Department of Plant Sciences

A pot culture experiment was conducted at the College of Horticulture, Kerala Agricultural University, India, to study the effect of potassium- magnesium interaction in plants using okra (Abelmoschus esculentus Moench) as the test crop. The experiment was conducted on an alluvial soil, sandy clay in texture, acidic (pH- 4.9), high in organic carbon, and medium in available phosphorus (P) and potassium (K). The treatments included factorial combinations of four levels of potassium from K0 to K3 (0, 15, 30 and 45 kg K2O ha-1 as muriate of potash) and four levels of magnesium (Mg) from Mg0 to Mg3 (0, 10, 20 and 30 kg MgO ha-1). At all K levels, combined with Mg application at 10 kgha-1, an increase was observed in dry matter production but at higher levels of Mg a decrease occured. Increasing the level of K from K0 to K3 in the presence of low levels of Mg caused a progressive increase in the yield while at higher Mg levels increasing K reduced the yield. Increased addition of K without Mg significantly increased the crude protein contents. Application of Mg generally decreased the crude protein content of harvested fruits. Increasing the rate of K application also progressively and significantly decreased the crude fibre. The magnitude of decrease was increased in the presence of Mg. At all levels of Mg, as the K application rates increased, the ascorbic acid content also showed a significant increase.

Addition of Mg caused a significant increase in the nitrogen (N) uptake at each level of K though the magnitude of increase diminished as levels of Mg increased. The application of high rates of Mg decreases the favorable effect of K on P uptake and hence Mg is seen to have an antagonistic effect on P uptake. A positive interaction existed between K and Mg on the uptake of K. At higher levels of K, a significant increase in K uptake was noticed as Mg levels were increased. Calcium (Ca) uptake was significantly reduced with increasing K levels especially in the absence of Mg. Though K application up to K2 caused a non significant increase in Mg uptake, further increase to K3 reduced the uptake. In the presence of a particular level of Mg, increasing the K levels did not bring about a significant variation in the sulphur uptake by the plant.