Basal Soil CO2 Respiration during an Organic Cropping Season.

Soil CO₂ respiration evaluates soil microbial activity and is often used in the lab to estimate carbon mineralization (C-min). Field measurements throughout the season would be useful to interpret effects of differing organic management strategies such as tillage and compost applications, which affect overall soil respiration and are affected by ambient soil-temperature and moisture. This study observes weekly C-min in freshly sampled soils removed from field plots and immediately tested by Solvita without moisture adjustment in both small (250 cc) and large (950 cc) jars to evaluate response to CO₂ concentration over 24hrs. Organic plots included Tilled, No-Till, No-Till-Tarped (Trial A) planted to cabbage. Compost plots included 0,10, 20, 50, 90 t a^-1 compost rates in high-tunnels planted to cucumbers. For the Organic trial, mean soil temperatures in Tilled and NT plots did not differ significantly and rose 1.2 and 1.0 C dy^-1, resp. over 60 days with slightly greater daily max/min in Tilled. C-Min rose in the first 3 weeks and then declined slowly over the season in all plots, possibly due to drying conditions, and was slightly to significantly higher in NT vs Tilled and NT-tarp, attributed to more roots from weeds proliferating in NT. For the Compost trial, C-min was highly significantly and linearly correlated to compost rate at each sampling point and declined 40% over the season, most likely due to declining compost substrate availability. Therefore, compost has a strong influence on microbial respiration effect over an entire season. We conclude that field soil Solvita CO₂ respiration conducted on freshly sampled minimally disturbed soils closely reflects management and soil treatments and may help gauge nutrient availability in organic systems.