Effects Of Different Fertilization Conditions On Phytoremediation Of Soil Polluted By Heavy Metals

Heavy metals are highly toxic,difficult to degrade,and have a cumulative effect in the soil.The increasing content of heavy metals in the soil will not only lead to a decline in soil fertility and enzyme activity,but also reduce crop yields,and will leaching into the groundwater through rainwater,and may also enter the food chain through plant absorption,thereby threatening human health.The treatment of heavy metal polluted farmland is one of the environmental problems that China urgently needs to solve.Phytoremediation has attracted much attention due to its environmental protection,economy,safety and environmental disturbance.However,due to the long repair cycle and the specificity of super-enriched plants,the research on in situ remediation of plants has been slow.Reasonable selection of enriched plants and appropriate auxiliary measures are the current research hotspots.In this study,two kinds of forage plants,alfalfa and ryegrass,were selected for the contaminated farmland soil around the gold mining area,anddifferent amounts of vermicompost and organic fertilizer were used as auxiliary measures.The effects of fertilizers on plant growth and development were discussed by measuring the physiological indexes and antioxidant enzyme activities of plants.The effects of different treatments on soil restoration were discussed by the content of heavy metals in plants and the content of heavy metals in soil and the proportion of various forms.The research results are as follows:(1)The application of vermicompost and organic fertilizer significantly increased the content of N and P in the soil,and increased with the increase of application rate,but had little effect on the K content in the soil;The organic matter contained in the fertilizer also becomes an important source of soil organic matter,and the increase is proportional to the amount of fertilizer applied;the amount of vermicompost and organic fertilizer can increase the cation exchange capacity of the soil,but there is no significant difference between the various amounts.(2)Alfalfa combined with vermicompost and organic fertilizer can promote the soil urease activity in the mid-planting period.High-dose vermicompost and moderate amount of organic fertilizer can increase soil urease activity,but the application rate of organic fertilizer is too high,which will inhibit enzyme activity.Ryegrass combined with vermicompost and organic fertilizer also promoted the soil urease activity in the mid-planting period,until the high-yield fertilizer in the late stage of planting still promotedthe activity.(3)The application of vermicompost and organic fertilizer can increase the plant height of alfalfa and ryegrass,the dry weight of the aerial part and the dry weight of the root.The effects of vermicompost and organic fertilizer on the activities of SOD,POD and CAT in the aerial parts and roots of alfalfa and rye grass were significant,and the antioxidant capacity of plants could be improved to different extents.(4)The application of vermicompost is beneficial to the accumulation of heavy metals Cu,Zn,As,Hg in the aerial parts and roots of plants,but the amount should not be too large,otherwise the promotion will become inhibitory.However,the application of organic fertilizer has no significant effect on the ability of plant aboveground parts to enrich heavy metals,but high-content organic fertilizers tend to enrich large amounts of heavy metals in plant roots.(5)Alfalfa combined with vermicompost can increase the bioavailability of Cu,Zn and As in the soil(weak acid extraction + reductive state),activate the heavy metals in the soil,and facilitate the absorption and enrichment of plants,but the application rate is not easy to be too large.Alfalfa combined with low-content organic fertilizer increased the bioavailability of heavy metals Cu,Zn and As in soil.Ryegrass combined with vermicompost treatment can improve the bioavailability of soil Cu and As;ryegrass combined with low-content organic fertilizer can assist ryegrass to activate Cu and Zn in soil,but the dosage should not be too large.The Hg content in the soil reached a minimum in August.