NITROGEN TRANSFORMATION IN ARABLE SOILS OF NORTH-WEST GERMANY DURING THE CEREAL GROWING-SEASON

Ln 1991, field experiments on loess (with winter wheat) and sandy soil s (with summer barley) were conducted to study N dynamics in the micro bial biomass and non-exchangeable NH4+. The measurements showed a mass change in microbial N, with a maximum increase of 100 kg N ha(-1) 30 cm(-1) from March to July in the loess soil, and a change for only 1 m onth (May) in the sandy soil. Plots treated with conventional levels o f N fertilizer (213 kg N ha(-1) on a loess soil to winter wheat and 13 0 kg ha(-1) on the sandy soil to summer barley), reduced levels of N ( 83% and 62% of the conventional N application), or no N showed no cons istent fertilizer N effect on microbial biomass N. From March to July, non-exchangeable NH4+ in loess soils under winter wheat decreased by 110 kg N ha(-1) 30 cm(-1) in conventionally fertilized plots and by 20 0 kg N ha(-1) 30 cm(-1) in a plot with no N fertilizer. After harvest, the pool of non-exchangeable NH4+ increased due to increasing mineral N concentrations in the soil.