Deciding When to Apply Phosphorus Fertilizer Based On Soil Test Results
In an unpredictable market, more growers are asking themselves: can my fields skip phosphorus fertilizer applications in the upcoming season, and if they can, how long will it take before soil test phosphorus drops?
A recent article from Greg LaBarge, a field specialist with Ohio State University Extension, published in Ohio’s Country Journal and Ohio Ag Net, uncovers the answer to these questions; and it all depends on your soil test results and field conditions. Local trial data and study findings reveal how soil-test phosphorus (STP) levels can help determine when a field truly needs fertilizer and when you might be able to delay application. Fields above the critical threshold for phosphorus (greater than 20 parts per million) are less likely to benefit from added phosphorus, whereas fields below the critical level are much more likely to show a measurable yield response to added phosphorus fertilizer.¹ A reduction in yield and profit are also more likely to occur in the absence of fertilizer application when STP levels are below the critical level.
The rate of decline in STP when fertilizer is not applied will depend on specific chemical properties of each individual soil. The article explores how soil conditions and field history can influence how quickly STP levels decline in the soil, and what the data says about applying phosphorus to your fields in the upcoming season. Insights shared demonstrate how soil testing data can help growers balance agronomic and economic goals while making more informed phosphorus management decisions.
To learn more about how soil testing can help you make data-driven decisions in the field, visit the following eKonomics resources:
The Dirt Season 4, Episode 34: How Soil Testing Helps Maximize Your Input Dollars
The Dirt Season 1, Episode 2: Interpreting Soil Test Results with Nathan Slaton
How To Analyze Your Soil Test Results
Is there a difference between phosphorus soil test methods?
How to Use Soil Sampling to Improve Nutrient Levels and Crop Yield
Source:
¹LaBarge, G. (2025). Can I Skip P Fertilizer? Ohio’s Country Journal and Ohio Ag Net. https://ocj.com/2025/10/can-i-skip-p-fertilizer/
