The heavy dark soil associated with floodable valley-bottoms is a

The heavy dark soil associated with floodable valley-bottoms is hydromorphic soil. Hydromorphic soil is also known as wetland soil and is characterized by its waterlogged nature. It is found in areas where the soil is frequently saturated with water, such as floodable valley-bottoms. Hydromorphic soil has a dark color due to the accumulation of organic matter, and it is also known to be very heavy, which makes it difficult to cultivate. On the other hand, lateritic soil is commonly found in areas with a tropical climate and has a reddish color, while ferrallitic soil is characterized by its yellowish or reddish color, and it is found in areas with a high concentration of iron and aluminum. Podzolic soil, on the other hand, is found in cold and humid regions, and it is characterized by its ash-gray color. Therefore, the heavy dark soil associated with floodable valley-bottoms is hydromorphic soil.