EFFETS DES DOSES DE BORE, DES REGIMES HYDRIQUES ET DU pH DES SOLS SUR LES RENDEMENTS DE LA LUZERNE ET DU LOTIER ET SUR L’ASSIMILABILITE DU BORE

Abstract

Alfalfa (Medicago sativa L. cv. Vernal) and birdsfoot trefoil (Lotus corniculatus L. cv. Leo) were grown under greenhouse conditions in order to determine changes in boron response and availability following variations in soil pH and soil moisture regimes. Three rates of boron applications were selected: 0, 1.5, and 3.0 ppm of B. Soil pH was adjusted to 5.0, 6.5 and 7.5, respectively. The soil moisture regimes were fixed as following: (1) very dry (H1) with soil moisture between 50% of field capacity and wilting point, (2) dry (H2), with soil moisture between field capacity and wilting point. (3) optimum (H3), with soil moisture between field capacity and 70% of this value. Boron fertilization was more useful to alfalfa than to birdsfoot trefoil. Optimum rate was found to be 1.5 ppm of B. On Ste-Rosalie clay, the yield increase due to boron was 22% on soils under the dry regime (H2) but was almost non-existant at the very dry (H1) and optimum water regime (H3). Boron application on Greensboro loam was more efficient on soils undergoing dry (H2) and very dry soil moisture regime (H1) than on soils where moisture conditions were optimum (H3). Dry matter yields were increased by a factor of 10 under dry (H2) and very dry (H1) soil moisture regimes compared to a factor of 4 under optimum soil moisture regime (H3). Under acid soil conditions, no yield increase was obtained following boron applications. Boron availability and response of the two legumes to B was also decreased by overliming soils to pH 7.4. The cyclic drought periods that happened under dry (H2) and very dry (H1) soil moisture regime produced similar effects. Boron availability and efficiency as plant nutrient was greatly reduced, if not annihilated, by the combined effect of repeated drought cycles and by either excessive soil acidity or overliming.