STUDY OF IMMOBILIZATION AND REMOBILIZATION OF NITROGEN-FERTILIZER IN CULTIVATED SOILS BY HYDROLYTIC FRACTIONATION

Nitrogen immobilization and remobilization from a fertilizer were dete rmined by hydrolytic fractionation of organic nitrogen with 6 M HCl in to acid-soluble distillable nitrogen (NSAD), acid-soluble nondistillab le nitrogen (NSAnD) and nonhydrolysable nitrogen (NnH) on the Ap horiz ons of eight different soils from Myzeqe (Albania), eastern France, an d tropical Mexico. The soils were fertilized with (KNO3)-N-15 and then incubated at 28 degrees C and 80% of the water holding capacity for 1 month. Mineral N was removed by extraction with a solution of CaCl2 a fter which rye grass was sown. The nitrogen taken up by rye grass was thus derived from soil organic matter. The three NSAD, NSAnD and NnH f ractions participate in both immobilization and remobilization. The NS AnD fraction was shown to be the most active fraction. Remobilization of the biomass was greater in the sandy brown soils than in the clayey soils, in which intra-aggregate immobilization would predominate. Evi dently, the physical and chemical properties of the soils have a real bearing on immobilization and remineralization of nitrogen fertilizer in cultivated soils.