Evaluation of legume-cereal seed mixtures for enhancement of soil fertility, carbon storage and biodiversity in a low-intensity olive orchard

The main aim of the LIFE+ OLIVECLIMA project is to trial the introduction of new cultivation practices for tree crops in order to find a cost-effective means of mitigating and adapting to climate change, through the increase of carbon sequestration by soils, and reduction of greenhouse gases emissions. In order to determine the benefits of using cover crops on soil fertility and biodiversity, an investigation with different combinations of legumes and oat has been conducted during 2014-2015 in Chania, Greece, in a low tree density rain-fed olive orchard covered dominantly by Oxalis pes-caprae weed. The treatments were: natural vegetation, bare soil, only oats, only Vicia sativa, mixture of four legumes with oats and mixture of five legumes with oats. Seed emergence and soil cover was monitored and soil was monthly sampled at three depths (0-10, 10-20 and 20-30 cm) for analysis. During plant growth, significant fluctuations in soil NO₃-N and NH₄-N content were recorded. Similarly, soil CO₂ emissions increased with plant growth and air temperature raise. Sowing cover crop mixtures is a promising soil management practice to increase soil fertility and enrich plant and microbial biodiversity in olive orchards especially when dominated by Oxalis pes-caprae a very aggressive weed in many Mediterranean areas.