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Predicting Yields of Two Bunchgrass Species

Four regression models were developed from various combinations of three plant characteristics (number of flowering culms, number of vegetative culms, and fourth longest leaf) to predict weights of individual plants of two bunchgrasses. The linear form of the three plant characteristics and one interaction (number of flowering culms times fourth longest leaf), together, were highly predictive for weights of needleandthread (Stipa comata Trin. and Rupr.), and for bottlebrush squirreltail (Sitanion hystrix (Nutt.) J. G. Smith) during 1962 and 1963.

Regression models 3 and 4, developed in this paper, may have high predictive value for other bunchgrass because they proved to be satisfactory on both a very leafy species and a very stemmy species. Except for the protected plants of squirreltail, both models had R² values greater than 0.89 for weights of each species during each of 2 years. Moreover, except for one group of data, standard deviations from regression were within 25% of the mean.

Key Words: Sitanion hystrix • Stipa comata • Regression models • Grass yield • Herbage production • Leaf length • Flowering culms • Vegetative culms

Received for publication June 16, 1969.