| Biochar is a stable carbon rich product obtained by pyrolysis of biomass under oxygen free or oxygen limited conditions.It has high carbon content,rich pores,large specific surface area,strong adsorption capacity and some nutrient elements.Because of its excellent physical and chemical properties,biochar can play a positive role in agriculture,environment and other fields.Potassium is the most nutrient element in biochar,and its content of available potassium is very rich.It can increase the content of available potassium in soil and promote the absorption and utilization of potassium by plants.The potassium contained in biochar and its regulation on Soil and crop potassium provide a new way to expand the source of potassium,reasonably and efficiently utilize potassium,and improve the utilization rate of potassium.At present,there are few studies on the formation and transformation of potassium in the process of biomass carbonization and the distribution and transformation of potassium in soil.Therefore,from the perspective of potassium utilization,this study used indoor and pot experiments to effectively combine "biomass-biochar-soil-crop" to study the formation and transformation of potassium in different sources of biomass in the process of carbonization,the transformation of potassium in biochar in different soils,the potassium availability of biochar in different soils and the influence of crops on potassium absorption and utilization In order to enrich the agricultural application of biochar and improve the absorption and utilization rate of potassium in biochar and crops,it provides theoretical basis and scientific basis.In this study,10 kinds of biomass,including corn straw,corn cob,rice straw,rice husk,soybean stem,soybean pod skin,peanut shell,coconut shell,bamboo and pine wood,were used to prepare biochar from different sources at 300 ℃,500 ℃,700 ℃ and 900 ℃,respectively Furthermore,the adsorption and desorption of potassium on the biochar were studied.On this basis,pot experiments were carried out: using different soil(albic soil,aeolian sandy soil,brown soil)and setting different carbon application rates(10,20,30 g / kg),to study the transformation of potassium in different soil,the potassium availability of biochar in different soil,and the effect of soybean on potassium absorption and utilization.The main results are as follows1.The change of different forms of potassium in biochar at different carbonization temperatures.The results showed that the total potassium content of different materials was higher than other carbonization temperatures after carbonization at 700 ℃;the water-soluble potassium content of biomass with different materials(except corn straw)increased with the increase of carbonization temperature;the exchangeable potassium content of other biomass except corn straw and soybean pod shell after carbonization at 500 ℃ was higher than other carbonization temperatures;biomass with different materials(except bamboo and jade)had higher potassium content than other carbonization temperatures With the increase of carbonization temperature,the content of insoluble potassium in biochar first increased and then decreased.When the carbonization temperature was 900 ℃,the insoluble potassium content in biochar was lower than other carbonization temperatures.2.Conversion of potassium in biomass at different carbonization temperatures.Except for corn straw and soybean pod,the conversion ratio of potassium to water-soluble potassium in all biomass materials at different carbonization temperatures is basically unchanged or increased;with the increase of carbonization temperature,the sum of exchangeable and non exchangeable potassium in biomass of different materials decreases,which is related to the conversion of exchangeable and non exchangeable potassium into water-soluble potassium and insoluble potassium With the increase of carbonization temperature,the insoluble potassium in biomass of different materials gradually decreases or disappears,which is related to the loss caused by carbonization process.3.The available K(water soluble K,exchangeable K and non-exchangeable K)in biochar can be used by plants.When the carbonization temperature was 300-700 ℃,the available potassium in different biochars increased with the increase of carbonization temperature.When the carbonization temperature was 300 ℃,the content and efficiency of potassium conversion from different biomass(except rice straw)were the highest.4.The analysis of isothermal adsorption curves of different biochars showed that the adsorption of potassium ion by biochars prepared from ten different raw materials was multilayer adsorption.The single-layer saturated adsorption capacity of bamboo biochar was higher than that of other materials at different carbonization temperatures.In the process of desorption,the first and fifth desorption amount of biochars with different materials prepared at different carbonization temperatures were higher than others.With the increase of carbonization temperature,the total desorption amount of biochar from different materials first increased and then decreased,and the total desorption capacity was the lowest at 900 ℃.Among different materials,the desorption of potassium from shell biomass and pine wood was lower than that of other biomass.5.The application of biochar can improve the contents of water soluble,exchangeable and non exchangeable potassium in different soils,and the action pathway of different forms of potassium in different soils is different.In the presence of biochar,different forms of potassium in aeolian sandy soil were positively correlated with saturated water content and exchangeable potassium;different forms of potassium in Albic soil had positive correlation or extremely significant positive correlation with soil heat capacity,p H and saturated water content;different forms of potassium in brown soil had positive correlation or extremely significant positive correlation with soil heat capacity and saturated water content.6.Biochar can promote the absorption and utilization of potassium by soybean plants,which varies with soil.Among them,the application of carbon in Albic soil can promote the absorption of potassium in whole plant(root,stem,leaf,pod)of soybean;in sandy soil,it can promote the absorption of potassium by soybean root,stem and leaf;in brown soil,carbon application can promote the absorption of potassium in different organs of soybean plants in different soil,but it can promote the absorption of potassium in different organs of soybean plants in different soil The effects were not consistent,among them,albic soil only promoted crop growth at the highest carbon application rate,dry matter accumulation in aeolian sandy soil decreased,while carbon application in brown soil promoted crop growth.7.Biochar can improve soil available potassium pool and increase the proportion of available potassium,but not all available potassium of biochar enters into soil available potassium pool,and part of available potassium enters into soil non available potassium pool.The average conversion rate of biochar available K into soil available K pool was 41.79%,72.94% and 17.02% in aeolian sandy soil,aeolian sandy soil and albic soil respectively.8.The conversion rates of available K from biochar to available K were different in different soils,which were aeolian sandy soil > brown soil > albic soil,with the average conversion rates of 43.87%,19.26% and 15.35%;the conversion rates of available K from biochar to slowly available K in different soils were brown soil > albic soil > aeolian sandy soil,and there was no transformation in aeolian sandy soil,but biochar in brown soil and albic soil The average conversion rates of available potassium from biochar were 53.68% and 1.66% respectively,and the conversion rates of available K from biochar to available K decreased in Albic Soil and aeolian sandy soil,but increased in brown soil.However,in different soils,the conversion rate of total K to slowly available K increased. |
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