Effects Of Monocropping Duration And Fertilization Regimes On Tomato Growth And Root-knot Nematodes

Due to the continuous monocropping of greenhouse vegetables and the large amount of mineral fertilizer input,especially the excessive application of nitrogen(N)fertilizer,caused the severe problems such as soil acidification,secondary salinization,imbalance of soil nutrient and frequent soil-borne diseases.In particular,the prevention and control of root-eating pests is a difficult task,and root-knot nematodes disease is one of the most world-wide distributed soil borne diseases.In this study,the effects of the interaction between continuous monocropping and fertilization on root-knot nematodes disease and the relationship between root-knot nematodes and tomato nutrient uptake were systematically investigated by integrating field and pot experiments.The effects of increasing continuous monocropping tomato on soil physicochemical properties,plant growth,nutrient uptake,plant defense enzyme activity and root-knot nematode disease by field sampling analysis,and compared the differences between organic fertilizer and mineral fertilizer treatment.Results showed that:(1)With the increase of monocropping duration,soil pH and the content of dissolved organic carbon(DOC)decreased,and EC value and the content of nitrate increased,reaching significant differences for mineral fertilizer treatment(p<0.05).(2)The root-knot index increased with the extension of tomato cropping,and organic fertilizer did not reduce the disease incidence of root-knot nematodes under the same continuous monocropping years.(3)Continuous monocropping decreased of tomato aboveground biomass,while increased root biomass.The application of organic fertilizer was more beneficial to plant growth than mineral fertilizer.(4)Continuous monocropping increased the total length,surface area,volume and average diameter of tomato root,and these values were the largest in continuous monocropping for four years with organic fertilizer application.(5)The contents of total N,phosphorus and potassium in the shoots were significantly decreased,while in the roots were significantly increased with the increase of monocropping years.(6)Continuous monocropping resulted in severe peroxidation of tomato cytomembrane and damage of protective enzyme system,but the organic fertilizer could enhance the resistance of plants.In order to mechanistically understand the relationships between root-knot nematode and plant nutrient uptake.The second instar larvae of root-knot nematodes with different densities(0,1000,5000 ind plant-1)were inoculated after the field soil was collected and sterilized.Results showed that:(1)With the increase of the inoculation density of root-knot nematode,soil pH increased first and then decreased,while the reverse was true for EC and nitrate content.(2)With the increase of the inoculation density,the root-knot nematode disease of tomato aggravated,and fertilization can aggregate such effect.(3)Both the increase of inoculation density of root-knot nematodes and fertilization could reduce aboveground biomass and increase the root biomass and average diameter of the root significantly.(4)Both the root-knot nematodes and fertilization promoted the accumulation of N in the root,reduced the uptake of N in the shoots.And with the increase of the inoculation density of root-knot nematode,both the uptake utilization efficiency and agronomic efficiency of N in the plant decreased.(5)The content of total N and total phosphorus in the root knots or the roots excluded root knots were significantly higher than those in the healthy roots after tomato infected with root-knot nematode,especially in the root nodules.Based on the soils of continuous monocropping for one year and four years,the effects of different fertilization measures(no fertilizer,mineral fertilizer,reduced 30%N application,vermicompost and mineral fertilizer,reduced 30%N fertilizer and vermicompost)on soil properties,plant growth,nutrient uptake,and the responses of root-knot nematodes were investigated.Results showed that(1)Vermicompost and mineral fertilizer co-application or N fertilizer reduction tended to increase soil pH,reduce the content of nitrate,and increased the content of DOC.And the combination of N fertilizer reduction with vermicompost could enhance this effect.(2)For the soils that have been continuously monocropping for the fourth year,single mineral fertilizer increased the number of root-knots or root-knot index,while vermicompost and mineral fertilizer co-application significantly reduced it.Especially the combination of N fertilizer reduction with vermicompost reached a significant difference level(p<0.05).(3)Vermicompost and mineral fertilizer co-application or N fertilizer reduction could improve the nutrient uptake of shoots and promote the growth of plant increase,partly due to the reduced N accumulation in roots via suppressing root-knot nematodes.In conclusion,this study deepened the understanding of root-knot nematode disease and its effect on plant growth and nutrient uptake under continuous monocropping and fertilization,and provided scientific basis for developing repair measures and prevention and control strategies for continuous cropping obstacles of vegetables.