The Chao Phraya Delta has four rice cultural regions each with distinct hydrographic conditions. They are; 1) the old delta, where transplant fields of short to medium-age varieties and broadcast fields of floating rice form a mosaic that reflects the topographic relief; 2) the fluvial part of the young delta, which is characterized by an expanse of floating rice; 3) the delta flat, which was formerly a monotonous area of broadcast deep-water but now accommodates rainy season transplanted rice, dry season transplanted rice, and traditional broadcast rice, depending on the type of irrigation facilities that have been introduced; and 4) the coastal zone, which is dominated by long-established transplanting of possibly non-photosensitive varieties of rice.