Spectroscopic Evidence of the Improvement of Reactive Iron Mineral Content in Red Soil by Long-Term Application of Swine Manure

Mineral elements in soil solutions are thought to be the precursor of the formation of reactive minerals, which play an important role in global carbon (C) cycling. However, information regarding the regulation of mineral elements release in soil is scarce. Here, we examined the long-term (i.e., 23 yrs) effects of fertilisation practices on Fe minerals in a red soil in Southern China. The results from chemical analysis and Fourier-transform infrared spectroscopy showed that long-term swine manure (M) treatment released greater amounts of minerals into soil solutions than chemical fertilisers (NPK) treatment, and Fe played a dominant role in the preservation of dissolved organic C. Furthermore, Fe K-edge X-ray absorption near-edge fine structure spectroscopy demonstrated that reactive Fe minerals were mainly composed of less crystalline ferrihydrite in the M-treated soil and more crystalline goethite in the NPK-treated soil. In conclusion, this study reported spectroscopic evidence of the improvement of reactive Femineral content in the M-treated soil colloids when compared to NPK-treated soil colloids.

土壤溶液中的矿质元素被认为是反应性矿物形成的前驱体，而反应性矿物在全球碳（C）循环中发挥着重要作用。然而，目前关于土壤矿质元素释放调控机制的相关研究仍较为匮乏。本研究针对中国南方红壤，探究了为期23年的长期施肥模式对土壤铁矿物的影响。化学分析与傅里叶变换红外光谱结果显示，长期猪粪肥（M）处理组向土壤溶液中释放的矿质元素总量显著高于化学肥料（NPK）处理组，且铁元素在溶解态有机碳的固持过程中占据主导地位。此外，Fe K边X射线吸收近边精细结构光谱分析表明，猪粪肥处理的土壤中反应性铁矿物主要以低结晶度水铁矿为主，而化学肥料处理的土壤中则以高结晶度针铁矿为主。综上，本研究通过光谱学证据证实，与化学肥料处理的土壤胶体相比，猪粪肥处理的土壤胶体中反应性铁矿物含量得到显著提升。