Ca-zeolites as Transitory Eco-System Engineers: Hydro-Pedological Evidence in Cracking Clay Soils (Vertisols) of Semi-Arid Marathwada Region, Maharashtra

摘要

Out of the area under cracking clay soils (Vertisols) in Peninsular India, nearly 5.6 % is occupied by Vertisols in the state of Maharashtra. Research endeavors on the genesis and management of Vertisols of semi-arid tropical (SAT) climate was accomplished during the last few decades for major regions of Maharashtra except Marathwada. But such effort needs to be extended to this region as precise information on the physical and chemical characteristics associated with the hydro-pedology of Vertisols developed in the alluvium of the Deccan trap basalt of the Marathwada region is not adequate enough to suggest appropriate management protocols to enhance their productivity. Majority of the Marathwada region support rain-fed agriculture with low productivity. Therefore, systematic studies on the SAT Vertisols of Marathwada region are warranted to know the extent of regressive pedogenetic processes that are operative in SAT Vertisols of this region and also to develop cause-effect relationship of natural soil degradation (if any) in presence of soil modifiers or ecosystem engineers like Ca-zeolites. Ten SAT Vertisols were selected in the districts of Buldhana, Parbhani, Osmanabad, Beed, Jalna and Aurangabad of Maharashtra state. These Vertisols contain Ca-zeolites in their basaltic parent materials. Ca- zeolites are considered as prolonged ecosystem engineers in supporting the successful enterprise for forestry, horticultural and cereal crops, and spices in non-calcareous and acidic Vertisols, Alfisols and Mollisols developed on the Deccan basalt or in its alluvium under the humid tropical climate of the Western Ghats and Satpura Regions for the several millions of years. In contrast, SAT Vertisols of Marathwada showed contrasting physical and chemical characteristics so much that their US Soil Taxonomic classes are Typic Haplusterts and Sodic Haplusterts. Due to the dominant pedogenetic processes like the formation of pedogenie CaCO_3 (PC) and illuviation of Na-satu-ratedfine clays, some Typic Haplusterts showed more exchangeable Mg percentage (EMP) than exchangeable Ca percentage (ECP) in their Bss horizons, which caused lowering of saturated hydraulic conductivity (sHC) at a value little over 10 mm hr~(-1), preventing strong swelling of plasmic fabric and rise ofpH near to 8.2 and above. Zeolites could not prevent the lowering of exchangeable Ca/Mg ratio < 1.5 almost throughout depth, rise in pH, exchangeable Na percentage (ESP) and EMP, weak swelling of plasmic fabric and reducing the sHC ? 10 mm hr1 in Sodic Haplusterts. This anomalous chemical environment in SAT Vertisols appears to be related to zeolite reserve and the rate of Ca ions release from zeolites amidst the formation of PC as the major pedogenetic process. Selective analytical method to quantify the amount of soil Ca-zeolites is still not available and in its absence the anomalous situation will continue to baffle the researchers. The rate of formation of PC must have been much higher than the rate of release of Ca ions from zeolites in SAT environments as evidenced from the impaired soils' hydraulic properties. This kind of hydro-pedological process would not support the irrigationpractice to raise agricultural crops including sugarcane in the Marathwada region of Maharashtra. Ca-zeolites have proved their worthiness as prolonged ecosystem engineers while supporting successful enterprise for various land uses in the Deccan basalt derived non-calcareous and acidic soils of the humid tropical (HT) climate. Since Ca-zeolites losetheir significance in the contemporary dominant hydro-pedological processes (regressive pedogenesis) theywould remain as transitory ecosystemengineers in SAT Vertisols of the Peninsular India in general and Marathwada region in particular.