USDA-ARS Mapping and Monitoring Soil Moisture and Salinity Across Orchard Crops Using Non-Invasive Tools - Postdoctoral Fellowship

ARS Office/Lab and Location: A research opportunity with the U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), located in Davis, California.

About the role

The Agricultural Research Service (ARS) is the U.S. Department of Agriculture's chief scientific in-house research agency, delivering cutting-edge solutions for agricultural challenges from field to table. This opportunity focuses on quantifying spatial variations in root zone soil moisture in orchard crops as a function of cover cropping.

Research will be conducted at the Sustainable Agricultural Water Systems (SAWS) unit, which aims to increase the efficiency and sustainability of irrigated agriculture in California, particularly for vine and tree orchard crops in the Central Valley. The unit studies water, carbon, and nutrient fluxes in agricultural lands, as well as groundwater geophysics and economics.

Research Project

Cover crops improve soil health in orchards by enhancing nutrient and moisture retention, reducing soil compaction, and attracting pollinators. However, their impact on root zone soil moisture availability and deep percolation remains poorly understood, creating uncertainties in modeling water and nutrient fluxes in semi-arid regions like California’s Central Valley.

This project will:

• Map moisture content using time-lapse electrical resistivity tomography (ERT) surveys and borehole nuclear magnetic resonance (bNMR) logging.
• Measure root water uptake with sap flow meters.
• Integrate data using physics-informed neural networks to translate apparent resistivity data into spatial maps of water content.

Participants will have access to USDA resources, including geophysical instrumentation, soil and plant sensors, laboratory and greenhouse space, and computational resources.

Learning Objectives

• Learn electrical geophysics and bNMR survey design.
• Deploy and maintain buried ERT arrays and bNMR access tubes for time-lapse data acquisition.
• Install and maintain sensors for sap flow, soil moisture, and salinity.
• Integrate diverse data streams (field measurements, remote sensing) into unified workflows for subsurface water content modeling.
• Apply physics-informed neural networks for hydrogeophysical modeling.
• Develop skills in manuscript preparation and presentation of results at professional meetings.

Requirements

• Currently pursuing or have received a doctoral degree in a relevant field (e.g., geophysics, hydrology, agronomy) within the past five years.
• U.S. citizenship required.

Preferred Skills

• Experience setting up and maintaining geophysical, soil, or agronomic sensor networks.
• Ability to lift and operate heavy equipment (50+ lbs) in hot, dry field conditions.
• Proficiency in coding (Python preferred).
• Experience with:
  • Near-surface geophysical survey design, acquisition, processing, inversion, and interpretation, or
  • Measuring and modeling root-zone soil moisture and nutrient dynamics.
• Familiarity with field instruments such as ERT, bNMR, soil moisture/salinity sensors, or sap flow meters.
• Experience with neural networks and machine learning tools.

Schedule

Full-time appointment starting in Fall 2026 (flexible start date). Initially for one year, renewable contingent on funding availability.

Pay

Annual stipend of $70,000 – $80,000, commensurate with educational level and experience.