Walter E. Riedell1, Shannon Osborne1, Thomas Schumacher2 and Joseph L. Pikul Jr.1, (1)USDA-ARS, Brookings, SD (2)Plant Science, South Dakota State University, Brookings, SD
Diversified crop rotations, which reduce risk associated with adoption of no-till soil management, may influence soil C sequestration and soil quality. This study measured effects of corn-soybean (C-S), corn-soybean-oat/pea hay (C-S-H), or corn-soybean-oat/pea hay-alfalfa-alfalfa (C-S-H-A-A) annual rotations on grain yield, stover/hay biomass, stover C, and soil C (0-7.5 cm depth) in soil converted to no-till management in 1996. Averaged over the last 2 yr of the experiment, grain yield from the corn phase of all rotations was 10.03 Mg/ha while soybeans yielded 1.84 Mg/ha. Corn stover remaining in the field after harvest was 10.61 Mg/ha and contained 4.80 Mg/ha C while that for soybean stover was 2.19 Mg/ha and contained 0.95 Mg/ha C. The oat/pea phase produced 5.35 Mg/ha hay while alfalfa produced 2.95 Mg/ha hay. Soil C sequestration rates, extrapolated from soil C measurements made in 1999 and 2007, were 142.4 kg C/ha/yr for C-S, 11.5 for C-S-H, and 253.1 for C-S-H-A-A. The C sequestration rate for C-S was intermediate between the other rotations. The greater C sequestration rate for C-S-H-A-A indicates that perennial forages included as rotational crops strongly increase soil C levels. The low C sequestration rate for C-S-H indicates that inclusion of oat/pea hay as a third rotational crop may not compensate for the reduction in the number of corn phases (and in the amount of stover C returned) that were present in the C-S rotation. Thus, greater crop rotational diversity when converting to no-till soil management may not always result in greater soil C sequestration.