Effect Of Long-term Fertilization And Soil Management Regimes On Soil Organic And Inorganic Carbon Storage On Loess Soil

As a major component of the global carbon cycle, soil carbon pool plays an importantrole in global carbon cycling research. Meanwhile the soil carbon sequestration inagro-ecosystem is closely related to soil use and management approaches. On the basis of the20years long term fertilizer experiment on a loess soil at the “Chinese National Soil Fertilityand Fertilizer Use Efficiency Monitoring Base of Loess Soil”, we investigated the impact ofcontrasting land use patterns and fertilizer management regimes with a relatively long timespan on the soil carbon pool of organic and inorganic. Eleven treatments were included, theyare: Fallow, Setaside, un-amended control （CK）, nitrogen （N）, nitrogen and potassium （NK）,phosphorus and potassium （PK）, nitrogen and phosphorus （NP）, nitrogen phosphorus andpotassium （NPK）, wheat/maize straw （S） with NPK （SNPK） and dairy manure （M） with NPK（M1NPK and M2NPK）. The results are as follows:Under different management regimes, the storage of soil organic carbon in the soils ofFallow and CK, with an equivalent soil mass to that of top20cm soil of CK, remainedunchanged relative to the soil prior to the commence of the experiment （Initial soil）, while itwas significantly improved on treatments of NP and Setaside with an annual increase of347kg/hm²and518kg/hm², respectively. Under different treatment, the storages of soil inorganiccarbon for CK, NP, Fallow and Setaside were dropped dramatically compared to initial soil,particularly for NP, on which it was even significantly lower than other three treatments. Fortreatments where nutrient management treatments were applied in conjunction with thecropping regime of winter wheat and summer maize rotation （exclusive of Fallow andSetaside）, the storages of soil organic carbon in plough layer soils on a equivalent mass basison all but NK treatment were markedly enhanced compare with those of CK and initial soil ina order of statistic significance as follow: M2NPK>M1NPK>SNPK>NPK≈NP>PK≈N, of which, the maximum increase was observed on M2NPK with an annual mean value of944kg/hm², and a minimum value of127kg/hm²on N. Whereas considerable decreases ofthe soil inorganic carbon storage in plough layer soils on an equivalent mass basis were foundon all treatment except for PK and M2NPK in comparison to initial soil value, this is probablydue to the acidification of the soil as the consequence of either precipitation or fertilization. The fact that the storage of inorganic carbon on PK and M2NPK, in ca. top20cm soils onequivalent mass, remained stable relative to their initial value might suggest that soil organiccarbon may convert to inorganic form under some circumstances. The results also exhibitedthat the soil bulk densities on treatments those receiving no organic manure were droppedsubstantially, this result implied that the soil carbon storage on an equivalent mass basis ratherthan the equivalent soil depth could be a better indicator of soil carbon changes.By measuring the δ13C and counting the equivalent mass soil carbon storage in the soilprofile down to100cm in CK、Fallow、NPK、SNPK and M2NPK, we found that all thetreatments stated above could increase the soil carbon sequestration, notably M2NPK, wherethe stock of soil total carbon was enhanced by60kg/hm²in100cm soil profile as comparedto the initial soil. Soil organic carbon pool is gradually reduced with increasing soil depth; ofwhich, the soil organic carbon in equipment mass in0-20cm account for about30%of thetotal reserves within100cm soil. The highest soil inorganic carbon stock was observed inabout20-40cm soil horizon with the storages ranged from33t/hm²to42t/hm², and thengradually decreased with increasing soil depth. Due to the influences as the results of soil bulkdensity, leaching, recalcification, acidification and interact of crop growing, the responses ofinorganic matter to land uses and fertilizer managements could not be simply accounted at thesoil in the depth of0-40cm. But it is clear to see the soil organic carbon is increased under40cm layer. This finding provides further evidence that the soil organic carbon could transformto soil inorganic carbon in Loess soil. all the results implicated that good nutrientmanagements could not only improve soil fertility, but could also help to sequestrate carbon inthe investigated soil either in organic or inorganic form.Soil carbonate is an important component of soil carbon of calcareous soil, itsmeasurement is of significance to soil carbon cycling research. Based on soil carbonateanalyses of Loess soil with a gradient of soil carbonate content, three methods fordetermination of soil carbonate, which are volumetric calcimeter method, CO₂absorptionmethod and TOC analyzer method, were compared. The results showed a significantcorrelation between three methods. CO₂absorption method exhibited lower variation andhigher recovery rate, which could reach to98.5%on average, although the operation was timeconsumption than the other two methods, suggested it is more suitable for measurementwhere a higher accuracy is needed.