Effect Of Biochar On Iron Reduction In Flooded Soils And Contribution Of Biochar To Bate Soil Salinization

The study of saline soil improvement had accumulated a lot of results in China,and the measures also showed diversity.In some areas "drought to change the water" measures showed a significant effect.However,in the process of " drought to change the water ",the salt still existed in the soil,so how to reduce the impact of salt effectively,is the core to promote the measure and expand the using range.Biochar is a kind of porous carbon solid formed by organic matter which managed with the process of thermal chemical conversion under hypoxic environment,and it has a physical,chemical and biological properties that are suitable for long periods of time and safe storage of carbon in the environment.The addition of biochar to the soil can not only change the ion balance in the soil,adjust the salt ion concentration and pH,but also can significantly improve the activity and diversity of microorganisms in the soil,improve the adhesion of microorganisms and promote the growth of soil microorganisms,and then strengthen the capacity of biological salt-resist and biological purification.Experiments conducted in major agricultural areas in China showed that with the application of biochar in saline-alkaline,contaminated soil and degraded-hardened soils,biochar showed eliminating low-yielding factors rapidly,avoiding and controlling heavy metal pollutions,and preventing salt rise effect,and so on.The application of biochar in saline soils can reduce soil’s pH and salt ion content,but the study was limited to dryland soils currently.After "drought to change the water",the soil formed an anaerobic environment.The microbial-mediated dissimilatory iron reduction process occupieed an important position in the soil anaerobic environment,and with the addition of biochar,salt ions,state of aggregation of microorganisms and organic matter could be changed,so the anaerobic microbiological process could also be changed.In addition,dehydrogenase activity is also an important parameter that characterizes the state of environmental redox,which is closely related to the activity and population information of microorganisms in soil.Therefore,it is important to study the effect and mechanism of the combination of "drought to change the water" and biochar in saline soil to reduce soil salinization.In this paper,we simulated "drought to change the water" by waterlogged incubation,and added biochar with different dosage and particle size into the incubation system.The pH,iron reduction process,dehydrogenase activity and the changes of free carbonate and bicarbonate in the system were analyzed,in order to explore the effect of biochar on the microbial process in flooded soil and the change characteristics of carbonate form in the submerged soil after the addition of biochar,and provide the necessary theoretical basis to elaborating the mechanism of action of biochar in flooded soil,and then clarify the mechanism of biochar in reducing soil salinization in " drought to change the water" measures.The main conclusions are as follows:(1)"Drought to change the water" measures reduced the pH of saline soil,promoted the Fe(III)reduction process and dehydrogenase activity,reduced the free carbonate content effectively.The pH,Fe(II)content,carbonate and bicarbonate content showed a significant correlation.(2)Biochar improved the dehydrogenase activity and iron reduction ability of JL,NX and TJ flooded soils,and the difference between the treatments of different biochar dosage was significant.The effect of different biochar dosage on dehydrogenase activity and iron reducing ability showed that the dehydrogenase activity and iron reducing ability increased with the increase of the dosage of biochar.Maximum iron reduction potential of JL,NX and TJ increased 1.3%-2.6%,1.5%-7.6%,0.3%-6.5%,respectively,and the maximum activity of dehydrogenase increased 57.9%-130.0%,53.3%-151.3%,63.8%-136.9%.Maximum iron reduction potential was significantly correlated with the time corresponding to the maximum rate of dehydrogenase production,both of which promoted each other during the culture.(3)The biochar improved the dehydrogenase activity and iron reduction ability in JL and TJ,and there were significant differences among the different particle sizes of biochar.The effect of different particle size of biochar on dehydrogenase activity and iron reducing ability showed that the dehydrogenase activity and iron reducing ability increased with the decrease of particle size.The increase of dehydrogenase activity accelerated the dehydrogenation and hydrogen production process,and H2 promoted microbial iron reduction process as an electron donor,meanwhile the increase of Fe(II)content can help dehydrogenase to accelerate the reduction rate of NAD+ and improve the activity of dehydrogenase.Dehydrogenase activity and iron reduction promoted each other during the incubation,and there was a significant positive correlation between them.The initial pH of soil affected the microbial reaction,and the effect of biochar on the activity of dehydrogenase and the process of iron reduction was different because of the different initial pH of the two flooded soils.(4)Under the condition of flooding culture,the addition of biochar increased the concentration of bicarbonate,that is to say,increased the dissolution of carbonate.The difference between the different treatments was that with the increase of the dosage of biochar and the decrease of the particle size,bicarbonate concentration increased.The initial pH of soil was an important factor restricting the dissolution of carbonate.The addition of biochar increased the ability of microbial iron reduction observably.The Fe(II)could be combined with CO32-to form precipitated iron compounds abstractly,which could reduce the harm caused by carbonate accumulation.There was a significant positive correlation and negative correlation between carbonate,bicarbonate concentration and pH during the culture.Biochar could not only adsorb the kations in the system,but also the action of biochar on microbes promoted the hydrogen and acid production in anaerobic culture system,which resulted in the decrease of kation content in the saline soil and the conversion of carbonate to bicarbonate or carbon dioxide,therefore it reduced the soil carbonate content and pH effectively,and showed the biochar’s effect of saline-alkali soil improvement in "drought to change the water".The improvement effect of biochar on saline-alkaline soil was different due to the different soil properties,but they all showed a prominent improvement effect with the increase of biochar dosage and the decrease of biochar particle sizes.