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Writer's pictureSeth Newell

Know the Lingo: Macro Nutrients N-P-K


Lesco 18-24-12 starter fertilizer bag
One of many fertilizer options on the market

Let's demystify those numbers found on the front of any bag of fertilizer. These numbers represent the three primary, or macro, nutrients in fertilizers, Nitrogen (N), Phosphorus (P), and Potassium (K). These nutrients are used in the largest volume by a growing plant each growing season. Each number correlates to a guaranteed percentage by volume of each nutrient. For example, a bag of 18-24-12 starter fertilizer is 18% nitrogen, 24% phosphorus, & 12% potassium.


How does each nutrient impact my lawn?


Nitrogen (N):

Benefit: Nitrogen is like the energy drink for your grass. It promotes lush, green growth and helps in the development of leaves and stems. It's crucial for overall plant development and is often associated with that vibrant color you want in a healthy lawn.

Function: Nitrogen is a key component of chlorophyll, the green pigment responsible for photosynthesis. This process is how plants convert sunlight into energy, fueling their growth.


Phosphorus (P):

Benefit: Phosphorus is the foundation for strong root development and is essential for flowering and fruiting plants. It's like the construction crew that builds the underground support system for your grass.

Function: Phosphorus is involved in energy transfer and storage, particularly in the form of ATP (adenosine triphosphate). This is crucial for root establishment and overall plant vitality.


Potassium (K):

Benefit: Potassium is the tough guy in the group, strengthening your grass against diseases, drought, and cold weather. It's like the bodyguard, providing resilience and durability.

Function: Potassium regulates many physiological processes in plants, including water uptake, enzyme activation, and photosynthesis. It plays a vital role in stress tolerance and overall plant health.


Is there a difference between nutrient sources?


This is where fertilizers can become much more technical in nature. A wide variety of results can be achieve once you understand the source of nutrients and how it is released in nature.


Nitrogen Sources:

  • Urea (46-0-0): Urea is a highly concentrated nitrogen source. It's cost-effective and provides a quick green-up for your lawn. Urea is versatile and can be used in various applications, including granular and liquid fertilizers.

  • Ammonium Nitrate (34-0-0): Ammonium nitrate is a fast-release nitrogen source. It dissolves quickly in water, making it readily available to plants. This makes it an excellent choice for a quick boost of nitrogen, promoting rapid growth.

  • Ammonium Sulfate (21-0-0): In addition to providing nitrogen, ammonium sulfate also supplies sulfur, which is another essential nutrient for plants, though it is utilized at much lower volumes. It's a quick-release nitrogen source, making it effective for promoting early-season growth.

  • Ammonium Phosphate (11-52-0): This source provides a significant amount of phosphorus along with nitrogen. It's beneficial for root development and flowering. It's often used when a boost in phosphorus is needed in addition to nitrogen.

  • Slow-Release Nitrogen (Polymer-Coated Urea, Organic Sources): These sources provide nitrogen gradually over an extended period. They promote sustained growth and reduce the risk of nitrogen leaching into the environment. Polymer-coated urea and organic sources like composted manure fall into this category.

Phosphate Sources:

  • Diammonium Phosphate (DAP) (18-46-0): DAP is a highly water-soluble fertilizer containing a high percentage of phosphorus. It's suitable for promoting root development and early plant growth. The nitrogen in DAP also provides an additional nutrient boost.

  • Monoammonium Phosphate (MAP) (11-52-0): Like DAP, MAP is water-soluble and provides a significant amount of phosphorus. It's often used when a quick boost of phosphorus is needed, such as during the early stages of plant growth. The ammonium nitrogen in MAP is also beneficial for plants.

  • Rock Phosphate (0-3-0 to 0-30-0): Rock phosphate is a natural, slow-release source of phosphorus. It contains phosphorus in a form that becomes available to plants over time as it breaks down. While it takes longer to show its effects, rock phosphate can contribute to long-term soil fertility.

  • Bone Meal (3-15-0): Bone meal is an organic phosphate source made from ground animal bones. It provides a slow-release form of phosphorus and is often used to promote flowering and fruiting in plants. It's a natural and sustainable option for phosphorus supplementation.

  • Triple Superphosphate (0-46-0): Triple superphosphate is a concentrated source of phosphorus, making it effective for promoting flowering and fruiting. It's a water-soluble form of phosphate, allowing for quick nutrient uptake by plants.

Potassium Sources:

  • Potassium Chloride (KCl or MOP) (0-0-60): Potassium chloride is a widely used, readily available source of potassium. It provides a high concentration of potassium per unit of weight. It's suitable for correcting potassium deficiencies and promoting overall plant health.

  • Sulfate of Potash (SOP) (0-0-50): SOP is a potassium fertilizer that also provides sulfur. It's a chloride-free option, making it suitable for crops sensitive to chloride. It's a good choice for promoting potassium uptake without the potential negative effects of chloride on certain plants.

  • Potassium Nitrate (13-0-44): In addition to providing potassium, potassium nitrate also supplies nitrogen. It's a water-soluble source of both nutrients, making it suitable for fertigation (fertilizing through irrigation). It's beneficial for promoting overall plant growth and development.

  • Langbeinite (Sulfate of Potash Magnesia) (0-0-22): Langbeinite is a natural mineral source of potassium, magnesium, and sulfur. It provides a balanced combination of these nutrients and is often used to promote flowering and fruiting in plants. It's a slow-release option.

  • Potassium Sulfate (0-0-50): Potassium sulfate is another chloride-free option that provides potassium and sulfur. It's suitable for crops that may be sensitive to chloride, and it helps improve the quality of fruits and vegetables.


In summary, nitrogen gives your lawn that lush green look, phosphorus supports root development and flowering, and potassium acts as a protector, enhancing your grass's resilience. The source of each nutrient will impact the immediacy of results and the length of affect. Balancing these nutrients is key to a well-rounded and healthy lawn care regimen.

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