The Effect Of Biochar's Application On Short-Range Ordered Minerals In Paddy Soils

The history of rice planting can date back to 7000 years ago in China.Rice,as the largest food crops,the planting area of which has reached as much as 400 million mu.Paddy soil,as the main land use mode in China,is an important resource for safeguarding food security in China.Therefore,it is very essential to study the accumulation and turnover mechanism of soil organic matter(SOM)in soil,which play important roles in enhancing the content and stability of SOM and improving soil fertility.Studies have shown that the formation of mineral-organo associations is the most important mechanism of SOM stability and accumulation.Soil amorphous nano(short-range ordered,SRO)minerals have larger specific surface area and higher bioavailability,the ability of which in stabilizing SOM is 6 times as much as crystalline minerals.Organic associations can be stored in the soil for 250,000 years.Biochar is a kind of solid material,and can be produced by pyrolysis of biomass material under complete or partial hypoxia.Its surface is loose and porous,with high surface area and high pH.It plays significant roles in stabilizing soil organic carbon(SOC)and thus improving soil fertility.However,the mechanism of accumulation and turnover of SOM in SRO minerals at the molecular level is not clear so far.In this paper,soils from a long-term location experiment were used to explore the concentration and form of SRO minerals,combined with synchrotron based techniques and X-ray photoelectron spectroscopy(XPS).Furthermore,using confocal laser scanning microscopy(CLSM),scanning electron microscopy with energy dispersive spectroscopy(SEM),and synchrotron based techniques to explore the minerals to SROs by Shewanella oneidensis transformation.The main results were listed as follows.(1)After 5 years of biochar application(2011-2015),chemical nitrogen,phosphorus and potassium(NPK)fertilization treatment not only resulted in soil acidification,but also decreased the SOM and dissolved organic carbon(DOC)in soil colloid.While BCNPK treatment significantly increased the soil pH,and thus alleviated soil acidification.The soil pH in different treatments were ranked as:The initial soil sample in 2011(6.52)>BCNPK(6.07)>Control(5.94)>NPK(5.67).Besides,the addition of biochar increased the soil total nitrogen,total carbon,C/N,SOM and DOC content,which could increase the capacity of storing the nitrogen and carbon,as well as the soil fertility.(2)The addition of biochar significantly increased the content of total metal and SRO minerals,while decreased the soil soluble minerals.The contents of iron,aluminum and silicon in Control treatment were the 4.0,4.1,and 4.1 times greater than those in BCNPK treatment,respectively.The contents of SOM and DOC were positively correlated with the content of SRO mineral.This result confirmed that the storage and turnover of SOM were consistent with the content of SRO minerals.(3)The main form of carbon in paddy soil colloid were aromatic C/C-C(H).Compared with NPK treatment,BCNPK treatment increased the percentage of aromatic C/C-C(H),and O-C=O,whereas decreased the percentage of C-O and C=O.The results of X-ray photoelectron spectroscopy(XPS)as well as XANES showed that compared with mere NPK treatment,the distribution of Al,Si,and Fe in the SRO minerals(such as ferrihydrite and allophane which have high specific surface area and high adsorption capacity)have increased under BCNPK treatment.(4)Incubation experiment showed that after 72 hours,the biofilm produced on the surface of biochar 's particle by the interaction between biochar and MR-1(M treatment).The biofilm contained a-polysaccharides,lipids,proteins,and total cells,which could provide a favorable microenvironment for microbial adsorption and further reaction on the surface of biochar.SEM coupled with EDS results showed that in M treatment,the biochar adsorbed more mineral elements,which formed Al-0 bond,Fe-O bond,OH bond and Si-O bond.This process would be in favor of the formation of SRO minerals.In summary,the results from field and laboratory incubation experiment showed that soil minerals were closely interacted with SOC in soils.The application of biochar could increase the content of SRO minerals.Meanwhile,the SRO minerals can facilitate the sequestration of SOC.Furthermore,the results from incubation experiment demonstrated that the interaction between minerals and MR-1 on the surface of biochar,could benefit for the formation of SRO minerals.