Differential effect of carbon sources on nitrogen transformation in Hawaiian soils
SummaryMineralization of native N was curtailed by addition of carbon sources in all soils tested. A readily available energy source, sucrose, accelerated and increased the immobilization of native as well as added N more than a slowly available energy source, sugar cane bagasse. Addition of N as ammonium sulfate increased CO2 production in only one out of five soils when no energy source was added. With energy source addition, N addition enhanced CO2 production in most soils. Without any treatment, the immobilization of added N was related to the C:N ratio of the soil; maximum immobilization occurred in the soil with the widest C:N ratio.
RATES OF IMMOBILIZATION AND RELEASE OP NITROGEN FOLLOWING ADDITIONS OF CARBONACEOUS MATERIALS AND NITROGEN TO SOILS
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 CO2 formation. This paper presents data of this type.
Influence of microorganisms upon the carbon-nitrogen ratio in the soil
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.