Spatial and Temporal Variability of Soil Respiration between Soybean Crop Rows as Measured Continuously over a Growing Season

An improved understanding of temporal and spatial variations in soil respiration is essential for measuring soil CO2 effluxes accurately. In this study, a field experiment was conducted to investigate the spatial and temporal variability of soil respiration between adjacent crop rows in a soybean (Glycine max L.) field. Soil CO2 concentration, water content, and temperature at a 7.5 cm depth were recorded continuously at 0 cm, 12 cm, 24 cm, and 35 cm from the plant row during the growing season. Root biomass at the corresponding locations was collected from the 0 to 10 cm and 10 to 20 cm soil layers at three growth stages. Seasonal CO2 efflux data showed that the minimum value appeared at the seeding stage, increased gradually, reached the maximum at the flowering and grain-filling stages, and then dropped steadily at the mature stage. Within a growth stage, CO2 effluxes related positively to soil temperature, but negatively to soil water content. In the early and vigorous growing stages of soybean crop, soil respiration showed apparent diurnal variations, and was most significant at the crop row location. Except for the seeding stage, CO2 effluxes at the crop row were larger than that of other locations, and effluxes at 35 cm from the row were representative of the mean CO2 efflux between adjacent rows. We concluded that the spatial heterogeneity of CO2 efflux between crop rows should be taken into consideration when measuring soil respiration in agricultural ecosystems.