Environmental Influences on Yield and In Vitro True Digestibility of Warm‐Season Perennial Grasses and the Relationships to Fiber Components¹

Abstract

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.

Using Leaf Traits to Rank Native Grasses According to Their Nutritive Value

“…According to these authors, temper- ature influences the rate of plant development, the relative proportion of leaf and stem weights and the tissue type within leaves or stems. Plants invest more carbon into structural components at high temperatures (Deinum and Dirven 1975), increasing the lignin (Dirven and Deinum 1977;Pitman and Holt 1982;Wilson et al 1991), and the neutral detergent fiber content (Henderson and Robinson 1982). An increase in temperature of 18C decreased the leaf blade digestibility by 6 g kg À1 for Dactylis glomerata, and by 5.3 g kg À1 for Festuca arundinacea (Duru et al 1995).…”

Harvest Timing Affects Switchgrass Production, Forage Nutritive Value, and Nutrient Removal

“…The objectives of this experiment were to (i) determine whether switchgrass could be harvested for greater nutritive value during the vegetative stage relative to early reproductive growth (boot stage); (ii) compare biomass yields of switchgrass harvested once vs. twice per year for bioenergy; and (iii) examine effects of N fertilizer rates on harvest systems. Although N fertilizer application is reported to increase forage quality (Fribourg et al, 1971(Fribourg et al, , 1979, prevailing weather conditions could affect crop response to N fertilizer (Sanderson et al, 1991) by affecting leaf-to-stem ratio (Griffin and Watson, 1982) and degree of lignification (Henderson and Robinson, 1982). Biomass yield was greatest and nutrient concentrations were least in the one-cut system.…”

Leaf Nutritive Value Related to Tiller Development in Warm-Season Grasses

“…Environmental conditions also affect nutritive value (Henderson andRobinson 1982a,1982b;Van Soest et al 1978). The strong correlation (PcO.05) between growing degree days and leaf IVDMD indicates that temperature had some influence on nutritive value.…”

“…High temperatures and low soil moisture reduced the nutritive value of Cynodon and Paspalum spp. (Henderson andRobinson 1982a, 1982b). Plant tissues produced in more extreme environmental stresses may result in lower nutritive value regardless of tissue age or stage of plant development.…”