Abstract: By treating agricultural crop residues and other nonwoody lignocellulosic plant substrates with H.sub.2 O.sub.2 at a controlled pH within the range of about 11.2 to 11.8, the substrates are partially delignified and unprecedented levels of the cellulose and hemicellulose as insoluble fractions are made available for subsequent use. The products of this treatment are nontoxic and are characterized by low crystallinity and near quantitative cellulase digestibility. They are useful as carbohydrate sources in ruminant feeds and as microbial feedstocks for commercial process such as the production of alcohol and generation of single-cell protein.