Soil CO2 fluxes following tillage and rainfall events in a semiarid Mediterranean agroecosystem: Effects of tillage systems and nitrogen fertilization

The response of soil CO2 flux to tillage operations and rainfall events was studied under semiarid Mediterranean conditions. The study was conducted on a barley monoculture agro-ecosystem during summer/autumn fallow periods in four consecutive years (2005–2008). The study compared three N fertilization levels (zero, medium; 60 kg N ha−1; high, 120 kg N ha−1) under three tillage systems (NT, no-tillage; MT, minimum tillage; CT, conventional tillage). Tillage operations led to a pulse of soil CO2 flux. This pulse was linearly related to soil CO2 flux on the day before tillage operations under MT (slope = 4.22) and CT (slope = 16.7), indicating the extent of soil disturbances. However, the associated soil CO2-C losses during tillage operations were reduced and similar among different tillage systems. The soil CO2 flux after rainfall was higher under NT, where it was linearly related to soil temperatures (0.15 × soil temperature–1.06). Soil CO2 fluxes decreased on the following days as the soil dried. N fertilization affected CO2 flux in 5 out of 35 observation days, with higher fluxes with N fertilization under conservation tillage systems. Emissions after rainfall events led to large soil CO2-C losses, and these were of higher magnitude under conservation tillage systems (NT and MT).