Relationship between soil organic matter and micropores in a long-term experiment at Ultuna, Sweden

Our study showed that long-term addition of organic matter to a fine textur ed soil (36.5% clay, 41% silt, 22.5% sand) resulted in an increase of both macro- and microporosity in the top soil layer. In terms of changes of the absolute pore volume, macropores were of main importance. However, in relat ive terms, the increase of microporosity was comparable to that of macropor osity (75% and 90%). Changes in porosity upon different organic matter leve ls had a marginal effect on the water storage capacity. Micropores with dia meters in the range of 1-30 mu m were highly significantly correlated to so il organic matter characteristics showing that there is a non-uniform distr ibution in relation to pores. Mechanisms leading to disproportionally high concentrations of soil organic matter in relation to micropores are discuss ed.