Soil volatile fingerprints: Use for discrimination between soil types under different environmental conditions

A conducting-polymer sensor-based electronic nose (E-nose) was employed for sampling the headspace volatiles of three soils (a sandy loam, a calcareous clay soil and a volcanic ash) at two soil water potentials (−0.7 and −2.8 MPa), three temperatures (16, 25 and 37 °C) and following the addition of nutrients such as glucose or wheat straw. Based on qualitative soil volatile fingerprint analysis, the aim was to test the E-nose potential for evaluating the influence of soil type and soil environmental conditions, as well as monitoring the impact of nutrient addition on soil microbial volatile production patterns. Principal component analysis (PCA) on normalised divergence data showed a clear discrimination between soil treatments accounting for 90% of the variance within the data set, irrespective of soil type. The non-specific sensor array was able to differentiate between soil types, and between soil samples under different temperature and water potential conditions. Following the addition of glucose or wheat straw into soil, a temporal discrimination between soil volatile fingerprints was obtained as response to nutrients, as well as between treated and untreated controls. This suggests that such non-specific sensor arrays for headspace monitoring may provide a rapid and non-invasive method for characterising soil microbial activity, as influenced by environmental factors and nutrient inputs.