Top dressing wheat with urea: when, how much and how on wet fields
Wheat is top dressed with urea in the first half of February, and by 20 February at the latest, because urea needs 20 to 30 days to turn into a form the roots can take up. After that date the advisory services recommend CAN or AN, which act faster. Nitrogen needs to be in the root zone as soon as the wheat starts growing after winter, and the rate is set by soil analysis, not by a table.
By Nikola Mojsa, MSc in Agricultural Engineering
The deadline for urea often falls when fields are waterlogged from snow and rain. By drone we top dress on time, on wet ground too.
When the first urea top dressing of wheat goes on
Urea should be spread by 20 February, so the nitrogen is ready when wheat starts its spring growth, that is, when temperatures settle above 5 °C (Agrosava). The Zrenjanin agricultural advisory service (PSS Zrenjanin) does not recommend urea after 20 February, because it needs 3 to 4 weeks to turn into a form the plant can take up; from then on it recommends CAN or AN, as soon as temperatures pass the biological minimum for growth (PSS Zrenjanin).
Many growers in Central Banat spread urea during frost, while the ground is hard and a tractor with a spreader can get into the field (PSS Zrenjanin). On the other hand, Prof. Vladimir Vukadinović warns that the first top dressing should not go on too early, on frozen ground while the crop is dormant, because nitrate nitrogen is leached from the root zone before the wheat can take it up (Agroklub).
- First top dressing, at tillering: urea in the first half of February, and by 20 February at the latest; CAN and AN from late February to early March.
- Second top dressing: 3 to 4 weeks after the first, and no later than the start of stem elongation.
Urea or CAN: how they differ
Urea has the most nitrogen, 46%, but it acts slowly and loses some of its nitrogen in warm conditions. With CAN (27% nitrogen) and AN (33%), half the nitrogen is available to the plant straight away, while the other half converts as urea does (Agrosava, PSS Zrenjanin).
| Urea | CAN | AN | |
|---|---|---|---|
| Nitrogen in the fertiliser | 46% | 27% | 33% |
| When the nitrogen is available to the plant | after 20 to 30 days | half at once, the rest later | half at once, the rest later |
| Window for the first top dressing of wheat | first half of February, by 20 February at the latest | late February and early March | late February and early March |
| Soil | can acidify the soil | for acid soils | for all soil types |
Sources (in Serbian): Agrosava, PSS Zrenjanin.
Urea loses the most nitrogen when it lies on the surface of warm soil, because the nitrogen escapes as ammonia gas. On calcareous and alkaline soils at higher temperatures, the loss reaches up to 30% of the nitrogen (Svetlana Jerinić, Dipl. Ing., Agro Info Net). According to Miroslav Borojević of PSS Vrbas, it takes 25 to 30 litres of rain per square metre after top dressing winter crops to help the nitrogen work, and light rain does not help (Agro Info Net). That is why a cold February is better for urea than a warm March: less nitrogen is lost to the air.
Specialists disagree about urea in the first top dressing. Prof. Vukadinović does not recommend it, because small plants at low temperatures take up ammonium nitrogen slowly (Agroklub). PSS Zrenjanin accepts it up to 20 February because of its price and nitrogen content, and Agrosava recommends it when no other fertiliser is available, on early-sown crops. Which fertiliser goes on your field is for you and your agronomist to decide; the drone spreads both urea and CAN.
How much urea per hectare for wheat
There is no single figure for every field: the rate depends on the nitrogen already in the soil and on the yield you are planning for. Wheat needs 20 to 25 kg of pure nitrogen per tonne of grain (Agrosava). How much the soil already holds is shown by an Nmin analysis (a test of mineral nitrogen in the soil) done before top dressing.
In more than 150 samples from wheat fields in Central Banat, the PSS Zrenjanin laboratory measured 23 to 235 kg of mineral nitrogen per hectare in the top 90 cm (PSS Zrenjanin), so one field can hold ten times as much as another. Without an analysis, Prof. Vukadinović allows 1 kg of nitrogen for every 100 kg of expected yield across both top dressings, up to 6.5 t/ha, which for 6.5 t/ha comes to 65 kg of nitrogen per hectare (Agroklub). Agrosava gives 100 to 150 kg of urea per hectare as a safe rate where the nitrogen balance is positive, noting that urea alone does not fix a larger nitrogen shortfall (Agrosava).
When more than 60 kg of pure nitrogen per hectare is needed, Agrosava splits it over two top dressings, in a ratio of 60:40 or 70:30. The second, corrective top dressing goes on 3 to 4 weeks after the first, and no later than the start of stem elongation, because that is when yield potential is set. We explain the timing and foliar feeding in Second top dressing of wheat and foliar feeding.
How many kilograms of fertiliser that is
One kilogram of nitrogen equals about 2.2 kg of urea, 3.7 kg of CAN or 3 kg of AN.
| Pure nitrogen per hectare | Urea (46%) | CAN (27%) | AN (33%) |
|---|---|---|---|
| 30 kg | 65 kg | 111 kg | 91 kg |
| 40 kg | 87 kg | 148 kg | 121 kg |
| 50 kg | 109 kg | 185 kg | 152 kg |
| 60 kg | 130 kg | 222 kg | 182 kg |
Top dressing wheat by drone, wet fields included
A wet field does not delay top dressing by drone: all we need is access to the edge of the field. After rain it is enough for the road to the field to dry, and if there is tarmac all the way, we top dress the same day, even after heavy rain.
The DJI Agras T70P spreads granules from 0.5 to 10 mm from a 100-litre hopper, up to 70 kg per flight. The spreading width ranges from 3 to 10 metres and is set according to the fertiliser, disc speed and flight height (DJI manufacturer data). At a rate of 100 kg of urea per hectare, one flight covers no more than 0.7 ha, so spreading takes more flights than spraying.
We work in winds up to 3 to 5 m/s; if the wind picks up, we pause and carry on as soon as it drops.
After top dressing, the next pass in wheat is the spring herbicide and fungicide spray, and the most important treatment is the fungicide at flowering. The timing of every treatment is on the wheat protection and feeding page.
What top dressing wheat by drone costs
Fertiliser spreading by drone costs €40 per hectare, whatever the area; check the price for your field in the calculator. Travel within 50 km of Opovo is free, and new clients get the first hectare free on a first order of at least 10 ha.
Foliar feeding costs the same as spraying: €25, €22 or €20 per hectare, for areas up to 20 ha, from 20 to 100 ha and over 100 ha. Discounts for three or more treatments on the same field in a season are in the drone spraying and feeding price list.
Frequently asked questions
In the first half of February, and by 20 February at the latest. Urea needs 20 to 30 days to become available to the plant, so after that date the advisory services recommend CAN or AN, where half the nitrogen is available straight away.
By drone, yes: a waterlogged field does not delay spreading. All we need is access to the edge of the field, and after rain it is enough for the road to the field to dry.
It depends on soil analysis and the planned yield. Wheat needs 20 to 25 kg of nitrogen per tonne of grain, and 50 kg of nitrogen equals about 109 kg of urea. Your agronomist sets the rate for your field, ideally based on an Nmin analysis.
Spreading urea by drone costs €40 per hectare, and foliar feeding €25, €22 or €20 per hectare, depending on the area. New clients get the first hectare free on a first order of at least 10 ha.
- First hectare free
- Free travel up to 50 km
Book your top dressing before 20 February
Tell us how many hectares of wheat you are top dressing, where, and how many kilograms of fertiliser per hectare you plan to apply. The rate sets the number of flights and the location sets the travel charge, so we can give you the price straight away and agree a date.