The Basic Research Of Physicochemical Properties Of Biochar And Its Application In Agriculture

Biochar, being the product of resource utilization of agriculture waste, is a kind of substance with high level of carbon and formed through low temperature pyrolysis process under anoxic or anaerobic conditions. Once applied into soil, it can not only increase the carton reserve, but also decrease the release of CO2. It can also improve the properties of soil in its physical, chemical and biological aspects, fortify the soil fertility and productivity. Meanwhile, it is found that the biochar works well in promoting plant growth, lowering the effectiveness of heavy metals and organic pollutants, etc. which has been mostly applied in the fields of agriculture and environmental protection. At present, reports on basic physicochemical properties of Biochar can be seen, but mainly focused on single factor research in aspects of different materials (e.g. bamboo and straw charcoal, etc) or diversified conditions of preparation. The researches on the physicochemical properties of biochar from various resources with different preparation condition are, by contract, relatively rare.Thus, this article took biochar, from various resources with different preparation temperatures, as research subject to study its basis properties. Further study on ammonium nitrogen adsorption was also carried out and through biochar modification, its effect on heavy metal adsorption explored. On the basis of this, biochar-based fertilizer was prepared and related experimental studies were conducted on peanut crop. The researching result provided not only data support and theoretical foundation for the function of biochar on physicochemical properties of soil and heavy metal adsorption, but also practice basis for further application of biochar in agricultural production. The researching results were as follows:1.The contents of carbon, nitrogen and hydrogen were different in the biochar that from diverse sources, and the carbon content was relatively higher increasing with the preparation temperature rising:At the preparation temperature of 550℃, the peak carbon content in the peanut shell biochar reaches to 78.56%, Both of the peanut shell and the corn stalk biochar were alkaline, and the alkalinity increases with the temperature rising, which is stronger in the corn stalk biochar than that in the peanut shell biochar, the pH value of the corn stalk biochar reaches to the peak of 10.23 when the preparation temperature is 550℃, which provides a good base for improving acid soil by the corn stalk biochar, as well as the reference frame for the subsequent exploitation and application of the carbon-based fertiliser. Nevertheless, from the microstructure point of view, the skeleton structure maintains well after the carbonisation, the structures of the corn stalk and the peanut shell biochar produced at 550℃ were distinct with the cellular structures, which possessing the characteristics of large specific surface werea and strong adsorption capacity. The carbon exists in aromatic nucleus in the corn stalk and peanut shell biochar with stable structure, where there were many oxygen-containing functional groups on the surface, which leads to high cation exchange capacity (CEC) in the biochar. With the temperature increase, the quantity of the alkaline functional group in the corn stalk biochar increases until reaching to the peak of 1.1578 mmol/g at 550℃; by contrast, the quantity of the acid functional group in peanut shell biochar decreases.2. The adsorption rates of both maize straw biochar and peanut hull biochar to ammonium nitrogen (NH4+) were relatively higher in the initial reaction stage (0-2h) with sharp rise in absorption mount and the equilibriums were reached after 4 hours with their absorption amounts around 753.29 mg/kg and 1003.70 mg/kg respectively. The absorption rates of them decrease with the increase of temperature. Within the range of pH between 5 and 9, their adsorption rates towards ammonium nitrogen (NH4+) go up with higher pH value. A better absorption effect is seen for both maize straw biochar and peanut hull biochar on low ammonium nitrogen (NH4+) solution with a NH4+removal rate of 83.33% and 95.33%, respectively. The absorption characteristics for ammonium nitrogen (NH4+) were more in line with Freundlich equation. Comparatively speaking, the peanut hull biochar had a better ammonium nitrogen absorption effect than that of maize straw biochar.3. The maximum unit adsorption rates of maize straw biochar and modified biochar on heavy metal Cd2+were 21.77 mg/g and 30.16 mg/g respectively with a corresponding removal rate of maximum 98.00% and 99.87%, respectively. The maize straw biochar and modified biochar both increase their capacity on Cd2+absorption with the increase of the equilibrium liquid mass concentration. However, the absorption rate and removal rate on Cd2+both ascend first with the increase of their initial pH values until they reach their peaks when pH value goes up to 5 with the maximum absorption and removal rates of 6.13 mg/g and 98.00% respectively. Their Cd2+absorption capabilities gradually dwindle with the rise of absorption temperature, but the modified biochar was less affected with a removal rate maintained around 99%. Their highest Cd2+absorption rates appear at 20℃ with the adsorption and removal rates at 6.02 mg/g and 94.68% respectively. The absorption time had a big influence on biochar. Before reaching the stable and equilibrium state, both the absorption and removal rate had experienced a quick climbing. Modification can increase the absorption rate of biochar. The Cd2+absorption rate of biochar per unit mass slows down with the increase of addition amount before reaching an equilibrium state. After modifying load, adsorption quantity increased. Under the same biochar dosing quantity, the smaller the particle size of biochar, the bigger the adsorption rate of Cd2+.4. With the increasing of initial concentration of heavy metal, both the maize straw biochar and modified biochar show an increase in the unit absorption rate and a decrease in removal rate of Pb2+. The unit absorption rate and removal rate of Pb2+first increase and then decrease with the increasing of pH. Both the unit absorption rate and removal rate of heavy metal Pb2+ go up with the increasing of absorption time and decreasing particle size. As the biochar dosing amount increases, the unit adsorption rate increases and the removal rate decreases. And compared to biochar, the adsorption of the modified biochar on heavy metal Pb2+was significantely improved.5. The biochar and biochar based fertilizer can, to some extend, boost the surface temperature of soil with an excellent soil temperature retainment effect. Biochar and biochar based fertilizer both can improve the pH level of soil, but the biochar based fertilizer performs better. However, with the increasing of application years of biochar based fertilizer, further study on this was required to evaluate the change of pH levels of soil. Worked as the soil conditioner, the biochar or biochar based fertilizer can absorb more moisture and nutrients, enhance soil nutrient absorbing amount and moisture holding capacity, improve soil moisture holding capability. Biochar or biochar based fertilizer can also lift the content of ammonium nitrogen and nitrate nitrogen.6. Biochar based fertilizer was a kind of slow released fertilizer which consists of biochar and other compound fertilizer. After putting into soil, biochar based fertilizer will release its nutrients slowly so that the supply for the whole growth period of peanut plant was guaranteed. Also it can ameliorate the traits of peanut plant, improve the quality and yield of peanut. As an excellent soil conditioner, biochar can effectively improve the physicochemical properties of soil, promote the adsorption and utilization of nutrient, reduce the dosage of fertilizer and increase the fertilizer using efficiency, thus bring down the environmental damage brought by overdosed fertilizer.