What is Slow Release Fertilizer?

What is slow-release fertilizer? Let’s take a closer look

A slow-release fertilizer might be your solution. Gardeners shopping for fertilizer usually face a confusing array of choices. There are many varieties of liquids, powders, and granules, all promising outstanding results, that many gardeners essentially give up and choose the most well-known package on the shelf. But two types of fertilizers are very popular among gardeners: the kinds called slow- and controlled-release.

These fertilizers have some similarities but they differ in key respects. Rather than releasing a quick dash of nutrients as liquid, soluble crystal, or granular fertilizers do, these fertilizers release their nutrients very slowly over a longer period.

Slow-release fertilizers yield their nutrients at a less likely rate that depends mainly on the actions of organisms in the soil. In variation, controlled-release (sometimes called coated) fertilizers release their nutrients at a specific rate over a particular period of time.


A Steady Diet for Plants

While no fertilizer is perfect for every garden or situation, yet slow- and controlled-release kinds provide many advantages for most of the home gardeners. They avoid the common “feast-or-famine” syndrome that happens when fast-release fertilizers are applied unevenly. Roots are surrounded by plenty of nutrients, but these soon wash away leaving roots to starve and die.

Likewise, fast-release fertilizers are very easy to apply but in excess, they damage the plant. But since slow- and controlled-release fertilizers release their nutrients out gradually, both of the potential problems are minimized.

Another great advantage of slow- and controlled-release fertilizers is that they are environmentally friendly. In many parts of the country, waterway, stream, and groundwater pollution is a major problem, and some of that pollution has been traced to fertilizers washing through or off lawns. Because these balanced fertilizers release nutrients slowly, they are not likely to contribute much to this kind of pollution.

In most of the cases, the temperature has the most important influence on release rates. Not only does it affect nutrient diffusion across the coating of controlled-release fertilizers, but it also exerts a big influence on microbial actions, and thus on the release of nutrients from slow release kinds.


Types of Slow Release Fertilizers

Two kinds of slow-release fertilizers are currently available. As they are cheaper than controlled-release kinds, they are highly used when the precision–and higher cost–of controlled-release is not required, and where natural organics are not desired.

Synthetic organics. Combining urea, a common form of nitrogen, with formaldehyde, produces many kinds of fertilizers. These are called methylene urea fertilizers. One example is light blue nitroform. The release rate is calculated largely by bacterial activity rather than by temperature and water.

Depending upon the manufacturer, nutrients can last weeks or months. Urea formaldehyde-based fertilizers are the main component of many lawn and garden fertilizers.

Natural organics Many of the gardeners prefer natural organics basically for their soil-improving qualities. Nutrient release rates are variable and determined by soil bacteria and fungi, both of which need warm soil temperatures to be active. The more biologically active the soil is, the faster the release rate. Examples of natural organics include cottonseed meal, soybean meal, fish emulsion, and manures.

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