Soybeans fix their own nitrogen. What holds yields back on Ontario ground is usually phosphate, potassium, or manganese.
Rhizobia bacteria in the root nodules supply the nitrogen the plant needs, so adding more nitrogen rarely pays. The real levers are phosphate for roots and pod fill, potassium for standability and finishing, and a handful of micronutrients. Manganese in particular shows up as a yield-limiter on Ontario fields with higher organic matter.
The nutrients most likely to limit soybeans yield, what each one looks like before you sample, and how to confirm.
Roots, nodules, pod fill.
Water handling, disease resistance, filling pods.
Photosynthesis and disease resistance.
Growth regulation, enzyme activity.
Normally fixed by rhizobia. Nitrogen shortage in soybeans almost always means the nodules aren't working.
Other things to rule out before you tissue-test or change the program.
What you see — Fluffy white growth on stems and pods, usually in dense canopies during a cool wet flowering period.
What to do — Wider rows, a lower seeding rate, and easing up on nitrogen all make the canopy less friendly to the fungus. Fungicide at flowering in high-risk years.
What you see — Yellow between the veins, then brown, on the upper leaves around pod fill. Leaves stay attached. Roots show grey or blue staining inside.
What to do — Variety selection is the main tool. Fields with a history don't clean themselves up — rotate and plant resistant varieties.
What you see — Severe yellowing of upper leaves with veins still green. Worst on high-pH, calcareous ground in cool wet springs.
What to do — Pick varieties rated for IDC tolerance. An iron chelate at planting can help on fields that see it every year.
What you see — Patches of short, yellow plants. Pull roots at first flower and look for small white or yellow females on them.
What to do — Sample soil and get an egg count. Rotate to corn or wheat. Plant resistant varieties, and rotate resistance sources so the nematodes don't adapt.
What you see — Flowers and small pods dropping during dry stretches in early flowering.
What to do — Not much to do in-season. The decisions that matter — drainage, potassium levels, population — are made before you plant.
Rates and timing for soybeans. We’ll match the specific product to what’s available for your season.
Phosphate moves slowly. Fall gives it time to settle into the root zone before planting. Especially important on clay.
If fall wasn't possible, spring still works. Don't skip the phosphate.
Manganese problems usually show up at early flower. Address them when you see them, not as a default.
Same crop, different ground — emphasis, placement, and timing shift.
Focus on phosphate and potassium — both move or leach on sandy ground. Watch manganese on higher-pH sand.
Phosphate is the limiter on clay. Broadcast at a higher rate to push past clay's tie-up — concentration carries the program. Wait for crumbly soil before planting.
Loam handles beans well with a simple phosphate-focused program. Watch potassium on fields that consistently yield high — you're pulling a lot out at harvest.
Our advisors live in Southwestern Ontario and farm here too. Reach out by phone or email.
Longer reads on the same topics.
Send your most recent reports and rotation plan. We’ll match what’s available for your season to your fields and walk you through rates, timing, and placement.
Talk to our team→Photos on this page come from Wikimedia Commons under public domain or Creative Commons licenses. Each is attributed to its author and linked to the source.
Images are for reference and may not match your exact field conditions. Always confirm a suspected deficiency with a soil or tissue test before treating. We do not imply endorsement by the photographers.
