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In recent years climatic fluctuations have been increasingly associated with seasonal variation in yield and quality of forage crops. Although considerable information is available concerning environmental influences on yield and quality of many temperate and tropical grasses, very little is known about these relationships in the major grasses grown in the southern U.S.A. The objectives of this study were to determine the relative influences of temperature (T) and photon flux density (L) on dry matter yield (DMY) and in vitro true digestibility (IVD) of four warm‐season perennial grasses grown at two soil moisture levels and to relate the differences in IVD to fiber component concentrations. Coastal and common hermudagrass [Cynodon dactylon (L.) Pers.], Pensacola hahiagrass (Paspalurn notatum Flugge), and dallisgrass (P. dilatatum Poir.) were grown in an artificial growth medium at 4 day/night temperatures (35/24, 32/21, 29/18, 26/15 C), four photon Aux densities (1,050, 840, 630, 420 µEm−2 sec−1 PAR) and two soil moisture levels in growth cabinets. After 14 and 21 days regrowth, DMY and IVD were measured. Regression equations were developed to predict DMY and IVD as functions of T and L at each soil moisture level and regrowth period. The study clearly showed that DMY of all grasses increased with increasing T and L. The imposed moisture stress sharply reduced DMY of dallisgrass (DAL) hut not of the other grasses. In all grasses IVD consistently decreased as T increased, resulting in maximum IVD at the lowest T. The effect of L on IVD ranged from positive to negative, depending on the grass and T. Maximum IVD values occurred at the high soil moisture (HM) level after 14 days regrowth. At the HM level maximum IVD of Coastal bermudagrass (COA), common hermudagrass (COM), and Pensacolabahia grass (BAH), respectively, was 5.7, 4.9, and 3.6 percentage units higher after 14 than after 21 days regrowth. In DAL at the HM level and in all grasses at the low soil moisture level, these differences due to age were only about one percentage unit or less. The Paspalum spp. averaged about seven percentage units higher in IVD than the Cynodon spp. Significant (P ≤ 0.01) negative correlations were obtained between IVD and previously reported concentrations of acid detergent fiber (ADF), cellulose, permaganate lignin (LIG), and silica in all grasses and concentrations of neutral‐detergent fiber in COA and COM. Although correlation coefficients were ≤ 0.50, hemicellulose concentration and IVD were positively correlated in all grasses. Strongest correlations were obtained between IVD and concentrations of ADF and LIG.

Evaluation and management of warm‐season perennial grasses are complicated by seasonal fluctuations in forage quality. Field studies have indicated that a significant proportion of this seasonal variation is due to environmental conditions. Due to confounding effects under field conditions the variation cannot be directly attributed to specific environmental factors. In this study, Coastal and common bermudagrass [Cynodon dactylon (L.) Pers.], Pensacola bahiagrass (Paspalum notatum Flugge), and dallisgrass (Paspalum dilatatum Poir.) were grown in an artificial medium under 4 day/night temperatures (35/24, 32/31, 29/18, 26/15 C), 4 photon flux densities (1,050, 840, 630, 420 µE m−2 sec−1 PAR) and two soil moisture levels (high and low) in growth cabinets to evaluate the relative influence of each factor on fiber component concentrations. Grasses were harvested at 14 and 21 days and analyzed for neutral‐detergent fiber (NDF), acid‐detergent fiber (ADF), cellulose (CEL), hemicellulose (HEM), permanganate lignin (LIG), and silica (SIL) concentrations. multiple regression analysis was used to obtain reduced prediction equations for evaluating responses of all measured variables to temperature (T) and photon flux density (L) at each soil moisture level. Prediction equations for fiber component concentrations of each grass included T effects at both soil moisture levels but did not consistently include L effects. Coefficients of determination (R2 values) for the prediction equations indicated that T and L effects on fiber component concentrations varied with the fiber component, grass, and soil moisture level. Concentration of NDF increased in the Cynodon species and decreased in the Paspalum species as T increased. In all grasses, predicted concentrations of ADF, CEL, LIG, and SIL increased with increasing T at both soil moisture levels, while HEM concentrations decreased. In all grasses L effects consistently influenced ADF, LIG, and SIL concentrations at both soil moisture levels and CEL concentrations at the low moisture level. Concentrations of ADF, CEL, and SIL decreased slightly, while LIG concentrations increased with increasing L. Although T effects consistently had greater influence in this study, both T and L and their interaction effects significantly influenced predicted fiber component concentrations. The data emphasize the importance of considering environmental influences when evaluating forage quality differences of warm‐season perennial grasses.

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