Nutrient Management Research Database

http://ucanr.edu/sites/nm/files/76751.pdf

Research on controlled-release fertilizers (CRF) in vegetable production has been conducted in California for several decades, and commercial CRF products have been marketed throughout most of that time. CRF remain niche products used on only a small percentage of vegetable fields. The potential advantage of CRF is maximized in production systems in which in-season nitrogen (N) leaching is significant but beyond the control of the grower, and where there are cultural constraints on in-season fertilizer application. Neither of those conditions is typical of the California industry. Annual rainfall in the major vegetable-producing regions averages less than 400 mm, with the majority of that received during winter months when vegetable production is limited; in-season leaching occurs almost exclusively from irrigation. The alluvial soils favored for vegetable production tend to be relatively fine-textured, with high water holding capacity that reduces N leaching potential. The widespread adoption of drip irrigation allows for efficient irrigation and for multiple applications of less expensive N fertilizers in synchrony with crop demand. Under representative California field conditions it has been difficult to show a horticultural benefit from the use of CRF, and the higher cost of these products has therefore limited their use. Future government regulation for water quality protection may require more efficient N fertilization practices, but significant expansion of CRF use is unlikely even under that scenario.

• Controlled release fertilizer (CRF) formulations decrease the rate at which applied fertilizer becomes plant available, broadening the time period that plants can use fertilizer after it is applied.
• CRF have been studied in California for several decades, but few growers incorporate them into their fertilization plans.
• CRF are of limited utility in most California vegetable production systems, due to limited rainfall during the months of vegetable production, the dominance of fine-textured soils that prevent leaching, and the widespread adoption of drip irrigation.
• This study looked at yield differences for 9 vegetable systems when CRF were used.

• CRF fertilizers only showed yield increases in 2 of the systems studied. Both of increases were observed in celery cropping systems.
• The common practice of splitting fertilizer between numerous sidedress applications minimizes risks of nitrate leaching.
• One of the increases in yield was attributed to rainfall totals that were 40% above average in that year, which increases the likelihood that nitrate would leach beyond the depth celery roots could access.
• The increased costs of CRF far outweigh the minimal benefits from their use.