Biomass Feedstock Storage for Quantity and Quality Preservation - Engineering and Science of Biomass Feedstock Production and Provision - page 180

Jung et al. [ 42 ] correlated lignin content and neutral detergent fiber digestibility.
The Klason method detected the most lignin in plant material, which for ethanol
production purposes is the conservative estimate. According to Jung et al. [ 42 ], the
neutral detergent fiber digestibility in grasses is correlated with Klason-determined
lignin amounts (KL) in a relationship that fits both C3 and C4 plant types and might
therefore apply to Miscanthus:

( )

2

% of neutral rgent fiber digestibility det =- 359 . KL + 103 9 . R = 0 49 . (7.4)

Plant degradability decreases with plant age because of an increase in plant lig-
nin with age. For the purpose of ethanol production from cellulose, it is therefore
useful to find an optimal balance between relatively high-fiber and low-lignin con-
tent as we select the plant shoot age at harvest. Jung et al. [ 42 ] also determined the
% dry matter digestibility in grasses as a function of Klason lignin % as follows:

( )

2

% Drymatterdigestibility =- 220 . %. KL + 845 R = 067 . (7.5)

where % KL is the acid digestible lignin by the Klason method in % of total dry
matter.
Cherney et al. [ 43 ] also reported data showing a correlation between percent
lignin content (of dry matter) and in vitro digestibility of dry matter. The following
trend line was extrapolated from the data in Cherney et al. ([ 43 ], Table 3):

( ) -

2

( ) +

% Drymatterdigestibility =- 0 6993 . %. %. L 4 1735 L 96 77 (7.6)

where % L = % lignin (dry basis).
Cherney et al. ([ 43 ], Table 3) reported data from which the following relationship
correlating perennial grasses shoot age with digestibility was extrapolated, assum-
ing a grass emergence date of April 15 in New York state (44′ 35 min latitude, 75′
7 min longitude):

=- ( +

% Drymatterdigestibility 26 34 . ln A d 174 94 . (7.7)

where A d = plant age in days. The following correlation between lignin dry matter
content and plant age was also extrapolated from the lignin % of dry matter and
plant age data reported in Cherney et al. ([ 43 ], Table 3):

= ( - %. L 3 1751 ln A d 882 . (7.8)

Chaves [ 41 ] correlated plant age with the content in nonstructural sugars, which
are readily fermented to alcohol ( R 2 = 0.28)

g non structural carbohydrates
kg drymatter

-

=+ ( -

( 2

53 174 . A 0 016 . A

d

+ ( - ()

2

% non structural carbohydrates - = 53 0 174 . . A 0 0016 . A (7.9)

d d