Short-term effects of repeated application of solid digestate on soil C and N dynamics and CO2 emission in a clay soil olive (Olea europaea L.) orchard

Olive orchards cultivation often has to face several soil degradation phenomena like organic matter depletion, reduction of biological activity and generalised loss of fertility. In these contexts, agricultural solid digestate has shown promising results in restoring fertility, although its sustainability has not been fully assessed. Therefore, to evaluate its common use in this agroecosystem, we conducted a field experiment to study the short-term effects of repeated amendment with solid anaerobic digestate on the integral fertility of an olive orchard grown in a clayey soil in Southern Italy. We compare the following treatments: unamended control, one-year and two-year solid digestate amendment application. During the experiment, we assessed changes in soil fertility and dynamics of C and N pools by measuring a set of chemical, biochemical and soil eco-physiological variables and by monitoring CO2 fluxes at field scale. Results showed growing benefits from single to repeated treatment with solid digestate, compared to the control, such as an increase of soil soluble C and N forms, organic matter and microbial pools with higher microbial activity and, despite a relative increase in CO2 field emission, microbial efficiency, thus proving to be a sustainable management for olive orchard agroecosystems.