EFFETS DE LA FUMURE POTASSIQUE ET DES RÉGIMES HYDRIQUES SUR LA RÉPONSE AU POTASSIUM DE LA LUZERNE ET DE LA FLÉOLE DES PRÉS

Abstract

The objectives of this study were to determine the changes in yield response and water use efficiency of alfalfa (Medicago sativa L. 'Saranac') and timothy (Phleum pratense L. 'Climax') to potassium applications and variations in soil moisture regimes. For each of the two test crops the factorial combination of the following treatments were replicated three times: three soils (Ste Rosalie clay, Greensboro loam, and Danby sandy loam), potassium (0, 25, 50 and 100 mg K kg−1 of dry soil) and three moisture levels: (1) optimal, 70–100% of available water (AW); (2) semi-dry, 0–100% AW; and (3) dry, 0–50% AW. Yield increases of 68% for alfalfa and 40% for timothy were produced by potassium applied to soil under the optimal moisture regime with almost no yield increase under dry soil moisture conditions. Water use efficiency was higher for alfalfa than for timothy, and increased with rates of potassium on Greensboro loam and Danby sandy loam but not on Ste Rosalie clay. Potassium content of alfalfa was lower when grown at optimal soil moisture than in the dry regime. Differences in potassium content between moisture regimes were small for timothy. Due to higher yields, potassium uptake by alfalfa was greater when soils were cropped at optimal moisture. However, less exchangeable potassium was found after the experiment in soils cropped to alfalfa in the optimal moisture regime than in soils under the dry moisture regime. Therefore potassium fertilizer was most effective at the optimal moisture level (near field capacity). Key words: Potassium fertilization, exchangeable potassium, soil moisture regime, potassium uptake, alfalfa, timothy