Guide
How to convert NPK into urea, DAP and MOP
A soil test gives pounds of N, P and K. The dealer sells bags of products. Here is the bridge.
The three products
- DAP (18-46-0): 46 % phosphate and 18 % nitrogen.
- MOP, muriate of potash (0-0-60): 60 % potash.
- Urea (46-0-0): 46 % nitrogen.
The order
- DAP = phosphate dose ÷ 0.46.
- MOP = potash dose ÷ 0.60.
- Urea = (nitrogen dose − 0.18 × DAP) ÷ 0.46: DAP already brings part of the nitrogen.
Example
A dose of 120-60-60 lb per acre on 40 acres: DAP 130.4 lb per acre, urea 209.8, MOP 100. For the field: 5,217 lb of DAP, 8,393 lb of urea, 4,000 lb of MOP. In 50 lb bags: 105 bags of DAP, 168 of urea, 80 of MOP.
Count the bags at the end
Round up once, on the whole field or the whole farm: a bag opened on one field is finished on the next.
With Seed Calc
Type the dose in the Fertiliser tab: the app does the three steps, counts full bags and the loose rest, and adds the season's fields together. It calculates your dose; it never suggests one. See Fertilizer calculator.
