Project Overview
Efficient nitrogen management requires close coordination of irrigation and fertilizer applications, as water movement within the soil directly influences nitrogen dynamics and plant uptake efficiency.
Recently, near-real-time nitrate-N sensors have emerged as a promising solution for monitoring soil N availability continuously within a crop’s active root zone; this allows growers to make timely, data-driven adjustments to irrigation and fertilization practices, improving nitrogen use efficiency and minimizing environmental losses. However, the accuracy and reliability of these sensors are influenced by several environmental factors; as such, additional field trials are needed to determine the field applicability of these sensors.
This study, conducted at the University of Arizona Yuma Agricultural Center (Yuma, AZ), evaluated the performance of near-real-time nitrate-N technology under organic and conventional iceberg lettuce production systems using subsurface drip irrigation.
Farmer Takeaways
- Near-real-time nitrate-N sensors have practical implications for improving nitrogen management in arid vegetable systems. When implemented properly, they can complement established fertilization guidelines by providing field-specific, time-sensitive data that helps growers evaluate the effectiveness of recommended fertilizer applications and make informed, in-season decisions/adjustments.
- Irrigation events significantly influence soil nitrate-N concentrations, and can either result in leaching (loss) or enhanced nutrient uptake. Nitrate-N sensors may perform best when soils are moist (i.e., when soil nitrate-N is most mobile/detectable), but may be less reliable under extremely dry soil conditions.
Project Objectives and Approach
To evaluate the performance of near-real-time nitrate-N sensors under organic and conventional iceberg lettuce production systems using subsurface drip irrigation
- A field study was established at the University of Arizona Yuma Agricultural Center (Yuma, AZ).
- Treatments included both a conventional and an organic iceberg lettuce production system. Nitrogen fertility strategies differed by production system, with the conventional system receiving a pre-plant application of 200 lbs synthetic N/acre in the fall, and the organic system receiving both a pre-plant application of 2,000 lbs chicken manure pellets (4-4-2)/acre in the fall and an additional side-dressing of 1,800 lbs organic fertilizer (9-6-1) in the spring.
- Irrigation scheduling followed locally-recommended practices.
- Nitrate-N and soil moisture sensors were installed after crop emergence, with each probe positioned midway between two healthy, representative lettuce plants. After installation, the soil surface was gently compacted and leveled to maintain consistent irrigation flow and prevent preferential water movement near the sensors.
- Sensor data was collected using the AquaSpy data management platform, with nitrate-N and soil moisture readings at 3-inch intervals (down to 24 inches) being transmitted hourly. Data were reviewed weekly.
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- Periodically throughout the growing season, soil samples were collected near select sensors and sent to a lab for analysis. Sensor and laboratory data were compared to assess the sensors’ accuracy and ability to detect temporal shifts in N availability under field conditions.
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Key Findings
Near-real-time nitrate-N sensors may be responsive enough to in-season irrigation and fertility events to provide timely, reliable data on N dynamics in both organic and conventional lettuce systems
- The sensors successfully captured relative changes in soil nitrate-N concentrations over time, including after fertilizer applications and irrigation events. This suggests that near-real-time nitrate-N sensors may be responsive enough to provide reliable N tracking under field conditions, with positive implications for precision fertilization and irrigation management.
Irrigation events result in significant soil nitrate-N fluctuations in both organic and conventional systems, and are correlated with nitrate-N sensor performance
- Irrigation events influenced soil nitrate-N concentrations throughout the growing season in both organic and conventional lettuce systems, with the largest fluctuations occurring after irrigation events.*
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- *Irrigation can either result in nitrate-N leaching (by pushing soluble nutrients down below the active root zone), or can enhance nitrate-N uptake (by transporting nutrients to the active root zone). Adequate water is essential for nutrient uptake, but too much can lead to nutrient loss.
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- Irrigation also influenced nitrate-N detectability by the sensors, with a significant correlation observed between sensor performance and soil water availability. Low soil moisture can restrict nitrate mobility, making it more difficult for sensors to detect. This suggests that near-real-time nitrate-N sensors may perform better in moist soil conditions.
Resources
Mohammed, A. T. (2025). Performance Evaluation of Nitrate-Nitrogen Sensing Technologies in Organic and Conventional Iceberg Lettuce Systems under Subsurface Drip Irrigation. University of Arizona Cooperative Extension.
Read MoreLocation
ArizonaCollaborators
Region
West/Southwest
Topic
Soil Health, Crop Nutrient Management, Tools and Technology
Category
Vegetables/Fruits
Year Published
2025
