Carbon dioxide emission from an organic soil amended with straw and wood chips

Drained and cultivated organic soils represent an important part of vegetable production in North America. However, the drainage required to cultivate these soils induces annual soil loss of 1 to 5 cm, which also leads to CO₂ emissions due to peat decomposition. One potential conservation strategy is adding plant-based amendments to organic soils to compensate for carbon loss. However, little is known about the impact of this conservation strategy on CO₂ fluxes. A greenhouse experiment was developed, using soil columns filled with organic soils collected from southwestern Quebec. Treatments were assigned to each column in a full block factorial experiment. Four types of biomasses (birch, willow, panicum, and miscanthus) at two different rates (6%, 20% v/v) constituted the treatments, in addition to an intact control and a disturbed control without amendment. The CO₂ fluxes emitted by soils were measured weekly using the static chamber method and infrared sensors over a period of 9 weeks, for a total of 1228 degree-days. Results showed that CO₂ emitted from the control soil columns (intact and disturbed) were 4.9 and 5.2 t C-CO₂ ha^-1 year^-1, respectively. Wood biomass amendment (birch and willow) had higher CO₂ emissions than straw biomass (panicum and miscanthus) with values of 6.5 to 9.1 t C-CO₂ ha^-1 year^-1 compared to 5.9 to 6.7 t C-CO₂ ha^-1 year^-1, respectively. Some treatments differ significantly from each other. The mass balance shows that only the 20% (v/v) amendments led to a positive net carbon balance or equilibrium.