Changes in cell wall composition and in vitro degradation of corn stover fractions (leaf, upper stem and lower stem) with advancing maturity and in response to NH; treatment were determined, and possible inhibitory mechanisms of lignin were evaluated. With advancing maturity, IVDMD decreased (P<.001), associated with decreases (P<.001) in CP and water soluble carbohydrates (WSC), and increases (P<.001) in NDF and ADF. The IVDMD of leaf was higher (P<.001) than of stems, associated with higher CP, hemicellulose:cellulose, and arabinan:xylan, and lower lignin methoxyl content.

A hypothesis of formation of reactive quinone methide intermediates from lignin during rumen fermentation was tested in vitro by incubating corn stover fractions with S-containing reducing agents. Sulphur incorporation into residual fiber occurred (P<.05), indicative of nucleophilic addition to quinone methide intermediates. Degradation of NDF was highly correlated with lignin methoxyl content.

The impact of lignin on cellulose degradation was studied using lignocellulosic hydrogels, in which hydroxypropylated or unmodified hardwood lignin was blended with cellulose. In vitro cellulose degradation of lignocellulose blends was higher (P<.01) than of control. Addition of lignin at incubation depressed (P<.01) cellulose degradation. Hydroxypropylation enhanced (P<.001) the increase in cellulose degradation with lignin blending, and reduced (P<.001) the inhibitory effect of lignin addition at incubation.

Treatment of drought-stressed corn stover with 3% aqueous NH₃ decreased (P<.05) NDF, compared to isonitrogenous NH₃ addition and control, associated with solubilization of hemicellulose. Esterified phenolic acids were released (P<.05) by NH₃ treatment in upper stem. The IVDMD and NDF degradation increased (P <.001) after ammoniation, with higher (P<.05) values for NH₃ treatment than NH₃ added in leaf.

The in vitro response to ammoniation of fractions of drought-stressed and non-drought stressed corn stover harvested in subsequent years was compared, using N-sufficient and N-limiting buffers. Response was highest (P<.001) for non-drought stressed stover fractions, and in N-limiting medium. Response appeared to be affected by high concentration of WSC in lower stalks of drought-stressed stover.