Effect Of Digested Pig Slurry Application On Soil Environmental Quality Of Poplar Plantation

Taking human and animal excreta or straw and so on as raw material, biogas slurry isproduced by residue of liquid state through modern anaerobic fermentation engineering. Thisstudy is based on poplar plantation as object, takes biogas slurry which is made of pig manure asraw material, depends on integrated business model of “raise pigs-biogas slurry-using forestland” which is invented by COFCO Corporation and Dongtai forestry center, according to5gradients of15m3（T1）、30m3（T2）、45m3（T3）、60m3（T4）、75m3（T5）which is designedof annual total fertilizing amount of biogas slurry per667m2of poplar plantation, discusses theeffect of different fertilizing amount of biogas slurry on poplar plantation soil environmentquality from EC, microbial biomass carbon and nitrogen, heavy metal and leachate. The studyresult showed that:（1）After using biogas slurry to fertilize soil, its EC had obviously increased, whichpresented outstanding positive correlation relationship between fertilizing amount of biogasslurry and the soil (the minimum of R2is0.840, the max is0.955). However, there is no obviousaccumulation relationship between the conductivities of each other which are both used biogasslurry to fertilize, which is limited on the increase of the content of soluble salt of soil, and notenough so far to produce salt damage on crops.（2）Using biogas slurry to fertilize will improve the content of soil microbial biomasscarbon and nitrogen. On the whole, the distribution of the content of soil microbial biomasscarbon and nitrogen is surface layer（0-20cm）>middle layer（20-40cm）>low layer（40-60cm）。Compared with the processing of CK, the range of the increase on the content of soil MBCof surface layer and middle layer of young poplar plantation is respectively21.32%-161.07%、26.48%-167.62%in April, and is respectively50.12%-183.29%、17.30%-208.75%in September;the range of the increase on the content of soil MBC of surface layer and middle layer of maturepoplar plantation is respectively4.29%-61.62%、3.05%-49.49%in April, and is respectively28.79%-157.67%、53.16%-160.30%in September; Soil MBC of low layer is rarely to beimpacted by using biogas slurry to fertilize. The range of the increase on the content of soil MBNof surface layer and middle layer of young poplar plantation is respectively29.96%-226.95%、37.27%-224.37%in April, and is respectively77.75%-329.19%、41.09%-307.99%in September;the range of the increase on the content of soil MBN of surface layer and middle layer of maturepoplar plantation is respectively6.05%-76.10%、11.21%-60.25%in April, and is respectively36.63%-189.33%、73.58%-234.10%in September.Using biogas slurry to fertilize obviously reduces C/N of microbial biomass of poplarplantation soil, which had changed community structure of edaphon in different degrees, andpromoted the conversion of soil from fungus type to germ type.（3）It will have different effect on the migration and accumulation of heavy metal underdifferent fertilizing amount of biogas slurry. Pb and Cu are accumulated in the surface layer without obvious characteristics of vertical migration, the distribution in soil layer is surfacelayer>middle layer and low layer; the distribution of Zn is surface layer> middle layer>low layer,which is rarely influenced by using biogas slurry to fertilize; the increase of the content of Cr isobviously in surface layer and middle layer, which is easy to migrate from surface layer tomiddle layer; Cd is obviously influenced by elution, and easy to migrate to middle and low layer.Both single factor index assessment results and Nemerow integrated index assessmentresults indicated that using biogas slurry to fertilize soil will bring definite pollution risk to soilbut with low degree. Potential ecological risk index assessment results indicated that the rank ofecological risk degree of5kind of heavy metal is Cd>Pb/Cu>Cr>Zn, synthetical potentialecological risk index RI and weighted risk index P are much less than150, the degree of risk isdepression. Under the fertilizing amount which is adopted by this lab, different content of heavymetal are all within the scope of second level of Environmental quality standard for soils（GB15618-1995）.（4）3months after using biogas slurry to fertilize at the second time, TN, NH4-N and TP insoil leachate which is0m、5m、10m from the T5treatment plot, the content of Pb、Cu、Cr、Zn、Cd are all within the scope of Quality standard for ground water（GB/T14848-93）andStandards for irrigation water quality（GB5084-92）, which had not found obvious polluted index,shallow groundwater had not been damaged, and its quality is up to standard.