Spatial and Temporal Patterns of CO2 Flux in Crop and Grass Systems.

Soil respiration exhibits high variation in space and time and assessing the space-time behavior of soil respiration in different land-use systems requires quantifying the variability structure and its dynamics. This study characterized spatial and temporal patterns of CO₂ flux in crop and grass systems. In situ CO₂ flux was measured at 60 locations 22 times (June 2010 to June 2011) in two-week intervals using a closed chamber method in combination with a photoacoustic environmental gas monitor. Soil respiration was highly variable in space, but its variability was structured in both land-use systems, with spatial correlation lengths varying between 5.5 and 55.8 m in the crop system and between 3.2 and 70.4 m in the grass system. Temporal variability of CO₂ flux was also high and structured in both land-use systems, with temporal correlation lengths varying between 75.3 and 193.4 days in the crop system and between 134.6 and 185.9 days in the grass system. The space-time field analysis of CO₂ flux demonstrated soil respiration behavior in both space and time domains and showed the magnitude of variability in one domain relative to the other. The heterogeneity of soil respiration was more pronounced in time than in space in both land-use systems. Soil respiration exhibited structured spatial and temporal variability and the variability dynamics in the crop system were different than in the grass system. These results indicate that land-use impacts small scale spatial and temporal variability dynamics of soil respiration, and these dynamics should be taken into account for experiment design, spatial and temporal associations with other variables, geostatistical mapping, and data interpretation.