Response of sweet potato cultivars to acid soil infertility factors. I. Effects of solution pH on early growth

Sweet potato [Ipomoea batatas (L.) Lam.] is cultivated on soils varying widely in chemical properties, but relatively little is known about the effects of pH on the growth of this crop. In commercial and subsistence agriculture, sweet potato is propagated mostly from stem cuttings. This paper reports effects of a range of pH treatments (3.5-8.0) in flowing solution culture on early growth from cuttings of 15 sweet potato cultivars. Root growth was either greatly reduced or inhibited at pH 3.5. Increasing the pH to 4.0 markedly increased root development. Further increases in solution pH from 4.0 to 8.0 did not appear to affect root growth in most cultivars. Top growth in most cultivars showed a tendency to increase when pH was increased from 3.5 to 5.5 before declining with further increases in solution pH. The sweet potato cultivars studied differed widely in their tolerance to low pH, producing 16-48% of maximum top dry mass at pH 3.5. Tissue analysis from selected cultivars showed that K and Ca appeared to be limiting at pH 3.5, while P may have been deficient at pH 8.0. Results of this study indicate that low pH per se does not appear to be a major factor responsible for poor sweet potato yields in acid soils.