What are controlled-release fertilizers?

March 15, 2022 – Many of us who enjoy gardening or grow plants in pots on the balcony use fertilizers that are characterized as "enhanced." They may have descriptions like "improved nutrient uptake," "6 months feeding" and "feed and forget." We use the fertilizer to provide extra nutrients to the plants we grow. The March 15^th Soils Matter blog reviews what makes these products enhanced fertilizers and how can they be so long-lasting.

According to blogger Kirsten Verburg, "sometimes the fertilizers contain organic sources that are slowly recycled by soil microbes and other life in the soil, releasing nutrients in the process. This too is a slow-release fertilizer."

However, where the fertilizers are sold and referred to as "controlled release," the fertilizer granules containing the nutrients are usually covered with a coating. The nutrients are released slowly through the coating. The idea is to make the coating such that it releases the nutrients just when the plant needs it. Or in other words, to ensure that release and plant uptake are "synchronized."

Many farmers use fertilizers and some of them are also interested in the use of controlled-release fertilizers. Just like in our garden, their use may reduce labor (and fuel) costs associated with fertilizer application.

These types of fertilizers need water to start releasing nutrients. Initially the fertilizer inside the coated pellet is dry. The coating allows water to move slowly inside the pellets, which then dissolves the fertilizer. The dissolved fertilizer then moves through the coating and becomes available to the crop. As time goes on, the concentration of fertilizer inside the granules reduces, which will cause a gradual slowing down of the rate of release.

To read the full blog, visit https://soilsmatter.wordpress.com/2022/03/15/what-are-controlled-release-fertilizers/ This blog is based on research by Dr. Verburg and her colleagues published in the Soil Science Society of America Journal.