All the following are fertile plains except

Out of the options provided, the "erosional plains" are not considered fertile plains. Fertile plains are those that are rich in nutrients and suitable for agriculture and farming. Erosional plains, on the other hand, are formed by wind or water erosion and are not known for their fertile soil. Loess plains are formed from wind-blown silt and have fertile soil due to the accumulation of nutrients. Alluvial plains are formed by the depositing of sediment by rivers and also have fertile soil. Flood plains are areas that are regularly flooded by rivers and also have fertile soil due to the depositing of nutrients from the floodwaters.