| Extensive investment of water and fertilizer in traditional agriculture has supported the national food supply and demand,but it has also brought great pressure on resources and environment.Therefore,improving the utilization efficiency of water and fertilizer has become an important way to coordinate agricultural production and ecological protection in Northwest China.The application of biochar in soil improves the original farmland soil ecological cycle function,which is of great significance to the growth and development of crops,but it also exposes some problems of unstable environment and application effect.Through literature review and experimental analysis,it is found that there are differences in physical and chemical characteristics of structural heterogeneity in biochar particles prepared by traditional pyrolysis.Taking this as the breakthrough point,this study discusses the mechanism of biochar heterostructure on the distribution characteristics of farmland soil water and fertilizer,and the yield increasing effect on the growth and development of typical crops.The research content provides a theoretical basis for deepening the understanding of the improved efficiency of biochar in the farmland soil environment.This study adopted the cross-research methods of"microstructure characterization-physical process analysis-field pilot application-simulation model construction",and set up three kinds of biochar with different structures(mm biochar(1 mm,BMPs)and micron biochar(1-2 μm.BUPs)and nano biochar(40-200 nm,BNPs)).The effects of biochar heterostructure on farmland soil environmental and corn yield were systematically analyzed from physics and chemical properties of biochar,pore structure and physical-chemical indexes of soil,soil water movement and nutrient migration characteristics,soil water,and fertilizer distribution characteristics of farmland,soil microbial community structure,and typical crop growth characteristics.The different characteristics of biochar heterostructure in improving soil water and fertilizer distribution and crop yield were clarified and the mechanism of biochar with different structures improving farmland soil environment was discussed.Through Structural Equation Model,the correlation between the main soil physical and chemical characteristics of farmland under the action of different structural biochar was clarified,and the suitable application of different structural biochar suitable for silty loam was put forward.The research conclusion was expected to provide new technical ideas for the sustainable development of agriculture in Arid Areas.(1)The differences in physical-chemical properties of biochar heterostructures and their effects on the pore structure and physical-chemical characteristics of improved soil were clarified.The apparent morphology of biochar with different structures was quite different,and the particle size is reduced from millimeter to nanometer,the fatty groups disappeared gradually,while the aromatic groups were retained,and the degree of aromatization was higher.The application of biochar with different structures reduced the soil porosity.However,there were differences in the mechanism of changing soil pore characteristics and the interval of affecting pore size under different kinds of biochar.Biochar with different structures changed the water stability of soil aggregates.BMPs was conducive to the structural stability of soil aggregates,while BUPs and BNPs reduced the water stability of soil aggregates.Due to the change of chemical group composition,BMPs were weakly hydrophilic,while BUPs and BNPs were completely water repellent.The application of biochar with three structures led to the decrease of soil solid surface energy;(2)The effects of biochar structural heterogeneity on soil hydraulic properties and solute adsorption and migration were clarified.The application of biochar with different structures reduced the soil saturated hydraulic conductivity Ks,and BMPs increased the soil saturated water content θs.Both BUPs and BNPs decreased the soil saturated moisture content θs.Biochar showed strong isothermal adsorption performance for PO43-in solution,and the increasing application amount of biochar could improve the adsorption capacity of improved soil for PO43-.Compared with BMPs,BUPs and BNPs showed better adsorption properties.In the process of soil solute penetration,biochar with different structures reduced the average water flow velocity v in soil pores and increased the dispersion λ,And as the application amount increases,λ values increased in turn.The effect of biochar with smaller particle size on the hindering penetration and loss of soil nutrients was more significant;(3)The influence mechanism of biochar structural heterogeneity on the distribution characteristics of "Water-Fertilizer-Bacteria-Enzyme" in farmland soil was revealed.Biochar with different structures has two effects on soil water holding capacity:positive promotion or negative inhibition.Compared with the unmodified soil,the average moisture content of improved soil increased in the BMPs application treatments,while the average moisture content of the soil decreased in the BUPs and BNPs application treatments.The application of biochar could significantly improve soil fertility,especially in the middle and later stages of the maize growth period.Compared with BMPs,BUPs and BNPs were more effective in the adsorption,retention,and slow-release supplement of soil nutrients.The application of biochar reduced the Shannon and Chaol indexes.In the abundance comparison of Cyanobacteria,with the decrease of biochar particle size,the relative abundance of improved soil gradually increased,which was greater than that of unmodified soil.In the abundance comparison of Gemmatimonadetes,BMPs increased the relative abundance compared with unmodified soil,while BUPs and BNPs decreased the relative abundance.The application of BMPs increased soil sucrase activity and phosphatase activity,and decreased soil urease activity,while the application of BUPs and BNPs decreased the activities of three kinds of soil enzymes;(4)The influence mechanism of biochar structural heterogeneity on the maize growth process was clarified.BMPs had a positive effect and could stably promote the growth of various maize growth indexes during the growth period.The effects of BUPs and BNPs on maize growth indexes were unstable in some growth stages and even have negative inhibitory effects.Due to the difference in particle size and application amount,biochar could not fully achieve the purpose of increasing maize yield.In the treatment of BMPs application,the maize yield increased with the increase of application amount.In BUPs application treatments,with the increase in application amount,the yield increased by 11.38%,22.67%,11.43%,and-4.22%respectively.In BNPs application treatments,the yield increased by 15.76%,23.53%,5.86%,and-15.79%respectively.The possibility of maize yield reduction might occur when the application amount of BUPs and BNPs exceeded 2.0%.Logistic model could better fit and analyze the development process of maize aboveground growth indexes under the action of biochar with different structures.From the results of the maize leaf area index,the application of BMPs shortened the duration of the rapid increase stage of leaf area,while BUPs and BMPs were similar to the control.From the results of maize aboveground biomass accumulation,the application of biochar with three different structures prolonged the time of the rapid increase stage.Proper application of micron biochar and below was better than millimeter biochar in increasing crop income and yield.Among them,the recommended application proportion of biochar of each particle size is:when the application amount of BMPs is 2.0%,BUPs biochar is 0.6%and BNPs is 0.6%,the crop harvest yield can obtain the best benefit.The structural equation model showed that the reduction of biochar particle size changed the proportion of soil water and fertilizer demand for maize growth.the correlation coefficients of soil moisture and nutrients on maize yield were the same with BMPs applied;When BUPs and BNPs were applied,the demand for maize yield for soil water was higher than that of soil nutrients. |
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