Mechanism Of The Changes In Aggregate-stability And Corresponding Cementing Material Caused By Fertilization Regimes In Red Paddy-soils

Aggregates is the most basic unit of soil structure,Its composition and stabilization have important effects on soil physical structure.Good aggregate structure helps to coordinate the four major fertility factors in soil,such as “water,fertilizer,gas and temperature”,and improve soil fertility.In the red earth of southern China,soil organic carbon and iron-aluminum oxides are the main cementing substances of aggregates,which play an important role in the formation and stability of the soil.The main role of iron-aluminum oxide in the formation of red earth paddy soil aggregates in the South has been reported,But in the red earth paddy soil with high organic matter content after long-term fertilization,whether or not the agglomerate's cement will change will require more theoretical support.This article takes a 34 years long-term positioning experiment of Hunan Agricultural University,Grouping aggregates using physical wet sieve grading,combining physical chemistry methods to group organic carbon,and determined the various forms of iron-aluminum oxide in the soil,to study the main distribution characteristics of aggregates,organic carbon,and iron-aluminum oxides and their response to changes in fertilization management measures in the past 4 years in different fertilization treatments and fertilization management measures for long-term fertilization of red paddy soils.The results can provide data support for the formation and stabilization mechanisms of red earth paddy soil aggregates after fertilization in the South.At the same time,it can provide theoretical guidance for the rational formulation of farmland fertilization schemes and sustainable ecological development of farmland.The main findings are as follows:1.>0.25 mm aggregate is the main component of aggregates in long-term fertilized red soil paddy soil.Long-term application of organic fertilizer can significantly increase the content of macroaggregates >0.25 mm and increase the stability of aggregates.The MWD and GMD of aggregates treated with organic manure over long term were significantly higher than those of single chemical fertilizers.After 4 years of change in fertilizer management measures,no treatment with organic fertilizer will result in a decrease in the content of macroaggregates,a significant increase in the content of microaggregates,and a significant decrease the WMD and GMD of aggregates.2.Long term fertilization of red soil paddy soil showed significant improvement in soil organic carbon and total nitrogen compared with chemical fertilizer treatment under constant organic fertilizer and high organic fertilizer.After 4 years of fertilization management,the organic carbon and total nitrogen content of the aggregates decreased significantly when the organic manure was stopped.Under different fertilization treatments,>2mm coarse aggregates had the highest contribution to total organic carbon,followed by 2-0.25 mm fine aggregates.In micro aggregates and powder clay,the contribution rate of organic carbon treated by chemical fertilizer was significantly higher than that of high organic fertilizer and high organic fertilizer.Multiple linear stepwise regression analysis showed that the stability of aggregates was closely related to the contribution of <0.053 mm and 2-0.25 mm fractions to organic carbon.3.Long-term application of organic fertilizer significantly increased the organic carbon content of various components in paddy soil of red earth,the treatment of high-level organic manures and organic manures increased the oxidizable organic carbon content relative to fertilizers by 330% and 176% respectively.After 4 years of fertilization management,the increase of organic manure increased the Oxidizable organic carbon content by 87.4% and 36.7% respectively.Free form is the main form of iron and aluminum oxides in red soil paddy soil,Except for free iron oxide and complex iron oxide,the other forms of iron and aluminum oxides have no obvious response to the changes of fertilization management measures.All organic carbon fractions showed significant or very significant negative correlation with micro aggregates,and the relationship between easily oxidized organic carbon and total organic carbon was positively correlated with GMD.There is a significant negative correlation between free iron oxide and >0.25 mm water stable aggregates,and the complex iron oxide has a significant positive correlation with it.4.The path analysis showed that the total organic carbon had a significant direct effect on the stability of aggregates under long-term fertilization(P < 0.05).The main factors affecting the stability of water stable aggregates larger than 0.25 mm are particulate organic carbon and easily oxidized organic carbon.Oxidized organic carbon,light group organic carbon and granular organic carbon under long-term fertilization mainly influence the average weight diameter of aggregate through the indirect influence on 0.25 mm water stable aggregate and total organic carbon.After the change of long-term fertilization and fertilization management measures,the main factors affecting the stability of aggregates are greater than 0.25 mm and water stable aggregates,Organic carbon has indirect effects on aggregate stability through >0.25 mm water stable aggregates.