Location: Agricultural Water Efficiency and Salinity Research Unit
2025 Annual Report
Objectives
Drought, climate change, and competition for resources are reducing the availability of irrigation water and farmland in arid and semi-arid regions, including the western United States. One strategy for maintaining or enhancing productivity in the face of diminished resource availability is to make greater use of marginal lands and alternative water sources. Sustainable use of impaired waters requires soil, water, and crop management practices that optimize crop production while minimizing the degradation of natural resources by salts and other contaminants. Advanced models and decision-support tools are needed to evaluate alternative management practices and to assist growers and water managers in satisfying increasingly stringent regulations.
Objective 1: Develop and deploy digital technologies, models, and best management practices for the management of saline and sodic soils and the safe use of alternative water resources for irrigation.
Sub-objective 1.A: Develop and evaluate an integrated system of sensors for site-specific irrigation management to control soil salinity and related adverse conditions when using degraded waters.
Sub-objective 1.B: Develop databases and machine learning models for rapid estimation of soil-hydraulic and related parameters needed in water quality models and decision support tools.
Sub-objective 1.C: Investigate wastewater reuse and water quality impacts on soil properties and contaminant loading to underlying and downstream water resources.
Sub-objective 1.D: Expand user-friendly, web-based informatics and modeling platform for the diagnosis and management of saline and sodic soils.
Objective 2: Develop comprehensive datasets for agricultural water use, crop productivity, and carbon balance in salt-affected, semi-arid regions for a range of crops using various management practices.
Sub-objective 2.A: Observe water use and crop productivity in contrasting mature citrus varietals to determine potential time periods for applying deficit irrigation for water conservation.
Sub-objective 2.B: Extend artificial intelligence tools for water, nutrient, and salinity management to perennial specialty crops in Southern California.
Objective 3: Determine the G x E x M interactions related to crop salt tolerance and drought resistance.
Sub-objective 3.A: Evaluate the impact of regenerative agricultural practices in wine grapes on productivity, water use, and resilience to abiotic stress.
Approach
This project uses a combination of field, plot, and modeling studies to develop knowledge and technologies needed to enable optimal use of fresh, degraded, and recycled waters for irrigation.
Under Objective 1, it is hypothesized that for saline soils a multi-sensor platform consisting of gamma-ray spectrometry and electromagnetic induction (EMI) instrumentation combined with Landsat 7 spectral imagery will improve the spatial delineation of salinity and matric and osmotic stress patterns at field scale. To test the hypothesis, the spatial distribution of salinity and texture using EMI alone, EMI and gamma-ray spectrometry in combination, and EMI and gamma-ray in combination with spectral imagery will be compared to ground-truth measurements. Three field sites in the southwestern U.S. containing a range of soil textures, salinities, and parent materials will be evaluated.
The robustness of the U.S. Salinity Laboratory (USSL) regional-scale salinity assessment model will be enhanced by: (i.) incorporating orchards and vineyards into the model; (ii.) modifying and validating ECa-directed soil sampling protocols for fields under drip irrigation; (iii.) evaluating the reliability and credibility of the USSL regional-scale model through validation with a separate data set; and (iv.) establishing the temporal stability of the USSL regional-scale salinity model.
Databases and machine learning models for rapid estimation of soil-hydraulic and related parameters will be developed. Soil hydraulic properties will be measured in the laboratory using evaporation and dew point methods. A new standardized database of training data for developing and testing pedotransfer functions will be produced. A web-based platform will be developed for disseminating information, tools, and recommendations for evaluating and managing saline irrigation waters.
Plot scale studies will be conducted at the USSL in Riverside, California. A vegetable crop will be grown in rows irrigated periodically with either synthetic or collected tertiary treated wastewater by surface drip lines. Waters will contain a baseline concentration of inorganic and prominent antibiotic contaminants adjusted to a range of salinity levels. A cross section of contaminant distribution and speciation across the wetting zone in relation to soil chemistry and mineralogy will be determined.
Under Objective 2, water use and crop productivity in contrasting mature citrus varietals will be monitored to determine possible time periods for applying deficit irrigation for water conservation. Uncertainties and variances between different monitoring techniques (eddy covariance, surface renewal, and simplified surface renewal) will be evaluated.
Under Objective 3, the Agricultural Input Management tool with Artificial Intelligence (AIM-AI) will be extended. AIM-AI is an artificial intelligence tool for water, nutrient, and salinity management currently being developed for Imperial, Coachella, San Jacinto, Salinas, and San Joaquin Valleys. The current project expands the reach of AIM-AI to specialty perennial crops in Central and Southern California, including citrus, dates, wine grapes, and avocados.
Progress Report
This report documents the FY 2025 progress of project 2036-61000-019-000D.
Objective 1 concerns the development and deployment of digital technologies, models, and best management practices for the management of saline and sodic soils and the safe use of alternative water resources for irrigation. Ongoing research in support of this objective has deviated from the original project plan and milestones owing to critical scientific, technical, and administrative support staff vacancies. Nevertheless, significant progress was made in FY25. ARS researchers in Riverside, California, evaluated the use of soil apparent electrical conductivity (ECa) and gamma-ray spectrometry (GRS) to map particle-size fraction across three micro-irrigated citrus orchards in California. Accurate soil maps are crucial for optimizing water and nutrient management in specialty crops, particularly in resource-constrained environments like California. Results showed that apparent electrical conductivity was a reliable predictor of soil texture, particularly sand and silt contents, whereas gamma-ray spectrometry displayed mixed results due to site-specific influences of soil mineralogy. The findings demonstrate that apparent electrical conductivity is highly effective for soil texture mapping in non-saline soils, while gamma-ray spectrometry may require field-specific calibration due to variations in local mineralogy. The integration of multi-sensor data offers promising pathways to reduce ground-truthing requirements and improve soil mapping accuracy for precision farming practice.
Also, in support of Objective 1, ARS researchers, assessed the feasibility of using high-resolution satellite imagery to predict the yield of Japanese squash (Cucurbita maxima) in Hollister, California. Accurate estimation of crop yield is essential for optimizing agricultural practices and ensuring food security. Traditional approaches to monitoring yield often rely on ground-based observations, which can be time-consuming and labor-intensive. The study found that the highest resolution satellite data was most effective in explaining squash yields on this small farm. High-resolution satellite imagery has considerable utility for timely and accurate identification of within-field yield variations, facilitating informed precision agricultural decision-making for growers. Progress on laboratory characterization of soil hydraulic properties in support of Objective 1 was limited due to the abolishment of a technical support position. Nevertheless, many soil sample analyses (e.g., particle size distribution, bulk density, saturation percentage, salinity) have been completed and a large database is being compiled. Progress continued the development of new software for assessing various soil, water, and plant processes, as well as providing information on the characterization and management of salt-affected soils. Discussions with USDA-NRCS regarding the possible development of software for their soil survey and engineering needs are ongoing.
Under Objective 1, ARS researchers have made the following advances regarding per- and polyfluoroalkyl substances (PFAS) in agricultural systems:
i.) Developing and testing biochar-based filtration systems for removing PFAS from recycled water. An assessment of candidate biochar materials for use in the system indicated that a pine biochar possessed the most optimal physical and chemical properties for PFAS removal (>90% removal in most cases). A pilot-scale treatment system was then developed using this biochar and it was demonstrated that this system was able to provide sufficient PFAS-free water to irrigate a commercial-scale greenhouse operation. The work will offer growers with PFAS-impacted irrigation water the opportunity to remove PFAS at relatively low-cost and prevent these compounds from entering irrigated crops via root uptake from the soil.
ii.) Assessing the leaching of PFAS from contaminated soil and the use of biochar as a mitigation strategy. In the absence of biochar, 93% of the compound perfluorooctane sulfonic acid (PFOS) was leached from the soil. With the application of biochar to the soil, the amount of PFOS leached was reduced to 81% (rice husk biochar), 58% (biosolids biochar), and just 0.4% (pine biochar). The excellent performance of the pine biochar was related to its physical and chemical properties. The leaching of the compound perfluorooctane sulfonic acid (PFBS), a type of PFAS, was also reduced to 16% using the pine biochar (vs 92% in the absence of biochar). Furthermore, no PFBS leaching was observed following thermal modification (in air) of the biochar. These results suggest that appropriate biochar application to soil may be an effective and low-cost approach to reducing PFAS leaching from contaminated soils and hence protect groundwater resources.
iii.) Quantified the uptake of PFAS by 16 different varieties of spinach (Spinacea oleracea). Variations in PFAS uptake across the varieties will be related to genetic differences between the plants. It is hypothesized that specific gene transporters will control the uptake and root-shoot translocation of PFAS. The results will be useful to growers who will be able to select low-PFAS accumulating spinach varieties for cultivation and hence reduce transfers of PFAS into the human food chain. The work will also help us understand why other crops might accumulate PFAS to differing degrees.
iv.) Studying the bioavailability of PFAS to earthworms and plants in soil (i) irrigated with PFAS-impacted recycled water or (ii) amended with PFAS-impacted biosolids. The impact of various pristine and chemically-modified biochars in reducing the bioavailability of PFAS via adsorption processes is also being quantified. This work is a collaboration between ARS researchers at Riverside, California, and University of California, Riverside, and will help inform growers and regulators of the beneficial impact of biochars in reducing PFAS transfers in agriculture, thereby protecting the human food chain.
v.) Worldwide, artemisia tea is widely consumed in the hope of preventing malaria. PFAS accumulation in plants has not been thoroughly investigated and their accumulation in Artemisia plants or tea was never reported. ARS researchers in Riverside, California, determined the accumulation and distribution of six PFAS in three genotypes of Artemisia. Plants were irrigated for 48 days with PFAS-free water or waters spiked with PFAS. Plants were separated into leaves, stems, and roots and analyzed by liquid chromatography to determine PFAS accumulation and distribution in Artemisia plants. PFAS molecules with a short carbon chain showed high levels of accumulation in the leaves of the plants. Long carbon chain PFAS were typically excluded from the plant, with low levels of accumulation in the roots. Leaf samples are being used to make tea according to an international protocol. The tea will be analyzed for the six PFAS added to irrigation waters. Results will be useful to worldwide artemisia farmers who use river and groundwater for irrigation of Artemisia crops highlighting the health implications associated with the use of contaminated water to irrigate edible crops, Artemisia, and other medicinal plants. In support of Objective 2, researchers at Riverside, California, continued the operation of three eddy covariance towers in citrus orchards in collaboration with a researcher from Parlier, California. A Research Associate at Riverside, California, continued work on evaluating satellite evapotranspiration estimates for these orchards, which resulted in a peer-reviewed article being published in FY25. Work in citrus has highlighted significant limitations in using the OpenET evapotranspiration algorithm and project for managing citrus irrigation. In support of Sub-objective 3.A., researchers at Riverside, California, continued a collaborative research effort on the impacts of regenerative agricultural practices on wine grape resilience to abiotic stresses. Farmer-directed treatment plans were continued in an experimental vineyard, ongoing soil and microbial samples were collected, and three monitoring stations (meteorology and soil moisture) were maintained in the vineyards. New work was initiated for evaluating soil amendments for treating chloroamines in irrigation water, which has resulted in grower concern. In support of Sub-objective 2.B., work by a Research Associate in Riverside, California, on an externally funded project (2036-61000-019-006-R) was evaluated for potential transferability to domains covered by this project plan. Ongoing work by a Research Associate in Riverside on an externally funded project (2036-61000-019-006-R) contributed significantly to Objective 2 of the CRIS project through enhanced satellite remote sensing of crop water use in specialty crops. FY25 work involved evaluating irrigation models with different soil database parameterizations, which had a significant impact on irrigation amount and frequency in a submitted publication currently under review. In support of Objective 3, chemical and biological soil analyses were completed in entirety for the initial time sampling point from regenerative management trials in Temecula. This includes assays for soil biological activity as well as advanced characterization of soil chemical properties related to soil health. Final sampling was performed for the time-resolved study probing conversion of a conventional vineyard to regenerative management. Basic soil properties were measured for soils collected in 2022 - 2025 to allow for assessment of response of soil variables to transition in management practices. Final analyses on the full set of soils from all years will be completed this year. These activities directly address the Goal/Hypothesis of Objective 3 by determining chemical and microbiological changes in vineyard soils following regenerative management practices.
Accomplishments
1. Reference soils and data diagnostics are necessary to validate soil microbial community sequence results. Soil biology is an important factor driving the productivity and sustainability of soils. To understand the diversity and function of soil microbes, DNA sequencing methods are now commonly employed, but reproducibility and the potential to introduce error throughout the workflow steps are ongoing challenges. In response to these challenges, ARS researchers in Riverside, California, working in collaboration with ARS researchers in multiple other states, conducted a cross-laboratory study to evaluate sources of variability in soil community sequencing experiments and develop diagnostics to detect errors. One of the seven sequencing runs in the experiment produced results that were clearly incorrect based on comparison to the other runs, yet the internal control (microbial mock community) and standard diagnostics did not suggest errors. This study provides new simple bioinformatic diagnostics to identify erroneous sequence results and recommends use of reference soils rather than simple “mock” communities to validate sequence runs. Researchers and commercial facilities following these guidelines can have greater confidence in the accuracy and reproducibility of soil community sequence results.
2. Conversion of agricultural waste and invasive plants into materials for wastewater treatment. Antibiotic resistance genes (ARGs) in wastewater represent an environmental health threat to land irrigated with treated wastewater. Removing these materials from wastewater is of critical importance to mitigate risks of wastewater reuse in agriculture. ARS researchers in Riverside, California, produced materials made from agricultural byproducts (nut shells, orange peel, manure, wood waste) and an invasive plant species (black mustard), and demonstrated the ability to effectively remove genetic material, such as ARGs, from water. This work provides a potentially cost-effective and environmentally friendly way to repurpose crop waste and invasive plant species into a material for wastewater recycling.
3. Identification of biochar properties that facilitate PFAS removal. Per- and poly-fluoroalkyl substances (PFAS) are long-lived contaminants of increasing concern for irrigation and drinking water supplies. It is known that biochar, the burnt remains of biomass, is capable of adsorbing PFAS, thereby removing these harmful compounds from water. However, removal effectiveness varies widely across biochar types that have differing biomass sources and production temperatures. For a diverse range of biochar types, ARS researchers in Riverside, California, identified the physical and chemical properties that are responsible for the adsorption of PFAS and used these to produce mathematical equations that can successfully predict how much PFAS can be removed from water. This work has helped identify highly effective biochar types that can be used for water treatment and will allow practitioners to reduce the cost of water treatment by enabling lower cost and more energy efficient biochar filters to be used in place of other approaches.
4. Caution needed for the use of satellite evapotranspiration models in citrus. Satellite remote sensing has been increasingly used for large-scale monitoring of crop water use, evapotranspiration (ET), and irrigation scheduling. Recently, an open-source ET platform (OpenET) has been implemented to provide water managers with free, daily data. Growers have expressed concern that OpenET may be used for regulatory actions, particularly in crops such as citrus with unique canopy characteristics and deficit irrigation. ARS researchers in Riverside and Parlier, California, measured ET at two citrus orchards in California to evaluate the accuracy of OpenET and a second satellite model (BAITSSS) informed by irrigation data. OpenET estimates were approximately 30% higher than actual measured ET, with a major bias in Spring. In contrast, the satellite model using irrigation data simulated ET to within 2% of measured values. These results indicate that citrus growers and water managers need to use caution with OpenET, and that further work is needed to effectively manage citrus crop water use with satellite information.
Review Publications
Dhungel, R., Anderson, R.G., French, A.N., Skaggs, T.H., Ajami, H., Wang, D. 2024. Intercomparison of citrus evapotranspiration among eddy covariance, OpenET ensemble models, and the water and energy balance model (BAITSSS). Agricultural Water Management. 304. Article 109066. https://doi.org/10.1016/j.agwat.2024.109066.
Li, N., Skaggs, T.H., Scudiero, E. 2025. In-season estimation of Japanese squash using high-spatial-resolution time-series satellite imagery. Sensors. 25(7). Article 1999. https://doi.org/10.3390/s25071999.
Scudiero, E., Schmidt, M.P., Skaggs, T.H., Ferreira, J.F., Zaccaria, D., Pourreza, A., Corwin, D.L. 2025. Apparent soil electrical conductivity and gamma-ray spectrometry to map particle size fraction in micro-irrigated citrus orchards in California. Frontiers in Plant Science. 16. Article 1512598. https://doi.org/10.3389/fpls.2025.1512598.
Silva, G.H.M.C., Araujo, P.R.M., Vieira, C.B., Araujo, J.K.S., de Souza Junior, V.S., dos Santos, J.C.B., Schmidt, M.P., Ying, S.C., Biondi, C.M. 2025. The role of soil organic matter quality and mineralogy controlling the highest mercury concentration of the Brazilian mangroves. Science of the Total Environment. 975. Article 179274. https://doi.org/10.1016/j.scitotenv.2025.179274.
Kadyampakeni, D.M., Anderson, R.G., Schmidt, M.P. 2025. Advancing salinity and nutrient management for irrigation science. Irrigation Science. 43:321-327. https://doi.org/10.1007/s00271-025-01023-y.
Pessoa, U.C., de Franca e Silva, E.F., de Oliveira, T.F., Ferreira, J.F., Rodrigues de Souza, E., Rolim, M.M., Oliveira da Silva, A., Santos Junior, J.A. 2025. Cilantro photosynthetic parameters in response to different flows of nutrient solutions prepared with brackish waters dominant in Na+, Cl-, or Ca2+. Water. 17(11). Article 1640. https://doi.org/10.3390/w17111640.
Vieira, C.B., Silva, G.H.M.C., de Almeida, B.G., Pessoa, L.G.M., Freire, F.J., de Souza Junior, V.S., de Melo, H.F., de Lima, L.G.G., do Nascimento Paiva, R.F., Ferreira, J.F.S., dos Santos Freire, M.B.G. 2025. Saturated hydraulic conductivity of nine soils according to water quality, soil texture, and clay mineralogy. Agronomy. 15(4). Article 864. https://doi.org/10.3390/agronomy15040864.
Ramos, M.P., Schmidt, M.P., Xuan, R., Ashworth, D.J. 2025. Biochar selection for removal of perfluoroalkyl substances from reclaimed water for agricultural irrigation. Biochar. 7. Article 56. https://doi.org/10.1007/s42773-025-00436-4.
Li, N., Skaggs, T.H., Ellegaard, P., Bernal, A., Scudiero, E. 2024. Relationships among soil moisture at various depths under diverse climate, land cover and soil textures. Science of the Total Environment. 947. Article 174583. https://doi.org/10.1016/j.scitotenv.2024.174583.
Shih, C., Anderson, R.G., Skaggs, T.H., Juang, J., Chen, Y., Jang, Y., Gu, R., Huang, C., Lo, M. 2025. Challenges and limitations of applying the flux variance similarity (FVS) method to partition evapotranspiration in a montane cloud forest. Agricultural and Forest Meteorology. 362. Article 110391. https://doi.org/10.1016/j.agrformet.2025.110391.
Kandhway, A., Scarpare, F., Liu, M., Nelson, R., Adam, J.C., Anderson, R.G., Conklin, M.H., Safeeq, M. 2024. Water use dynamics of almond and pistachio crops in the Mediterranean region amid climate change. Agricultural Water Management. 307. Article 109219. https://doi.org/10.1016/j.agwat.2024.109219.
Schmidt, M.P., Rupp, S., Ashworth, D.J., Phan, D., Bhattacharjee, A., Ferreira, J.F., Men, Y., Ibekwe, A.M. 2025. Feedstock selection influences performance and mechanism of DNA adsorption onto biochar. Environmental Nanotechnology, Monitoring and Management. 23. Article 101040. https://doi.org/10.1016/j.enmm.2025.101040.