Effects Of Long-term Soil Management Regimes On Storage Of Soil Inorganic Carbon And Its Relationship With Organic Carbon In A Manural Loess Soil

In arid and semiarid areas, the soil inorganic carbon(SIC) is the main part of soil carbon library; its storage is estimated to be 2-10 times than soil organic carbon(SOC) storage. Hence, the investigation of the effects of soil management regimes exerted on soil inorganic carbon pool is of significant in reducing CO2 emissions, which is one of the most important greenhouse gases. We measured the inorganic carbon profile distributions and storages in different soil management regimes of a rainfed and an irrigated experiment on loess soil, both of which has lasted for 24 years at the “Chinese national soil fertility and fertilizer use efficiency monitoring base of loess soil”, with an attempt to seek the relationship in between. There were eleven treatments in irrigated fertilizer experiment, they are:un-amended control(CK), nitrogen(N), phosphorus and potassium(PK), nitrogen and potassium(NK), nitrogen and phosphorus(NP), nitrogen phosphorus and potassium(NPK), maize straw with NPK(SNPK) and two dose of dairy manure(M) with NPK(M1NPK and M2NPK),Set aside and Fallow. The rainfed experiment was including CK, NP, NPK, MNPK, Set aside and Fallow treatments. We also spiked the Ca2+ at five levels to soils with contrasting organic carbon contents, one of which has been subjected to CK treatment and another to M2 NPK treatment for 24 years, and incubated for 6 weeks, to study the changes of soil inorganic carbon during the process of organic matter mineralization.The results are as follow:The distribution of inorganic carbon in the soil profile(0-300 cm) showed the similar pattern as "S" curve in which the content of inorganic carbon was higher on topsoil(0-40 cm), then rapidly declined with increase in soil depth and reached the lowest value at the 80-140 cm depth, and then gradually increased and reached a maximum value at 160-180 cm depth, thereafter declined again to the bottom.Under irrigation condition, Setaside showed a significantly higher SOC content than Fallow in 0-20 cm soil horizon. Balanced fertilization treatments showed significantly higher SOC than CK, with an ascending magnitude order of: CK<NP ≈NPK<SNPK<M1NPK<M2NPK. The Fallow showed significant higher SIC stock than Setaside and Cropping in 0-100 cm soil profile. Under cropping system, the soil inorganic carbon stocks in 0-100 cm depth in M2 NPK treatment was significantly higher than others. However, in 0-300 cm soil profile the SIC stocks: Fallow showed a significantly higher value than Setaside. The SIC stocks in M1 NPK and M2 NPK treatments were significantly lower than other fertilizer treatments. The SIC stocks in 0-100 cm depth was significantly positively correlated with topsoil organic carbon content, while SIC stocks in 0-300 cm depth was negatively correlated with topsoil organic carbon content. The results indicated that the marked increase in SOC content as a result of fertilization, especially of organic manure application do not necessarily be accompanied with increase in SIC sequestration.Under rainfed condition, the Cropping showed a significantly higher SIC stock than Setaside and Fallow in 0-100 cm soil profile. The SIC stocks of 100 cm soil profile on fertilizer treatments were significantly higher than CK. However, in the 0-300 cm soil profile the SIC stock of NPK treatment was substantially lower than CK、NP、MNPK, and no differences were observed between the later three. The Setaside showed a significantly higher SOC stock than Fallow and Cropping in 0-100 cm soil profile, and the SOC stocks in fertilization treatments were markedly higher than CK following the order of: CK<NP≈NPK<MNPK. Whereas, the fertilizer treatments showed significant higher SOC stocks than CK in 0-300 cm soil profile, but no difference between each other. No significant relationship between SOC and SIC was found.During the 42 days of incubation, the SIC content was declined with the decreasing soil pH. The content of SIC was increased with the increasing Ca concentration. Addition of Ca could lead to more inorganic carbon sequestration in soil with low SOC content(soil from CK traetment). Soil pH and calcium has a significant positive interaction effect on the inorganic carbon content under low SOC soil.