Short-term changes in soil biochemical properties as affected by subsidiary crop cultivation in four European pedo-climatic zones

The goals of conservation agriculture are to preserve and enhance the soil resource base and the environment. Subsidiary crops (SCs), such as Trifolium, Medicago, Vicia, Brassica, Raphanus spp., are important components of conservation agriculture since they maintain the soil resource. However, the importance of SC species and environment on soil microbial communities are not well known. The overall objective of this study was to assess the effect of various subsidiary crops cultivation on soil microbial biomass and activity at four sites across Europe. The experiments were conducted during 2014 and 2015 at sites in the Nemoral (Sweden SLU), Oceanic (United Kingdom ORC), Continental (Switzerland AGS) and Mediterranean north (Italy UNI) pedo-climatic zones. The specific objectives were to determine: (i) the effect of SC growth on soil microbial biomass and activity, (ii) the site-specific effect of SC growth on soil biochemical properties. The SCs consisted of leguminous or brassicaceous species sown after wheat harvest, or clover species under-sown in wheat. At 0–30 cm depth, microbial carbon and nitrogen increased under SCs at most sites indicating that SCs cultivation may favor soil biological fertility. Effects of SCs were similar in the pedo-climatic zones where air temperatures are never below 0 °C (ORC and UNI). Arylsulphatase was the most sensitive enzyme to legumes in the Mediterranean north (UNI). Chitinase activity was enhanced by SCs in the Oceanic and Nemoral pedo-climatic zones. High precipitation and the low average temperature, typical of Continental and Nemoral zones, may represent limiting factors for soil enzyme activity under all selected SCs. Among the four pedo-climatic zones, the Mediterranean north represented the most suitable environment to promote SC growth and soil coverage. This study showed that SC cultivation affects soil quality enhancing biochemical activity; however the SCs effect were influenced by the different pedo-climatic conditions.