Evaluating Root Biomass Effects on the CO2 Flush from Laboratory Dried and Rewetted Soils.

Monitoring soil health is important to ensure soil function in natural and agricultural ecosystems. Soil health is currently monitored comprehensively using a suite of indicators related to physical, chemical and biological soil properties. There is a need for soil tests that can be performed simply and inexpensively by soil testing laboratories or producers. One such test that is used commercially is based on the ‘CO₂ burst’, which is the CO₂ released after drying and rewetting. Although more CO₂ released after drying and rewetting is assumed to indicate a healthier soil, the soil factors affecting the amount of CO₂ released are not well understood. The amount of living root biomass in soil, which has the potential to strongly affect the CO₂ burst, changes throughout the growing season. Root growth affects the amount of root exudates and soluble C in soils, and also stimulates microbial populations. A better understanding of how root biomass affects the CO₂ burst has the potential to affect how this test is used, e.g. sampling could be recommended to occur at a specific time of year or results could be interpreted in light of current crop. We established a field experiment on tilled soil with a gradient in plant density. Barley was planted at a density of 350-450 plants per square meter. Densities of 100%, 50%, 25%, and 0% of the planting density were established by thinning and weeding. There were 5 replicate plots of each density. Soil were sampled adjacent to a middle plot row and CO₂ was measured by a Li-Cor for 24 hours after drying and rewetting. Water-soluble carbon, microbial biomass, and root biomass were also measured.