Alfalfa nutritive quality for ruminant livestock as influenced by ambient air quality in west-central Alberta

Alfalfa ( Medicago sativa) nutritive quality response to ambient ozone (O 3), sulfur dioxide (SO 2) and oxides of nitrogen (NO x ) were assessed at three locations in west-central Alberta, Canada (1998–2002). Yield data were segregated into high and low relative to overall median yield. Ozone concentrations (hourly median and 95th-percentile) and precipitation ( P) contributed 69 and 29%, respectively, to the variability in crude protein (CP) concentration in low-yielding alfalfa, whereas mean temperature ( T) and relative humidity (RH) collectively influenced 98% of the variation in CP in high-yielding alfalfa. Three-fourths of the accounted variation in relative feed value (RFV) of low-yielding alfalfa was attributable to P, T and RH, whereas median and 95th-percentile hourly O 3 concentrations and SO 2 and NO x exposure integrals contributed 25%. In contrast, air quality, (mainly O 3) influenced 86% of the accounted variation in RFV of high-yielding alfalfa, and T and P collectively contributed 14%. Exposure to ambient concentrations of phytotoxic air pollutants affected nutritive quality of alfalfa for ruminant livestock in a yield-dependent manner.