Novel Soil Decomposition Sensor: Field Studies and Design Improvements

  The sensing of soil microbial and enzymatic activity continues to be a challenge, as current techniques are typically limited to the laboratory, and are time and labor intensive. In addition, such offsite assessments are not necessarily reflective of in situ bio-chemical-physical processes. We previously presented a novel printed decomposition sensor comprising a poly(hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and carbon composite material, wherein the sensor response correlated with the microbial activity in incubated soils [1]. In field trials carried out in the Yorkshire Dales (UK) these devices showed a clear correlation with measured soil microbial biomass carbon. These sensors consisted of a single fuse-like resistive element and as such were subject to stochastic effects in soil, requiring large numbers of devices to be used in order to address variability in field measurements. Here, we present a novel hardware solution to mitigate these stochastic effects by parallelizing multiple printed sensing elements on custom printed circuit boards (PCBs). The first instantiation of this approach showed to be effective at smoothing out sensor response in potato farms in the Upper Midwest region of the United States. In order to further shape the signal response of these decomposition sensors, we explored different parallel topologies by varying the number of sensing elements, element width, and element length. We discuss the advantages and disadvantages of these different topologies. [1] Atreya, M.; Desousa, S.; Kauzya, J.; Williams, E.; Hayes, A.; Dikshit, K.; Nielson, J.; Palmgren, A.; Khorchidian, S.; Liu, S.; Gopalakrishnan, A.; Bihar, E.; Bruns, C. J.; Bardgett, R.; Quinton, J. N.; Davies, J.; Neff, J. C.; Whiting, G. L. A Transient Printed Soil Decomposition Sensor Based on a Biopolymer Composite Conductor. Adv. Sci. 2022, 2205785, 1–10. https://doi.org/10.1002/advs.202205785.