The Effect Of Biochar And Organic Fertilizer On Albic Soil And Its Mechanism

Albic soil is mainly distributed in the northeast of Heilongjiang and Jilin provinces,which is a typical low-yield field in China.Its sub-surface-albic layer is acidification,low fertility,compactness,poor permeability of water and air.Restricted by its own properties,there are certain obstacles in agricultural production,limiting the sustainable development of arable land resources.In view of the physical and chemical properties of albic layer,improving the physical structure of the soil is the key to enhancing its ground strength.Biochar is a by-product of high carbon content,complex pore system,high surface area,strong adsorption capacity,and certain organic matter and mineral components,which is produced by the thermal cracking of organic matter such as crop straw under the condition of limited oxygen supply.It is called“black gold”.The effective combination of biochar and organic fertilizer is an effective way to achieve sustainable and green agricultural development.In this study,maize straw biochar and microbial fermentation organic fertilizer was used as amendments in a pot experiment to investigate the effects of different application rates of biochar（0%,0.5%,1.0%,and 2.0%）and organic fertilizer（0.5%）on the microscopic pore structure,chemical property and micro-ecological environment of albic soil,as well as the effects of soil environmental changes on wheat plant characteristics.The aim of this study was to provide a theoretical basis for the improvement of albic soils by biochar and organic fertilizer technology.The main research results were obtained in the following aspects:（1）After the application of biochar,soil constraint factor such as low porosity and poor permeability in the albic layer were gradually improved.The albic layer soil had low porosity and poor connectivity,with an overall porosity 72.53%lower than humic layer.After the biochar amendment,the overall porosity of the albic layer soil increased by 48.19%and the total pore volume decreased by 33.61%.The pattern of change in the number of pores was negatively correlated with the overall porosity（P<0.05）,indicating that multiple small pores in the soil were expanded into one large pore.The increase in macroporosity in the soil was 62.14%and the increase in lean porosity was79.96%.The Volumetric Euler-Poincarédecreased by an average of 27.44%.When biochar was applied at 2%,the soil water content increased by an average of 37.78%,bringing it gradually closer to the soil without albic layer.The particle size distribution of soil aggregates in albic soils was dominated by microaggregates,however,the most significant increase in the proportion of macroaggregates（P<0.05）was observed during the biochar and organic fertilizer amendment.At 2%biochar application,the most significant（P<0.05）improvement in aggregate stability indicators(MWD,GMD and R_0.25)was achieved when combined with organic fertilizer,with an average increase of 48.51%,16.98%,and 64.42%respectively.Redundancy analysis showed that macroporosity and lean porosity contributed 30.6%and 8.8%to aggregate stability,respectively.（2）The application of biochar and organic fertilizer effectively increased soil carbon and nitrogen pool in the albic layer and alleviated soil acidification.The thicker the albic layer,the more acidified the soil is.Correlation analysis showed that biochar had a significant positive effect（P<0.01）on the reduction of acidity in albic layer.The combined application of biochar and organic fertilizer had the most significant effect on p H improvement,increasing p H by 38.53%from 4.36 to 6.04.In the dynamic changes of soil carbon pool,it was found that the thicker the soil albic layer was,the more unfavorable the accumulation of soil nutrients.The average soil TOC was only6.81 g·kg^-1 when the albic layer thickness was 25 cm,and 7.80 g·kg^-1 when the albic layer thickness was 5 cm.When the biochar application rate was 2%,TOC and C/N increased most significantly,which gradually approached the C and N levels of the humus layer.Compared with biochar application alone,the combined application of biochar and organic fertilizer significantly increased TN level（P<0.05）,which could effectively improve soil nutrient content and slow down nitrogen loss.Organic fertilizer or biochar combined with organic fertilizer significantly affected TOC（P<0.05）.When the biochar application rate was 2%,the changes of aggregate size were the most significant（P<0.05）.Macroaggregates could store more C,N,particulate organic matter,and labile organic matter than microaggregates and silty clay fractions.Under the condition of organic fertilizer application,soil EOC level increased significantly（P<0.05）.However,increasing the proportion of biochar application negatively affected soil EOC/TOC,which was reduced by 19.95%on average compared with B1 treatment.In the dynamic changes of soil DOC,the combination of biochar and organic fertilizer increased soil DOC content in the 25 cm albic layer by 171.11%on average.Under the condition of organic fertilizer application,soil DOC/TOC significantly increased（P<0.05）.The thicker the albic layer,the lower the MBC and MBN levels.The combination of biochar and organic fertilizer had the best improvement effect,with the highest increase of 130.93%and 66.86%.（3）Biochar effectively alleviated the negative effects of soil structure and functional degradation on soil enzyme activity in the albic layer,and there was a positive synergy between its application and organic fertilizer.The activities of catalase,invertase,and urease in the albic layer were increased by 376.18%,117.22%,and166.55%,respectively.The synergistic effect of biochar and organic fertilizer on urease activity was significant.The contribution rates of soil environmental factors p H,DOC and TN to soil enzyme activities were 51.0%,12.6%and 5.1%,respectively.In the Alpha diversity analysis,combining the diversity indices of Simpson,Shannon,Chao1and Pielou＿e,it was found that the most significant increase in microbial community abundance was found when biochar was applied at 1%in combination with organic fertilizer,with an increase of 43.87%.When biochar was applied at 2%,the relative abundance of the dominant bacterial communities,Proteobacteria,Actinobacteriota and Gemmatimonadota,increased by 15.46%,14.25%and 4.68%respectively.In contrast,the relative abundance of Acidobacteriota decreased by an average of 41.64%.Ascomycota,Basidiomycota and Mortierellomycota were the dominant fungal phyla in the albic layer.The highest increase in relative abundance of Ascomycota and Basidiomycota was observed at 0.5%organic fertilizer application,with 34.13%and26.36%respectively.The relative abundance of TN and TOC to the bacterial community was 50.3%and 23.1%respectively,while the relative abundance of the fungal community was 40.5%and 27.5%respectively.The soil amino acid metabolism,energy metabolism,prokaryotic cell community and cellular metabolism were enhanced during the improvement of biochar with organic fertilizer.The enrichment of Animal＿Pathogen,Dung＿Saprotroph and Wood＿Saprotroph in the soil was also significantly increased.（4）The porosity of biochar significantly increases soil porosity,increasing capillary and aeration pore space,effectively alleviating the structural barrier of the albic layer which is not conducive to crop growth and root extension.The application of biochar with organic fertilizers helps to enhance the continuous supply of water,nutrients and other materials to the root system in the later stages.The water content of wheat plants increased by an average of 96.54%and the dry weight of wheat plants increased by an average of 20.97%in the treatment with biochar and organic fertilizer.The root system characteristics of wheat plants in the albic layer soil were best in the biochar application alone（2%）,where the total root surface area increased by 117.84%,the number of root tips increased by 43.55%and the number of forks increased by181.03%.Principal component analysis showed that TN,C/N,DOC,and R_0.25contributed 28.5%,11.1%,5.7%,and 4.9%to the physiological indicators and root growth of wheat plants,respectively.In the bacterial community,the contribution of Proteobacteria,Myxococcota and Actinobacteriota was 29.1%,17.1%,and 9.6%,respectively.Among the fungal communities,the Mortierellomycota,Ascomycota and Basidiomycota contributed 41.4%,19.2%and 10.5%,respectively.Results from the structural equation model showed that biochar and fertilizer indirectly promoted plant biomass and root elongation by increasing carbon,nitrogen fractions and microbial community abundance.On the other hand,the physical structure had the greatest direct effect on the total root surface area of the plant to support a robust and developed root system in the albic layer.In this study,the rational application of biochar and organic fertilizers is a potential soil improvement technical measure to improve the pore structure,increase C and N levels,reduce acidification,improve the microecological environment,and promote crop root growth.This study will provide a scientific basis for the conservation and sustainable use of albic soil resources in the northeast region.