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The rates of decomposition of 10 kinds of finely‐ground woods and the corresponding barks at two nitrogen levels were determined in the laboratory by measuring CO2evolution over periods varying from 53 to 800 days. The following species were studied: California incense cedar, cypress, redwood, western larch, eastern hemlock, red fir, white fir, Douglas‐fir, red cedar, and Engleman spruce. The woods and barks of all of these species were considerably more resistant to biological attack than is shortleaf pine sawdust. California incense cedar, cypress, redwood, eastern hemlock, and red cedar, were decomposed to the extent of < 7% during a 2‐month period. The comparative resistance of woods and barks to decay varied for individual species but the average values for the 10 species were similar. Due to the slow rates of decomposition, the soil was able to furnish adequate available nitrogen for maximum rates of decomposition for all of the wood products, and supplemental nitrogen was not needed.

Numerous experiments have been reported (1, 4–8) that show the quantity of nitrogen required by soil microorganisms in the decomposition of carbonaceous materials, such as straw. These values usually vary between 1.1 and 2.0 per cent of the dry weight of readily decomposable plant materials, including the nitrogen originally present in the plant material, and are often much lower for very woody materials (2). In such experiments, immobilization and mineralization proceed simultaneously; that is, nitrogen that is first immobilized may be in part released later. Nitrogen requirement values, as ordinarily obtained, are, therefore, net values for the given experimental period chosen by the investigator. Few data have been published that show quantitatively how nitrogen tie-up and release vary at short intervals of time and also with rate of CO2formation. This paper presents data of this type.