"Once you apply phosphorus, the soil fixes it, locks it up, and you just threw your money away." Sound familiar? Dan Kaiser, Extension nutrient management specialist at the University of Minnesota, tackles this claim head-on in his Minnesota Crop News piece "Is ‘fixed'P lost? 4 things to consider."

1. Not all P is used the first year
In a best-case scenario, about 65% of applied P is taken up; the rest remains in the soil-retained from past additions or mineral sources. Over time, this retention boosts efficiency.

2. Reaction loss
Phosphorus can react with calcium, iron or aluminum depending on soil pH. But that doesn't mean it's gone. In soils with pH 7.5, spring application helps ensure next season's availability.

3. Smart P management pays
Don't apply P out of fear. If soil tests are optimal, the soil itself supplies most needs. Tailoring applications based on test results-especially when fertilizer costs are high-can reduce inputs without compromising yields.

4. Soil tests stand the test of time
The Bray-P1 and Olsen tests remain reliable after 60 years of data (up to 2024 in MN). Newer tests like Haney or Mehlich-3 haven't yet demonstrated superior predictive power or ease of use.

FAQs

Products claiming to release fixed P: independent research shows no miracle fixers-spend wisely.

Low crop prices: trim fertilizer use based on test needs.

Sloping fields: incorporate P to prevent runoff loss.

Best timing: soils with extreme pH benefit from spring application; neutral soils, timing is flexible.