EFFETS DES RÉGIMES THERMIQUES ET HYDRIQUES, DES pH DU SOL ET DE LA FUMURE PHOSPHATÉE SUR LA RÉPONSE AU PHOSPHORE DE LA LUZERNE

Abstract

The objectives of this study were to determine the effects of phosphorus application, air temperature, soil moisture regime and soil pH on the yield response of, and soil phosphorus availability to, alfalfa (Medicago sativa L ’Saranac’). The following treatments were used in factorial combination: three moisture regimes: (1) semi-dry, with soil moisture between FC (100% of available water or field capacity) and WP (0% of available water or wilting point), (2) optimal, between FC and 70% of available water, (3) wet, between saturation point and FC; three rates of phosphorus in the form of disodium phosphate (0, 12.5 and 25.0 P kg−1 of dry soil; and three soil pH levels: original (5.2 or 5.7), 6.5 and 7.5. Half of the alfalfa was grown in a warm greenhouse section with a minimum daytime temperature of 25 °C and 19 °C at night and the other half in a cool section with a daytime minimum of 15 °C and 9 °C at night. Although shoot yields were higher under warm than under cool conditions, yield response to phosphorus was greater under cool than warm growing conditions. Yield increases due to phosphorus were linear under optimum and wet soil moisture regimes and nonsignificant under the semi-dry regime. Phosphorus application increased root weight by 18% under the cool regime compared to 14% in the warm greenhouse. Phosphorus uptake by alfalfa increased with increasing rates of soil-applied P, except in semi-dry soils at warm temperature, where no effect of P on P uptake was recorded. Phosphorus uptake increased significantly with soil pH and was higher under warm temperature and optimal water regime.Key words: Phosphorus fertilization, available phosphorus, alfalfa, soil moisture regime, air temperature, phosphorus uptake