Regulation Of Long-term Fertilization On Iron Oxides And Organic Carbon Preservation In Soils

The binding of soil organic carbon and soil minerals plays an important role in the preservation of soil organic cabon,while the quantities of soil iron oxides are corresponding with the quantity of soil organic carbon.The objectives of this study were to explore:1)the regulation of long-term fertilization on soil iron oxides,2)the relationship between the dissolved organic carbon and dissolved minerals in soil colloids within different fertilization treatments from four kinds of soils,and 3)the relationship between soil organic carbon groups of soil colloids and iron oxdies,that is the mechanism of preservation of soil organic carbon connected with soil iron oxides.With the research results above,we can make a contribution to enriching the basis of the modern agriculture management,and providing a basis for soil carbon sequestration,fertility and sustainable utilization of soil resources.The main conclusions are listed as follows.1)After the long term fertilization experiments for more than 20 years,the soil pH in the NPK treatments were generally the lowest,followed by CK treatments,and the soil pH of organic fertilizer adding treatments like NPKM or M were always the highest,which indicating that the application of chemical fertilizer was one of the main reasons for soil pH depression;adding organic fertilizer helped to improve the soil pH status and enhance soil buffer capacity.All the fertilization treatments in the five long-term experiments can improve soil nitrogen supply capacity effectively,while the organic and chemical combined fertilization NPKM performed the best.Total iron contents in soils depressed in organic fertilizer added treatments which happened in five long-term experiments,one reason could be soil water soluble iron increased in organic fertilizer added treatments,which enhanced the dissolution of soil iron metastasis.2)The responds of DOC in soil colloids for fertilization were different in the four types of soils,the S-M organic fertilizer treatment in Shenyang brown soil,the G-NPK treatment in black soil of Gongzhuling,the U-NPKM treatment of gray desert soil in Urumqi,the Q-NPKM and Q-M treatments in Qiyang red soil,the contents of DOC in soil colloids from them showed increases compared with the control treatment CK,indicating that NPKM treatment was the optimal choice to improve soil colloids DOC content.3)The contents of DOC and soluble mineral elements in soil colloids from each soil type were close related,and these contents were higher in organic fertilizer added treatments like NPKM and M than chemical fertilizer treatment NPK.This may be caused by the addition of organic fertilizer which improved the composition of soil colloids and enriched the soil nutrient elements.Based on the long-term fertilization experiments,the correlation between DOC and mineral elements in soil colloids from different soil types was associated with the contribution made by mineral elements to organic carbon preservation.we infered that in different soil types,organic carbon preservation was promoted by different kinds of mineral elements.4)These four soil types,represented the typical soil types of northern and southern China respectively.The reactive Fe content in brown soil,black soil,grey desert soil in northern China ranged from 3.95 to 13.35g/kg,at a relatively low level,while more than 36.0g/kg in red soils of southern China.Therefore,Fe should play different status of the participants in the preservation of SOC in different soils.5)In different soil types,the C-1s NEXAFS spectrum shapes of soil colloids from different fertilization treatments were similar,indicating that soil organic carbon fractions in soil colloids were similar to each other.The spectra peak fitting results of C-1s NEXAFS for all the soils showed that the contents of components were generally ordered as follows:Carboxylic C(288.4-289.1eV)>Alkyl C(287.6-288.3 eV)>Carbonyl C(289.9-290.2eV)>O-alkyl C(289.2-289.8eV)>aromatic C(283-286.1eV)or Phenolic C(286.2-287.5eV).The component ratio of each C group in different soil types was of difference in quatity;in the same soil type,each C component was of difference in quatity in different fertilization treatments.6)Different iron oxides associated with the preservation of different organic carbon groups,but the coefficient of the linear corelation between iron oxides and organic carbon fractions was not high enough,indicating that the combination between iron oxides and organic carbon fractions were rather complex.From the perspective of soil iron reactive degree(Fed/Fet),Alkyl C(287.6-288.3eV),Carboxylic C(288.4-289.1eV),O-alkyl C(289.2-289.8eV)were highly reactively in long-term accumulation of organic carbon,and were affected easily by the content of soil reactive iron.In summary,the interactions between different forms of soil iron oxides and soil organic carbon groups were different.The kinds and quantities of soil iron oxides were based on the soil types and fertilization treatments,long-term fertilization played an important role in regulation of the types and quantities of iron oxides and organic carbon components,and the preservation of soil organic carbon.