THE CARBON-NITROGEN RATIO IN RELATION TO THE ACCUMULATION OF ORGANIC MATTER IN SOILS

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Abstract
Vari-ous organic materials were applied at a uniform rate to an Ellsworth silt loam soil low in organic matter, and the C: N ratio was adjusted at definite levels by use of NH4NO3. The incubation period covered 1 yr. Measurements of organic C and N were made at monthly intervals. With a given C:N ratio, the microorganic processes were similar, regardless of organic materials added. A ratio wider than 10:1 causes loss of organic C from the soil; a ratio narrower than 10:1 leads to saving of organic C. A wide ratio causes nitrate depression over several months, whereas a narrow ratio leads to formation of nitrates. Wide-ratio materials may be sources of energy for N-fixation, but this N will not be available to crops until losses of C have narrowed the C:N ratio to about 10:1. Applications of phosphates do not cause appreciably greater N-fixation; sufficient N to narrow the ratio to about 15:1 favors N-fixation.