How to Apply UAN-32 to Winter Wheat: Step-by-Step Guide (2026)

What you will need#

For a 100 ha application of UAN-32 you need a boom sprayer with an 18–36 m boom, a 2,500–5,000 L tank, and coarse-droplet nozzles (AI, TTI, or AirMix 04–05). UAN itself — at 200–300 kg/ha physical mass (64–96 kg/ha actual nitrogen) — works out to 20–30 tonnes for 100 ha per season. Additionally: a pH meter for the working solution (target pH 6.0–7.0), a 1 L measuring cylinder for nozzle calibration, and GPS with automatic section control for uniform application. Early-spring top-dressing on frozen-thawed soil only needs a standard sprayer on low-pressure pneumatic tires — wide tracks are unnecessary. A urease inhibitor (NBPT) is optional for applications after April or on the sandy soils of Polissia, where volatilization losses climb above 10% once soil temperature passes 15 °C.

Step 1: Calculate the total nitrogen rate#

The standard Ukrainian Ministry of Agrarian Policy recommendation for winter wheat is 120–180 kg/ha of actual nitrogen across the season. Use 140–160 kg/ha for the Steppe and Forest-Steppe, and 160–180 kg/ha for Polissia because losses are higher on light soils. Subtract any nitrogen applied in the autumn with the main tillage (usually 20–40 kg/ha from NPK compounds) and the residual soil nitrogen from an autumn soil test. The remainder is the spring top-dressing with UAN-32. Example: a 160 kg/ha target, 30 kg/ha applied in autumn, 15 kg/ha residual, spring top-dressing = 160 − 45 = 115 kg/ha of N. In physical mass that is 115 ÷ 0.32 = 359 kg/ha, rounded to 350 kg/ha. For a 100 ha field this amounts to 35 tonnes of UAN-32, or roughly 6,200,000 UAH at April 2026 EXW prices from OSTCHEM or Group DF.

Step 2: Split the dose into two applications#

Spring top-dressing runs as two separate passes. The first (60% of the dose) goes on frozen-thawed soil during the re-greening stage, when soil temperature hits 3–5°C. In 2026 that lands in late February to early March for the Steppe, the first half of March for Forest-Steppe, and the second half of March for Polissia. The second pass (40% of the dose) goes on during the tillering-to-stem-elongation stage (BBCH 29–31), once air temperatures stay between 8 and 15°C consistently. The second pass drives grain quality — gluten and protein content. For the example from Step 1 (350 kg/ha total), the first pass is 210 kg/ha and the second is 140 kg/ha. Applying everything in one operation reduces nitrogen uptake efficiency by 15–20%.

Step 3: Set up the sprayer and nozzles#

UAN-32 requires coarse-droplet nozzles rated 0.4–0.5 gal/min (AI 04 or 05). Fine-droplet herbicide nozzles DO NOT WORK — they scorch leaves because the droplet spectrum is too fine. Flush the tank and plumbing with clean water before filling. Check the pressure: target 2.5–3 bar (no higher — high pressure shrinks the droplets and increases leaf burn). Calibrate every nozzle flow with a measuring cylinder: the coefficient of variation (CV) must stay at or below 5%. Replace any off-spec nozzle. Section control avoids double application on overlaps. On headlands and odd-shaped field edges, use manual section control or GPS automation to keep rates consistent.

Step 4: Make the first top-dressing pass#

Run the first pass in dry, overcast weather at 0–10°C, with wind under 5 m/s and no rain forecast for four hours after application. Sprayer speed: 8–12 km/h (faster drifts, slower overloads the pump). The working solution is either straight UAN or UAN diluted 1:1 with water to cut the burn risk. Start from the field edge and drive parallel to the plowing direction for uniform overlap. Switch off sections through GPS on turns (John Deere JDLink, Trimble TMX-2050, Topcon X35). After application, flush the sprayer plumbing with clean water — UAN crystallizes on drying and blocks nozzles. Log the work: date, field ID, rate applied, weather conditions, operator, and the UAN batch serial — critical if you later need to file a nitrogen-content claim with the supplier.

Step 5: Make the second pass with a herbicide tank-mix#

The second pass can be combined with a herbicide spray in a tank-mix — the headline advantage of UAN. Compatible herbicides: 2,4-D amine salt, dicamba, MCPA, florasulam, thifensulfuron-methyl (reduced rates). UAN concentration in the tank-mix must stay under 25% of the total volume — above that, leaf burn starts. Tank fill order: 1) half the water, 2) start the agitator, 3) herbicide (WP/WG formulations first, solutions later), 4) UAN, 5) the rest of the water. Run a jar-test before filling the full tank — 500 ml of the mix in a clear jar, wait 30 minutes for any precipitate. Spraying: speed 8–10 km/h, pressure 2.5 bar, temperature 10–18°C, out of direct sun (before 10:00 or after 17:00). On intensive varieties like Favoritka and Zolotokolosa, add 0.5–1.0 L/ha chlormequat chloride to the same mix to prevent lodging.

Troubleshooting the common problems#

Leaf burn. Causes: fine-droplet nozzles, pressure above 3 bar, temperature above 22°C, application without dilution at rates over 200 kg/ha. Fix: switch to AI 04–05 (TeeJet, Lechler, Agrotop), drop the pressure to 2.5 bar, apply only at 10–18°C, dilute UAN 1:1 with water at rates above 180 kg/ha. Clogged nozzles. Cause: UAN crystallization on dried nozzles, or precipitation from incompatible tank-mix. Fix: flush the system after every use, run a jar-test before every new mix. Uneven application. Cause: worn nozzles with CV over 5%, or inconsistent speed. Fix: replace nozzles every two seasons, control speed with GPS (±1 km/h is accurate enough). Foaming in the tank. Fix: add an anti-foam adjuvant at 0.05% of volume (Silwet Gold or equivalent) when the mix contains both a WG herbicide and UAN.