RESPONSE OF SOIL AGGREGATE STABILITY TO MANURE AMENDMENTS IN THE ULTUNA LONG-TERM SOIL ORGANIC-MATTER EXPERIMENT

The present paper deals with the long-term effects of bare fallow and organic treatments on soil aggregate stability. Soil samples were coll ected from plots of the long-term soil organic matter experiment in Ul tuina/Sweden, which is already running for 38 years. Soil aggregate st ability (SAS) showed a clear response to soil management. SAS increase d in following order: bare fallow < no-N < green manure < peat less th an or equal to farmyard manure. Humus contents of the plots had a sign ificant impact on SAS. Incfeasing C-org-contents generally enhanced ag gregation. However, the unfavourably high C/N ratio of peat treatments and the resulting small size of microbial biomass led to a distinctly lower positive influence of accumulated soil organic matter in case o f peat additions.