EFFECTS OF POTASSIUM FERTILIZER AND FALL HARVESTS ON ALFALFA GROWN ON THE EASTERN CANADIAN PRAIRIES

Abstract

The objectives of the study were to determine the effect of soil and fertilizer potassium (K) on the yield and chemical composition of alfalfa (Medicago sativa L.), and whether fall harvesting (October) had detrimental effects on alfalfa grown under the relatively cool and short growing season of the Eastern Canadian Prairies. Vernal alfalfa was sown on five soils, two high and three low in amounts of exchangeable K. Three harvests were taken each year in June, July, and October at the full bud stage. The soils were rated on their potential potassium supplying power (PKSP). The effect of fertilizer K on increasing the availability of soil K and on the K and N composition of the forage were measured. The PKSP of the soils was not related to initial levels of exchangeable K. However, soils with low exchangeable K and low PKSP required an annual application of 200 kg K/ha to produce maximum yield. There was response to K fertilizer on only one of the soils with high exchangeable K, and then only to the first increment. At maximum yield on all soils, the K and N contents of the forage at full bud were greater than 2.0% and 3.0%, respectively. When the K content of the forage was less than 1%, severe winter injury occurred and yields decreased. With adequate K fertilizer fall harvesting had no detrimental effects on alfalfa production. Comparisons of the K and N contents of the forage indicates that increasing the concentration of K available to the crop may have a beneficial effect on N-fixation. Key words: Medicago sativa L. ’Vernal’, potential potassium supplying power, nitrogen fixation