Once established, cassava can grow in areas that receive just 400 mm of average annual rainfall. But higher yields have been obtained with much higher levels of water supply. Research in Thailand indicates that maximum root yields are correlated with rainfall totalling about 1 700 mm during the fourth to eleventh month after planting. Cassava also responds well to irrigation. In trials in Nigeria, root yields increased sixfold when the quantity of water supplied by supplementary drip irrigation matched that of the season’s rainfall.