Evaluation of the CO2 flush as a soil health indicator
2020
Laffely, Audrey | Erich, M Susan | Mallory, Ellen B.
The CO₂ flush is recommended as an indicator of soil biological health. We conducted field and greenhouse experiments to evaluate the effect of several factors likely to influence C mineralization (presence/absence of plants, plant species, time of season, N fertility) on the CO₂ flush. The field experiment was conducted with barley grown in 2017 (two sampling times) and 2018 (three sampling times). In greenhouse experiments, barley was grown for 4, 6, or 8 weeks; barley, corn, crimson clover, soybean, and ryegrass were grown for 4 weeks; and corn and barley were grown for 5 weeks at 4 levels of N. All had unplanted controls. Root biomass, microbial biomass carbon (MBC), dissolved organic carbon (DOC), and the amount of CO₂-C released during 24 h after rewetting dried soil were measured. MBC was determined by the microwave method, and DOC was extracted by water with C quantified using a Shimadzu TOC-VCPH. A LI-COR infrared gas analyzer was used to quantify CO₂. We found that planted soil had a greater CO₂ flush than bare or unplanted soil, but the difference was not large, ranging between 15 and 40%. Root biomass did not consistently correlate with the CO₂ flush. In unfertilized soils, the CO₂ flush was not influenced by plant species. In fertilized soils, the CO₂ flush was significantly higher in soils planted to corn than soils planted to barley at the two highest nitrogen levels. We found strong correlations between DOC and the CO₂ flush, and inconsistent correlations between MBC and the CO₂ flush. Because the CO₂ flush was not strongly influenced by collection time, plant species, or N fertility, the CO₂ flush may be a robust soil health indicator among different crops and sampling times.
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