Changes of EUF-N and EUF-K fractions in three deep grey-brown luvisols during 18 months under fallow

Summary The EUF-N and EUF-K contents of deep grey-brown luvisols under fallow were investigated over a period of 18 months.EUF-NO₃-N increased continuously during the spring and summer of 1983, reaching their peak in September/October. They declined in the winter of 1984, and increased again during the spring and summer of the same year.During the spring and winter EUF-N_org was higher than EUF-NO₃-N. A decline in EUF-N_org due to mineralization was associated with an increase of EUF-NO₃-N. EUF-N_org increased due to mobilization of soil N in April/May. EUF-N_org also increased in autumn 1983 as a consequence the incorporation of mineral nitrogen into this fraction. When mineral N was incorporated EUF-NO₃-N declined.EUF-N_org in the subsoil was lower than in the topsoil. EUF-NO₃-N in the subsoil decreased as EUF-N_org increased. It may therefore be assumed that the higher the content of EUF-N_org in the subsoil the more mineral nitrogen will be immobilized.