Don't Freeze that Pre-Sidedress Nitrate Soil Test!

Key Takeaways

• OSMC now bans freezing PSNT soil samples
• Freezing raises nitrate readings, skewing nitrogen recommendations
• Over 50% of PSNT recommendations changed by freezing effect
• Up to 16% of cases risk $60/acre losses
• Immediate adoption required for accurate nitrogen management

Pulse Analysis

The Pre‑Sidedress Nitrate Test (PSNT) has become a cornerstone of nitrogen management for corn growers across Ontario, offering a rapid, field‑specific assessment of soil nitrate levels. By tailoring in‑season nitrogen applications, PSNT helps farmers avoid the twin pitfalls of under‑fertilization, which can depress yields, and over‑fertilization, which drives input costs and environmental runoff. The Ontario Soil Management Committee (OSMC), a joint body of researchers, extension specialists, and industry stakeholders, oversees the scientific integrity of these recommendations, ensuring they reflect the latest agronomic evidence.

A recent study led by Dr. Josh Nasielski and Ken Janovicek at the University of Guelph revealed a surprising flaw: freezing soil samples before laboratory analysis artificially elevates measured nitrate concentrations. The distortion was large enough to shift nitrogen recommendations in more than 50% of the tested plots, and in up to 16% of cases it translated into economic losses exceeding $60 per acre due to under‑application. Beyond the direct financial hit, mis‑applied nitrogen can exacerbate nitrate leaching, threatening water quality and contravening sustainability goals that are increasingly embedded in provincial agricultural policy.

The OSMC’s swift amendment—prohibiting freezing and urging cool, rapid shipment of samples—aims to restore the reliability of PSNT data. For growers, the change means tighter control over input budgets and a clearer path to meeting both profit and environmental targets. Soil‑testing laboratories will need to adjust logistics, but the operational shift is modest compared to the potential gains. As other jurisdictions watch Ontario’s approach, the updated handling protocol could set a new benchmark for nitrogen management practices across North America.