Measuring Legume Content in Pastures Using Digital Photographs

Quantifying botanical composition is important for evaluating the effects of management on legume content and of legume content on pasture yield and quality. The standard for measuring botanical composition is hand separation of clipped samples. An alternative is taking point counts of botanical components on photographs of the pasture. The latter was tested on a rotationally stocked pasture, with photos taken at 24 random sample areas, areas clipped at ground level, and samples hand separated into grass, legume, and forb fractions. Photos were evaluated with a grid in Microsoft PowerPoint. Point counts were calibrated to hand-separated values using linear regression. Grass and legume point-count components were not significantly different from hand-separated values (P = 0.05) but underestimated the forb fraction. Calibration regressions had R2 values ranging from 0.45 to 0.98. The precision of this technique is dependent on the number of photos per pasture, the number of points counted per photo, and the number of paired samples taken for calibration. In cool-season grass–clover pastures, 12 or more photos per pasture and 100 or more points per photo are a good balance between photo number and points per photo. For calibration, 12 or more paired samples should be used. Photo point counts appear to be a practical method of measuring grass, legume, and forb components in rotationally grazed pastures. IntroductIon Quantifying the botanical composition in pastures is important for measuring the effects of management on legume content and the effect of legume content on forage yield and quality. Quantifying legume content in pastures is also important since it can have a significant impact on animal performance. In Virginia, orchardgrass–clover pastures produced the same steer gain per acre as orchardgrass alone fertilized with 200 lbs. N/acre/year (Blaser et al., 1969), but at a lower stocking rate and higher gain per head. In West Virginia, 30% legumes in pastures increased backgrounding calf average Published in Forage and Grazinglands DOI 10.2134/FG-2011-0143-MG © 2014 American Society of Agronomy and Crop Science Society of America 5585 Guilford Rd., Madison, WI 53711 All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. West Virginia Univ., Morgantown, WV 26506. Received 9 Apr. 2013. *Corresponding author