Tillage effects on soil carbon balance in a semiarid agroecosystem

Tillage systems may affect soil C sequestration, with a potential impact on crop productivity or organic matter mineralization. We evaluated crop yield, C inputs to the soil, and in situ CO2–C fluxes under no-till and conventional tillage (disk tillage) during the 3- to 6-yr period from the installation of an experiment in an Entic Haplustoll of the Semiarid Pampean Region of Argentina to elucidate the mechanisms responsible for possible management-induced soil organic matter changes. Yield and biomass production were greater under no-till than disk tillage for all the crops included in the rotation (oat [Avena sativa L.] + hairy vetch [Vicia villosa Roth ssp. villosa], corn [Zea mays L.], wheat [Triticum aestivum L.], and oat). This result was attributed to the higher soil water content under no-till.

Carbon inputs to the soil averaged 4 Mg C ha–1 yr–1 under no-till and 3 Mg C ha–1 yr–1 under disk tillage. Soil temperature was similar between tillage systems and CO2–C emission was about 4 Mg C ha–1 yr–1, with significant but small differences between treatments (0.2 Mg C ha–1 yr–1). Carbon balance of the soil was nearly equilibrated under no-till; meanwhile, greater C losses as CO2 than inputs in crop residues were measured under conventional tillage. Organic C in the soil was 5.4 Mg ha–1 higher under no-till than the disk tillage treatment 6 yr after initiation of the experiment. Results showed that in our semiarid environment, C sequestration occurred under no-till but not conventional tillage. The sequestration process was attributed to the effect of the tillage system on crop productivity rather than on the mineralization intensity of soil organic pools.