Potassium and Magnesium Interaction in Alfalfa (Medicago sativa L.)

Alfalfa (Medicago Sativa L.) absorbs large amounts of soil potassium (K) and magnesium (Mg). K fertilization increases alfalfa yield but the changes in the yield as influenced by combined K and (or) Mg fertilization, are not known. Our hypothesis is that K and Mg antagonistic relationship will influence the yield of alfalfa. The objective of this study was to determine influence of K and Mg fertilization on alfalfa yield and yield components during the three yr experimental period. The experiment was a factorial with four K levels (0, 100, 200 and 300 kg K2SO4. ha-1) and three Mg levels (0, 100 and 200 kg MgSO4 ha-1) arranged in the form of a randomized complete block design with three replications. Application of K increased alfalfa dry matter (DM) production. Total K removal in the herbage increased linearly with increasing K rates and reached 1440 kg K ha-1 with the application of 300 kg K2SO4. ha-1 yr-1, compared with 900 kg yield ha-1 in the control treatment. Addition of Mg partially affected DM production. K fertilization depressed plant tissue Mg concentration and Mg uptake. Also, addition of Mg fertilizer decreased plant K uptake. Incremental additions of K increased alfalfa grain yield, K concentration and uptake in the third year after establishment. Mg fertilization did not influence grain yield and Mg content in grains. After harvesting, soil ammonium acetate extractable K (Ke) decreased considerably in check plot (127 mg. kg-1), but it increased with increasing K rates.