Disstribution Of Iron Oxides And C Sequestration In Red Paddy Soil

Iron oxide in soil was active, and was considered to have an important role in C sequestration. In order to explore the effect of iron oxides in carbon sequestration, the contents and the components of the soil organic matter in bulk soil was investigated, and two methods was used to determine the relationship between the iron oxides and the soil organic matter in different size aggregates of paddy soil, based on analyzing the distribution patterns of iron oxides in different treatments composed of N, P and K fertilizer and combined application of chemical fertilizer with green manure (Astragalus), rice straw and pig manure from a long-term experimental field. Furthermore, incubation experiment was carried, which control conditions by adding organic materials and ferrihydrite during wetting and drying cycles. The results were as follows:Two methods were used to determine the contents of Feo and Fed. Take the method of1,10-Phenanthrolinethe as an example, showed the phenomena of increasing Feo content (10.5%-58.5%) and Feo/Fed value (19%-76%), but decreasing Fed content (0.4%-13.8%) in bulk soil. The content of Feo and Fed in different size of fractions of soil decreased as the following order:250-53μm,<53μm,2000-50μm. However, the value of Feo/Fed decreased as<53μm,250-53μm,2000-250μm.Treatments composed of N, P and K fertilizer and combined application of chemical fertilizer with green manure (Astragalus), rice straw and pig manure enhanced the content of the SOC in the soil, the content of SOC was13.7%-31.8%higher in organic fertilizer treatments than the CK. The content of SOC in different size of fractions in soil decreased as the following order:250-53um,2000-250μm,<53μm, and exhibited positive, negative and positive correlates with Feo, Fed, and Feo/Fed respectively. It is worth mention that the recalcitrant carbon seemed more correlated to the iron oxides, for it had larger correlation coefficient.The incubation experiment results show that soil pH was decreased, Eh was increased and also the rate of CO2emission was increased after adding different organic materials. The content of complex iron was decreased remarkablely during the wetting-drying cycles, but Pig farmyard manur could enhance the formation of the complex iron.These results suggest that the interaction between iron oxides and soil organic carbon is complicated. Organic material could activate the iron oxides. Mechanism of the C sequestration depends largely on the distribution variation and the activity of the iron oxides by long-term fertilizer managements in paddy soil.