The Study On Located Observation In The Dynamic Change Of Oxidation-reduction And Iron And Manganese Oxides Content In Shenyang Brown Soil

Soil oxidative reduction potential(ORP)has a profound effect on the formation and development of soil,the change of mineral element valence and the formation of iron and manganese neoplasms.Beginning in 1920,China's research scholars on the soil ORP research mainly concentrated in southern China's tropical and subtropical regions,the main research object is waterlogging soil,forest soil,paddy soil and so on.The relationship between soil ORP and soil iron and manganese oxide(IMO)and the mechanism of formation of iron and manganese neoplasms were still studied in the study of ORP in the northern soil(later in the 1990s)Not clear.Shenyang,which is located in the northeastern region of Shenyang,is cold and long in winter,alternating in cold and thaw in spring.The dry and wet soils in summer and autumn are obviously affected,and the effect of soil oxidation and reduction potential is larger.Even in the zonal soil(brown soil)Iron and manganese new body appears.In this paper,the soil moisture,temperature,ORP and IMO contents of soils were studied from September 2013 to October 2016 for four consecutive years.The results were as follows:From March 18th to April 1,2015,the dynamic changes of ORP during freezing and thawing alternation were observed,and the relationship between ORP and free iron oxide was analyzed to explain the mechanism of occurrence of iron and manganese neoplasms in Shenyang brown soil.Research provides a solid theoretical basis.The main results are as follows:(1)Under the influence of the combined effect of soil water and heat conditions,the redox potential(ORP)of the soil layer in the brown soil of Shenyang fluctuates,and the dry season is larger than that in the rainy season.During the intercropping period(mid-March and early April),the soil ORP decreased first(near or below 300 mV).During the dry and wet alternation period(May to August),the soil ORP was larger and alternately(200 to 500 mV).The oxidation and reduction potential of the same soil layer decreases with the increase of precipitation.During the period of freeze-thaw and dry-wet alternation,the ORP of each soil layer had a significant negative correlation with soil water content(freezing and thawing alternation r surface =-0.655*,rsoil layer=-0.676*,r bottom soil area =-0.579*,P<0.05,n=24;dry and wet alternating period r suface =-0.586*,r soil layer=-0.685*,r basal soil =-0.553*,P<0.05,n= 48).(2)The content of iron-manganese oxide(IMO)in each soil layer fluctuates with the seasonal variation of the climate.During the freezing and thawing alternation period,the IMO of different soil layers increased obviously,and the change of the wet and dry times was larger and alternately.Soil ORP has a good linear relationship with the change of IMO in different forms and the ORP of the soil layer and the subsoil layer showed a significant correlation with the effect of the surface ORP on the different forms of iron oxide(r free state ?0.756**,r Amorphous= 0.664**,P<0.01,n = 48)Negative correlation and reached a significant level(soil layer r free state =-0.474*,r Amorphous =-0.486*;basal soil r free state =-0.557*,r Amorphous=-0.671*,P<0.05,n = 48).In summary,IMO can better reflect the changes of soil redox environment.At the same time,the effect of ORP on the activation of IMO was not significant(P>0.05).Soil ORP had a good correlation with IMO during freeze-thaw and dry-wet alternation,which affected the activation or aging process.(3)Shenyang Brown began to thaw in mid March,late March through soil thawing period,freezing and thawing cycles for 10?15 d;soil from the surface downward and upward to the lower soil melts,soil thaw depth gradually deepened,the frozen layer thickness becomes thin,70?80 cm soil thawing the soil through at last.Alternate freezing and thawing thawing period(thawing permafrost layer interface and junction formation)monimolimnion,soil moisture saturation,for the formation of reducing environmental conditions.(4)Soil ORP decreased gradually with the increase of melting thickness,and the water content of 40?70 cm soil layer maintained the highest value.Soil ORP was at the lowest value(close to or even lower than 200 mV)for 4 to 5 days,the soil permeability decreased,the soil was restored from the reducing environment to the oxidative environment,and the ORP reached the normal value(between 300 and 400 mV).(5)During the freeze-thaw cycle,the upper layer of soil(0?0 cm)soil thawing interface with little change completely through when the free iron oxide,the range of 36.9?44.2 g/kg,while the lower layer(50?100 cm)of free iron oxide changes greatly,in the range of 42.5?57.1 g/kg.That is,when the upper soil is completely neutralized,the content of free iron oxide is lower than that at the beginning of thawing,while the lower soil layer is higher than the beginning of thawing.There was a close relationship between soil ORP and free iron oxide in this period and reached a significant level,The functional relation is y ?-0.0002x2-0.21x+89.042(r =-0.676**,P<0.01,n=45).