UQ eSpace

Abstract

Sweet potato (Ipomoea batatas (L.) Lam.) is an important tropical root crop grown and consumed throughout the world. It is generally believed to be tolerant of low fertility soils, and is grown widely on acid soils in the tropics. These soils cover extensive areas of the tropics, and pose major infertility problems for the crops produced. Little is known, however, about the effects of individual acid soil infertility factors on the growth of sweet potato, or of the genotypic variation within this crop in tolerance to these factors. The present study was undertaken to investigate the effects of low pH, low calcium (Ca) and high soluble aluminium (Al) on the growth of sweet potato. This study involved the use of non-flowing and flowing solution culture techniques using solutions comparable in composition with those reported for soil solutions from tropical acid soils. Two solution culture studies showed that sweet potato is moderately to highly tolerant of low solution pH, good growth being achieved by a number of the cultivars at pH 4.0. Growth was very poor at pH 3.0 or 3.5. The 15 sweet potato cultivars studied differed widely in their response to low solution pH. However, between the pH range of 4.0 to 7.0, growth did not appear to be affected, although there were differences among the cultivars tested. At pH 8.0, sweet potato growth was severely depressed, possibly due to low P uptake by the plants. The tolerance of sweet potato to low pH made it possible to study the effects of low Ca and high soluble Al at pH 4.2. An increase in Ca concentration in solution from 4 to 1328 µM generally had a positive effect on sweet potato grown in solution at pH 4.2. Sweet potato appears to have a lower solution Ca requirement than many of the other plant species. In this study, most of the 15 sweet potato cultivars tested were tolerant of low Ca (45 µM). Nevertheless, the cultivars differed widely in tolerance with relative top yields at 45 µM Ca ranging from 56% to 104%. Cultivars LO323 and L135 were the least tolerant to low Ca while L46 and L49 were the most tolerant cultivars.