EFFETS DU pH ET DES REGIMES HYDRIQUES DES SOLS SUR LES RENDEMENTS ET LA TENEUR EN Mn DE LA LUZERNE ET DU LOTIER CULTIVES EN SERRE

Abstract

Alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.) were grown under greenhouse conditions, on Ste-Rosalie clay and St-Jude sand adjusted at pH of 5.0, 6.5 and 7.5, in order to determine the effect of soil pH and soil moisture regimes on the yields of the two legumes. Three soil moisture regimes were used: (1) humid (H1), with soil moisture between saturation point and field capacity; (2) optimum (H2), with soil moisture between field capacity and 70% of this value; (3) dry (H3), with soil moisture between 50% of field capacity and wilting point. Under the dry soil moisture regime (H3), birdsfoot trefoil behaved in the same way as did alfalfa. Their drought resistance decreased as the soil pH increased. Dry matter yields were reduced by 61.5% when soils were limed at the pH of 7.5. Under the humid soil moisture regime (H1), the productivity of alfalfa decreased much more than that of birdsfoot trefoil. The effect of excess soil moisture on alfalfa was mostly observed on the unlimed soils. Under these wet and acid soil conditions, alfalfa was intoxicated and suffocated due to high exchangeable manganese content and poor soil aeration. Liming soils to the pH of 7.5 decreased exchangeable Mn in soils to a non-toxic level and alfalfa could then grow well enough to transpire off the excess of soil water. Birdsfoot trefoil was much less influenced by soil acidity and poor drainage than alfalfa was.