In-situ Decomposition Sensor Output Correlates with Soil Health Indicators

Monitoring of microbiological processes in soil is important for understanding and improving soil health and agricultural productivity. Despite its significance, microbiological measurements are currently difficult to make in-situ and in real time. Evaluation of microbially-mediated soil processes usually involves manual sampling followed by laboratory analysis, which can be costly, time consuming, physically intensive, non-continuous, and reduces capacity for measuring changes at high temporal and spatial resolution, thereby 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, allowing for wide distribution of sensors that collect time-series data for decomposition rates. Here, we tested the use of novel sensors for the evaluation of soil microbial processes. This comprises the first large-scale field deployment of these sensors, which use a biodegradable composite conductor that transduces microbial decomposition of substrates to a change in electrical resistance. Sensors were installed for 50 days across 44 experimental plots of a long-term grassland biodiversity restoration experiment, including treatments with additions of synthetic fertilizer, manure, mixed seed, and red clover, causing significant differences in soil microbial activity. Soil biological properties commonly used as soil health indicators, including microbial biomass and enzymatic activities related to carbon, nitrogen and phosphorus cycling, were measured using standard laboratory methods. Sensor responses were compared to these conventional soil health measures to better understand their potential utility by considering the signals of sensors within a set decomposition window and individual sensor degradation rates across various timescales, and correlating changes in signal variability with soil measured properties. All statistical approaches found positive correlations between the sensor signal and laboratory measurements of microbial biomass carbon and soil organic carbon, and some approaches found correlations with enzymatic measurements. These findings demonstrate the potential for the proxy measurement of soil microbial processes in-situ using readily distributable printed decomposition sensors, thereby supporting their potential for low-cost, high-resolution temporal and spatial monitoring of complex soil biological parameters and their ability to provide new insights into soil health.