Inspection Services Blog

Research Update: Controlled Release Nitrogen Fertilizers

Project Title: Field Evaluation and Demonstration of Controlled Release Nitrogen Fertilizers in the Western United States
Project Leaders: Charles Sanchez, University of Arizona, and Richard Smith, University of California Cooperative Extension Monterey County
Project Status: Complete

Overview: Controlled Release Nitrogen (CRN) has the potential to increase nitrogen use efficiency in desert vegetable production systems, by better matching nitrogen release with crop demand.

Background: Controlled release nitrogen fertilizers are standard granular fertilizers encased in a polymer coating. The coating temporarily shields the nitrogen from interactions with the soil solution delaying its release. Release time depends on temperature, moisture, placement, and coating thickness. CRN is thought to be beneficial to growers due to its potential to increase nitrogen use efficiency and provide application flexibility.

The success of CRN depends on how well the product’s nitrogen (N) release rate matches crop N demand throughout the season. Releasing the N too slowly can deprive crops of the N required for growth and releasing the N too quickly can result in crop damage or N loss due to leaching, volatilization, or denitrification. The use of CRN should be customized to the production system and crop demand.

Methods: Over the course of this project, from 2015 to 2018, several experimental demonstrations were conducted at University Research Centers and grower production sites in the Low Desert and Central Coast regions. These demonstrations compared standard grower practices with traditional soluble nitrogen sources, and various programs containing controlled release or enhanced efficiency fertilizers. The various trials where evaluated on iceberg and romaine lettuce, spinach, broccoli, cauliflower, cabbage, onions, artichokes, potatoes, sweet corn, peppers, tomatoes, and watermelons.

Findings: The experimental demonstrations took place under a wide variety of crops, soil characteristics, and grower management practices. For detailed information on the individual demonstration projects and their results please see the final report:

In general, the probability of CRN exhibiting benefits increased in scenarios where irrigation methods were less efficient and where coarse textured soils were present. There was also a trend with increased benefits being exhibited for longer term crops such as broccoli. Overall, demonstrations showed that well managed CRN technologies can offer economically viable and environmentally sound N management practices for vegetable crop production.

Impact: Over the span of this project, numerous evaluations provided a base understanding of CRN technologies in vegetable crop production. Additionally, the demonstration projects left an impact on grower cooperators and some of the growers have since adopted the use of CRN in their fertility programs.

To increase grower adoption in the future, technical support from suppliers and researchers should help growers match products with their unique crop production systems to optimize the benefits of CRN technologies.

Final Report: The final report for this project and a project factsheet are available:


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