Soil degradation during the period 1967–1995 in Bangladesh

Abstract

Changes in soil pH, exchangeable acidity, contents of exchangeable bases (Na, K, Ca, and Mg) and available phosphorus within the top 100 cm layers during the period 1967–1995 were evaluated in this study. Over the 27 y period, mean soil pH decreased slightly (0.07 to 0.49 unit) in all the physiographic units. Exchangeable acidity increased slightly (< 1 kmol ha-1) in Ganges Floodplain (GF), Brahmaputra Floodplain (BF), and Meghna River and Estuarine Floodplain (MF), moderately (4.5–13.7 kmol ha-1) in Old Himalayan Piedmont Plain (OHP), Northern and Eastern Piedmont Plain (NEP), and Chittagong Coastal Plain (CCP), and sharply (25.6–60.2 kmol ha-1 ) in the other units except in Tista Floodplain (TF) where a decrease of 1.8 kmol ha-1 was observed. Exchangeable Na showed a positive change in OHP, GF, Madhupur Tract (MT), MF, and CCP but a negative change in the other units. All the physiographic units showed a decline in the contents of exchangeable K, Ca, and Mg except for OHP and MT which exhibited an increase in the contents of exchangeable K. Effective CEC decreased in all the physiographic units except in Barind Tract (BT). Available phosphorus level showed an increase in TF, GF, MF, Surma-Kushiyara Floodplain (SKF), and NEP but a decrease in the other units over the same period. During the period 1967–1995, OHP and MT exhibited a decline in all the characters except for exchangeable K. Soils in TF, GF, MF, SKF, and NEP showed an improvement in available phosphorus but a decline in the other elements. BT, BF, and CCP showed a decline in all the fertility characters. Generally in the soils of Bangladesh the contents of exchangeable cations declined with signs of progressive acidification. However, available phosphorus changed positively or negatively for various physiographic units over the same period. Natural and anthropogenic effects played important roles in the decline of these soil characters in Bangladesh.