ASHS 2025 Conference

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.