Effect of different set-aside management systems on soil nematode community and soil fertility in North, Central and South Italy

Abstract The current Common Agricultural Policy (CAP) 2014–2020 of the European Union (EU) proposed some environmental attempts to contrast the biodiversity decline and mitigate the effects of intensive agricultural management systems. In the present work, the results of the effectiveness of set-aside management to enhance soil nematode biodiversity and soil fertility are reported. In a mid-term experimental trial, three different set-aside managements, with mowing in May or July and without mowing, were compared through conventional rotation to provide management indications in the context of Good Agricultural and Environmental Condition (GAEC) Standard 4.2 in fields located in three sites (North, Central and South Italy). Soil fertility was evaluated by determining available phosphorous, total organic carbon and carbon humification. Soil nematode diversity was explored by examining soil nematode community structure, assessing Maturity (MI), Plant Parasitic (PPI), Basal (BI), Enrichment (EI), Structure (SI), Channel (CI) indices and diversity-weighted abundance. The results indicated that set-aside management moderately increased the available phosphorous and organic carbon content and humification remained low; the greatest increase in organic matter was obtained with mowing in May, period not permitted by Standard 4.2. The set-aside efficiency was associated with the previous crop rotations, and the major advantages were found after intensive crop rotations. In general, under set-aside management the nematode colonizer species, mainly bacterivores, increased in abundance and richness while plant parasitic nematodes and predators remained constant. Mowing carried out in July (the permitted period by Standard 4.2), weakly improved the soil nematode community structure by increasing k-strategies within nematode populations. Interestingly, the indices confirm that shifts in nematode community composition occurred more as a result of previous management than of five years of set-aside managements: specifically, the site characterized by the longest and the most conservative rotation, showed the highest values in MI, PPI, EI, SI indices. The use of diversity-weighted abundance expressed as biomass showed that free living nematodes involved in nutrient mineralization (bacterial and fungal feeders) and plant parasitic nematodes are not efficiently regulated by predation. Finally, as many nematode families are affected by soil organic carbon content, the low organic carbon increases found under set-aside management systems likely determined a low improvement of soil nematode biodiversity.