Effect of nitrogen and water stress on growth and yield of sweet potato

Water stress and low soil fertility have been identified as major reasons for low tuber yield in sweet potatoes (Ipomoea batatas) in developing countries in the tropics. This study was designed to determine effects of N fertilizer application on water use and yield of sweet potato, and to understand physiological processes leading to the effects of water stress on yield. Two field experiments were conducted in south-east Queensland. In each experiment there was an irrigated trial and a water-stressed trial. Dry matter production and tuber yield at maturity, and radiation interception, leaf relative water content, fibrous root length and soil water content during water stress periods were determined. Addition of nitrogen (N) at 50 kg/ha increased plant growth and tuber yield under irrigated conditions. In the water stress trials, N application increased canopy interception of solar radiation and fibrous root growth but had no effect on water uptake, dry matter production and tuber yield. A prolonged water stress period appeared to override any potentially positive effect of N application. The results also show that sweet potato in a long growing environment can recover from severe water stress which develops during early growth stages.