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Factors affecting soil organic matter conservation in Mediterranean hillside winter cereals-legumes cropping systems

Facteurs de conservation de la matière organique des sols en collines méditerranéennes : cas des systèmes de cultures associant céréales et légumineuses

Abstract : Soil conservation is an important issue for farming and environmental protection in Mediterranean areas. Hillside farming systems, based on winter cereals and legumes, are common in these areas and are the target of several environmental policies. Soil organic matter (SOM) is widely used to assess the environmental performance of these cropping systems. Nevertheless, few studies have considered soil conservation practices in hillside systems in terms of implementing more effective agro-environmental policies for these areas. This paper compares the SOM conservation of different winter cereal based cropping systems within Mediterranean hillside crops/livestock farms. Seventeen cropping systems were characterised by on-farm surveys in the inland hilly area of Grosseto (Tuscany, Italy). For each cropping system, we performed a SOM balance, based on Hénin-Dupuis’ equation, using either local environmental databases or data from on-farm surveys. Differences between cropping systems were analysed by the Kruskal-Wallis test. On average, the cropping systems identified did not guarantee SOM conservation and varied considerably from farm to farm, however, some practices seemed to have a positive performance, e.g. cropping systems of cattle farms. According to the literature, annual SOM balance differs significantly depending on crop rotation length and longer crop rotations performed better than shorter ones. However, we found a local effect indicating that this better performance was influenced by local farmers' cooperatives, which to some extent counteracted the negative effect of crop rotation length. There were significant differences in the performance of dairy sheep and cattle farms (-1031 kg ha-1 yr-1 vs +103 kg ha-1 yr-1, respectively). This suggests that the presence of livestock did not have the same favorable effect on soil conservation in Mediterranean systems and that this factor should be more investigated. Surprisingly, in our sample, for the same crop rotation length, livestock density did not affect the annual SOM balance. Due to the high variability in local cropping systems and soil characteristics, further surveys on a larger farm sample and field soil measurement are needed to confirm these trends and validated the regional soil database. However, our results shed light on the soil conservation effects of Mediterranean hillside cropping systems of winter cereals and legumes, and could support the local implementation of agro-environmental measures.