SENose: An under U$50 electronic nose for the monitoring of soil gas emissions

Abstract

Tropical soils are major players on CO2 emissions and C cycling on earth. However, it is in tropical countries where scientists can have the most limited access to analytical tools needed for research on these processes. This paper describes the construction and test of a less than U$ 50 chamber for monitoring of multiple soil gas emissions. The system consisted on an array of three MQ series gas sensors placed into an airtight container, a PIC microcontroller and a custom-built software developed for data capture and visualization running on a laptop. A modified multiplexing of sensors was also incorporated in order to allow the parallel analysis in up to eight samples. The chamber, hereafter called SENose (short for Soil Electric Nose), was tested in two separate experiments. The first study used the three sensor array system in soil samples from Colombia and Ecuador, which were separated into two groups in order to study their gas emission patterns in D(+) glucose induced respiration tests. For a second experiment using a multiplexed sensor array in a different set of Colombian soil samples, gas emission patterns were obtained from autoclaved soil with reduced microbial activity, which were further contaminated with diesel oil as C source.During the first study, in replicated 22h continuous runs SENose clearly showed differences in soil respiration patterns of these soil samples, and a prominent timing differential increase in gas production after spiking D(+) glucose, a proxy for organic C, as a substrate. Results of the second study showed a clearly different pattern of gas emissions in diesel oil contaminated samples, when microbial activity was reduced by soil autoclaving. Moreover, two groups of non-autoclaved soil subsamples differing only in diesel oil addition could also be differentiated with basis on their respiration patterns after some hours of gas tracking. Based on these results we foresee a great potential from the use of this low cost system in fields such as soil microbiology, fertility, biotechnology and environmental sciences, where processes such as microbial activity, plant nutrient availability or soil pollutant turnover are tracked by monitoring their gas emission patterns.