Detection of soil microbial activity by infrared thermography (IRT)

Abstract

The determination of microbial activity is important for assessing soil fertility or indicating soil contamination. There exist several well established methods like calorimetry or respirometry. With these methods large samples campaigns are relatively elaborate and they do not allow a detection of spatial patterns of microbial activity.In this paper we present a new method to study microbial activity using infrared thermography (IRT). This method is based on the fact that microbial activity produces heat due to respiration. The main advantages of this method are: (i) spatial patterns of microbial activity can be determined, (ii) measurements are easy to conduct, (iii) both sample volume and sample number can be large, and (iv) measurements can potentially be conducted in situ without soil disturbance.Two laboratory experiments were conducted. 8 samples of a Cambisol A horizon were treated with a glucose mixture while 8 were used as reference. Surface temperature distributions on the samples were measured using an IR camera. The microbial activity of glucose treated samples was also determined by CO2 and heat production measurements using respirometry and calorimetry, respectively. In the second experiment a glass container was filled with the same soil treated with glucose. Half of the soil in the container was additionally contaminated with copper.Differences between surface temperatures between treated and untreated samples measured with the IR camera corresponded well with respirometer and calorimeter measurements. The predefined pattern of soil contamination in the second experiment could be well detected using the IR camera.The new method is a useful tool to easily and rapidly determine microbial activity on large numbers of samples simultaneously. Furthermore, spatial distributions of soil contamination are detectable. If more precise information about microbial activity in soil samples is required, the classically used methods are favorable.