CO₂ Shift And Its Effect Of Source And Sink In Karst Soil Under Different Improvements

Under the geological background,the formation rate of soil is slow,the soil horizon is thin,the conservation of soil fertility and water is bad,and the low yield soil can account for more than 60 percentage of the total soil area.The karst dynamic system,which is mainly composed of carbon-water-calcium,is sensitive to the external environment change.The rocky desertification area in Southwest China is 90 thousand square kilometers,and the contradiction between humans and land is prominent.It is an important issue to realize the production benefit and ecological benefit maximization on the limited land.Soil carbon sequestration field test was carried out in Guohua rocky desertification comprehensive treatment reasearch base with three solutions: Filter Sludge?LN?,Filter Sludge + Straw + Biogas Surry?LNJZ?and Filter Sludge + Straw + Cow Manure?LNJN?.The soil CO₂ shift and its source and sink effect to atmosphere under different improvements were compared.Main research progresses are as followes:?1?The speed,volume and depth of CO₂ produced by the decomposition of modified substances in soil were affected by different improvements.Under LN improvement,in the first year,the soil CO₂ concentration is significantly higher than that of the second year.During the first year of the rainy season,there was a single peak.30 cm and 10 cm soil depth of CO₂ is the most affected by filter sludge decomposition."Filter Sludge + Straw + Slurry" : early decomposition of modified substances is fast,nutrient is easy to leaching.The single peak phenomenon of “Filtered Sludge” improvement disappeared.Comparing with the LN improvement,the increase of CO₂ is more stable and sustainable.Soil profile CO₂ concentration :40cm>30cm>20cm>10cm.CO₂ accumulated in the depths of the soil.Under LN improvement,CO₂ produced by modified substances decomposition was the most slow and lasting,and CO₂ increase was greater than that of other improvements in the following year.CO₂ of shallow soil is higher than that of deep layer.CO₂ accumulated in shallow layer of soil.?2?Under LN improvement,carbon emissions by soil-air interface increased by 35.2t CO₂/km²,and carbon emissions decreased by 212.9t CO₂/km² after the application of Straw and Biogas Slurry,and carbon emissions increased by 279.5t CO₂/km² after Straw and Caw Manure application.These were related to the accumulation of soil CO₂ in deep and superficial layers with two combinations.Soil improvement had influence on the diurnal variation of soil respiration.Diurnal variation of soil respiration under LNJZ and LNJN delay three hours.Soil improvement improved soil CO₂ concentration,which inhibited soil respiration.At night,the inhibition decreased,and soil respiration rate and the near surface atmospheric CO₂ concentration at night were higer than that in the daytime.?3?[Ca²⁺+Mg²⁺]/HCO₃^-?equivalent concentration?of all the modified and controlled soil water were greater than 1,which indicated that the sulfuric acid and nitric acid were involved in the dissolution of carbonate rocks in the soil,and it is necessary to deduct this part of HCO₃^- to calculate the net consumption of soil water CO₂.There are a large amount of calcium salt and sulfate in the Filter Sludge,which result in the type of soil water being Ca-SO4.According to the law of ion conservation,the concentration of ions involved in karstification is calculated.At the peak of fertilization,the net consumption of CO₂ in the soil of the test area was negative.The reason was that the H+ of the inorganic acid and HCO₃^- in the water caused the CO₂ to overflow from the water.Under LN improvement,pH value decreased and severe degassing of HCO₃^- and H+ occurred in soil water.Eventually,although the soil dissolution rate increased,the average annual contribution rate of carbonate was-0.32 with an annual reduction of CO₂ consumption 0.66mmol/L.Application of Straw and Biogas Slurry greatly weakened the degassing effect caused by Filter Sludge,and reduced the degree of enhancement of soil erosion rate,resulting in CO₂ annual net consumption increased by 0.065mmol/L;Application of Straw and Caw Manure caused serious degassing in August,and weakened the degassing effect in other months,resulting in almost unchanged annual net consumption of CO₂.In summary,the "Filter Sludge + Straw + Biogas Surry " improvement program is conducive to the accumulation of soil CO₂ to the depths.Not only reduced the soil carbon emissions by 212.9 tCO₂/km²,but also increased the soil water CO₂ net consumption of 0.065mmol/L.It is a better improvement program.