Table 3. Total volatile fatty acids (VFA) concentration and VFA molar proportions of corn stover and grain harvested at different periods

Corn stover Corn grain SEM p-values
Early Mid Late Early Mid Late Harvest (H) Fraction (F) H × F
3 h
Total VFA (mmoles/100 mL) 55.56b 56.11b 86.48a 38.97c 32.94d 35.55cd 3.31 *** *** ***
Molar proportion (mmoles/100 mmoles) C2 66.50ab 68.18a 66.74b 61.83c 60.98d 60.32d 0.65 *** *** ***
C3 21.80c 19.22c 23.12b 21.62b 24.36b 25.43a 0.81 * ** ***
C4 8.78c 8.66c 7.56d 10.94a 10.50a 10.34b 0.34 *** *** *
C5 0.84b 1.07b 0.74c 1.65a 1.12a 1.04b 0.15 *** *** ***
C2/C3 3.06a 3.56a 2.89b 2.86b 2.51b 2.37c 0.13 *** *** ***
6 h
Total VFA (mmoles/100 mL) 65.62 67.52 71.28 40.65 41.26 48.46 8.58 NS *** NS
Molar proportion(mmoles/100 mmoles) C2 65.81 69.04 64.11 60.97 59.69 61.54 1.62 NS *** **
C3 21.95b 20.12b 24.71a 22.92b 25.65a 25.1a 1.51 ** ** **
C4 9.17b 7.62c 8.42c 11.30a 10.66b 9.82b 0.48 *** *** **
C5 0.85c 0.87c 0.81d 1.44a 1.15ab 0.99b 0.56 * *** NS
C2/C3 3.00a 3.44a 2.60b 2.66b 2.35c 2.46c 0.67 ** *** ***
12 h
Total VFA (mmoles/100 mL) 84.01b 112.26a 103.34ab 51.62c 49.94d 49.29d 10.16 * *** *
Molar proportion (mmoles/100 mmoles) C2 64.97b 65.51b 70.66a 59.25c 57.67d 57.97d 1.63 * *** ***
C3 22.13d 19.25d 23.03c 25.04b 26.59b 27.32a 1.6 * *** *
C4 9.74 7.38 8.5 11.58 12.41 11.36 0.96 NS *** *
C5 0.93b 0.75c 0.87c 1.21a 0.93b 0.99b 0.14 * ** NS
C2/C3 2.94a 3.68b 2.86a 2.37c 2.18d 2.14d 0.21 ** *** ***
24 h
Total VFA (mmoles/100 mL) 86.82b 158.81a 137.72a 60.64d 57.89d 69.34c 7.4 *** *** ***
Molar proportion (mmoles/100 mmoles) C2 63.74 66.54 68.12 56.37 54.73 53.51 2.48 NS *** *
C3 24.14 24.2 22.53 26.97 28.19 29.79 1.65 NS *** *
C4 9.06 6.81 6.84 12.94 13.21 13.52 1.18 NS *** *
C5 0.91 0.78 0.81 1.13 1.18 1.01 0.35 NS *** NS
C2/C3 2.65 2.75 3.04 2.09 1.95 1.81 0.22 NS *** *
48 h
Total VFA (mmoles/100 mL) 96.28c 159.90a 124.00b 76.51f 90.56d 83.99e 9 *** *** ***
Molar proportion (mmoles/100 mmoles) C2 63.78 67.33 66.16 51.85 52.93 54.23 2.36 NS *** NS
C3 24.55 23.84 23.3 28.52 29.51 28.7 2.1 NS *** NS
C4 8.6c 6.47d 7.78cd 14.8a 13.23ab 13.47ab 1.31 * *** NS
C5 0.91c 0.73d 0.83c 2.04a 1.87a 1.56b 0.18 * *** *
C2/C3 2.61 2.23 2.91 1.82 1.82 1.83 0.33 NS *** NS
72 h
Total VFA (mmoles/100 mL) 104.24c 162.14a 131.87b 93.56d 89.78e 84.49f 2.85 *** *** ***
Molar proportion (mmoles/100 mmoles) C2 62.89 64.29 63.47 50.81 50.88 52.4 1.98 NS *** NS
C3 24.6 26.54 25.46 28.59 27.45 26.62 1.72 NS ** NS
C4 8.82 6.7 7.97 14.24 14.62 15.07 1.3 NS *** NS
C5 1.23 0.8 1.03 3.31 3.33 2.72 0.35 NS *** NS
C2/C3 2.56 2.42 2.51 1.78 1.87 1.98 0.2 NS *** NS
Means in the same row with different superscripts are significantly different.
p < 0.05,
p < 0.01,
p < 0.001.
SEM, standard error of means; NS, not significant; C2, Acetate; C3, Propionate; C4, Butyrate; C5, Valerate; C2/C3, ratio of acetate to propionate.