Soil Mineralogy and Clay Minerals

Abstract

Soil mineralogy indicates primarily the parent materials from which the soil has developed. It also translates valuable information regarding the past climatic conditions and how the transition from past to present day climate occurred. This chapter highlights the physical phenomena like swelling and shrinkage, aggregation and thixotropy as strongly related to the mineralogical composition of soils. Similarly, chemical phenomena like adsorption and desorption of heavy metals (e.g. Zn, Cd, Pd etc.), and fixation of P and K depend on a great extent on soil mineralogy, especially clay mineralogy. Clay minerals form bonds of varying strengths with soil humus resulting in clay-humus complexes of varying stability. Distribution of non-labile and labile C in soil is also closely related to the different clay minerals present in soil. Such relations of clay minerals with soil organic matter have great implications on soil C-sequestration. The clays and clay minerals are not only the integral part of soils but also the driving factors in the dynamics of edaphology and pedology. The chapter covers different aspects of mineralogy of Indian soils based on the studies conducted since the 1950s to till date. Information on the mineralogical compositions of all the major soil groups of India has been presented. Efforts are made to link soil mineralogy with pedogenesis and climate. Some site-specific soil features related to soil mineralogy, e.g. effect of zeolites on fertility of calcareous Vertisols, presence of dioctahedral smectites in ferruginous Alfisols, spatial association of red and black soils, interstratification of kaolinite with smectite at some sites have been documented. Thereafter, the impact of soil minerals on different soil physical and chemical properties followed by the interaction of clay minerals with humus and different pesticides and other soil pollutants have also been established. The chapter ends with the findings of some advanced studies on soil mineralogy as carried out by Indian researchers.