| As an important aspect of soil degradation,soil alkalization will cause soil environment deterioration,nutrient loss and fertility reduction,which will reduce soil quality and productivity.However,organic materials,such as biochar,organic fertilizer and wood vinegar,have important application value in ameliorating soil physical and chemical properties,improving soil structure and quality,increasing soil nutrient content and fertility,optimizing soil microbial community structure,and promoting crop growth and yield increase.In this study,Enteromorpha prolifera was used as raw material to prepare biochar through different pyrolysis temperatures and modification methods.Typical biochar was screened by SEM,FTIR,XRD,BET and element analysis.Combined with indoor experiments and field positioning experiments,the improvement of physical and chemical properties of alkaline soil and the regulation mechanism of soil structure,water movement and microenvironment were systematically studied by applying organic materials alone or in combination.This paper discussed the improvement effect of organic materials on alkaline soil,the evolution law of soil structure and its quantitative characterization,and clarifies the mechanism of organic materials on the water movement of alkaline soil and its ecological function,so as to provide a new way and scientific basis for the improvement of typical alkaline soil in Ningxia.The main results are as follows.(1)Three pyrolysis temperatures(300℃,400℃ and 700℃)and three modification methods(unmodified,20%FeCl3 and 6%chitosan modified)were set to prepare Enteromorpha prolifera biochar by low oxygen slow temperature control method,and its characteristics were characterized and evaluated.The results showed that pH,ash content,C,N,O,H,specific surface area,average pore diameter and pore volume of the modified biochar emerged different trends with the increase of pyrolysis temperature.Compared with unmodified treatment,FeC13 and chitosan modification were helpful to improve the physical and chemical properties and pore structure of biochar,enhance the degree of carbonization and aromaticity,heighten the hydrophilicity and polarity,and the comprehensive effect is best when the pyrolysis temperature was 400℃.In summary,M1T2(20%FeCl3 modified,pyrolysis temperature 400℃)and M2T2(6%chitosan modified,pyrolysis temperature 400℃)can be selected as typical biochar for subsequent tests.(2)To study the influence of the combination of Enteromorpha prolifera biochar and organic fertilizer on the change rule of alkaline soil structure and its mechanism,three-dimensional reconstruction of soil pore structure was carried out by using X-CT tomography technology,and its quantitative characterization was studied by multifractal theory.The results showed that applying proper amount of biochar and organic fertilizer increased the content and stability of alkaline soil aggregates.In the second year,the mechanical stability and water stable aggregates of 0～20cm soil layer were increased by 12.52%and 29.87%,respectively,while MWD and GMD were increased by 29.67%and 54.97%,compared with those in the CK,which promoted soil aggregation and enhanced the stability and corrosion resistance of soil structure.The soil porosity and permeability were improved by applying proper amount of biochar and organic fertilizer.In the second year,the maximum porosity of 0～20cm soil layer was 27.94%,and the maximum permeability was 29.1736 μm2,which improved the soil pore structure and soil water seepage.The correlation study showed that,among the soil pore characteristic parameters and hydraulic parameters,the soil pore diameter was highly significantly positively correlated with the residual water content with a correlation coefficient of 0.54,and negatively correlated with the parameter n with a correlation coefficient of-0.53,while soil porosity was positively correlated with α,the correlation coefficient was 0.67.(3)The effects of applying Enteromorpha prolifera biochar on the infiltration,evaporation and soil water characteristic curve of alkaline soil were studied,and the soil hydraulic parameters and soil water movement were estimated and simulated,respectively,by combining the swarm intelligence optimization algorithm(improved PSO and WOA algorithms)and Galerkin finite element method.The results showed that,Kostiakov can be used to fit the soil infiltration process of different biochar treatments,and the function relationship was satisfied:f(t)=at-b,which was better than Philip.The soil cumulative evaporation(CE)and time(t),in the first and second stages of soil water evaporation under different biochar treatments,was satisfied with CE=at and CE=bt0.5,respectively.Different algorithms were used to invert the VG model parameters under the condition of biochar application.The improved PSO and WOA algorithms have higher accuracy and robustness(the error was less than 2%),and the improved WOA algorithm has faster convergence speed.Galerkin finite element method was used to simulate the soil water movement,and the simulated values of sample points were in good agreement with the measured values,indicated that the model constructed in this study could be better reflected the dynamic changes of soil water under the condition of biochar application.(4)The effects of the combination of Enteromorpha prolifera biochar and organic fertilizer on the changes of enzyme activity,microbial community structure,flora composition and diversity of alkaline soil were studied,and the mechanism of the changes of soil physical and chemical properties on soil microecology were analyzed.The results showed that the combination of biochar and organic fertilizer increased the soil nutrient content and fertility level,significantly,and greater than that under single material treatment.The soil pH of biochar application alone was significantly increased,while that of other treatments was reduced to varying degrees.The mixed treatment increased the activities and Et of four enzymes,including URE,ALP,INV and CAT,and improved the microbial community structure of rhizosphere soil,significantly,and increased the diversity of soil bacteria and fungi.Among them,the maximum increase of URE was 82.62%,ALP was 112.18%,IBV was 136.36%,and CAT was 62.66%.In addition,through the correlation analysis of soil environmental factors,soil microbial community composition and diversity and dominant species network,it was found that the changes of soil microbial community structure and diversity was mainly related to the results of changing the physical and chemical properties and nutrient content of pH,SOM,TN and TK,in alkaline soil,by the application of biochar and organic fertilizer.(5)The effect and mechanism of the combination of Enteromorpha prolifera biochar and wood vinegar on the improvement of alkaline soil and the increasement of crop yield were studied,and the comprehensive effect was evaluated by using the fuzzy membership function method.The results showed that pH,alkalinity,total salt content and bulk density of 0～40cm layer of Takyr Solonetzs,were reduced by the compound treatment,and the physical and chemical properties of the soil were improved,significantly.The compound treatment increased the availability of soil nutrients,the overall enzyme activity level,effectively promoted the flocculation of soil colloidal particles,and improved the soil aggregate structure,enhanced the growth of oil sunflower and its yield-increasing over 1500 kg·hm-2,significantly.And the comprehensive evaluation value of 2%Enteromorpha prolifera biochar and 2%wood vinegar was 0.94. |
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