Effect Of A Novel Biochar Based Compound Fertilizer On Immobiliztion Of Heavy Metal In Farmland Soil-wheat(Triticum Aestivum).

Soil heavy metal pollution is a serious global concern,adversely affecting crop production and human health.To provide an environmental-friendly remediation technique with low cost,high heavy metal immobilization efficiency and fertility effects,we synthesized a biochar-based compound fertilizer?BCF?with corn straw biomass,diatomite,triple superphosphate and urea under different temperatures?300�C,450�C and 600�C?and mixture proportions?5:1:1:x and 10:1:1:x?.Field experiments were conducted to investgate the impact of ten kinds of fertilizers?including single biochar,BCF and chemical fertilizer?on soil heavy metal availabilty and its effect on the accumulation in wheat plants,as well as its application effects on soil p H,CEC,and SOM were evaluated.The stabilization mechanisms were explored through specific surface and porosity analyzer,Fourier transform infrared?FTIR?,field emission scanning electron microscope?FE-SEM?images and energy-dispersive X-ray spectroscopy?EDS?analysis.The results showed that:?1?Laboratory characterization with different instruments and methods showed that the surface structure of the single biochar gradually broke up with the increase of temperature.In addition,with the increase of pyrolysis temperature,the specific surface area and total pore volume of all biochar materials significantly increased,while the average pore diameter and acid functional groups significantly decreased.After the modification of diatomite and triple superphosphate,a large amounts of Si,P and N were embedded into the surface of BCF.Compared with single biochar,some new functional groups appeared on the surface of BCF,such as N-H,PO43-,Si-O-Si and Si-H.Moreover,the specific surface area and pore volume of BCF significantly increased,and the surface appeared to be coarser,and more small pores appeared atop the large pores.?2?With the treatments of single biochar and BCF,the properties of farmland soil were significantly improved,hence bringing soil p H value,CEC and organic matter content upgrading.Meanwhile,the effect of biochar materials on the soil properties enhanced with the increase of applied amount and pyrolysis temperature.In particular,when B600 was applied at the dose level of 1800 kg?ha^-1,compared with CK group,the soil p H value and SOM increased by 3.03% and 23.01%,respectively,and increased by 7.18% and 29.50%,respectively,compared with FK group.When B5PN600 was applied at 1800 kg?ha^-1,the CEC of treated soil was the most prominent,increased by 14.59% and 14.61% respectively compared with CK group and FK group.?3?The contents of Cd and Zn in the soil of wheat field are much higher than the risk control values of agricultural land.The proportion of DTPA-heavy metal to the total heavy metal can effectively reduced by applying Bx and BCF,the proportion of Cd,Zn and Pb decreased proportionally with the increase of applied amount and pyrolysis temperature.All biochar materials can effectively reduce the proportion,specifically in the order of B5 PNx > B10 PNx > Bx.Notably,when applied at 1800 kg?ha^-1,the proportion of availability Cd,Zn and Pb in the soil treated with B5PN600 was the lowest,which was significantly lower than that of 16.16% and 16.24%,9.13% and 9.47%,11.24% and 11.66% in CK group and FK group,respectively.?4?Bx and BCF,as exogenous nutrient sources,provided P,N,Si and other exogenous nutrients needed for wheat growth,thus promoted the growth of wheat,including grain weight,1000-grain weight and biomass.The increasing application and pyrolysis temperature of biochar materials have been accompanied by an increase of the biomass of different wheat tissues.B5 PNx had the most significant effect on growth,particularly,when B5PN600 was applied at 1800 kg?ha^-1,the grain weight,1000-grain weight and biomass of wheat were all the maximum,increasing by 38.11% and 16.22%,10.96% and 6.38%,32.52% and 24.58%,44.10% and 23.93%,respectively,compared with CK group and FK group.?5?Heavy metal contents in different wheat tissues,compared with CK and FK,significantly decreased with the application of BCF and single biochar.In particular,B5 PNx had the most significant effect on inhibiting heavy metal uptake in wheat plants.Under 1800 kg�ha^-1 addition levels,compared with CK group,B5 PNx reduced Cd,Zn and Pb content in wheat root by 43.19%,22.03% and 48.63%,by 24.30%,36.59% and 14.01% in seed shell,by 26.58%,18.10% and 34.27% in grain,respectively.Additionally,by 32.21%,18.44% and 33.63% in wheat root,by 17.50%,32.22% and 13.79% in seed shell,by 26.52%,15.26% and 31.08% in grain,respectively,compared with FK group.The bioconcentration factors of Cd,Zn and Pb in wheat root decreased by 37.46% and 35.84%,29.58% and 33.30%,21.91% and 26.14%,respectively,compared with the CK and FK groups,when B5PN600 was applied at 1800 kg?ha^-1.meanwhile,the bioconcentration factors of Cd,Zn and Pb in wheat grain decreased by 25.62% and 20.11%,25.87 and 28.59%,35.98% and 37.70%,respectively,compared with the CK and FK groups.It is thus clear that B5PN600 treatment had significant effect on inhibiting Cd uptake in wheat root and grain,compared with the CK and FK groups.BCF and Bx can effectively inhibit the bioavailability and mobility of heavy metal in farmland soil,thereby inhibiting the accumulation of heavy metal by wheat roots and grains,ultimately reducing the risk of heavy metal accumulation in wheat edible parts.It could be concluded that B5PN600,as a low-cost soil additive,can be considered as the most promising tool to immobilize heavy metals and improve soil,meanwhile having optimum inhibation of metal accumulaition in wheat tissues assisting the growth of plants.