How Long does it Take for Granular Fertilizer to Dissolve?

Plants, like humans, require a variety of nutrients to thrive and develop properly.

There are 17 essential nutrients that plants need to grow, and most of them can be found in the soil. However, over time these nutrients get depleted, which is where fertilizer comes in.

Fertilizer comes in many different forms including liquid, granular, and powder. And while all forms of fertilizer work essentially the same way, the way they are delivered to plants can differ.

Granular fertilizers are ground-up, small pieces of fertilizer that typically dissolve slowly, which means they release their nutrients gradually over time.

This is ideal for crops because it allows the plants to uptake the nutrients steadily over time.

Once the granular fertilizers have been applied to the soil, it will take anywhere from a few hours to start providing nutrients to the plants.

However, nutrient uptake typically continues over a period of weeks or even months.

This period of time is called the fertilizer’s “release period.” The release period mainly depends on the type of fertilizer, granule size, soil moisture, and climate.

In warm, moist climates, the fertilizer will dissolve more quickly than in cold, dry climates due to the increased biological activity on the soil.

Other agricultural practices like tillage, irrigation type, and irrigation frequency can also impact the rate of fertilizer dissolution.

What does affect how quickly the fertilizer dissolves?

Granular fertilizers aren’t a single uniform product with a one-type chemical makeup. They vary in composition, size, and density which all impact how long it takes for them to dissolve.

Therefore, there are a lot of factors to consider that affect how long it takes for granular fertilizer to start dissolving and maintain nutrient release.

Let’s take a closer look at some of those factors that influence the speed of dissolution.

Climate

Climate conditions such as temperature and humidity affect how fast the fertilizer dissolves.

Warmer climates enhance biological and chemical activity in the soil which leads the fertilizer to dissolve faster.

Humidity also plays a role in how fast the fertilizer breaks down. Water molecules attach to the surface of fertilizer particles and help dissolve them.

The higher the humidity, the more water molecules are available to attach to the granules which speeds up the dissolving process.

Tillage

Tillage is a soil management practice that disturbs the soil by mechanically breaking it up.

This can be done with a tractor or other piece of equipment and is often used to prepare the soil for planting crops.

Usually, when you till the soil, it brings fresh oxygen and water to the surface which helps speed up the fertilizer dissolution process.

However, if you till the soil right after you apply the fertilizer, it can bury the granules too deep and prevent them from dissolving.

Soil Type

The type of soil can also affect how long it takes for granular fertilizer to dissolve.

Nutrient density, water retention, and drainage qualities of the soil all play a role in how fast the fertilizer dissolves.

For example, clay soils have high nutrient density and good water retention, but they don’t drain well.

This means the fertilizer will stay in place longer and dissolve more slowly than in sandy soils which have low nutrient density, poor water retention, and good drainage.

Also, the pH of the soil also impacts how fast the fertilizer dissolves. If the pH difference between the soil and the fertilizer is too large, it can create a chemically reactive environment and increase the dissolution process.

Irrigation

The frequency and method of irrigation also affect how quickly the fertilizer dissolves.

Continuous irrigation (like with a sprinkler system) helps dissolve the fertilizer more quickly than intermittent irrigation (like with a drip system).

Because the water is constantly wetting the soil and providing nutrients, the dissolution process happens more rapidly.

And if you irrigate frequently, the fertilizer will dissolve more quickly than if you irrigate less frequently.

We can granular fertilizer as toilet cleaning balls, the more regularly you flush, the less time it will take for the granules to dissolve and release their cleaning action.

Fertilizer Composition

Not all granular fertilizers are created equal. There are so many different types of fertilizers on the market today, each with its own chemical makeup.

Granular Urea, Granular Triple Superphosphate (TSP), Granular Monoammonium Phosphate (MAP), Diammonium Phosphate (DAP), and Ammonium Phosphate are just a few examples and we aren’t even discussing the products with hybrid granular composition.

Each of these granular fertilizers has different-sized particles, densities, and water solubilities.

So, depending on the type of fertilizer that you use, it can dissolve at different rates.

Fertilizer Particle Size & Shape

The size and shape of the fertilizer granules also affect how quickly they dissolve.

The smaller and more spherical the granule, the faster it will dissolve. This is because there is more surface area available for the granule to interact with the applied soil environment.

There is round (spherical or egg-shaped), cubic, rectangular, and even irregular-shaped granules on the market.

For example, urea and DAP are spherically shaped while potash is irregularly shaped.

Crushing Strength

International Fertilizer Development Center defines crushing strength as resistance to deformation or fracture under pressure (IFDC, 1986).

Crushing strength is useful in assessing granular handling and storage features, as well as pressure restrictions applied during bag and bulk storage.

Crushed fertilizer dissolves more quickly than whole granules that aren’t damaged. This is because the smaller pieces have more surface area available to interact with the soil and dissolve quickly.

How to control the release rate of nutrients from granular fertilizers?

Most of the time, you don’t need to control the release rate of nutrients from granular fertilizers.

Because fertilizers products are manufactured to release nutrients over a planned period of time designed by the manufacturer.

The rate of nutrient release from commercial granular fertilizers is relatively consistent. However, in certain cases, you may need to control the release rate of nutrients.

This can be due to variations in the soil type, climate, or irrigation method. If you need to adjust the release rate of granular fertilizer, there are several methods you can use.

One way to adjust the release rate is to change the soil environment. For example, if the pH of the soil is too high or low, it will affect the dissolution process. You can also adjust the release rate by changing the irrigation method or frequency.

Another way to control the release rate is by physically changing the granules. This can be done by crushing the granules or purchasing smaller/larger-sized granules depending on your application.

Also, the way the fertilizer is stored can affect the dissolution process. For example, if you store fertilizers in a hot, humid environment, the granules will dissolve more quickly than if you store them in a cold, dry environment.

Conclusion

The time it takes for granular fertilizer to dissolve will depend on the type of fertilizer, the particle size and shape of the granules, the crushing strength of the granules, and the environmental conditions like the soil pH and climate.

Most of the time, you don’t need to worry about controlling the release rate of nutrients from commercial granular fertilizers.

But you should rather be worried over application rates that can damage not only your plants but the environment as well.

In certain cases though, you may need to adjust the release rate of nutrients depending on your soil and climate conditions. You can do this by changing the soil environment, irrigation method or frequency, and/or physically crushing the granules.

And lastly, always store fertilizers in a cool, dry place, and follow the manufacturer’s guidelines for proper handling and application.