Large Area Distributed Real Time Soil (DiRTS) Monitoring

Advancing our understanding of the soil ecosystem, especially the dynamics of nitrogen species, is critical for improving soil fertility, increasing crop productivity, managing greenhouse gas fluxes, and protecting environmental quality. This project presents convergent research to develop the next generation, integrated sensing system for large area, in situ, high resolution spatio-temporal monitoring of dynamic nitrogen species, specifically ammonium and nitrate, as well as soil moisture, potassium and salinity. The wireless Distributed Real Time Soil (DiRTS) monitoring network is comprised of (1) soil-penetrable sensor motes with advanced microfluidics mimicking plant root-like water intake, (2) robust electrochemical sensors for ammonium, nitrate, potassium and salinity utilizing ultra-low power circuit architectures for readout and digitization, (3) long range wireless data communication using emerging standards, and (4) advanced algorithms for geospatial mapping of soil mineral nitrogen, potassium, salinity and moisture. The platform will address fundamental weaknesses in our understanding and control of nitrogen species in both unmanaged (e.g. forest) and managed (e.g. agriculture) soils. Beyond the technical impact, the proposed research effort will offer educational and training opportunities for undergraduate and graduate students through innovative curriculum and for farmers and other soil management practitioners through publicly available training modules on design and deployment of the wireless Distributed Real Time Soil (DiRTS) monitoring platform.

The DiRTS platform will make several notable scientific contributions: (1) Continuous capillary-driven sampling of the target soil nutrients mimicking the natural water intake by roots and transpiration through aboveground plant parts; (2) Ion sensitive electrodes utilizing embedded desalination to improve selectivity, and utilizing redundancy and Bayesian calibration to improve sensitivity; (3) Circuits for readout and digitization operating below 0.5V power supply and nanowatt level power dissipation; (4) Event-driven sampling and wireless communication using probabilistic sensor scheduling based on available power and data importance; and (5) State of the art statistical machine learning based approaches for generating high resolution spatio-temporal chemical maps from irregularly sampled data. All technology will be validated using actual, in-situ measurements of the target variable using the sensing mote and DET/DGT sensors in an experimental forest-BIFoR-FACE of the Birmingham Institute of Forest Research. Following validation, the sensing mote will then be fitted inside greenhouse gas auto-chambers in the FACE facility for concomittant sensing of dynamic nitrogen species and N2O fluxes to be monitored using a PICARO greenhouse gas analyzer and mapped using DiRTS sensor network. This proposal brings together experts in engineering, biogeosciences and chemistry from the US and UK, with strong backgrounds and expertise in relevant areas of sensing, electronics, microfluidics, biogeochemistry, soil science, signal processing and sensor networks, for successful execution of this project.

Overview:
Motivated by the National Academy of Engineering (NAE) grand challenge of "Managing the Nitrogen
cycle", and the National Academy of Sciences (NAS) call for "Breakthroughs in Field Deployable
Sensors for Advancing Food and Agricultural Research", this project presents a convergent research to
develop the next generation, integrated sensing system for large area in situ spatiotemporal monitoring of
both dynamic nitrogen species, specifically ammonium and nitrate, as well as soil moisture and salinity.
Towards this goal, we propose a distributed wireless network of soil-penetrable sensor motes with
advances in microfluidics that mimics plant-like water intake, robust electrochemical sensors for
ammonium, nitrates etc., ultra low power circuit architectures for readout and digitization, long range
wireless communication using emerging standards, and advanced algorithms for geospatial mapping. The
platform will address the fundamental weakness in our understanding and management of nitrogen
species in unmanaged (e.g. forest) and managed (e.g. agriculture) soils.

Intellectual Merit:

The proposed wireless Distributed Real Time Soil (DiRTS) monitoring platform makes several notable
intellectual contributions: (1) Continuous sampling of soil micronutrients mimicing the natural water
intake and transpiration in plants using the capillary (wicking) effect in multifilament threads and
evaporation (2) Ion sensitive electrodes utilizing redundancy and Bayesian calibration for enhanced
sensitivity; embedded desalination to improve selectivity to ammonium and nitrate (3) Sub-0.5V circuits
for readout and digitization consuming nanowatt level power (4) Event-driven sampling and wireless
communication using probabilistic sensor scheduling based on available power and data importance; (5)
Sparsity-based and stochastic gradient descent based approaches generating high resolution spatiotemporal
chemical maps from irregularly sampled data and (5) All technology validated using actual, insitu
measurements in an experimental forest, with soil science investigation quantifying N2O fluxes to be
monitored and mapped using DiRTS sensor network. This proposal brings together experts in
engineering, geosciences and chemistry with a strong background and expertise in relevant areas of
sensing, electronics, microfluidics, biogeochemistry, signal processing and sensor networks, needed for
successful completion of this project.

Broader Impacts:

Empowered by the proposed DiRTS monitoring platform, the new and improved understanding of the
complex dynamic nitrogen transformational processes in soil will have broad applicability for agricultural
and environmental monitoring and management. The system will help optimize fertilizer treatment
thereby saving costs while improving food security and reducing contamination of soil and water sources
from fertilizer run-off. Sensors for ammonium, nitrates, salinity and moisture, with ultra low power
circuits will have broad applicability for wearable health monitoring, point of care diagnostics, and food
water and air quality monitoring. Advanced geospatial mapping algorithms will be useful in processing
data from a wealth of sources such as satellite data for weather and agriculture. There are opportunities
for licensing and commercialization through the Tech Transfer offices at the participating universities.

Beyond technical impact, proposed research will offer educational and outreach opportunities
through (1) interdisciplinary two-term course development for undergraduate and graduate students on internet of things (2) Training modules on the design and deployment of the DiRTS monitoring platform available to practitioners and (3) diversity outreach through mentoring enable via successful established programs such as Leadership Alliance, Bridging Engineers for Success at Tufts, and Access to Birmingham Uni outreach activity at BiFOR-FACE.