The short answer: Not necessarily. Price per tonne tells you what fertilizer costs to buy. It does not tell you what the crop pays for each pound of phosphorus it can actually access. Tie-up, placement, release pattern, root access and timing can change the economics enough that a higher-priced tonne can produce a lower effective cost per useful pound of P.
The first number: cost per pound of P2O5 applied
Start with the straightforward comparison: fertilizer cost per acre divided by pounds of P2O5 applied per acre. This is useful because it removes the distraction of different fertilizer analyses. But it is still only an application-cost metric.
Two products can have a similar cost per applied pound and very different behaviour in soil.
The second number: cost per pound remaining accessible
Water-soluble phosphate reacts quickly after application. Depending on soil chemistry, phosphorus can be sorbed or precipitated into forms that become less immediately available to roots. This is the “tie-up” problem: the phosphorus is still in the soil, but its short-term accessibility can decline.
That is why source, placement and timing matter. Banding can reduce contact with soil and improve early access. Root-activated sources such as struvite use a different release mechanism. Mycorrhizal fungi can expand the soil volume explored by compatible roots.
Do not turn availability assumptions into fake precision
There is no single universal percentage of MAP that every crop recovers in year one, nor one fixed efficiency number for every alternative phosphate. Soil pH, calcium, iron and aluminum chemistry, moisture, temperature, crop, placement and yield level all matter.
Use availability assumptions as scenarios, not guarantees. The purpose of the calculation is to test how sensitive the economics are to different levels of crop access, not to pretend the soil is a spreadsheet.
A better phosphate decision
Compare at least four things: cost per pound applied; expected placement and seed-safety constraints; the release/tie-up behaviour of the source; and the agronomic value of any additional nutrients such as magnesium.
Then ask whether the program gives the crop adequate P early, adequate P later, and enough stand establishment to use it. That is fertility economics, not commodity-price comparison.
Related reading: Why Tie-Up Is the Most Expensive Thing in Your Phosphate Bill, Fertility Is Not the Same Thing as Fertilizer.
Related products
- CG P2X
- CG Synchro 50 MAX
- TAPP2X
- AGTIV REACH
