Quality and morphological characteristics of alfalfa as affected by soil moisture, pH and phosphorus fertilization

Abstract

Alfalfa (Medicago sativa L. ’Saranac’) was grown in a greenhouse on Ste-Rosalie clay and Danby gravelly sandy loam to determine the effects of phosphorus fertilization, air temperature, soil moisture regime and soil pH on chemical composition and plant morphology. The following treatments were applied in factorial combination: three moisture regimes (1, semi-dry, with soil moisture between field capacity or 100% of available water and wilting point or 0% of available water; 2, optimal, between field capacity and 70% of available water; 3, wet, between saturation point and field capacity), 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 (natural, near 5.4, 6.5 and 7.5). Half 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 was grown in a cool section with a daytime minimum of 15 °C and 9 °C at night. Quality of alfalfa was generally improved by water deficit as shown by decreased concentrations of acid detergent fiber (ADF) and acid detergent lignin (ADL) and increased concentrations of crude protein (CP). Cold temperatures decreased ADF content which indicates that quality of alfalfa grown under cold compared to warm temperature regimes is better. Phosphorus fertilization seemed to have more effects on plant morphology and quality under cold than warm temperature regimes. In general, concentrations of CP, ADF and ADL, stem length, leaf area and the number of stems increased in parallel with soil pH. The data indicate that low temperature and low soil moisture regimes were generally associated with higher quality alfalfa than were high temperature and wet soil moisture regimes.Key words: Alfalfa, soil moisture regime, air temperature, phosphorus fertilization, soil pH