Influence Of Biocharon Retention Of Nutrition And Fractionations Of Heavy Metal In Soil

Leaching of mineral nutrients from paddy soils is generally serious in southern China,which leads to a substantial waste of fertilizers and prevalence of water.Meanwhile,the extensive mining and smelting plenty of heavy metals from underground into open on the surface of the earth environment for a long time,causing serious pollution of soil.However,is known about the effect of biochar incorporation on fertility of subtropical red paddy soil,and have a very strong capacity to absorb and fix the mentals.In this study,water hyacinth derived biochar?BCW?and Fe-modified BCW?BCW-Fe?were prepared.The impact of BCW on soil nutrients level?N/P/K?and acid leaching loss was investigated with1-12month incubation followed by column test.Based on a full characterization of the physiochemical properties of the two biochars,the immobilization of As/Hg/Cd with BCW and BCW-Fe was investigated with an acidic and multi-metal contaminatedsoil from a gold mining site.The main result are as follows:?1?The results showed significant increases in soil pH,CEC and total amount of N and K with BCW addition,but a notable decrease in available P was determined with prolonged incubation time.In column leaching test with simulated acid rain,BCW addition significantly reduced the total leached amount of NH₄⁺-N,NO₃^-N in different conditions,However the total leached P was little increased with prolonged incubation in dry soil and total leached K was increased by20.8-62.7%,which could be mainly originated from the enriched water-soluble K in BCW.?2?Characterization showed that the magnetic biochar made the mass fraction of H,O have increased 29.2%and 12.6%respectively,and specific surface have increased from 23.17m²·g^-1 to 55.11m²·g^-1,the total pore volume have increased from 0.13m³·g^-1 to 0.30m³·g^-1,the percentage of iron have increased from 1.49%to 14.53%.?3?With the incorporation of BCW and BCW-Fe,soluble As in the neutral and acidic extractions was significantly reduced by 84.9-91.6%and 64.9-96.8%,respectively.Meanwhile,Hg levels in the extractions were decreased from 0.04-0.03?g·L^-1 to 0-0.02?g·L^-1 with BCW and BCW-Fe addition.Regarding Cd,the most prominent immobilization was determined with BCW under neutral condition and BCW-Fe under acidic condition.?4?With the application of the two amendments,an apparent transformation of the easily exchangeable and carbonate-associated As,Hg,Cd to their non-labile Fe/Mn oxide and organic bound forms has been unraveled with the sequential extraction.For example,with the addition of BCW and BCW-Fe,the more labile pool of As including the easily exchangeable and carbonate-associated fractions was decreased by0.3%and 3.1%,respectively.In parallel,Hg in these two fractions was reduced by 2.3%and 3.4%,respectively,in the BCW and BCW-Fe treatments.Similarly,the more labile Cd was decreased by 7.7%and14.9%with the above two treatments.These results indicate the important potential of BCW in retaining major soil nutrients and reducing their leaching from red paddy soils over one year.At the same time the effective and simultaneous immobilization of soil As,Hg,Cd can be achieved with this Fe-modified biochar derived from water hyacinth under acid precipitation,which also provides a strategy for an effective management of invasive species.