Interpretation of tissue analysis for potassium nutrition in tropical root crops dependent on sodium concentration

摘要

Solution culture studies were used to study the effects of K and Na supplies in tannia (Xanthosoma sagittifolium (L.) Schott.), sweet potato (Ipomoea batatas (L.) Lam.) and taro (Colocasia esculenta (L.) Schott.) At low K supply, Na ameliorated symptoms of K deficiency and increased growth in tannia, and to a lesser extent in sweet potato, but not in taro. None of the species responded to Na at adequate K supply. Differences in response to Na were attributable to differences in Na uptake into plant tops. Taro exhibited a high level of Na exclusion, while tannia displayed little or no exclusion. An increase in the supply of Na decreased the critical K concentration for deficiency (i.e. 90% of maximum yield) in index leaves from 2.9% to 1.2% in tannia, and from 4.8% to 2.5% in sweet potato. The critical K concentration in taro was 3.3%, irrespective of Na supply. To overcome the problem in tannia and sweet potato of determining the critical concentration relevant to a leaf sample of unknown K status, a relationship was established for each species relating the critical K concentration to the concentration of Na in the index leaves.