We studied fodder radish carbon turnover as affected by soil tillage in Foulum, Denmark. Actively growing fodder radish monoliths from direct-drilled (DD) and conventionally tilled (CT) plots were extracted and labelled regularly with 14C isotope across their entire growth period. At the end of the fodder radish growth cycle, labelled biomass was harvested and incorporated into the same monolith. These monoliths were destructively sampled at biomass incorporation, 4, 8 and 18 months after incorporation. For each sampling period, soil and root samples were taken at 0- to 10-, 10- to 25-, and 25- to 45-cm-depth increments for determination of 14C distribution and retention. Carbon-14 declined significantly with increasing soil depth at each sampling for the two tillage practices (P < 0.05). We further observed significantly higher 14C at 0–10 cm for DD than for CT at 4 and 8 months after biomass incorporation. For the 10–25 cm depth, 14C was significantly higher for CT than for DD, 4 and 8 months after incorporation. However, despite these depth-specific differences, cumulative (0–45 cm soil depth) 14C retention was similar for DD and CT treatments for all the sampling periods. On the basis of a CN-SIM model forecast, we estimated that over a 30-yr period of continuous autumn fodder radish establishment, at least 4.9 t C/ha fodder radish C with a residence time of more than 20 yr could be stored in the soil.
Soil Use and Management, 2013, Vol 29, Issue 2, p. 191-198