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Environmental Relationships with Forage Quality of Warm-Season Perennial Grasses¹

Seasonal patterns of digestibility of warm-season perennial grasses in the southwestern U. S. A. generally show peaks in early spring and low values in mid-summer. This research was conducted to determine if the patterns of digestibility of kleingrass (Panicum coloratum L.), green sprangletop [Leptochloa dubia (H.B.K.) Nees], and plains bristlegrass (Setaria macrostachya H.B.K.) were related to temperature, rainfall, relative humidity, and daylength under field conditions. Two selections of kleingrass (‘Kleingrass 75’ and Kleingrass 75-25), and one each of green sprangletop and plains bristlegrass were harvested at 2, 4, and 8-week frequencies during 1978 and 1979. Samples were separated into leaf and stem fractions with in vitro digestible organic matter (IVDOM) determined each fraction. From analyses with all four grasses combined, leaf and stem IVDOM was negatively correlated with temperature (r-values from –0.353 to –0.419, all significant at 0.001 level) and daylength (r-values as great as –0.378 with all significant at least at the 0.01 level). In general, leaf and stem IVDOM was positively correlated with measures of moisture conditions (r-values up to 0.523 and 0.445 for rainfall and relative humidity, respectively).

The environmental factors monitored were used in multiple regression models of leaf IVDOM, stem IVDOM, and percent leaf. Statistically significant models were obtained in most cases with R² values up to 0.96. However, in a few cases less than 20% of the variation in IVDOM was accounted for by models maximizing R² (with R² values as low as 0.12). Distinct r elationships are apparent from these analyses; although, R² values, partial regression coefficients, and individual environmental factors contributing significantly to the models were too variable for these models of leaf and stem IVDOM and percent leaf to be of general use. Overall trends in digestibility can be anticipated from knowledge of environmental factors, but forage digestibility cannot be accurately predicted from macroenvironmental factors.

Key Words: IVDOM • Panicum coloratum • Leptochloa dubia • Setaria macrostachya • Seasonal forage quality patterns • Temperature • Daylength • Moisture

² Assistant professor, Univ. of Florida, Agric. Res. Ctr., Ona, FL 33865, former graduate student, Texas A&M Univ.; and professor, Soil and Crop Sciences Dep., Texas A&M Univ., College Station, TX 77843.

Received for publication October 19, 1981.

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