ABSTRACT
Expansion of shifting cultivation onto hilly lands and salinization has increased areas of degraded land in Bangladesh. High hill areas cover about 756,700 ha, of which 32,500 ha are under shifting cultivation. In these areas, topsoil loss is about 1.5 million t y−1. The total area in low hill areas is about 573,900 ha out of which 20,900 ha are under arum, ginger, turmeric, pineapples, etc. and the soil loss is estimated to be about 1.0 million t y−1. Lack of drainage capacity, flash floods, burial of fertile land by sandy debris, and landslides are off-site effects. Deforestation, acidification, dwindling organic matter contents, and nutrient depletion are evident in the eroded soils. Increase of cropping intensity accelerates nutrient mining and unbalanced use of fertilizers results in imbalance of soil nutrients. In the uplands more areas are low in P, K, and S than in areas under wetland cultivation. Zinc deficiency has increased under intensive irrigated rice cultivation and Mg, B, and Mn are also reported to be low. Long-term data indicate a decrease in soil nutrient contents and pH values in the extensively cultivated soils of Bangladesh. About 1.8 million ha of land are tidally flooded and waterlogged, of which 0.8 million ha of land are flooded daily to a depth of 60–80 cm during summer. Salt-affected areas increased significantly from 0.83 million ha from 1964–1976. The areas with low pH (4.5–5.5) and extremely low pH (2.0–4.0) are 34,900 and 62,000 ha respectively. About 2.3 million ha of land have adverse physical conditions and about 1.7 million ha are vulnerable to river bank erosion. To address these issues appropriate ameliorative measures with suitable farming practices are required.
