N:P

fertilisers

1. What Are $N:P:K$ Fertilisers?

• N:P
  fertilisers contain nitrogen $(N),$ phosphorus $(P),$ and potassium $(K),$ which are essential nutrients for plant growth.
• The ratio of $N:P:K$ is printed on the fertiliser bag.
• Example: 3:15:26 $(N:P:K)$ means:
  • $3$ parts nitrogen $(N)$
  • $15$ parts phosphorus $(P)$
  • $26$ parts potassium $(K)$

2. Understanding Fertiliser Labels

• The number in brackets (e.g., 26%) indicates the percentage of fertiliser by mass in the bag.
• The remaining content (gypsum, lime, sand) acts as a filler to bind the fertiliser and make it easier to handle.
• The total mass of the bag is printed, allowing for calculations of nutrient content.

3. Step-by-Step Calculation of Nutrients in a Fertiliser Bag

Step 1: Identify the Mass of the Bag

• Example: 10 kg bag.

Step 2: Find the Percentage of Fertiliser

• Given: 26% of the bag is fertiliser.
• Calculation: $\text{Mass of fertiliser} = \frac{26}{100} \times 10 = :highlight[2.6 \text{ kg}]$

Step 3: Find the Total Nutrient Parts

• Example ratio: 3:15:26
• Total nutrient parts $= 3 + 15 + 26 = :highlight[44]$

Step 4: Calculate the Percentage of Each Nutrient

$\% N = \frac{3}{44} \times 26 = :highlight[1.77\%]$

$\% P = \frac{15}{44} \times 26 = :highlight[8.86\%]$

$\% K = \frac{26}{44} \times 26 = :highlight[15.36\%]$

Step 5: Calculate the Mass of Each Nutrient in the Bag

$\text{Mass of N} = \frac{3}{44} \times 2.6 = :highlight[0.18 \text{ kg}]$

$\text{Mass of P} = \frac{15}{44} \times 2.6 = :highlight[0.89 \text{ kg}]$

$\text{Mass of K} = \frac{26}{44} \times 2.6 = :highlight[1.54 \text{ kg}]$

4. Key Takeaways

• N:P
  ratios indicate the proportion of nitrogen, phosphorus, and potassium in fertilisers.
• The percentage in brackets (e.g., 26%) shows how much of the bag is actual fertiliser.
• Step-by-step calculations help determine the mass of nutrients in the fertiliser.