Do Maize Roots and Shoots Have Different Short-Term Degradability under Field Conditions? A Field Study of ¹³C Natural Abundance Resolved CO₂ Emissions

Field experiments suggested root-derived C contributed more than shoot-derived C in build-up and long-term preservation of SOC, but this was not confirmed in lab-based incubations. The question then emerges as to whether this contradiction is due to the absence of a comparable physical disturbance as introduced in incubation experiments. In this study, a shoot and root exclusion approach and natural-¹³C labeling technique were applied to confirm and time the differential degradation of maize (zea mays) shoots and roots under field conditions.

A field trial with five treatments and 3 replicates started in fall 2016 in Melle, Belgium on a light-sandy loam textured soil. We compared maize fields where roots were removed as T₀, where roots were chopped and incorporated back to the soil as T_mr, or where roots stayed in situ as T_ris with C₃ crop fields with maize root (T_C3r) and shoot (T_C3s) incorporation. Soil respiration was estimated based on both LI-8100 automated soil CO₂ flux and chamber-based trace gas flux measurements. The maize fraction in soil respiration was calculated from δ¹³C value of CO₂ and monthly decomposed maize-C was estimated by maize-CO₂ flux and temperature. The results showed that T_C3s displayed a higher CO₂ flux than other treatments and most of both maize roots and shoots were decomposed after 12 months.

Higher maize-CO₂ emission of T_C3s could be caused by more maize-C being incorporated in the soil. In fall 2017, the experiment was repeated. Beside the five treatments, an extra treatment with the same amount of shoot-C as root-C in T_C3r was incorporated in the C₃ crop field (T_C3s’) was included to evaluate the quantity effect of C input. CO₂ flux and its δ¹³C of each treatment was monitored by cavity ring down spectroscopy (CRDS). Currently, soil CO₂ flux measurements in the second year are still on-going thus more information will be presented at the ISRR-10 conference.