Soil moisture extraction under fully irrigated conditions was the same in BollgardII and conventional varieties, except where season length allowed later crop and leaf growth in the conventional variety. *BollgardII grown under fully irrigated conditions maintained a yield advantage and required 6.3ML/ha of irrigation water as opposed to 7.0ML/ha for the conventional full irrigation treatment. *A greater reduction in water use efficiency was apparent in BollgardII where moisture stress was experienced at or close to cut-out, except where late season rainfall alleviated this stress.