Influence of microorganisms upon the carbon-nitrogen ratio in the soil

Abstract

Various investigations on the decomposition of organic matter in the soil have brought out the fact that there exists a more or less constant ratio between the carbon and nitrogen content of the soil, whatever the ratio between these elements in the organic matter originally added to the soil. This ratio varies from 8: 1 to 12: 1, i.e. for every 8 to 12 parts of carbon, there exists in the soil one part of nitrogen; the average ratio is about 10 to 1. Brown and O'Neal (1923), for example, found that the ratio of the carbon to the nitrogen in a Carrington loam is 12: 1 to 13: 1, while, in the case of a Tama silt loam, the ratio may go down to 10: 1. According to Sievers (1923), the ratio of carbon to nitrogen in the soil is about 11·6: 1. Russell (1923) stated that, although there is about 40 times as much carbon as nitrogen in the original plant residues, the ratio will drop down to 10 to 1, before these residues have been very long in the soil. This ratio seemed to be in a stable position, for which no explanation could be suggested. Fraps (1922) found the ratio of carbon to nitrogen in the surface soil to be 9·2: 1 and in the subsoil 8·3: 1; he suggested, therefore, to judge the percentage of organic carbon in the soil from the percentage of nitrogen present.