THE INFLUENCE OF DIFFERENT FERTILIZATION PRACTICES ON CONCENTRATIONS OF ORGANIC-CARBON AND TOTAL NITROGEN IN PARTICLE-SIZE FRACTIONS DURING 34 YEARS OF A SOIL FORMATION EXPERIMENT IN LOAMY MARL

The concentrations of organic C and total N in five different particle-size fractions were studied under different mineral and organic fertilizer regimens by examining soil samples from the 34-year-old soil-formation pot experiment Hu 3 in Rostock. The C and N concentrations were generally highest in the clay fraction and decreased in the order medium silt > fine silt > coarse silt and sand. For nearly all years and size fractions the following order was obtained for C and N concentrations under the various fertilizer regimens: Compost > farmyard manure > straw + mineral fertilizer > mineral fertilizer. The various particle-size fractions and fertilizer regimens differed in the development of soil organic matter levels. Consequently, characteristic redistributions were found in the proportions of C and N in the various particle-size fractions, particularly after organic fertilizer was no longer applied (years 20-34). This experimental phase was characterized by decreased organic C and increased total N concentrations, and increased proportions of C and N in the clay-size at the expense of the sand fractions.