Effects of Sodium on Potassium Nutrition in Three Tropical Root Crop Species

ABSTRACT

The potassium (K) nutrition and high K requirement of tropical root crops may be affected by their sodium (Na) status, as has been observed in a number of plant species. Solution culture was 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 attributed to differences in Na translocation to plant tops. At maximum Na supply, the Na concentration in index leaves averaged 1.82% in tannia, 0.205% in sweet potato, and 0.0067% in taro. An increase in the supply of Na resulted in a shift in 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.

Keywords:

• critical concentration
• potassium
• sodium
• solution culture
• sweet potato
• tannia
• taro

ACKNOWLEDGMENTS

AusAID and the Papua New Guinea Department of Agriculture and Livestock are gratefully acknowledged for providing a scholarship and study leave, respectively, to enable S.R. Ivahupa to undertake postgraduate studies at the University of Queensland. The Australian Centre for International Agricultural Research (ACIAR) funded research through Project 9101, “Nutritional Disorders of Tropical Root Crops.” Mr. G. Walters, Mr. W. Bean, Mrs. J. Mercer, Mr. G. Kerven, Mr. D. Appleton, Mr J. Oweczkin, and Mrs. J. Priest are thanked for their assistance with the experimental work.

Notes

¹Due to an error in nutrient delivery, treatments K₄Na₃ and K₄Na₄ in the sweet potato experiment were discarded from the analysis. Statistics given are for analysis of treatments K₀ to K₃ only, excluding data from the K₄ treatment. A separate analysis of Na₀ to Na₂ across all K treatments was used to establish that dry weight at K₄ did not differ significantly from that at K₃.

¹Due to an error in nutrient delivery, treatments K₄Na₃ and K₄Na₄ in the sweet potato experiment were discarded from the analysis. Statistics given are for analysis of treatments K₀ to K₃ only, excluding data from the K₄ treatment. A separate analysis of Na₀ to Na₂ across all K treatments was used to establish that the K concentration at K₄ differed significantly from that at K₃.

¹Due to an error in nutrient delivery, treatments K₄Na₃ and K₄Na₄ in the sweet potato experiment were discarded from the analysis. Statistics given are for analysis of treatments K₀ to K₃ only, excluding data from the K₄ treatment. A separate analysis of Na₀ to Na₂ across all K treatments was used to establish that the Na concentration at K₄ differed significantly from that at K₃.