Winter cover crop effects on soil structural stability and microbiological activity in organic farming.

In a field experiment based on a five-year crop rotation (pea, potato, barley undersown with red clover, red clover and winter wheat), several soil parameters, porosity, number and biomass of earthworms, total nitrogen, organic carbon, percentage of water stable aggregates and enzymatic activity, were studied during 2013 and 2014, the first and second year, respectively, since the first rotation concluded. This rotation was managed under three organic farming systems: Organic 0 (control), Organic I (with winter cover crops lately incorporated into the soil as green manure) and Organic II (with the same cover crops plus a yearly amendment of 40 t ha^-1 of cattle manure). Crop rotation had a yearly positive effect on the soil bulk density, and enhanced the percentage of air filled pores; nonetheless, despite the leguminous crops in the rotation, all the systems presented a yearly decrease in total nitrogen in 2014. Cover crops along with manure only had a significant effect on enzymatic activity; however no significant effect was found in soil organic carbon content, soil particle aggregability or number and biomass of earthworms. This was connected with the intensive tillage carried out in the systems, the weather conditions and the characteristics of the organic amendments. However according to other studies these results could be transient and further long-term investigations will be needed. [ABSTRACT FROM AUTHOR]