Comparison of two alkali trap methods for measuring the flush of CO2

Soil biological activity is a key feature of healthy soil. The flush of CO2 during the first few days after rewetting of a dried soil is a rapid indicator of soil biological health, but variations in approach require testing and calibration. A 3-d incubation method (25 degrees C, 50% water-filled pore space, acid titration) was compared with a 4-d incubation method (similar to 20 degrees C, capillary wetted, electrical conductivity) from two long-term field experiments in Missouri (silt loam soils) and North Carolina (sandy loam and loamy sand soils). The two methods were related (p < .001) to each other (r(2) = .93, n = 211 for Missouri soils and r(2) = .68, n = 126 for North Carolina soils), but results differed in absolute value in an unexpected manner. Differences in incubation time (3 vs. 4 d), temperature (20 vs. 25 degrees C), and water delivery (50% water-filled pore space vs. capillary wetting) were major factors affecting relationships between methods. Time and temperature were predictable and scalable factors, but water delivery approach likely caused random variations specific to soil type. Both methods were able to discern depth stratification of soil biological activity, but subtle differences due to landscape position and soil texture were detected only with the 3-d method. We suggest that greater standardization of soil biological activity protocols based on key factors of soil moisture, temperature, and time of incubation be adopted to improve reliability and value to stakeholders.