Date of Award

Winter 1-17-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Plant, Soil, and Environmental Sciences

Advisor

M. Susan Erich

Second Committee Member

Ellen Mallory

Third Committee Member

Jean D. MacRae

Abstract

Soil that has been dried and rewetted has been observed to release a ‘burst’ or ‘flush’ of carbon dioxide (CO 2 ) upon rewetting. This CO 2 flush has been proposed as an indicator of soil health. This may be a valuable indicator of soil health, however the CO 2 flush has yet to be fully evaluated. Roots and root exudates influence the soil in a variety of ways that may impact the CO 2 flush, such as increasing aggregation, organic carbon (C), and microbial biomass. We conducted both field and greenhouse experiments to elucidate the relationship of root biomass to the CO 2 flush. The field experiment was conducted with barley grown at Rogers Farm, Old Town, ME in 2017 (two sampling times) and 2018 (three sampling times). Three greenhouse experiments were conducted in the Roger Clapp Greenhouse. In Experiment 1, barley was grown for 4, 6, or 8 weeks; in Experiment 2, barley, corn, crimson clover, soybean, and ryegrass were grown for 4 weeks; and in Experiment 3, corn and barley were grown for 5 weeks at 4 levels of nitrogen. All had unplanted controls. We measured root biomass, microbial biomass carbon (MBC), dissolved organic carbon (DOC), and the amount of CO 2 -C released during 72 hours after rewetting dried soil. Roots were quantified by wet sieving, rinsing, and drying. MBC was determined by the difference between microwaved and non-microwaved samples, and DOC was extracted by water. For both, C was quantified with a Shimadzu TOC-V CPH . For the CO 2 flush, dried soil was rewetted in sealable jars containing a septum, and the CO 2 in the headspace was quantified using an infrared gas analyzer. We found that planted soil had a larger CO 2 flush than bare or unplanted soil, but the effect was not large. Root biomass did not consistently correlate with the CO 2 flush. In unfertilized soils, the CO 2 flush was not influenced by plant species, but in fertilized soils, the CO 2 flush was significantly different between corn and barley. We found strong correlations between DOC and the CO 2 flush, and inconsistent correlations between MBC and the CO 2 flush. Because the CO 2 flush was not strongly influenced by collection time or plant species, the CO 2 flush may be a robust soil health indicator among different crops and sampling times. Our findings of a strong correlation between the CO 2 flush and DOC suggest that DOC could be explored as an indicator of soil health across a range of soils and regions.

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