Archive Article: January, 2010
For many horticultural nurseries, turf managers and agricultural farmers, controlled release fertilizers have become an important part of their supplemental plant nutrition program. There are many advantages to using a controlled release fertilizer, and before choosing one, it is important to know the three S’s: safe, simple and sensible.
Advances in Controlled Release Fertilizers
Why were controlled release fertilizers developed originally? They were developed to slow or control the release of nutrients over time. With a controlled release fertilizer, the full amount of nutrients can be applied at the time of planting, or at the earliest stages of growth, thereby continuously releasing the nutrients to the plant’s roots over time so the plant can adapt to its nutrient needs. The goal is to choose a controlled release fertilizer for the crops being produced; thereby maintaining optimum nutrient ranges for those crops during the growing season.
How it works
How does the controlled release fertilizer process work? It begins after application when soil moisture enters an encapsulated fertilizer and the nutrients inside the coated granule dissolve but are not yet released. Once in a solution, the encapsulated nutrients can release slowly and consistently for months to the root zone through diffusion. The longevity of release is determined by the coating thickness and temperature of the soil. Upon completion of the release of nutrients, the coating membrane will collapse and microbially-decompose into naturally occurring carbon dioxide, ammonium and water. This process occurs with substrates that are encapsulated such as homogenous ammonium nitrate based nitrogen-phosphorus-potassium (N-P-K), ammonium nitrate based homogenous (N-P-K) with micronutrients or single nutrient source compounds such as urea.
Simple - This wholesale nursery in Hollister, CA grows perennials with controlled release fertilizers at a low rate.
Safe
Nitrate contamination of groundwater has become a serious problem in North America. Controlled release fertilizers are intended to maximize the efficiency of nutrients while minimizing the potential risk for negative environmental effects such as leaching and runoff. Excess nutrient runoff from nurseries or farms can end up in streams, rivers, lakes and oceans. In the United States the Clean Water Act was originally enacted in 1948 and totally revised by amendments in 1972. The law was primarily directed at point of source pollution, and amendments in 1987 authorized measures to address non-point sources of pollution, such as storm water runoff from farm lands, golf courses, nurseries or forests. Non-point source pollution includes sediments, pesticides and nutrients. The use of a controlled release fertilizer is appealing from the viewpoint of increasing fertilizer efficiency and minimizing environmental pollution.
Soil texture affects how nutrients and water are retained in the soil. Clays and organic soils hold on to nutrients and water longer than sandy soils. As water drains from sandy soils, it often carries nutrients along with it through the soil profile. When nutrients leach through sandy soils, they are not available for use by plants. Sandy soils are extremely vulnerable to nutrient loss through leaching. A research study on the Differential Leaching of Nutrients from Soluble vs. Controlled Release Fertilizers conducted at the Citrus Research and Education Center, University of Florida in 1992 by Ashok K. Alva1 concluded that “controlled release technology offers an important capability for minimizing leaching losses of nutrients.” It doesn’t matter if you are growing ornamental plants in Oregon, strawberries in California or citrus in Florida - the crops you are growing demand the utmost safety and performance. Controlled release fertilizers improve nutrient uptake in crops grown by decreasing the potential of nutrients lost to groundwater.
Simple
Fertilizers have been around for thousands of years to supplement nutrients in growing media. It is widely known that the benefits provided by the additional nutrients may depend on when they are delivered to the growing media and in turn available to plants growing in the media. Sudden delivery of too much fertilizer can be wasteful or even detrimental, causing soluble salt injury to the plants. Delivery of too little fertilizer or delayed fertilizer of an adequate amount may starve plants. It is beneficial to provide fertilizer that delivers relatively uniform rates of nutrients to the growing media over a period of time.
When growing a diverse range of crops growers want to keep their fertilizer program simple while giving the plants the nutrition they need for optimal performance. For a significant amount of the container grown nursery business in the United States, growing “color” has become more common and is defined by growing a plant from start to finish and sold in one season.
“Growers will also save money on labor, equipment and the cost of repeated fertilizer applications.”
A research experiment was done in 1999 and 2000 at the Department of Horticultural Science, Mountain Horticultural Crops Research and Extension Center at North Carolina State University by Richard Bir titled Fast Tracking Color Crops: Does Fertilizer Count?2 In the experiment, controlled release fertilizers from four different companies were applied once at the beginning of the experiment with completely soluble fertilizers applied weekly. The fertilizers were applied at three rates so that all plants were fertilized at a rate that was calculated to provide the same amount of nitrogen per pot per month from the different sources of fertilizers for each test species. The conclusion was that “controlled release fertilizers consistently produced the best growth regardless of the company providing the fertilizer.” Twice as much growth on Buddleia ‘Pink Delight’, 2.5 times as much growth for Echinacea ‘Bright Star’ and 1.5 times as much growth for Pennisetum orientale were measured as fresh weight at the end of the experiment from controlled release fertilization.
In another experiment titled Slow Release vs. Water Soluble Fertilization Affects Nutrient Leaching and Growth of Potted Chrysanthemum published in the Journal of Plant Nutrition3, Charm and Delano chrysanthemums were planted in a peat-based root medium using standard greenhouse cultural practices. Fertilizer treatments included: (1) alternate liquid fertilizer of a water soluble N-P-K formulation alternated with tap water, (2) constant liquid fertilizer, (3) controlled release fertilizer and (4) slow release tablets. The end result was that the root dry mass was higher for plants that received the controlled release fertilizer, more than double for those that had the constant liquid fertilizer. It was determined that “the resulting larger root system which developed with controlled release fertilizer compared to liquid feed fertilization may be considered an advantage of using a controlled release fertilizer instead of frequent applications of high concentrations of soluble fertilizers”.
Some growers can grow 300 to 400 different varieties of flowering annuals and perennial plants. In those types of situations, it may be difficult to try to determine the best rate of controlled release fertilizer for each variety. One must look at maximizing nutrient efficiency as well as monetary payback to the grower. Rates and type of controlled release fertilizers could be determined by container size, longevity of the crop grown, or crop similarities. Sometimes additional controlled release fertilizer or water soluble fertilizers maybe needed to maximize crop growth.
Sensible
Growers are demanding more from their fertilizers today than just a source of plant nutrients. They want reliable products that can help them move plants to market quicker with better quality at a lower cost. Using controlled release fertilizer makes sense, because they have the ability to keep nutrients available to the crop during its life cycle. There is greater nutrient uptake efficiency to the plant using a controlled release fertilizer, and more nutrients are protected from loss since they are metered out daily.
The use of water soluble fertilizers can result in the loss of nutrients through leaching, volatilization and immobilization in soils. Controlled release fertilizers allow the maximum amount of nutrients to be taken up by the plant, and reduce lost nutrients due to leaching or volatilization. Growers will also save money on labor, equipment and the cost of repeated fertilizer applications. Additionally they will have peace of mind knowing they are using a product benefiting the environment.
The technology being utilized today to encapsulate fertilizers is state-of-the-art, which has been refined over the last five decades. Growers who utilize these controlled release fertilizer technologies are achieving results that go beyond a plant’s nutritional needs, they are achieving results that impact their bottom line as well.
