Significance of the Formation of Calcium Carbonate Minerals in the Pedogenesis and Management of Cracking Clay Soils (Vertisols) of India

Abstract

Micromorphological studies were performed in order to understand the factors and processes involved in the formation of calcium carbonate (CaCO3) in twenty three soil series of Vertisols representing sub-humid, semi-arid and arid climatic regions of Peninsular India. The study indicates that Vertisols contain both pedogenic calcium carbonate (PC) and non-pedogenic calcium carbonate (NPC) irrespective of the ecosystems to which they belong. The NPCs are part of the parent material of Vertisols. Dissolution of NPCs and recrystallization of dissolved Ca2+ ions are responsible for the formation of PCs. Vertisols of arid and semi-arid climates contain more PC in their soil control section (SCS) than those of sub-humid climates. Formation of PC is the prime chemical reaction responsible for the increase in pH, the decrease in the Ca/Mg ratio of exchange site with depth and in the development of subsoil sodicity. Petrographic and scanning electron microscopic (SEM) examination of quartz, feldspars and micas indicate little or no alteration, discounting the possibile formation of smectite during Vertisol formation. X-ray diffraction (XRD) analysis of clays indicates that smectites of Vertisols are fairly well crystallized and do not show any sign of transformation except for hydroxy interlayering. The preservation of the crystallinity of smectite and the lack of transformation of primary minerals thus validate the hypothesis of positive entropy change during the formation of Vertisols.The precise cause-effect relationship between CaCO3 of pedogenic and non-pedogenic origin, and exchangeable Mg, Na and Ca percentages (EMP, ESP and ECP) has been established in the study. This indicates that impoverishment of Ca2+ ions on the exchange sites of Vertisols needs to be controlled by rehabilitation methods that can replenish Ca2+ ions, and thus the study provides relevant information for future land resource management programmes not only on Vertisols of India but also on similar soils occurring elsewhere.

Microtopography as a factor in the degradation of Vertisols in central India

“…Its expansion beyond 1Á4 nm on glycolation of K-saturated and 300 C-heated samples indicates that it possesses a small layer charge. No difference in the nature of the smectite were detected among the soils of MH and ML positions, and no hydroxy-interlayered smectite, as reported elsewhere in sodic black soils (Kalbande et al, 1992;Srivastava et al, 2002), was found.…”

ICRISAT, India Soils:Yesterday, Today and Tomorrow

“…Black soils in sub humid ecosystems contain less CaCO 3 and maintain higher Ca/Mg (exchangeable) ratio (>2) than those in dry areas like Kasireddipalli. We predict that if appropriate management techniques are adopted, the Ca/Mg ratio (Figure 10 f ) could be 2 or higher 28,39 . Higher Ca/Mg ratio helps black soils in the wetter climate to maintain good physical conditions and in better productivity than the SAT black soils.…”

“…Similar rise in CaCO 3 in red soils could have been observed if they were analysed for CaCO 3 in similar SAT soils of southern peninsula 22 . These carbonates coated by Fe-Mn mottles 28 may not effervesce in field with dilute HCl, but in laboratory with 100 mesh soil samples the presence of carbonates has been ascertained 29 . In earlier report on red soils (Patancheru) CaCO 3 was not reported 15,18 , but pristine red soils (as collected for the present study) show the presence of climatically induced pedogenic CaCO 3 in SAT environment.…”

“…This is also reflected in reduced Ca/Mg ratio in soils (Figure 6 g). Concentration of extractable Mg down the depth of soil along with extractable Na, especially in red soils (Figure 6 i) indicates the initiation of subsurface sodicity which might affect the entire soil if management intervention is not adopted in SAT areas 11,19,26,28 . Cation exchange capacity is controlled by soil colloids (mostly clay) and organic matter.…”

Natural Chemical Degradation of Soils in the Indian Semi-Arid Tropics and Remedial Measures

“…Therefore, in addition to the aridity of the climate, the texture has an important role in the accumulation of carbonates in soils 28 . The accumulation of soil inorganic carbon (SIC) in terms of formation of PC in soils hitherto was considered as an undesirable natural endowment as it caused the impairment of soil productivity 1,29 . The formation of PC in the arid climate enhances the pH and also the relative abundance of Na + ions on soil exchange sites and in the solution; and the Na + ions in turn cause dispersion of the fine clay particles.…”