Availability of Carbon and Nitrogen Contained in Different Soil Particle-Size Fractions

Abstract

The behaviour and availability of soil organic-C and -N were studied by means of soil particle-size fractionation techniques. In a first experiment, three soils were incubated with 14 C-glucose or 14 C-cellulose and K 15 NO 3 for 104 weeks at 28°C and were fractionated at different sampling dates. The radioactivity was preferentially incorporated in the sand and coarse clay fractions for the cellulose treatment, and in the coarse clay, light silt and soluble fractions for the glucose treatment. All fractions for the glucose treatment and the sand fraction from the cellulose treatment were responsible for the mineralization of organic- 14 C during incubation. With the glucose and cellulose treatments, organic- 15 N was incorporated in the coarse clay, light silt and soluble fractions, and inorganic- 15 N produced during incubation was derived essentially from mineralization of these fractions. In a second experiment, 15 N labelled soil materials (0-2, 2-20, 20-50, 50-200 μm fractions and whole soil) were then separately incubated for 224 days at 28 °C in shaken liquid media. For the calcic cambisoil, the labelled-N contained in the clay and sand fraction was more available than in the silt fraction. For the loamy soil, all fractions exhibited comparable 15 N mineralization rates, except for the 20-50 μm fraction. At the same time, the non-labelled-N present in all fractions appeared to be less mineralizable than recently immobilized 15 N.