Soil Carbon Dioxide Flux and Organic Carbon Content: Effects of Tillage and Nitrogen Fertilization

Abstract

Th e response of soil CO2 fl ux to long-term tillage practices (no-tillage, NT; minimum tillage, MT; conventional tillage, CT) and N fertilization level (zero; medium, 60 kg N ha–1; high, 120 kg N ha–1) was studied during three growing season in a rainfed Mediterranean agroecosystem. Soil CO2 fl ux was related to the crop growth, with the highest fl ux during spring (i.e., March–May). Tillage and N fertilization eff ects on soil CO2 fl ux during growing seasons depended on weather conditions: greater soil CO2 fl ux under MT and NT on dry years, greater under CT and MT on a wet year. Nitrogen fertilization aff ected soil CO2 fl ux during this wet growing season: fl ux with N fertilizer additions was higher than fl ux on the unfertilized plots. Th irteen years aft er establishment of the experiment, the soil organic carbon (SOC) stock under long-term NT was 3.9 Mg C ha–1 greater than under CT and 4.3 Mg C ha–1 greater than under MT. Th e SOC stocks with N fertilizer additions were 4 Mg C ha–1 greater than the stock on unfertilized plots. Th e increase of C inputs with N fertilization was more pronounced under NT than under MT or CT. For this reason the increased response of SOC stock to N fertilization is expected under NT in a longer period of time. Th e product between soil water content and soil temperature explained between 75 and 94% of the seasonal variability of soil CO2 fl ux. However, soil CO2 fl ux and SOC stock were hardly related.