The bio-organic fertilizer can reduce the soil bulk density and increase the total soil porosity during cucumber continuous cropping.The soil bulk density in control increased by 5.19%over time.Bio-organic fertilizer can reduce the soil bulk density and increase the total soil porosity.The bulk density of bio-organic fertilizer treatments decreased by 9.63%～20.71%and total soil porosity increased by 10.46%～24.39%compared with control.With the increase of biological organic fertilizer content,soil moisture content,saturated water content,field capacity,wilting coefficient,available water content and saturated hydraulic conductivity increased.The application of biological organic fertilizer can also optimize the aggregate particle size distribution.The 0.5～1 mm and 0.25～0.5 mm aggregate increased with the increasing of biochar application.While the<0.25 mm aggregate content declined with biological organic fertilizer increasing in the same season.The average mass diameter of soil aggregates increased with the application of bio-organic fertilizer,and the fractal dimension of soil aggregates decreased gradually.(2)The bio-organic fertilizer can decrease soil acidification and secondary salinization during cucumber continuous cropping.There were no significant change in soil pH of B2 treated with bio-organic fertilizer,while the soil electrical conductivity of B1 and B2 reduced by 8.57%～12.60%and 9.71%～11.69%,respectively,compared with CK from the first season to the fourth season of cucumber ripening period.The application of bio-organic fertilizer decreased the contents of total nitrogen,total phosphorus and total potassium and improve the contents of soil organic matter in the process of cucumber continuous cropping.The soil organic matter in B1 and B2 treatment increased by 39.30%～83.91%,compared with CK in the mature stage of cucumber in the same season.The application of bio-organic fertilizer can also increase the content of available nutrients in soil of continuous cropping cucumber.The peak value of soil nitrate nitrogen,ammonium nitrogen and available phosphorus content were found in B2(20t ha-1),the nitrate nitrogen,ammonium nitrogen content in bio-organic treatment increased by 6.15%～21.97%and 2.63%～14.71%,as compared with control.In the process of planting four consecutive quarter of cucumber,applying of 20 t/hm2 biological organic fertilizer in all treatments increase content of soil available phosphorus between bio-organic treatment and control increased from 5.98%～10.78%in the first quarter to 17.74%～22.52%in the fourth quarter.(3)One-time application of bio-organic fertilizer can increase the activity of urease(SUR),catalase(SCAT),sucrose(SSC)and phosphatase(SPP)in soil of continuous cropping cucumber,indicating that bio-organic fertilizer can maintain the activity of soil microorganisms for a long time.The activities of soil urease,catalase,sucrose and phosphatase in different treatments of the same cucumber mature stage were shown in the order of B2>B1>CK.The soil microbial biomass carbon and nitrogen contents in each treatment were determined in these 4 seasons.It can be seen that from the first season to the fourth season of maturity of cucumbers,the soil microbial biomass carbon and nitrogen contents in the treatment with bio-organic fertilizer presented a change rule in first increase and then decrease.The soil microbial biomass carbon and nitrogen contents were all higher than those in the control treatment.At the mature stage of cucumber in the fourth quarter,the soil microbial biomass carbon and nitrogen contents in B2 treatment increased by 13.90%and 38.79%,respectively,compared with the control.The differences reached a significant level.(4)In the process of continuous planting cucumber for 4 seasons after one-time application of bio-organic fertilizer,the application of bio-organic fertilizer can significantly increase the soil total organic carbon,activated carbon pool,slow effect carbon pool and inert carbon pool.With the increase of successive cropping seasons of cucumber,the proportion of soil inert carbon pool in the bio-organic fertilizer treatment increased gradually,which enhanced the soil carbon sequestration capacity.After continuous planting cucumbers for 4 seasons,the accumulated soil organic carbon mineralization amount and the average daily mineralization amount in the bio-fertilizer treatment were higher than those in the control treatment.The soil organic carbon mineralization amount reached the maximum rate at the 10th to 15th days of the culture experiment,in which the average daily mineralization amount of organic carbon in the B2 treatment was 15.98 mg/kg.(5)Bio-organic fertilizer can increase the cucumber yield by 3.93%～36.04%in the process of continuous planting for 4 seasons,which indicated that bio-organic fertilizer can slow down the cucumber yield decline caused by continuous cropping.Bio-organic fertilizer can promote the absorption and utilization of nitrogen and potassium,especially phosphorus in cucumber plants and fruits.With the increase of the application amount of bio-organic fertilizer,the nutrient utilization rate of nitrogen,phosphorus and potassium increased by 25.27%～53.25%,by 36.59%～63.62%and by 33.45%～50.54%,respectively.(6)There were significant correlations between soil biological indicators(4 kinds of enzyme activity and soil microbial biomass carbon and nitrogen content)and bulk density,porosity and soil fertility indexes and there were extremely significant positive correlation between soil organic matter content and soil biological indicators.Meanwhile,there were significant correlations between the four kinds of enzyme activity and soil total organic carbon,active carbon library,slow carbon library and inert carbon library in the process of continuous cucumbers cropping(P<0.05).The path analysis results showed that the influences of soil urease and inverses activity on soil organic carbon mineralization were directly or indirectly.The principal component analysis results showed that all soil indexes can explained by 3 principal components,the contribution rate of these three components was 85.69%,where PC1 explained 62.14%of the total variance,PC2 and PC3 explained 17.34%and 6.21%,respectively.The results from PC1 showed a preponderance of soil bulk density,nutrient content and enzyme activity.The results showed that 20 t/hm2 bio-organic fertilizer is the optimal fertilizer application rate for improving soil quality. |
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