SWITCHGRASS (PANICUM VIRGATUM L.) FORAGE QUALITY AS INFLUENCED BY INTERRELATIONSHIPS AMONG BIOLOGICAL, CHEMICAL, MORPHOLOGICAL AND ANATOMICAL DETERMINANTS

EDWARD KEITH TWIDWELL, Purdue University

Abstract

A study was conducted to investigate the dry weight composition, forage quality and anatomical degradation of switchgrass (Panicum virgatum L.) morphological components. At the earliest harvest date (flag leaf just visible) the leaf blade had the highest relative dry weight percentage (47.0%). At the latest harvest date (3/4-inflorescence emergence) the leaf blade, leaf sheath, stem and inflorescence components had relative dry weight percentages of 26.4, 20.1, 36.4, and 17.1%, respectively. The leaf sheath and stem had similar herbage nitrogen concentrations, while the leaf sheath had in vitro dry matter disappearance (IVDMD), neutral detergent fiber, lignin, and 96-hour (h) extent of cell wall digestion values that were intermediate between the stem and leaf blade. With maturation (28 days) the stem had the largest increase in lignin (38.8 g kg$\sp{-1}$) and the largest decline in IVDMD (210 g kg$\sp{-1}$). These results indicate that the stem is the major morphological component causing a decline in herbage quality of switchgrass.^ Three-millimeter portions of leaf blade, leaf sheath, and stem tissue were incubated in rumen fluid for 24 and 48 h and then analyzed for anatomical degradation with a computer-based optical image analyzer. Anatomical components were categorized as being intact, partially degraded, or completely degraded on an area percentage basis. The mesophyll area of the leaf blade was 23% partially and 77% completely degraded after 48 h of incubation. The leaf sheath parenchyma was more resistant to complete degradation than the leaf blade mesophyll. The leaf sheath also had 16.7% of its cross-sectional area occupied by tissues in which at least 70% of the area was intact after 48 h of incubation, compared to only 4.9% for the leaf blade. These factors apparently cause the leaf sheath to have a lower IVDMD than the leaf blade. The stem had 24.5% of its cross-sectional area occupied by tissues that were at least 85% intact after 48 h of incubation, and it appears that it is the resistant nature of these tissues that causes the stem to have the lowest IVDMD of the three morphological components. ^

Degree

Ph.D.

Subject Area

Agronomy

Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server
.

Share

COinS