Preliminary Mechanism Study On The Effect Of Fertilization On Reactive Minerals And Their Carbon Sequestration In Upland Red Soil

Red soil is widely distributed in China with the total areas up to 2.18 million square kilometers.Its arable land accounted for approximately 28%in the national cultivated land areas.However,due to the long-time irrational use of land,the problems of soil degradation is extremely serious.The intrinsic reasons for the degradation of red soil are related to characteristics of ferrallitic weathering,acidification,and anti-corrosion.Most importantly,human factors are becoming dominant in accelerating the process of soil degradation,e.g.,the long-term and excessive use of chemical fertilizers.As a result,the content of soil organic matter showed a gradual downward trend in agricultural ecosystems.Therefore,it is an important topic to improve the soil fertility,especially increasing the contents of soil organic matter(SOM),in red soil region.The iron and aluminum minerals in the soil is the main mechanism of soil carbon sequestration and fertility improvement in red soil.In this paper,red soil was collected from a long-time fertilization experiment station at Jinxian,Jiangxi province.The objectives of this paper were 1)to characterize soil colloid after long-term fertilization treatment by analyzing the relationships between soluble organic carbon and soluble mineral elements,soil total carbon and reactive mineral,2)to conduct the semi-quantitative analysis of organic carbon,nitrogen fractions and mineral elements(Al,Si)in soil colloids by XPS technique,3)to in-situ analyze the binding capacity between organic carbon and mineral elements by NanoSIMS images,and 4)to exploring the influence of plant roots on soil reactive mineral and organic carbon cycle by combining different aperture sieves and indoor pot experiment.The results achieved from this paper would provide theoretical and technical support for the optimization of agricultural management and the development of sustainable agriculture.Main results of this paper are listed as follows.1)The results of upland red soil in Jinxian Jiangxi long-term location experiment station showed that long-term NPK treatment could not only lead to red soil acidification but also decrease the concentration of soluble organic carbon in soil colloid and decrease soil fertility.While long-term M or NPKM treatments could significantly ameliorate the acidity of red soil,improve the ability of soil nitrogen supply and carbon storage.The order of soil pH is NPK(4.60)<CK(5.33)<NPKM(5.73)<M(5.94)after long-term fertilization treatment.2)Long-term NPK treatments could not increase the amount and activity of reactive minerals in soil.However,long-term M or NPKM treatments could release iron aluminum silicon mineral elements from bulk soil,thus improving the content of soil reactive minerals.Meanwhile long-term application of organic fertilizer can make the stable aromatic units and substituted alkanes C-C(H)in organic matter turn into more activated phenols,ethers,carbonyl,carboxyl C-O,C=O,COO-,thus strengthening the binding capacity of organic carbon with minerals and eventually enhancing the soil carbon sequestration capacity.3)The results of XPS,XANES showed that the distribution of iron,aluminum and silicon elements in the reactive minerals has increased under long-term M or NPKM treatment when compared with NPK treatment.NanoSIMS results further showed that M or NPKM treatments improved the binding of iron and aluminum minerals with soil organic carbon when compared with NPK treatment.4)NanoSIMS images showed that the organic-inorganic complexes in the soil colloid had a significant spatial heterogeneity in the sub micron level.5)Indoor pot experiment results showed that soluble silicon content was low in mesh 0.45?m sieve compared with the soil in mesh 1000?m sieve,while,the soluble aluminum content was increased and the contents of active mineral elements(Feo Alo Sio)all significantly reduced,indicating that the dissolution effect of root exudates promotes the release of mineral elements in the soil,which is beneficial for the turnover and storage of new carbon.In summary,by combining long term fertilization experiment and pot cultivation experiment,we show the interaction between soil mineral elements and soil organic carbon cycle affects soil carbon storage.The reactivity of minerals in the soil can promote the carbon sequestration and in return the newly added soil organic matter may also promote the activation of minerals in soil which will improve soil carbon sequestration and soil fertility.