Corn stover cell wall composition changes considerably throughout the yearly growth period and also varies significantly between the various fractions of the plant (i.e. leaf vs. stem).  Previous studies have shown that variations in cell wall composition (i.e. cellulose, hemicellulose and lignin) can have a substantial influence on pretreatment recalcitrance, enzymatic digestibility, and maximum achievable sugar yields.  It is reasonable to assume that, due to differences in composition, different stover fractions could have different optimal pretreatment conditions and corresponding sugar yields.  Maximum sugar yields from individual fractions would be one criterion for determining which fractions should be left on the field for erosion control following harvest.  Assuming no other factors, it would be most logical to harvest the least recalcitrant biomass and leave the remainder.

Ammonia Fiber Expansion (AFEX) followed by enzymatic hydrolysis was performed on four different corn stover fractions (stem, leaf, husk and cob) from both September (early) and November (late) harvests.  The objective of this project was to determine: 1) whether individual stover fractions have different optimal AFEX conditions and whether this is different from previously optimized values for homogeneously milled corn stover and 2) which fractions give the highest glucose and xylose yields.  Based on the maximum glucose, xylose and total sugar yields from the individual fractions, optimal harvest scenarios, assuming 30% and 60% dry matter left on-field, were determined.