Departments of Engineering and Plant and Animal Sciences, Nova Scotia Agricultural College, Truro, Nova Scotia, Canada A Comparison of Methods Used to Determine Biomass on Naturalized Swards R. C. Martin, T. Astatkie, J. M. Cooper, and A. H. Fredeen AuthorsÕ address: Dr R. C. Martin, Department of Plant and Animal Sciences, Dr T. Astatkie (corresponding author; e-mail: tastatkie@nsac.ns.ca), Department of Engineering, Ms J. M. Cooper, Department of Engineering, and Dr A. H. Fredeen, Department of Plant and Animal Sciences, Nova Scotia Agricultural College, PO Box 550, Truro, Nova Scotia, B2N5E3, Canada With 3 figures and 3 tables Received July 1, 2004; accepted August 13, 2004 Abstract An experiment was conducted in 2000 to compare simple visual estimate, sward height and rising plate meter (RPM) methods for determining forage biomass in mixed-species, naturalized, rotationally grazed dairy and beef pastures. Measurements were taken pre- and post-grazing on 10 sampling dates at the dairy pasture, and post-grazing at 13 sampling dates at the beef pasture. For each sampling date, the effectiveness of each method for estimating the actual biomass from a quadrat was evaluated using regression analysis. The results for the visual estimate method were not consistent, with non-linear relationships occurring early and late in the season. While the meter stick was most effective in the dairy pasture, the RPM was most effective in the beef pasture. Species composition and structural characteristics of the stand were important factors affecting accuracy of biomass estimation. Equations developed for each method and site using data from all dates had low R 2 -adjusted values, and were unreliable predictors of biomass. The results from individual sites and dates were extremely variable, with no single method effective in all circumstances. To estimate forage biomass in mixed- species, naturalized pastures, standard quadrat harvesting remains the most reliable method, provided that enough quadrats are clipped to adequately represent a given area. Key words: dry matter — forage biomass — pasture — rising plate meter — sward height Introduction Canada’s Atlantic region has tremendous potential to produce forage for ruminant consumption. This potential has been largely untapped: it has been estimated that stocking densities on most pastures in the region could be doubled (Firth 2001). In an effort to improve pasture management and the production of ruminant systems in Atlantic Canada, the Atlantic Pasture Research Group has been conducting gra- zing experiments using beef and dairy herds. Although the opportunities in Atlantic Canada are limited for grazing of uniform ryegrass (Lolium perenne L.) pastures (Kunelius et al. 2004), many farmers are managing mixed-species naturalized pastures. These pastures are charac- terized by a diversity of species and variability of species distribution throughout the pasture. Mean- ingful research into pasture management in the region should include studies of naturalized pas- tures, but determining forage biomass in mixed- species naturalized pastures can be challenging. The most accurate method to estimate forage biomass is to clip the forage from a quadrat and determine the dry matter weight, but this can be time consuming. A number of researchers have investigated alternative methods of estimating forage biomass (Haydock and Shaw 1975, Murphy et al. 1995, Harmoney et al. 1997, Virkaja¨rvi 1999, Benkobi et al. 2000, Sanderson et al. 2001). In relatively uniform stands of single forage species or two-species mixtures these methods can be effective. Gourley and McGowan (1991) compared the rising plate meter (RPM) to direct plot harvesting in a stand of white clover (Trifolium repens L.) and perennial ryegrass (L. perenne L.) and found that the techniques were similar in their ability to detect significant differences in herbage biomass among various fertilizer treatments. In addition, the RPM allowed a 47 % reduction in labour expended. In mixed-species stands results have been less consistent. Murphy et al. (1995) compared three methods (capacitance meter, sward stick and RPM) of measuring forage biomass pre- and post-grazing with quadrat yields in a natural multiple-species sward dominated by Kentucky bluegrass (Poa pratensis L.) and white clover. J. Agronomy & Crop Science 191, 152—160 (2005) Ó 2005 Blackwell Verlag, Berlin ISSN 0931-2250 U.S. Copyright Clearance Centre Code Statement: 0931–2250/2005/9102–0152 $15.00/0 www.blackwell-synergy.com