This fertilizer calculator takes the figures you already have and applies the relationship behind fertilizer calculations for you, giving phosphate (p₂o₅) rate, potash (k₂o) rate and fertilizer rate from potassium (k), nitrogen (n), n rate, phosphorus (p), fertilizer bag weight and lawn area.
What Is the Fertilizer Calculator?
The fertilizer calculator works out phosphate (p₂o₅) rate, potash (k₂o) rate and fertilizer rate from potassium (k), nitrogen (n), n rate, phosphorus (p), fertilizer bag weight and lawn area.
Biological relationships are usually approximations rather than exact laws, so the output is best treated as an estimate with a sensible range around it.
How the Fertilizer Calculation Works
The calculation applies the relationship as published, step by step, so each intermediate value can be checked against the underlying theory.
Keep the units consistent throughout. Mixing a percentage with a proportion is the single most common source of an answer that is out by a factor of a hundred.
Assumptions Worth Knowing
Any relationship used here assumes a constant rate, a representative sample, or a stable population. Real populations rarely meet those conditions for long, so treat the answer as a guide.
Where the inputs are field measurements, a single misread value can shift the result noticeably. Measure carefully and record what you used.
A Worked Example
Working through an example, with potassium (k) set to 10, nitrogen (n) set to 5, n rate set to 2, the calculator returns fertilizer rate of 40, and you need of 2.15, and phosphate (p₂o₅) rate of 40. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out phosphate (p₂o₅) rate?
Enter potassium (k), nitrogen (n), n rate, phosphorus (p), fertilizer bag weight and lawn area. The calculator then works through the relationship and reports phosphate (p₂o₅) rate, potash (k₂o) rate and fertilizer rate.
What does the fertilizer actually calculate?
It takes potassium (k), nitrogen (n), n rate, phosphorus (p), fertilizer bag weight and lawn area and converts them into phosphate (p₂o₅) rate, potash (k₂o) rate and fertilizer rate using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter potassium (k)?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Does anything you type get stored?
No. The whole calculation runs inside your browser, and nothing you enter is uploaded, logged or sent anywhere.
Is the answer exact?
It is as exact as the formula and the inputs allow. The method itself is the standard one for this problem, so the only sources of error are the figures you enter and the precision you ask for.