Evaluating Controlled-Release Fertilizer

controlled-release fertilizer
A drone photo of a replicated on-farm
corn trial in Suwannee county testing
various rates of controlled release
fertilizer sources in spring 2020 — photo De Broughton, UF/IFAS

[dropcap]C[/dropcap]orn is an important crop for Florida’s agriculture industry with nearly 100,000 acres annually. Producers, Extension agents and researchers are studying corn nitrogen fertilization programs and methods to improve fertilizer uptake efficiency, to increase profitability and to reduce impacts to water resources.

Why Controlled Release?

Projects on controlled-release sources of nitrogen in corn, watermelons and carrots are ongoing at the University of Florida Institute of Food and Agricultural Science’s North Florida Research and Education Center, Suwannee Valley in Live Oak, Florida.

The focus is to help producers evaluate different nutrient management strategies, increase the return on investment for fertilizer inputs, improve nutrient stewardship and decrease the impact on water resources. Researchers hope to gain a better understanding of the efficacy of implementing the 4R’s of nutrient stewardship — right rate of fertilizer, right placement, right source and right timing — simultaneously in corn production and other row crops.

How Does It Work?

Controlled-release fertilizers are typically applied once at the beginning of the crop season. Each fertilizer prill or granule is coated with a polymer-based material that protects the fertilizer and releases it over time. With this technology, the rate of release of the nutrients in the soil depends on temperature.

The release rate also depends on the type and thickness of the coating. Release rate customizations by crop are manufactured based on projected growing season temperatures, crop growth cycle and crop needs. Most assume this type of technology is the same as a slow-release fertilizer, but that is not the case. Slow-release fertilizers typically break down nutrients based on moisture; however, with Florida’s unpredictable climate that is not a viable option.

In comparison, split applications of conventional fertilizers require more trips across the field adding to labor and fuel costs. Although controlled-release fertilizers are more expensive at purchase, with fewer trips across the field, there is a potential to maintain or reduce overall cost.

If reduced rates can be proven to consistently perform equal to conventional fertilizer programs, this technology may become more commonly adopted by farmers, which could ultimately result in reduced nitrogen leaching.

Benefits of Controlled-Release Fertilizer

► Reduced Environmental Impact: A major long-term benefit of using controlled- release fertilizer on crops is to the local environment. With this source, nutrients are released slowly and at a rate the plant can better use. The amount of nutrients lost through infiltration is thought to be much lower than through conventional water-soluble types of fertilizers.

Nitrogen in the form of nitrate is very mobile in Florida’s sandy soils. With irrigation or heavy rainfall, the loss of nutrients is reduced compared to using water-soluble fertilizers, as the nutrient is bound within the coating of the fertilizer prill.

Additionally, less water may be needed, which is usually drawn from a groundwater source, because a conventional practice is to apply liquid nitrogen through an overhead pivot while irrigating corn.

Convenience: Another possible benefit of using controlled release is the peace of mind a producer receives in knowing the plants will receive the nutrients needed to grow a good crop, regardless of unexpected rainfall events. During times when corn has been rainfed continuously without the need for water, a grower using a water-soluble fertilizer must decide whether to fertilize plants and add excess water to the crop, or risk having a nutrient deficiency.

Using the traditional soluble source depends on the irrigation system, and a water source to be delivered to the crop. A controlled-release source will continuously release fertilizer without the need for irrigation, as increasing temperatures break down the polymer coating of each prill.

This is designed to take place over a specific timeframe, customized to the growth needs of the specific crop it is applied to. There is potential for this fertilizer source is to be applied only once, unlike water-soluble fertilizers.

Reduced Application Costs: Labor, fuel and equipment wear and tear are always a concern for growers. The incorporation of a controlled-release source can reduce labor costs by eliminating the need to mix and monitor water-soluble fertilizers. It also limits the need for expensive injection equipment or additional passes of broadcast spreaders through the field for those using a dry soluble product.

This also eliminates the chance of improperly mixing a water-soluble fertilizer, which can cause excess nutrients to be applied unintentionally.

Controlled-Release Fertilizer Trials

To verify these advantages, controlled-release fertilizer research is ongoing. In addition to research trials at the North Florida REC, a regionwide effort is planned for on-farm evaluations across the region in 2021. Interested corn and watermelon growers have been sought for on-farm trials.

Working with regional Extension agents and producers are Harrell’s Fertilizer, Pursell Agri-Tech, Mayo Fertilizer, the Florida Department of Agriculture and Consumer Services, and the Suwannee River Water Management District. CS

Article by De Broughton, Regional Specialized Agent, Row Crops, and Hailey Raulerson, Extension Assistant, UF/IFAS NFREC-Suwannee Valley.

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