Studies of nitrogen immobilization and mineralization in calcareous soils part 1 distribution of immobilized nitrogen among soil fractions of different particle size and density
Ladd, J.N.; Parsons, J.W.; Amato, M.
Soil Biology and Biochemistry 9(5): 309-318
.**GRAPHIC**. was immobilized in a calcareous clay and a calcareous sandy soil during incubation of each soil with glucose and wheat straw. Changes in the distribution of immobilized 15N amongst soil extracts and soil fractions of different particle size and density were determined during periods of net N immobilization. The nature of the organic-C amendment, but not soil type, significantly influenced both the distribution of the immobilized 15N and the pattern of changes of the organic-15N of soil fractions with time. In straw-amended soils, .apprx. 20% of the organic-15N became associated with a light fraction, sp. gr. [specific-gravity] < 1.59, the remainder becoming distributed mainly amongst the silt and clay fractions. In glucose-amended soils, very little (< 1.2%) of the 15N was immobilized in the light fraction, sp. gr. < 1.59, most being rapidly distributed amongst the silt and clay fractions. During a period of complete immobilization, organic-15N was transferred from the fine clay to the silt and coarse clay fractions. Silt, coarse clay and fine clay components from glucose-amended soils sampled at the end of the net immobilization phase were further fractionated densimetrically into light (sp. gr. < 2.06) and heavy (sp. gr. > 2.06) subfractions. The organic-15N of respective light subfractions accounted for 43-64% of the total organic-15N of the silt, 1-9% of that of the coarse clay and 19-21% of that of the fine clay fractions.