Changes in soil organic carbon fractions in a sequence with cover crops

Advances in cover crops practice, in the context of potential benefits for annual crop production and sustained soil quality were studied. A soybean-maize sequence with five winter cover crops (CC) species were studied at the Marcos Juárez INTA Experimental Station, Córdoba, Argentina. Common vetch (VS), hairy vetch (VV), rye (R), triticale (T) and hairy vetch (VV) + triticale (T) mixture were tested as well as a control treatment (Ct) without a CC. The CC effect on the dynamics and balance of the soil organic C (SOC) and its fractions were examined. Maize and soybean yields did not show significant differences between the control and the CC treatments. The SOC stratification (0-0.10 and 0.10-0.20 m) with accumulation of residue on surface was due to the concentration of SOC and fractions that decreased with depth. The gramineous crops were more efficient in biomass production with more C input into the soil. Triticale showed positive C balance in OC and in the easily degradable fraction (labile) and an increase in the residue decomposition rate. CC had a positive impact on the more stable C stock (recalcitrant OC) in the sub-superficial layer than in the superficial one. The gramineae input was evident in the superficial layer and the most stable OC fraction, was concentered in the sub-superficial layer. Organic soil fractioning by particle size have been shown to be useful indicators for detecting changes produced by management practices in most experiments. This study demonstrated that the effect of cover crops on SOC and the labile fraction in the upper soil layer was strongly related with the high residue production.