Study On Geochemical Control Factors And Regulation Of Soil Aggregates In Northeast China’s Black Soil Region

Soil is the critical material basis for human survival,and soil security is an important part of national security.Black soil is a kind of high-quality land resource with good character,high fertility and suitable for farming,and it is the best soil for grain production.A large area of black soil is called black soil region.As one of the four major black soil regions in the world,the black soil region of Northeast China is an important base for heavy industry,agriculture,forestry and animal husbandry production and energy,which plays an irreplaceable role in safeguarding regional ecological environment security,national food security and agricultural sustainable development.In recent years,due to the changes of natural environment and the influence of human factors,soil erosion and soil degradation in the black soil region have been very serious.In view of the urgent situation and severe challenge facing the degradation,restoration,utilization and protection of black soil in Northeast China,it is urgent to strengthen the protection and management of black soil.As the basic unit of soil structure,the formation and stability of soil aggregates play an important role in reflecting soil structure and characterizing soil quality.Therefore,so as to curb soil degradation,build soil agglomeration structure,and improve the quality of cultivated land,it is of great theoretical and practical significance to study the grain size distribution characteristics of aggregates and the factors affecting the formation and stability of soil aggregates,and to determine the influence of geochemical factors on the formation and evolution of soil aggregates in the process of soil evolution.At the same time,elucidating the geochemical process of soil aggregate fragmentation and construction can also provide a new theoretical basis for protecting the quality of black soil cultivated land and curbing soil degradation.In this paper,the black soil region of Northeast China was selected as the research object,and systematically expounded the distribution and geochemical characteristics of soil aggregate size of all cultivated soil types in the black soil area.Through quantitative experiments,the correlation of geochemical internal factors(organic matter,cation exchange capacity,salt content)and external factors(temperature,humidity,land use,fertilization)with aggregate size distribution and their effects on aggregate stability were clarified,and the correlation between each factor and aggregate stability in different soil types was explained.In the process of soil evolution,the geochemical changes of soil aggregates under the influence of different factors were determined.Further,the geochemical process of soil aggregate fragmentation in black soil and soil aggregate construction in degraded soil(saline-alkali soil,meadow soil,albic soil)was quantitatively simulated through experiments,which provided new theoretical references for curbing soil degradation and improving soil quality of cultivated land.The main conclusions and results of this thesis are as follows:1.Most soil species in the black soil region of Northeast China have good structure,only saline-alkali soil and aeolian sandy soil have poor aggregate stability and soil structure.It is found that the soil structure of some subtypes of soil in brown soil,cinnamon soil,chernozem soil,chestnut soil,meadow soil and alluvial soil is beginning to deteriorate,and it is believed that the phenomenon of soil salinization occur due to improper soil use.2.Increasing organic matter content,cation exchange capacity,water content,and fertilizer application have a positive effect on the stability of soil aggregates,while the increase of soil salt content and freeze-thaw cycles have a negative effect on the stability of soil aggregates.The stability of soil aggregates in saline-alkali soil used as paddy field is better than that in dry field,while the aggregates in meadow soil,albic soil and black soil used as dry field are more stable than that in paddy field.Under the influence of geochemical factors,the general geochemical process of formation and evolution of soil aggregates is as follows: aggregate structure is formed and stable → aggregate structure is basically maintained;aggregate stability is poor → large aggregates begin to break and aggregate structure begins to destroy → large aggregates break up and aggregate structure is destroyed.3.Introducing salt to black soil and conducting several freeze-thaw cycles will cause the large aggregates in the black soil to break up.Salt content from Ⅰ → Ⅱ → Ⅲ→ Ⅳ,the degradation trend of black soil was as follows: black soil → albic soil →meadow soil → saline-alkali soil.Soil and water conservation should be strengthened in the process of soil utilization for albic soil.For meadow soil and part of albic soil subclass,attention should be paid to prevent salt accumulation.For some meadow soil and albic soil subclasses,salt accumulation should be prevented and soil salt leaching should be accelerated.For saline-alkali soil,soil water evaporation should be reduced and soil salt leaching should be accelerated.4.Adding exogenous organic matter to different degraded soils(saline-alkali soil,meadow soil,albic soil)and keeping constant temperature and humidity under appropriate moisture content can promote the formation of new aggregate structure in soil and improve soil quality.For saline-alkali soil,with the level of organic matter content from Ⅳ → Ⅲ → Ⅱ → Ⅰ,the soil changes as follows: saline-alkali soil →meadow soil → albic soil → black soil.The quality of cultivated soil can be improved by reasonable application of fertilizer,straw mulching and organic acid addition.For meadow soil,with the level of organic matter content from Ⅲ → Ⅱ → Ⅰ,the soil changes as follows: meadow soil → albic soil → black soil.The quality of cultivated soil can be improved by applying fertilizer reasonably.With the change of organic matter content level from Ⅱ to Ⅰ,the process of agglomeration construction can be accelerated,and the soil change shows the trend of albic soil to black soil.The speed of soil quality improvement can be improved by straw mulching and organic acid addition.