About

Precision agriculture relies on the exact application of macronutrients to maximize crop yield while minimizing environmental runoff. Farmers and gardeners must often blend elemental fertilizers to achieve a specific nutrient profile that matches their soil test recommendations. This calculator uses stoichiometry to determine the exact mass of individual fertilizer sources required to meet a target Nitrogen (N), Phosphorus (P), and Potassium (K) requirement for a defined land area. It accounts for multi-nutrient inputs (such as Diammonium Phosphate which contributes both N and P) to prevent over-application.

Formulas

The calculation solves for the mass of each source material required to meet the specific elemental target. Since some sources provide multiple nutrients, the logic typically prioritizes Phosphorus P and Potassium K first, then adjusts the Nitrogen N source to fill the deficit.

For a target nutrient mass M_target and a source analysis percentage P_source:

Mass=M_targetP_source ÷ 100

When using a multi-nutrient source like DAP (18-46-0) to supply Phosphorus, the Nitrogen credit is calculated as:

N_credit = Mass_DAP × 0.18

The final Nitrogen source requirement is the target Nitrogen minus any credits from other components.

Reference Data

Common Name	Formula/Description	N-P-K Value	S (Sulfur)	Mg (Magnesium)
Urea	CO(NH₂)₂	46-0-0	0%	0%
Ammonium Nitrate	NH₄NO₃	34-0-0	0%	0%
DAP (Diammonium Phosphate)	(NH₄)₂HPO₄	18-46-0	0%	0%
MAP (Monoammonium Phosphate)	NH₄H₂PO₄	11-52-0	1%	0%
Triple Superphosphate	Ca(H₂PO₄)₂	0-46-0	0%	0%
Muriate of Potash (MOP)	KCl	0-0-60	0%	0%
Sulfate of Potash (SOP)	K₂SO₄	0-0-50	17%	0%
Calcium Nitrate	Ca(NO₃)₂	15.5-0-0	0%	0%
Magnesium Sulfate (Epsom)	MgSO₄	0-0-0	13%	10%
Ammonium Sulfate	(NH₄)₂SO₄	21-0-0	24%	0%

Frequently Asked Questions

Phosphorus and Potassium sources are often distinct or fixed (like Potash or Superphosphate). However, sources like DAP (Diammonium Phosphate) contain both Nitrogen and Phosphorus. By calculating the P source first, we can determine how much "free" Nitrogen is added to the mix and subtract that from the total Nitrogen requirement. This prevents over-fertilizing with Nitrogen.

A negative result for the Nitrogen source indicates that your selected Phosphorus or Potassium sources act as "hot" fertilizers, supplying more Nitrogen than your target requires. For example, if you need very little Nitrogen but high Phosphorus, and you use DAP (18-46-0), the Nitrogen naturally included in the DAP might exceed your target. You would need to switch to a P-only source like Triple Superphosphate.

This tool calculates the raw weight of active fertilizer components needed. If you are mixing a batch for a spreader (e.g., '1 ton of mix'), the sum of the components might be less than 2000 lbs. The difference should be made up with an inert filler like sand, limestone, or clay to ensure the spreader distributes the nutrients evenly across the field at the calibrated flow rate.

Not always. Some combinations are hygroscopic (absorb water) or chemically reactive. For instance, mixing Urea with Ammonium Nitrate creates a critical relative humidity point that turns the mix into sludge. Always consult a compatibility chart before storing blends for long periods. Immediate application reduces this risk.