A biological product evaluation trial was conducted in late summer 2025 to assess the effects of various biological products on romaine lettuce production near Soledad, California. The study took place at Huntington Farms, following standard commercial practices typical for the Salinas Valley. Lettuce was planted in mid-July and managed with conventional irrigation and fertility practices, including a total nitrogen application of approximately 162 pounds per acre.
The trial included nine treatments: a grower standard control without biological products and eight programs using different biological products. Each treatment was replicated four times to address field variability. Researchers measured marketable and unmarketable plant counts, estimated fresh yield by hand-harvesting plants, and determined dry matter yield by oven-drying samples.
Results indicated that marketable plant populations were consistent across all treatments, with only a 3.3% difference between the lowest and highest averages. “This narrow range indicates that none of the biological products influenced crop establishment or early-season stand survival under the conditions of this trial.” Average fresh weight per plant varied by just over 6%, while marketable yields differed by about 5.8%. Dry matter yield had a slightly wider spread but still showed no statistical differences among treatments or compared to the control group.
Drone-based NDVI imagery collected during the season revealed no consistent differences in canopy vigor among treatments, further supporting harvest results that suggested similar growth patterns regardless of product use.
“Results from this single site-year indicate that, under late-summer conditions with adequate fertility and irrigation, the evaluated biological products did not provide measurable benefits to romaine lettuce yield, and stand, compared with the grower standard practice,” researchers stated. They added that when nutrients and water are sufficient, potential advantages from biological products may be difficult to observe.
The findings align with other research showing that responses to biological products can depend heavily on environmental context. Benefits may become more evident under reduced-input systems or stressful growing conditions such as heat or limited water—circumstances not present during this trial.
UC Agriculture and Natural Resources (UC ANR), which is affiliated with the University of California (https://ucanr.edu/), supports research like this through its statewide network of local offices and Research and Extension Centers (https://ucanr.edu/). UC ANR applies university expertise to benefit communities across California through science-based practices (https://ucanr.edu/) and collaborative initiatives in agriculture, environment, nutrition, youth education, and more (https://ucanr.edu/).
Looking ahead, UC Cooperative Extension (UCCE) will collaborate with California State University, Monterey Bay on another round of trials in 2026. The new protocol includes greenhouse screening tests to identify top-performing products before field evaluations at commercial or research sites. A final greenhouse test will validate field findings. Products will be tested under three nitrogen rates—100%, 80%, and 60% of recommended levels—to better understand their performance across varying nutrient inputs.
For those interested in participating in future trials or seeking additional information, contact Paramveer Singh at psbsingh@ucanr.edu or call 831-214-8621.
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