Grazing, tilling and canopy effects on carbon dioxide fluxes in a Spanish dehesa

There is increasing interest in carbon sequestering capacity of agroforestry systems especially in relation to climate change. Appropriate implementation of silvopastoral practices in dehesa systems may contribute to their sustainability; improve soil carbon (C) and nitrogen (N) storage capacity while reducing the carbon dioxide (CO2) flux from the soil to the atmosphere. The response of soil respiration (Rs) to grazing and tilling practices and trees canopy influence were studied in a dehesa ecosystem in the center of Spain from July 2008 to February 2010. Four different treatments were established: non grazed-non tilled; non grazed-tilled; grazed-non tilled and grazed and tilled. In all the treatments Rs, soil temperature (Ts), soil moisture (Ms), soil C and N stocks were measured. Grazing reduced Rs by 12 % across all experiment. Increments of 3 Mg/ha in C stocks and 0.3 Mg/ha in N stocks in grazing soils were observed. Although, no clear tilling effect on Rs was found, a decrease of 3.5 Mg/ha in soil C stocks and 0.3 Mg/ha in N stocks was detected in tilled soils. Presence of tree canopy induced increases in Rs, soil C and N stocks; while decreases in Ts were observed, but grazing decreased the tree canopy influence on annual C losses by Rs. The Ms constrained the temperature response of Rs during the experiment, and meaningful Q10 values were only obtainable during the wettest time, ranging from 2.5 to 5.7. Grazing and tree canopy had a positive influence in the ability of soils to store soil C and N, while tilling had a negative effect on soil C and N store capacity in this study. Maintaining the beneficial practices and improving tillage management in this area may have important consequences in carbon sequestration capacity in this dehesa system.