CORN ROOT INFLUENCE ON AUTOMATED MEASUREMENT OF SOIL CARBON DIOXIDE CONCENTRATIONS.

Carbon dioxide (CO2) production is a more desirable indicator of soil carbon (C) dynamics than CO2 flux at the soil-air interface, which is significantly influenced by the gas-transport condition of the soil. Production of CO2 can be computed from CO2 concentrations if high-temporal measurements are made. Our objective was to design, implement, and test an automated CO2 measurement system that requires low maintenance but provides high-temporal resolution of CO2 concentrations in soil. The CO2 sensors were located at different soil depths from 10 to 60 cm, with and without roots, to measure the effect of corn (Zea mays, L.) root activities on CO2 concentrations over time. A direct comparison indicates that soil CO2 measured with the automated measurement system represents CO2 of soil surrounding the sensor. Computed CO2 production was highest in the soils above 20 cm. A peak of soil CO2 concentration occurred after each of the major rain events. The amplitude of the peaks decreased with depth. Differences between the CO2 concentrations in the root and root-excluded soils were small between rainfall events and large at and after rain. Soil CO2 concentration showed diurnal variations at the 10-, 20-, and 40-cm depths, whereas it was hardly detectable at the 60-cm depth. The automated CO2 measurement system is a useful tool for gaining knowledge of CO2 production in soils over time and across depth and of contributions from roots and bulk soil to total CO2 production in soils.