SOIL DEGRADATION DURING THE PERIOD 1961-1995 IN BANGLADESH .2. SELECTED CHEMICAL CHARACTERS

Changes in soil pH, exchangeable acidity, contents of exchangeable bas es (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) i n all the physiographic units. Exchangeable acidity increased slightly (<1 kmol ha(-1)) in Ganges Floodplain (GF), Brahmaputra Floodplain (B F), and Meghna River and Estuarine Floodplain (MF), moderately (4.5-13 .7 kmol ha(-1)) in Old Himalayan Piedmont Plain (OHP), Northern and Ea stern Piedmont Plain (NEP), and Chittagong Coastal Plain (CCP), and sh arply (25.6-60.2 kmol ha(-1)) in the other units except in Tista Flood plain (TF) where a decrease of 1.8 kmol ha(-1) was observed. Exchangea ble Na showed a positive change in OHP, GF, Madhupur Tract (MT), MF, a nd CCP but a negative change in the other units. All the physiographic units showed a decline in the contents of exchangeable K, Ca, and Rig 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 inc rease in TF, GF, MF, Surma-Kushiyara Floodplain (SKF), and NEP but a d ecrease in the other units over the same period. During the period 196 7-1995, OHP and BIT exhibited a decline in all the characters except f or exchangeable K. Soils in TF, GF, MF, SKF, and NEP showed an improve ment in available phosphorus but a decline in the other elements. BT, BF, and CCP showed a decline in all the fertility characters. Generall y in the soils of Bangladesh the contents of exchangeable cations decl ined with signs of progressive acidification. However, available phosp horus changed positively or negatively for various physiographic units over the same period. Natural and anthropogenic effects played import ant roles in the decline of these soil characters in Bangladesh.