Agronomy Journal Journal of Natural Resources and Life Sciences Education
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Published online 1 November 1982
Published in Agron J 74:1089-1091 (1982)
© 1982 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
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Indirect Estimation of Grass-Legume Rations in Mixed Swards1

K. D. Johnson, V. L. Lechtenberg, J. J. Vorst and K. S. Hendrix2

The legume to grass ratio in mixed pasture and hay swards is an important determinant of forage yield and quality. Ratio measurements, determined on the basis of the relative weight of the grass and legume components, are time-consuming and tedious. Studies were conducted to evaluate a method for estimating the grass and legume ratios in mixed swards on the basis of neutral detergent fiber percentages. Samples of alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and ladino clover (T. repens L.) were mixed with tall fescue (Festuca arundinacea Schreb.) in known proportions. Samples were analyzed to determine neutral detergent fiber percentages. The legume and grass proportions were estimated by solving simultaneous equations for each mixture. Coefficients of determination (r2) between known and predicted values ranged from 0.92 to 0.98. The standard deviation (SD) between known and estimated values ranged from 2.26 to 5.56 percentage units. When the difference between the neutral detergent fiber percentage of the grass and that of the legume was altered mathematically, the SD increased exponentially as the difference between the neutral detergent fiber percentages of the grass and the legume approached zero. Acid detergent fiber did not accurately assess legume and grass proportions in mixed swards.

Key Words: Neutral detergent fiber • Species composition • Medicago sativa L. • Trifolium repens L. • Trifolium pratense L.

1 Contribution of the Purdue Univ. Agric. Exp. Stn., West Lafavette. IN 47907. Journal PaDer No. 8778

2 Assistant professor, professor, professor, Dep. of Agronomy; and associate professor, Dep. of Animal Sciences, Purdue Univ.

Received for publication October 21, 1981.




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