6 Factors That Determine Granular Micronutrient Fertilizer Quality 

What is the most effective way to ensure that you’re receiving high-quality micronutrient granular fertilizers when importing them? In our experience, six factors must be considered. We’ll go over each of these factors in detail and show they influence fertilizer quality in this blog post. 

Granular micronutrient fertilizer importers must pay attention to the following quality indicators:

  • Whether the main nutrients meet the content standard
  • Heavy metal levels
  • Particle size uniformity
  • Particle hardness
  • Fertilizer release time
  • Moisture levels

This guide to gauging granular micronutrient fertilizer quality will expound further on the above factors. Fertilizer importers will not want to miss this!

Whether the Main Nutrients Meet the Content Standard

Granular fertilizer contains a series of micronutrients. Each of these nutrients is critical for the short-term and long-term health of plants and crops.

Depending on the level of nutrients in the granular fertilizer, the fertilizer will receive a fertilizer grade. This grade is the standard for which the fertilizer is expected to achieve.

For example, a package of granular fertilizer with a label that reads 10-10-10 is expected to contain 10 percent of each nutrient.  

This granular fertilizer meets standards because it has the appropriate levels of nutrients.

When a granular fertilizer formula surpasses the recommended levels of nutrients or, even more detrimentally, contains less than the recommended amount, that fertilizer no longer meets quality standards.

Selling granular fertilizer at too high of a concentration to customers can lead to crop and plant death. After all, overfertilization is always a risk, as the crop receives too many nutrients and can wilt or stop growing. 

Under-fertilizing crops–which can occur when using granular fertilizer with less than the recommended concentration of nutrients–also slows a crop’s growth and could harm its health. 

Heavy Metal Levels

Granular fertilizer may contain impurities, often in the form of heavy metals. The heavy metals that can end up in fertilizer include mercury (Hg), arsenic (As), cadmium (Cd), and lead (Pb). 

Soil naturally contains heavy metals, at least some level of them. The concentrations of the metals are low enough that soil health is not impacted nor is the health of any plant or crop that’s grown in that soil. 

However, when the heavy metal content of granular fertilizers exceeds the standard, and those heavy metals combine with the heavy metals already present in the soil, then a crop’s health could be in danger. 

So, when you import fertilizers, it is very important that these heavy metal levels are equal to or less than the standards you require.

Particle Size Uniformity

Your company should establish a standard for the particle size of each piece of granular fertilizer that passes through the production line and ends up bagged, sealed, and imported to customers around the world. 

The particle size should accommodate the diameter of each granule. While your company will have its own rules, you might opt for a diameter of two to four millimeters as an example. 

Then you can use parameters such as the Uniformity Index or UI as well as the Size Guide Number or SGN to determine where your granular fertilizer lands on the scale. 

UI measures granule diameter consistency. You’d place a selection of granular fertilizer on a screen to determine the particle size. The particle size that 95 percent of the fertilizer achieves is your standard.

You’d then take that particle size and divide it by the particle size at which 10 percent of your retained granular fertilizer is (when 90 percent is passing through a screen).

Finally, you’d multiply that number by 100. 

A higher UI is best, with a UI of 50 acceptable and a UI of 100 desirable.

The Size Guide Number takes the diameter of an average granular fertilizer particle in millimeters. Next, multiply that number by 100 and you have the SGN.  

Particle Hardness

Outside of particle size, particle hardness is another benchmark of quality for granular fertilizer importers to prioritize. 

The International Fertilizer Development Center created rules around crushing strength, which is how well granular fertilizer can resist fracturing or deforming when pressure is applied. A fertilizer’s crushing strength is represented in kilograms per granule.

The speed of the operating discs as well as the spread width when granular fertilizer undergoes production can both determine the hardness of the granules. The higher the spinner disc speed and the wider the spread, the harder the granular fertilizer usually is. 

Soft granular fertilizer has a spinner disc speed of under 700 rotations per minute or rpms. A spinner disc speed of over 700 rpms but not exceeding 800 rpms produces medium-hard granular fertilizer.

Finally, hard granular fertilizer is that which experiences a spinner disc speed of more than 800 rpms.

A customer may want different levels of particle hardness. What’s important when importing granular micronutrient fertilizer is determining the hardness of the granules using the measures above and then accurately reporting on that hardness on the technical data sheet.  

Fertilizer Release Time

Another quality indicator when importing granular fertilizer is its release time. 

Some types of micronutrient fertilizer are slow release. This means that the nutrients in the fertilizer are released into a crop’s soil incrementally over time to fulfill the nutrient needs of that crop for long periods such as four to six months. 

Other types of fertilizer enter the crop’s soil immediately and fulfill its nutrient requirements. However, the user would have to reapply the fertilizer more often.

As has been the case with the other quality indicators we’ve discussed, customers will want different fertilizer release times. Clarity is critical in ensuring customer satisfaction. 

Moisture Levels 

The last factor at play when determining the quality of granular micronutrient fertilizer is the moisture level. 

The fertilizer manufacturing process requires operators to maintain the correct moisture levels throughout. This ensures that they will have a quality product at their end of it all!

Fertilizer will already contain moisture, make sure the moisture content meets your requirements.

Another point to note is that you need to pay attention to the storage conditions when storing fertilizer to avoid moisture. If you want to learn more about it, you can check this blog we wrote before, How Long Can You Store Granular Fertilizer?


Granular micronutrient fertilizer importers mustn’t ignore the six quality indicators discussed today. It will help you find qualified fertilizers when importing it.   

OFertilizer has more than two decades of experience in fertilizer production. Our granular fertilizers pass authoritative third-party testing such as SGS as well as customer self-testing. When you choose OFertilizer, there’s no question that you’re choosing quality.

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