Effects of flood protection on soil fertility in a Riverine floodplain area in Bangladesh

Abstract

Abstract The study compared the nutrient status of flood‐protected and ‐exposed soils in the Chandpur Irrigation Project (CIP) southeast Bangladesh. Significant differences in nutrient concentrations between protected and exposed soils were correlated with differences in deposited river‐borne sediments, irrigation water quality, local topography, cropping practices and fertilizer applications. Significant differences in nutrient concentrations were measured within soils before and after the monsoon season. Sediments deposited in agricultural lands following river flooding were significantly higher than local topsoils in organic matter, nitrogen, potassium, calcium, sulphur, magnesium and manganese, but significantly lower in copper and zinc. Nutrients contributed in dissolved form by floodwaters were low by comparison to those introduced by sediment deposition. Nitrogen‐fixing blue‐green algae were abundant in surface water and attached to vegetation in both flood‐exposed and ‐protected areas. We concluded that river‐borne sediments are potentially valuable sources of soil nutrients. Depending on the topography of agricultural lands in relation to sediment‐bearing rivers and on the physical and chemical nature of the sediments, their exclusion from agricultural lands by embankments could be a potentially negative impact of flood control developments in some areas in Bangladesh.