Long-term Effects Of Fertilization On Soil Inorganic Carbon Change And Its Mechanism

Soil inorganic carbon?SIC?is an important carbon pool in arid and semi-arid regions and plays an important role in the carbon cycle of terrestrial ecosystems.The fertilization system is one of the agronomic management measures that has the strongest impact on SIC.Different fertilization measures have important impacts on the SIC changes.Based on 40 years of long-term fertilization experiments on the Loess Plateau,and six treatments were chosen for this work:unfertilized control?CK?,nitrogen fertilizer annually?N?,nitrogen and phosphorus?P?fertilizers annually?NP?,straw plus N added annually and P fertilizer added every second year?NPS?,farmyard manure added annually?M?,and farmyard manure plus N and P fertilizers added annually?NPM?and deserted arable land?F?.Supported by stable carbon isotopes,this research hoped to carry out long-term effects of different fertilization on the SIC changes and its mechanism,to explore the change rule of long-term fertilization on SIC in the soil profile,to reveal the mechanism of long-term fertilization on the formation of pedogenic carbonate?PC?in SIC,to clarify the contribution of SIC to carbon emissions,to determine the carbon sequestration potential of SIC and its contribution to soil carbon emission,and finally,to provide scientific theory and technical support for carbon sequestration and emission reduction of SIC in dry land in China.The main results and conclusions were showed as follow:?1?Long-term effects of fertilization on soil inorganic carbon pool in different soil profilesThe application of organic fertilizer was more beneficial to the accumulation of soil organic carbon and inorganic carbon pool compared with long-term?40 years?application of chemical fertilizer.Compared with unfertilized control?CK?,under different soil depth profiles,long-term application of chemical fertilizer?N and NP?reduced SIC reserves.In 0-60 cm soil layer,application of chemical fertilizer?N and NP?reduced SIC reserves by 10.9-17.2%.What's more,M and NPM treatments not only significantly increased SOC reserves,but also increased SIC reserves by 8.5-18.8%,thereby significantly increasing STC reserves by 21.6-33.1%.In addition,in the 0-150 cm soil layer,compared with unfertilized control,NP,NPS,M and NPM treatments increased soil organic carbon reserves by 8.1-26.3%,and long-term application of chemical fertilizers?N and NP?reduced the reserves of soil total carbon?STC?by about 6%,and M and NPM treatments increased STC reserves by 9.7-12.4%.There was a positive correlation between SOC and SIC in soil profile.?2?Long-term effects of fertilization on the formation of pedogenic carbonate in different soil profilesAnalysis using stable carbon isotope technology showed that,in the 0-60cm soil layer,compared with CK,all fertilization treatments reduced the primary carbonate?LC?reserves and increased the PC reserves,and the application of chemical fertilizers?N and NP?significantly reduced LC reserves by 23.8-59.7%,and increased PC reserves by 4.3-32.8%.In addition,M and NPM treatments significantly increased PC reserves by 37.1-47.0%,but did not significantly reduce LC reserves.In the 0-60cm soil profile,there was a very significant positive correlation between SOC and PC.Long-term application of organic fertilizer could promote the accumulation of PC and the transformation from SOC to SIC,which provided a preliminary basis for organic fertilizer to promote the carbon retention of SIC in dryland.?3?Effects of soil inorganic carbon and organic carbon on CO₂ emissionsStudies using the?¹³C natural abundance method showed that the contribution of SIC to CO₂emission was 9.3-34.9%in farmland soil.Compared with CK,the application of chemical fertilizers?N and NP?did not significantly increase the proportion of SIC to CO₂ emission.It was likely that the long-term application of nitrogen fertilizer has led to the dissolution of a large number of carbonates in the early stage and reached a state of equilibrium in the later stage.Compared with NP treatment,except for NPS treatment measured after wheat sowing,NPS,M and NPM treatments measured after wheat sowing,after wheat blooming period and during leisure period declined the proportion of SIC to CO₂ emissions by 24.2-69.7%,20.0-48.6%and 36.4-60.4%respectively.In wheat growths period and during leisure period,in a comparison with CK,the application of chemical fertilizer?N and NP?slightly reduced the cumulative soil CO₂ emissions and the cumulative CO₂ emission caused by SOC,while NPS,M and NPM treatments all showed significant increase.In addition,the application of chemical fertilizer?N and NP?reduced the cumulative CO₂ emission caused by SOC.Compared with NPM treatment,M treatment significantly increased the cumulative CO₂ emission caused by SIC.