Potassium nutrition, ionic relations, and oxalic acid accumulation in three cultivars of Setaria sphacelata

Abstract

The effects of potassium and nitrogen fertilization on growth, chemical composition, ionic relations, and oxalic acid levels in the Nandi, Kazungula, and Narok cultivars of Setaria sphacelata have been studied. Potassium response curves have been derived and their use in predicting 'critical potassium levels' in these grasses discussed. Cation-anion balances (total inorganic cation concentrationndash;total inorganic anion concentration) have been calculated and the effects of potassium and nitrogen fertilization on ionic relations are discussed. The Kazungula and Narok cultivars contained higher levels of the cations calcium, magnesium, sodium, and ammonium when grown under limiting potassium conditions than when supplied with adequate potassium. The Nandi cultivar was similarly affected but did not accumulate sodium. All plants with high levels of potassium in their tissues also contained high levels of nitrate when the nitrogen supply was adequate. The cation-anion balance increased with increasing potassium fertilization in all cultivars but there was an interaction between potassium fertilization and nitrogen fertilization. Potassium and nitrogen fertilization resulted in large increases in oxalic acid levels. It is shown that the amount of oxalic acid accumulated is related to the cation-anion balance.