Soybean School: Fine-tuning P & K for yield and economics

"On this episode of the RealAgriculture Soybean School, University of Guelph assistant professor Dr. Adrian Correndo stresses that soil testing is essential when evaluating phosphorus investment. He notes that around 15 ppm phosphorus will allow farmers to achieve 95 per cent of relative yield. Below that critical level, responses to P fertilizer on responsive soils commonly range from 3 to 15 bu./ac, with a median near 10 bu./ac."

"A similar story holds for potassium. Critical soil test levels sit near 90-100 ppm K, with below-critical soils showing a typical 3 to 13 bu./ac yield response. Above those levels, average responses shrink to around 2 bu./ac. Economically, most 2026 scenarios suggest 60-70 lb/ac K2O on responsive soils can be justified, whereas soils tests above the threshold seldom return enough yield to cover costs."

Soil testing determines economic returns from phosphorus and potassium for soybeans. Approximately 15 ppm soil phosphorus yields near 95% relative yield; below that, P fertilizer responses commonly range 3–15 bu./ac with a median near 10 bu./ac. Using current price ratios, fields below 15 ppm often show economic responses near 50–60 lb/ac P2O5, while additional P above 15 ppm usually does not pay. Critical potassium levels sit near 90–100 ppm; below that K responses typically range 3–13 bu./ac, while above them responses average about 2 bu./ac. Most 2026 scenarios justify 60–70 lb/ac K2O on responsive soils; above-threshold K rarely covers costs.

Read at Realagriculture