The Thai never lacked a rich food supply. Peasants planted rice for their own consumption and to pay taxes. Whatever remained was used to support religious institutions. From the thirteenth to the fifteenth century, however, a remarkable transformation took place in Thai rice cultivation. In the highlands, where rainfall had to be supplemented by a system of irrigation that controlled the water level in flooded paddies, the Thai sowed the glutinous rice that is still the staple in the geographical regions of the North and Northeast. But in the floodplain of the Chao Phraya, farmers turned to a different variety of rice--the so-called floating rice, a slender, nonglutinous grain introduced from Bengal--that would grow fast enough to keep pace with the rise of the water level in the lowland fields (see Crops , ch. 3).
The new strain grew easily and abundantly, producing a surplus that could be sold cheaply abroad. Ayutthaya, situated at the southern extremity of the floodplain, thus became the hub of economic activity. Under royal patronage, corvee labor dug canals on which rice was brought from the fields to the king’s ships for export to China. In the process, the Chao Phraya Delta--mud flats between the sea and firm land hitherto considered unsuitable for habitation--was reclaimed and placed under cultivation.