In-situ decomposition sensor output correlates with soil health indicators

Abstract

Monitoring of soil microbiological processes can inform strategies to improve soil health and agricultural productivity. Biological soil health measurements are currently difficult to make in-situ and in real time, usually involving manual sampling and laboratory analysis. This is costly, time consuming, resource intensive, and cannot measure changes at high temporal and spatial resolution, limiting the ability to make prompt informed land management decisions. Low-cost soil sensors manufactured using printing techniques offer a potential scalable solution to these issues. Here, we tested the use of novel sensors for the proxy evaluation of soil microbial processes, hypothesizing that sensor decomposition rates may be related to manual soil sampling measurements. This is the first multi-plot field deployment of sensors which use a biodegradable composite conductor to transduce microbial decomposition of substrates to a change in electrical resistance, providing time-series decomposition rate data. Sensors were installed for 50 days across 44 experimental plots of a long-term grassland experiment with varying historical treatments and significant differences in soil microbial activity. Early failures and unresponsive substrates reduced the included sensor count to 31. Measurements commonly used as soil health indicators, including microbial biomass and enzymatic activities related to nutrient cycling, were determined using standard laboratory methods and compared to sensor responses. Three statistical approaches found positive correlations between the sensor signal and laboratory measurements of microbial biomass carbon and soil organic carbon, and some approaches found weaker correlations with enzymatic measurements. Although this experiment is limited in scope to a single experimental field and season, these initial findings show promise for enabling the proxy measurement of soil microbial processes in-situ using low-cost, scalable printed sensors.