ASHS 2025 Conference

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While approximately 80 to 90% of the sprinkler-applied water to a strawberry crop is lost through runoff, deep percolation and evaporation, all the strawberry fields in Ventura County are still irrigated with overhead sprinklers during crop establishment. Even though water use-efficiency for the in-season irrigation is on average high, the escalating regulatory pressure to achieve sustainable groundwater use in California, and therefore limiting water availability, will demand further efficiency. This study quantified differences in water use, yield, canopy coverage and root depth between drip tape (DT) and micro-sprinkler (MS) irrigation during crop establishment at a commercial field located in Oxnard, CA during the 2023-2024 and 2024-2025 growing seasons. This abstract shares the results of the second season. The treatments were applied during the first 42 days after planting, after which drip tape became the only irrigation method. The irrigation scheduling of the MS treatment was defined by the irrigator (grower standard), while the DT irrigation was guided by tensiometers and field observations. All other production practices remained the same. Each treatment was replicated four times in a randomized complete block design, with an area of 0.15 acre per plot (7 beds of 175ft long). Total water use during establishment was 74.4% greater for the MS treatment compared to DT (5.8 and 3.4 acre-in, respectively). Marketable yield up to March 31 was very similar between treatments (19,268 and 19,420 lb/acre for DT and MS, respectively) and not statistically significant (p-value = 0.9517). Although not statistically significant, canopy cover MS was 9 and 11% greater at 1 month and 3 months after planting, respectively. Root depth measured at 1 month after planting was very similar and not statistically different (p-value = 0.9496).

Walnut is currently grown on over 400 thousand acres in California with the majority of production in the Northern San Joaquin Valley (NSJV). The recurring droughts and climate change in California will likely increase the uncertainty in water supply to walnuts and other specialty crops. Site-specific irrigation is critical to cope with these challenges. Knowing the water use of walnuts is crucial in optimizing irrigation management since it affects nut quality, and productivity. Unlike traditional methods, which are often limited by spatial coverage, high costs, and less precise crop coefficient values, satellite remote sensing offers a cost-effective, widely accessible solution. It enables large-scale evapotranspiration (ET) estimation with increasing adoption in irrigated agriculture, providing a valuable tool for water management. This study compares OpenET models, an open-source database providing ET estimates, against commercial in-situ surface renewal ET sensor. Utilizing OpenET platform provides a good opportunity for growers to improve water use efficiency. Such improvements could lead to the adoption of publicly available irrigation management tools and ensure healthier tree development, better resource utilization, and more resilient orchards in the face of climate change. Based on the data of 2024 season, the Satellite Irrigation Management Support (SIMS) model had the highest accuracy in estimating actual ET when compared to measurements from a commercial in-situ surface renewal system in the orchard, with a mean percent error (MPE) of -18.45%, and R² and mean absolute error (MAE) values of 0.88 and 0.03 inches/d⁻¹, respectively, followed by the Ensemble model. In contrast, the SSEBop model showed the lowest correlation with ETa, with an R² of 0.77 and a relatively high MAE of 0.06 inches, indicating a higher level of uncertainty in its estimates which could potentially lead to over-irrigation if adopted without correction. Based on these findings, growers can confidently incorporate the OpenET SIMS model into their irrigation scheduling, ultimately enhancing water use efficiency. However, further validation through replication over a second year and across multiple sites is essential to substantiate these findings.

Water scarcity is one of the major challenges facing the agricultural industry, necessitating the use of treated wastewater for irrigation purposes. However, not all crops can effectively utilize this water, as it may have negative effects on plant growth, including disruptions in nutrient uptake and photosynthesis. This study aimed to evaluate the effects of treated wastewater on the growth of rose-scented geranium (Pelargonium graveolens) and English lavender (Lavandula angustifolia). The experiment was conducted between 2022 and 2023 at the University of Fort Hare, Dikeni, South Africa. Two harvests were carried out in May 2023 (Harvest 1) and October 2023 (Harvest 2). Five irrigation treatments were applied to both geranium and lavender plants, consisting of treated wastewater from Dikeni town mixed with tap water at varying proportions: 0%, 25%, 50%, 75%, and 100% (v/v). Water and soil used were tested for nutritional composition. Treatments commenced four weeks after transplanting from cuttings, and the experiment followed a completely randomized block design with four replications across four blocks. The results showed no treatment differences in stem diameter, number of shoots, or plant height across treatments for both plant species during the two harvesting seasons. However, English lavender plants irrigated with 25% wastewater exhibited a slight increase in plant height at week 11, while geranium plants treated with 75% wastewater showed an increased plant height from week 5 until harvest at week 11. Additionally, plants receiving the 25% wastewater treatment produced the highest number of shoots from week 8 to week 11. These findings suggest that treated wastewater, both in its diluted and undiluted form, did not adversely affect plant growth. Therefore, it has the potential to serve as an alternative water and nutrients source for geranium and lavender plants, which farmers could utilize in collaboration with local municipalities to mitigate water scarcity challenges. However, further studies, particularly under open-field conditions, are needed to validate these results.

Runoff containing excess nitrogen (N) and phosphorus (P) is detrimental to environmental and human health. Bioreactors are biological treatment systems that can be used to combat these problems, which often consist of a lined trench filled with a carbon-rich media (often woodchips) to promote biological remediation through denitrification and other processes. Various carbon-rich organic materials, such as woodchips and sugarcane bagasse (a byproduct of sugarcane production), can be used to fuel biological processes, whereas inorganic materials, such as expanded shale, can provide binding sites for P adsorption as well as physical stability within medias. Raingarden installations utilize similar concepts for trapping runoff water and remediating contaminants; however, the inclusion of ornamental plants provides aesthetic appeal, an important consideration in urban and suburban areas. Seven unique medias were evaluated to determine potential to a.) remediate N and P from runoff and b.) support plant life. An aged pine bark/sand media commonly used for landscape beds (bed mix; BM) served as the control. Organic carbon sources (woodchips (WC) and sugarcane bagasse (SB) to support bacterial communities) and several inorganic materials (including expanded shale (S) and activated aluminum (AA) to bind P) were blended with BM to provide potential enhancement of nutrient removal capabilities. Media blends were homogenized by hand before being transferred into media containers (MC; 2.36 L of substrate per container), wherein Hibiscus moscheutos ‘Luna Pink Swirl’ seedlings were transplanted. Pots were placed within plastic containers (leachate containers (LC)), which served as a collection receptacle for leachate. Simulated runoff water containing N and P was prepared and applied to each replicate, after which leachate was analyzed and collected as sub-samples. Simulated runoff applications were limited in the initial phase of the study (one application per week; three total) and intensified in the final phase (three applications per week; nine total), with all leachate volumes collected between applications. Health and growth of Hibiscus was assessed via SPAD readings, growth index, and destructive harvest at the termination of the study. While the growth of all Hibiscus replicates was generally equivalent between treatments, it was observed that BM amended with SB produced more shoot biomass. Additionally, leachate nutrient content and water chemistry dynamics were influenced by several of the investigated amendments.

Green infrastructures, when implemented, need to consider the specifics of the local area and climate. The semi-arid climate along Colorado’s front range creates a challenge for plants in green infrastructure systems such as bioretention facilities and green roofs. These plants experience inundation and fast infiltration during rain events and long periods of hot and dry conditions between storms. To accommodate these periods of inundation and drought, Colorado native plants were evaluated due to their adaptation to the challenging conditions that occur in green infrastructure. The experiments in this study are intended to build upon existing work performed by our collaborators and funders Mile High Flood District, the City and County of Denver, and Colorado State University. We aim to improve green infrastructure facility design by using new bioretention media mixes, amended native soils with 5% compost (SSC) and amended native soils with biochar and zeolite (SBZ), green roof components/systems, new plant growth and establishment strategies, and lower irrigation regimes. In 2023 and 2024, data on plant survivability were collected from the bioretention facilities and the green roofs using 100 containerized and bare-root plants. The five native Colorado species selected were Agastache rupestris, Liatris ligulistylis, Amorpha canescens, Ratibida pinnata, and Schizachyrium scoparium. L. ligulistylis, in container, had a higher survival rate after one year on the green roof, on the other hand, it had a low survival rate after a year in the bioretention facilities. The bare-root L. ligulistylis had a higher survival rate, especially in the SSC media. A. canescens, bare-root, had a higher survival rate in the SSC media, while only 25% survived in the SBZ media. All other species overwintered and grew larger the second year on the green roof and bioretention facilities. The Colorado native plants tolerated challenging conditions better than the nonnative plants in the surrounding area.

Understanding the partitioning of evapotranspiration (ET) into soil evaporation and plant transpiration is critical for improving irrigation management in young orchards with limited canopy cover. This study focuses on partitioning ET in a 4-year-old drip irrigated pistachio orchard located in the Mesilla Valley, Southern New Mexico, using the Conditional Eddy Covariance (CEC) method. The orchard is equipped with a high-frequency eddy covariance system along with sensors to make meteorological measurements. The CEC approach was applied to identify and isolate flux contributions under specific atmospheric conditions, thereby separating transpiration-driven and evaporation-driven fluxes. The CEC separates fluxes using conditional sampling based on the hypothesis that when transpiration is dominant, CO₂ and H₂O fluxes should be highly correlated. Preliminary results show that the total ET values measured from June to August varied between 1.5 and 4.5 mm/day, with about 20% contributed through transpiration from the plants in the year 2024.

Lettuce (Lactuca sativa) is a key winter vegetable with significant consumptive water use in the Lower Colorado River Basin, especially in Yuma, AZ. Generally, lettuce requires about 300 – 400 mm to produce a desirable crop, which can vary significantly depending on irrigation method, soil type, field slope, temperatures, and planting window. However, the magnitude of the quantified differences in seasonal evapotranspiration and crop water productivity among different irrigation scheduling strategies under the subsurface drip irrigation method for organic vs. conventional iceberg lettuce production systems has not been sufficiently investigated. Field experiments were conducted in the fall 2024 growing season at the Valley Research Center at the University of Arizona Yuma Agricultural Center, Yuma, Arizona. This project was conducted in a one-acre field (half-acre organic field and the other half conventional field) under the subsurface drip irrigation method with two irrigation scheduling strategies (sensor-based irrigation (SI) and traditional irrigation (TI) based on growers' standard decision basis that is common in the Yuma area. The field was planted with the iceberg lettuce variety SVLD0023 on October 29th, 2024, on Gadsden clay loam soil. The fertilizer treatments imposed included (1) organic fertilizer, (2) combined biostimulant and organic fertilizer in an organic lettuce field, (3) nitrogen, and (4) combined biostimulant and nitrogen in a conventional lettuce field. Each treatment was replicated three times within each experimental block. Each experimental unit had three beds, and each bed was approximately 120 feet long and 3.5 feet wide, with a randomized complete block design. The objectives of this project include: (1) quantify and compare the seasonal iceberg lettuce evapotranspiration between organic and conventional iceberg lettuce production systems, (2) measure and compare the crop water productivity, and irrigation water use efficiency between two irrigation scheduling strategies for organic and conventional iceberg lettuce production systems, and (3) quantify and compare improvements in soil water retention under the combined application of biostimulant and organic fertilizers in organic lettuce versus the combined application of biostimulant and nitrogen in conventional lettuce. Data collection is currently in progress and will be analyzed in a manner consistent with the experimental design and the objectives of the study. Results will be presented with preliminary conclusions and directions for further research.