Elsevier

Environmental Pollution

Volume 149, Issue 1, September 2007, Pages 99-103
Environmental Pollution

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

https://doi.org/10.1016/j.envpol.2006.12.009Get rights and content

Abstract

Alfalfa (Medicago sativa) nutritive quality response to ambient ozone (O3), sulfur dioxide (SO2) and oxides of nitrogen (NOx) 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 O3 concentrations and SO2 and NOx exposure integrals contributed 25%. In contrast, air quality, (mainly O3) influenced 86% of the accounted variation in RFV of high-yielding alfalfa, and T and P collectively contributed 14%.

Introduction

Alfalfa (Medicago sativa) is grown extensively throughout Alberta, Canada for hay, pasture, dehydration and seed production. Over the past 50 years, harvesting of forested areas and development of pulp, oil and gas industries have contributed to acceleration of land clearing and development of field crop and livestock operations in the west-central region of the province. Collectively, the non-agricultural activities represent potentially significant sources of phytotoxic air pollutants, and their impact on sensitive crop species such as alfalfa has been identified as a major air quality issue in the region. The principal phytotoxic air pollutants of concern in the study area are sulfur dioxide (SO2), oxides of nitrogen (NOx or NO, nitric oxide + NO2, nitrogen dioxide) and ozone (O3).

Impacts of exposures to ambient and elevated levels of nitrogenous and sulfurous air pollutants and of O3 on metabolism, growth and nutritive quality of herbaceous vegetation have been documented in both field studies and controlled-environment experiments (Dreisinger and McGovern, 1970, Bell, 2000, Furlan et al., 2004, Krupa et al., 2004a). Although the effects of exposure to elevated concentrations of individual air pollutants on alfalfa yield have been reported (Dreisinger and McGovern, 1970, Skärby, 1984, Cooley and Manning, 1988), little is known about such effects on nutritive quality, and even less is known about their combined effects and relative importance compared with meteorological or growth-regulating variables (Muntifering et al., 2006). Because alfalfa is an economically important livestock forage crop and its nutritive quality is used for pricing alfalfa hay in Canada and the US (Linn and Martin, 1989), we applied a holistic concept of airshed management to assess effects of exposure to ambient concentrations of multiple phytotoxic air pollutants on alfalfa nutritive quality through an integrated consideration of total pollution emissions in the west-central region of Alberta.

Section snippets

Materials and methods

Nutritive quality response of alfalfa (M. sativa L., cv. ‘Beaver’) to ambient concentrations of atmospheric SO2, NOx and O3 was assessed at three sites in west-central Alberta, Canada over five growing seasons (1998–2002). At each site, there were two main harvests (one primary-growth in early July and one re-growth in early September) of alfalfa per growing season per study plot, and air quality and select meteorological parameters (global solar radiation, temperature, relative humidity, wind

Results

Across all 67 harvests for which data were considered in detailed modeling of alfalfa yield, primary-growth alfalfa had higher concentrations of NDF (P < 0.006), ADF (P < 0.022) and lignin (P < 0.092), lower (P < 0.0001) concentration of CP, and lower (P < 0.004) RFV than did re-growth alfalfa (Table 1). Similarly, high-yielding alfalfa had higher concentrations of NDF (P < 0.0001), ADF (P < 0.0001) and lignin (P < 0.0001), lower (P < 0.031) concentration of CP, and lower (P < 0.0001) RFV than did low-yielding

Discussion

Nutritive quality is a very important consideration when buying or selling alfalfa hay, and CP concentration has been used traditionally as one measure of alfalfa nutritive quality for ruminant livestock. However, CP concentration alone is not a fully satisfactory predictor of nutritive quality in forages across a broad range of growing conditions, and other factors such as concentrations of cell-wall constituents, which in turn influence intake and digestibility by ruminant livestock, are more

Acknowledgements

We acknowledge the support of the members of the West Central Airshed Society (WCAS) of Alberta (http://www.wcas.ca/home/home.php) for sponsoring the air quality – alfalfa yield study and for their permission for Elaine Ryl (field coordinator) to provide us with the plant materials used in the present investigation.

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