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What else is in a NPK fertilizer bag besides NPK?

Nov. 16, 2021

When you open a bag of fertilizer for your plants, you may see pink, blue, yellow, white or gray fragile material.

Ever wonder what all those little particles listed on the label of npk compost are made of?

The use of anything other than compost or organic fertilizer can poison the soil and plants or burn them. That's why we should consider soil testing for trace elements and determining what nutrients are present in the soil.

 

NPK 15-15-15 Compound fertilizer with trace elements

 

Organic Fertilizer NPK Ratio

A typical home garden plant fertilizer mixture includes an analysis of the "fertilizer number" printed on the fertilizer bag to ensure the percentage or NPK ratio of nitrogen, phosphorus and potassium in the mixture.

N: Nitrogen promotes leafy growth.

P: Phosphorus stimulates root growth, builds strong tissue and helps flower development.

K: Potassium - improves water use, disease resistance, fruit quality and size

 

The 5-10-5 mix contains 5% N, 10% phosphate and 5% potassium. This adds up to 20%.

 

What else is in the fertilizer bag but NPK?

"But why not 100% plant-based food?" , the gardener might want to know. "What's the remaining 80%?"

Part of the 80% may consist of other essential micronutrient fertilizer ingredients - nutrient minerals such as: copper, zinc, boron, manganese, magnesium.

At least one manufacturer includes these trace minerals, although the bag label does not specify the amount of trace minerals used.

However, most of that 80% is there because no gardener on earth wants to touch 100% of their plant food with a 10-foot pole - let alone put it on a flower!

The truth is that a simple nitrogen-phosphorus-potassium combination is practically impossible. Pure nitrogen is a gas (78% of air is nitrogen) and it does not readily combine with other minerals.

With the exception of legumes (clover, alfalfa, peas, etc.), any plant must combine nitrogen with other minerals in order to use it.

As far as its chemical activity is concerned, pure phosphorus is the opposite of nitrogen. In fact, it must always be kept underwater because this dangerous stuff will burn up when it comes in contact with air.

Almost as bad - pure potassium. It needs to be submerged in oil to prevent it from combining with moisture in the air. If a piece of potassium falls into water, it will explode violently.

For other reasons, other pure minerals are equally useless for plant growth. Metallic minerals such as zinc, copper, manganese, magnesium and boron are virtually useless to plants if supplied in the form of metal fragments.

 

Combinations of combustible fertilizers with other materials

Rather than selling a dubious mixture roots can absorb and store from the soil, fertilizer industry manufacturers provide and include a safe, clean, healthy, sometimes odorless, unwanted gas with a green mixture, some fire hazards, and various scrap metals.

Nitrogen may be carried by chemical compound fertilizers, ammonium sulfate (an industrial by-product). This is a white, water-soluble material made of nitrogen, hydrogen, sulfur and oxygen and contains about 20% nitrogen.

May be phosphoric acid in plant food or phosphate fertilizer from calcium superphosphate, which is about one-fifth phosphoric acid and the rest for oxygen, hydrogen, calcium and sulfur.

Calcium superphosphate is made by treating mined phosphate rock with sulfuric acid. This process makes the phosphate more readily available to plants.

Potassium requirements are met by the addition of potassium chloride, potassium sulfate or manure salts containing potassium, with the rest being carrier minerals.

 

Mixing of bagged fertilizers

All of these raw materials and several others are assembled in separate large storage areas in the fertilizer blending plant.

Carefully weighed portions of each fertilizer product are transferred in batches to a rotary mixer that can mix one or two tons of granular fertilizer at a time. During the mixing process, some of the nitrogen in the mixture may be added in the form of liquid fertilizer - such as ammonia.

After leaving the mixer, the fertilizer (plant food) is transported by crane or ring belt to a storage pile, where it "cures" for several weeks. The curing process allows the raw materials to complete their interaction with each other and ensures that consumers receive a granular, flowable product.

At the end of the curing period, the plant-based food is remixed, screened and bagged ready for delivery to hardware, garden centers and mass retailers.

Therefore, the 5-10-5, 6-10-4 lawn fertilizer ratios and similar ratios on the outside of plant food bags are only partially illustrative.

 

With calcium and sulfur "carrier" elements, plus trace minerals, there is more to growing edible fertilizers than the numbers suggest. Any questions about NPK fertilizer, feel free to contact us.

 

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