Do soil carbon sequestration and soil fertility increase by including a gramineous cover crop in continuous soybean?

Cover cropping is a farming practice that may improve C sequestration and soil fertility, but these effects can vary under different edaphoclimatic conditions. The effects of including a winter gramineous cover crop (CC) in continuous soybeans were evaluated in three long-term experiments (8 yr) on one coarse-textured soil and two fine-textured soils in the Pampas region of Argentina. The impacts of CC on soil C sequestration, soil nutrient availability, soil organic C (SOC), and N contents of soil particle size fractions were also determined. The inclusion of CC only increased SOC stock by 3.1 Mg ha(-1) in the coarse-textured soil (CTS). The labile C fraction in the 0-5-cm depth increased in both the CTS and the fine-textured soils (FTS) by 263% and 93%, respectively. Soil N also increased in the labile fraction by 119% and 112% when a CC was used in the CTS and FTS soils, respectively. Moreover, the inclusion of a CC decreased soil P availability in one experiment (4.9 kg ha(-1)) and increased soil manganese in two experiments (11 kg ha(-1) on average). The inclusion of a gramineous CC in a soybean monoculture increased the C balance, particularly in coarse-textured soils. Considering that soil N was similarly affected, the C/N ratio was not impacted.