Studies On Redistribution Of SOC And Soil Respiration Under Water Erosion At Black Soil In Northeast China

With the development of black soil reclamation,the soil erosion had become more serious,and it had made the loss of SOC and fertility seriously.This study was about the soil erosion and the redistribution of carbon.The object of this study was the typical slope cropland which was in the northeast black soil area in Heilongjiang Qinggang.The situ monitoring and simulate rainfall had been used to measure the change of soil respiration rate and the relationship between soil respiration and hydrothermic factors in different slope positions?summit,slope-shoulder,slope-back,slope-toe?,and the redistribution characteristic.We analyzed the impact of soil erosion on the speed of C migration,the deposit rate and the soil respiration rate,and expected to offer scientific basis for formulating reasonable technology of fertility promotion and scientific assessing soil respiration in erosion farmland.The main results were as follows:?1?During the progress of erosion,SOC and DOC were redistributed,the content of SOC and DOC were different in different slope positions.The DOC content in slope-back was respective 33.5%?22.9%?15.4%higher than the content in summit,slope-shoulder,slope-toe.The SOC content in slope-toe was respective 17.3%,8.0%higher than the content in summit,slope-shoulder.The SOC content in slope-shoulder was respective 8.6%higher than the content in summit,slope-shoulder.The content of DOC of surface soil from high to low in turn was slope-shoulder(20.7 mg kg^-1),slope-back(18.9 mg kg^-1),summit(17.0 mg kg^-1),slope-toe(14.3 mg kg^-1),respectively.The content of DOC of surface soil in slope-shoulder and slope-back were respectively 44.8%,32.2%?p<0.05?significant higher than slope-toe's.The settled layer of SOC was at 20-40 cm.In 2016 the yields in slope-back and slope-toe were respective 45.9%and 39.3%higher than the yield in summit,and respective 45.6%?39.0%higher than the yield in slope-shoulder,The yields in different slope position were different.In 2015,the yields in slope-back and slope-toe were respectively 42.6%and 55.9%higher than the yield in summit,and respectively 26.9%,38.8%higher than the yield in slope-shoulder.?2?The results of soil respiration monitoring showed that the flux of soil respiration in summer was higher than it in spring and autumn,and in toe-slope it was significant higher than that in summit,shoulder-slope,back-slope?p<0.05?.The relationship between the flux of soil respiration and soil temperature was linear correlation in all positions?p<0.05?.The flux of soil respiration and soil volatile water content had no significant correlation?p>0.05?.The accumulation emission of soil respiration in toe-slope was highest(1921.23 g CO₂ m^-2),and it was respectively significant higher than these in back-slope(1624.80 g CO₂ m^-2),in shoulder-slope(1564.97 g CO₂ m^-2),and in summit(1424.51 g CO₂m^-2)by 18.5%,22.8%and 34.9%?p<0.05?.These indicted that different slope positions have different law of soil respiration.It should be done for us to completely consider the differences of different slope positions.If we wanted to have a scientific evaluation about the soil respiration of slope cropland,and reduce the deviation caused by using the monitoring results in flat ground to assess the soil respiration in slope cropland.During the spring maize growth seeding,the correlation between soil respiration and soil moisture content at summit,slope-shoulder,slope-back were significant.But the correlation between soil respiration and soil temperature at four slope positions were not significant.The research showed that the distribution of SOC would make the soil respiration rate increase,and it would be easier influenced by soil moisture content than soil temperature.?3?Simulated rainfall experiments showed that during the soil erosion process,the SOC and DOC loss rate would present linear with the increase of rainfall intensity.The slope of the linear relationship between SOC loss rate and rainfall intensity were all 0.002 in 3°,5°and 7°slope croplands.But the s the loss rate of DOC were different.They were respective 0.077 in 5°slope cropland;0.067 in 3°slope cropland;0.038 in 7°slope cropland.Under the condition of simulation,the rate of change between the loss rate of DOC and the rainfall intensity was different,but the rate of change about SOC was same in slope cropland with different gradients.The results of field monitoring showed that the main losing loctions of were at summit and slope-shoulder.The losing intension of runoff,sediment,SOC and DOC respectively were 166.67 ml m^-2,0.37 g m^-2,36 mg m^-2 and 1.6 mg m^-2.