annual crop water requirement (CWR) of sugarcane in Sri Lanka

In Sri Lanka, sugarcane is commercially cultivated in dry and intermediate zones where annual rainfall exhibits peculiar bimodal pattern of distribution. The total annual rainfall receives in the intermediate zone varies from 1750 to 2500 while in sugarcane growing areas of dry zone, it varies from 1500 to 1700 mm. The annual crop water requirement (CWR) of sugarcane varies from 1200-1500 mm per annum and it depends on the local climatic conditions, variety and crop growth. Generally, the rainfall receives in these areas sufficient to meet the considerable fraction of crop water requirement of sugarcane but balance has to be supplied externally by irrigation to obtain higher crop growth. The normal crop cycle of sugarcane is 12 months. Thus, commercial planting under irrigation is carried out usually in every month, available rain-water could be utilised to the maximum efficiency while reducing irrigation water demand by planting sugarcane to coincide higher water demanding stages of crop growth to rainy periods and manipulation of other agronomic practices accordingly.