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Soil carbon dioxide flux in agricultural ecosystems
Abstract
Although present in the atmosphere in very small proportions, CO$\sb2$ plays an important role in the global carbon cycle. Soil CO$\sb2$ flux was studied in two agricultural ecosystems: maize (an annual) and alfalfa (a perennial). In maize, soil CO$\sb2$ flux was significantly higher at the within row (WR) position compared to the between row (BR) position. Weighted flux in maize ranged from 0.11 to 0.4 mg CO$\rm\sb2\ m\sp{-2} s\sp{-1}$ (25.9 to 94.3 kg CO$\sb2$-C ha$\rm\sp{-1}\ day\sp{-1}$) in 1992 and from 0.05 to 0.28 mg CO$\rm\sb2\ m\sp{-2}s\sp{-1}$ (11.8 to 65.98 kg CO$\sb2$-C $\rm ha\sp{-1}\ day\sp{-1}$) in 1993. Maize flux was higher in 1992 compared to 1993. Lower soil temperatures and higher soil moisture (precipitation was 55% above normal in 1993) may have influenced the low flux rates in 1993. Maize soil CO$\sb2$ flux was significantly different than alfalfa flux in both years. In 1992, maize flux was higher than alfalfa flux at mid-season. Alfalfa flux was higher in 1993 compared to 1992. Flux in alfalfa ranged from 0.10 to 0.3 mg CO$\rm\sb2\ m\sp{-2}s\sp{-1}$ in 1992 (23.6 to 70.7 kg CO$\sb2$-C $\rm ha\sp{-1}\ day\sp{-1}$) and from 0.25 to 0.39 mg CO$\rm\sb2\ m\sp{-2}s\sp{-1}$ (58.9 to 91.9 kg CO$\sb2$-C $\rm ha\sp{-1}\ day\sp{-1}$) in 1993. We examined diel (i.e. 24 hour) soil CO$\sb2$ flux on selected days in 1992. The trend in CO$\sb2$ flux showed a minimum flux in the morning and a maximum flux in the late afternoon or evening which appeared to be related to the diel variation in soil temperature. A multiple regression of flux against soil moisture, soil temperature, and LAI explained 47% of variability in within row maize, 32% in between row maize, 45% in weighted maize, and 48% in alfalfa (using the soil temperature and moisture terms only) and a Q$\sb{10}$ of about 2 using daily averaged flux. In maize, the relative contribution of the root plus rhizosphere towards surface CO$\sb2$ flux was estimated to average 54% over a growing season. Seasonal soil flux in maize was estimated to be 5500 kg C ha$\sp{-1}$ (June through September) in 1992 and 4600 kg C ha$\sp{-1}$ (June through October) in 1993. In alfalfa, seasonal flux was estimated to be 4400 kg C ha$\sp{-1}$ in 1992 and 5600 kg C ha$\sp{-1}$ in 1993 (June through September). Mean concentrations of CO$\sb2$ in the soil air at different depths under maize ranged from less than 1% (10000 ppmv) to 8.5% (85000 ppmv). Soil air CO$\sb2$ varied over both depth and diel and seasonal time.
Subject Area
Agronomy|Biogeochemistry|Soil sciences
Recommended Citation
Mielnick, Patricia Carole, "Soil carbon dioxide flux in agricultural ecosystems" (1996). ETD collection for University of Nebraska-Lincoln. AAI9712521.
https://digitalcommons.unl.edu/dissertations/AAI9712521