Micromorphological Criteria to Identify Calcium Carbonates of Pedogenic (PC) and Non-Pedogenic (NPC) Origin in SAT Soils and Their Relevance to Pedogenesis and Management

The soils of arid and semi-arid climates in India are moderately to highly calcareous. Soils of the Indo-Gangetic Plains (IGP) and ferruginous soils of southern India under semi-arid tropical (SAT) environments are marked by the presence of pedogenic calcium carbonate (PC) and the absence of non-pedogenic calcium carbonate (NPC). However, in the Vertisols of India, the presence of both PC and NPC is commonly observed. In the field, it is very difficult to distinguish both these forms of calcium carbonate (CaCO3) and also in the laboratory because both forms react equally with hydrochloric acid. To distinguish these two forms of CaCO3, the outstanding role of micromorphological studies has been realized by pedologists and earth scientists in India. This innovative analytical tool of the early twentieth century has helped to understand precisely the processes of formation of PC and NPC, and their relevance in the soil formation of the SAT climate. This chapter highlights the key micromorphological features of PC and NPC that can be easily identified under the microscope. Research results so far obtained have expanded the basic knowledge of the contemporary pedogenesis of SAT soils.