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Modification in Chemical Properties of Straw during Decomposition¹

ABSTRACT

Oat straw samples were allowed to decompose for periods varying up to 15 months; changes in functional groups and chemical properties followed as a function of time. Carbon increased in the whole residues and decreased in the lignin fraction while hydrogen decreased in both. Selective demethylation occurred in the lignin but methoxyl content of the complete residues remained about constant. Carboxyl groups as determined by esterification increased progressively, accompanied by decreases in hydroxyl. Carboxyl in the lignin fraction was in good agreement with exchangeable hydrogen determined by an iodometric titration procedure in contrast to lack of agreement between corresponding values in the whole residues. Cation exchange capacity of the straw residues and of their lignin component increased as decomposition progressed.

Absorption of oxygen by alkaline suspensions of the residues was determined in a Warburg respirometer and found to increase with length of decomposition period. Most of the total oxygen uptake during an arbitrary 8-hour period could be attributed to the lignin fraction.

Some chemical properties of organic matter preparations from five soils were compared with corresponding values for the decomposed residues.

¹ Contribution from the Department of Agronomy, Cornell University. Presented before Div. III, Soil Science Society of America, Dallas, Tex., Nov. 19, 1953.

² Assoc. Professor of Soil Microbiology.

Received for publication November 27, 1953.