Annual Legume Cover Crops Enhance The Sustainability of Rainfed Olive Orchards: From Leaf Ionome to Tree Physiology
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The olive sector has an important economic, social, cultural and ecological relevance in the Mediterranean region, where tillage and herbicides application still are generalized practices, although the recommendations of UE policy for a more sustainable agriculture. Cover crops with self-reseeding legumes of short-cycle, with mulch of dead vegetation during the dry season, is our option for soil management in olive tree rainfed orchards, as they provide protection against erosion, improve the physical and chemical properties, nitrogen fixation and soil moisture, enhance biodiversity and landscape beautification, while contribute to mitigation and adaptation to climate change and enable the organic production mode. The experiment was carried out during 2016 and 2017 on a commercial orchard (cv. Cobrançosa) in Northeast Portugal. The treatments laid out were: (1) ordinary tillage techniques used by local growers (two tillage trips per year) and (2) a mixture of 11 self-reseeding annual legumes (AL). The results revealed that cover crops influence positively the tree water status during the drought season, as well the nutritional status, namely the foliar concentrations of nitrogen, magnesium and manganese, both during the winter resting period and in summer, at endocarp sclerification. As a result, AL trees presented greater physiological performance during the summer, as evidenced by higher net photosynthetic rate, mainly due to inferior stomatal limitations, lower investment of resources in defensive metabolites, and enhanced yield. These results indicate that cover cropping should be included in the portfolio of adaptive management strategies against climate change, contributing to the sustainability of rainfed orchards.
