Rice requires high temperature (above 24°C) and a good amount of rainfall (more than 150 cm). These conditions favour rice cultivation in Kerala. But wheat is cultivated mainly in temperate regions. It requires 10°C to 26°C temperature and 75 cm of rainfall for its cultivation.These conditions are not present in Kerala, which is a tropical region.
Alluvial soil is suitable for rice cultivation. Well drained alluvial soil is ideal for wheat cultivation. Kerala which receives more than 200 cm rainfall does not have well drained alluvial soil.
Since the above mentioned geographical factors are not present in Kerala, wheat is not cultivated here.