The potential of reducing tillage frequency and incorporating plant residues as a strategy for climate change mitigation in semiarid Mediterranean agroecosystems

Improved soil management in rainfed Mediterranean agroecosystems can be a powerful strategy to mitigate the current atmospheric CO2 increase, through soil carbon sequestration and stabilization. In this work, we assess the effects of different soil management practices (conventional tillage, CT, reduced tillage, RT, reduced tillage plus green manure, RTG, and no tillage, NT) on soil CO2 flux dynamics and carbon sequestration in two organic rainfed almond (Prunus dulcis Mill.) orchards under semiarid conditions. Soil CO2 flux, temperature, and moisture were measured monthly over two-three years, and shortly after tillage operations. The soil aggregation distribution (including micro-aggregates occluded within macro-aggregates) and associated organic carbon content were measured after four years of implementation. No significant differences in CO2 emissions among the soils subjected to the distinct management practices were observed at either site. On the one hand, shifting from CT to RT or RTG increased the OC content by 56% on average in all aggregate sizes. On the other hand, suppressing tillage only increased the OC content (by 24%) in the macro-aggregates. Moreover, improved soil management practices modulated the response of soil CO2 flux to temperature and moisture in these semiarid Mediterranean agroecosystems. According to our results, soil CO2 flux under the conventional tillage treatment was more sensitive to temperature increments than with the reduced tillage treatments, indicating that bare soils will be more vulnerable to organic carbon mineralization with ongoing global warming. On the contrary, the incorporation of plant residues under the reduced tillage treatments promoted soil aggregation and organic carbon preservation, making soils more resilient to abrupt changes in temperature and moisture under these treatments.