Nitrogen
Urea volatilisation: how much nitrogen do you really lose?
By the Fert Directory editorial team · Published 17 October 2026 · Last updated 17 October 2026 · Not yet reviewed by a qualified agronomist
Direct answer
Across 21 Australian field sites in a national GRDC project, surface-applied urea lost a median 8% of its nitrogen as ammonia gas, but the range ran from 0% to 48%. Soil with low cation exchange capacity, wet soil at spreading, and dry, windy weather without follow-up rain push losses up. Drilling urea into the soil cuts them sharply.
Key numbers
| What | Figure | Source |
|---|---|---|
| Median loss, national GRDC project (21 sites) | 8% of applied N (range 0–48%) | GRDC 2026 |
| Field-measured loss, broadcast urea (Australian cropping soils)Measurements described as sparse and sporadic | 11.7% fallow (5.4–27%); 8.1% in-crop (0–29%) | GRDC 2021 |
| Soils with CEC above 25 cmol/kg | losses consistently below 10% | GRDC 2026 |
| Drilling urea 5 cm deep (Goondiwindi trial) | 1 kg N/ha or less lost per 100 kg N/ha applied | GRDC 2026 |
| Rain needed to wash urea in | more than 10 mm within a week | GRDC 2026 |
| Planning figure for Vertosols | 10% of applied N | GRDC 2026 |
| Lab study, acidic sandy soil with low pH buffering | up to 25% of applied N | Soil Research 61(7), 685–696 (peer-reviewed) 2023 |
What volatilisation is
Spread urea needs moisture (moist soil, humidity, dew, rain) to dissolve and turn into ammonium. That reaction raises soil pH around the granule, and in alkaline conditions some ammonium becomes ammonia gas, which escapes if it forms at the surface. GRDC researchers explain that loss mostly happens in the first one to two weeks.
How much is lost in Australian field studies
- Median across 21 sites in the national GRDC nitrogen-loss project: 8% of applied N, range 0–48%.
- A 2021 GRDC summary of Australian field measurements found 11.7% on fallow (range 5.4–27%) and 8.1% in-crop (range 0–29%), and said the measurements were sparse and sporadic.
- At Horsham on a Vertosol (45% clay) losses were 8.2% and 9.2% over two seasons; at Minnipa on a sandy loam Calcarosol with free lime they were 19.6% and 13.7% (GRDC 2026).
What pushes the loss up or down
| Lower risk | Higher risk |
|---|---|
| Dry clay soil, still and non-humid conditions, enough rain within a few days to wash urea in | Wet or humid soil followed by dry, windy weather with little or no rain |
| High CEC soils (above about 25 cmol/kg consistently lost under 10%) | Low CEC, sandy, low organic matter soils; low pH buffering, even when acidic |
| Drilled or banded into the soil | Thick stubble or pasture holding granules off the soil |
| More than 10 mm of rain within a week of spreading | Dew, humidity or light rain that dissolves urea without moving it into the soil |
The Goondiwindi trials showed one trap: in a dry winter spell with heavy dews and no meaningful rain, urea still dissolved, and loss climbed past 10 kg N/ha and was still rising when measurements stopped. Urea spread ahead of a forecast front that does not arrive is not safe indefinitely.
Can you cut it?
- Incorporate. GRDC says banded or incorporated N should have negligible volatilisation in most cases. In one Queensland trial, drilling urea 5 cm deep cut loss by about 90% compared with spreading.
- Time it with rain. Spreading on dry soil is not a problem by itself; the risk is moisture that dissolves urea without washing it in. The authors suggest delaying spreading to avoid wet-soil-before-a-dry-spell and humid, no-rain windows.
- Urease inhibitors (NBPT). A worldwide review found NBPT-treated urea reduced ammonia loss by about 53% on average, and a GRDC summary says about half. In the Goondiwindi trial there was no difference when rain arrived on time, so the benefit shows up when rain is delayed. The inhibitor costs extra; check the economics. One manufacturer (Incitec Pivot Fertilisers) states its NBPT product inhibits urease for up to 14 days.
- Consider a different N source on at-risk soils. Urea vs ammonium sulphate covers the lime caveat.
What we could not verify
- The 48% upper range comes from the GRDC Queensland paper's summary of the national project; we have not read the underlying national paper (Schwenke et al. 2026).
References
- Volatilisation of surface-applied urea on Queensland Vertosols: how much nitrogen is lost and what drives it? (Silburn C, Lester D, Schwenke G, Macpherson I, Bell M; GRDC Update Papers, 2026; Grower research summary. Checked 2026-10-17.)
- Nitrogen loss pathways. How much N is lost when urea is not mechanically incorporated after application? (Schwenke G (NSW DPI); GRDC Update Papers, 2021; Grower research summary. Checked 2026-10-17.)
- Nitrogen loss pathways – how much do we lose and in what form under different situations (Schwenke G (NSW DPI); GRDC Update Papers, 2022; Grower research summary. Checked 2026-10-17.)
- How much urea N is lost as volatilisation (Adhikari K, Luo Z, Armstrong R, Wilhelm N, Schwenke G; GRDC Update Papers, 2026; Field trial report. Checked 2026-10-17.)
- Ammonia volatilisation losses from urea applied to acidic cropping soils is regulated by pH buffering capacity (Hearn LO, Barton L, Schwenke GD, Murphy DV; Soil Research 61(7), 685–696 (peer-reviewed), 2023; Peer-reviewed paper. Checked 2026-10-17.)
- Agronomic efficiency of NBPT as a urease inhibitor: A review (See article; Journal of Advanced Research (PubMed Central), 2018; Peer-reviewed review. Checked 2026-10-17.)
- Planning nitrogen applications and rethinking potential urea nitrogen volatilisation losses (Laycock J (Incitec Pivot Fertilisers); Incitec Pivot Fertilisers (manufacturer; commercial interest in Green Urea NV), 2024; Manufacturer technical article. Checked 2026-10-17.)
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