It’s amazing how there are odd crops that have emerged much earlier and growing well from an earlier April cloudburst.
I have been asked about topdressing strategies particularly for the newly emerged crops.
There will always be enough fallow soil nitrogen and starter nitrogen (N) to get cereals to tillering/first/second node stage.
At the past group farmer meetings, we pushed the use of deep soil nitrogen testing one month to six weeks before sowing to determine the soil nitrogen in the 0-60cm soil profile.
Deep Ns above 80kg/N are good. What was yours?
Another way of determining soil N is from soil N mineralisation, using the formula Nov-March rain x 0.25 + 17.5 x topsoil organic carbon percentage (that we usually put down as 1.2 OC%.)
The calculated kilograms of N/ha were: Cobram 52kgN/ha, Barooga 77kgN/ha, Finley 31kgN/ha and Tuppal 53kgN/ha.
Usually, 46kgN =100kg/ha urea.
A reminder that wheat and barley need 50kgN/tonne and canola 80kgN/tonne.
Winter and spring soil mineralisation assists if there is rain or irrigation.
For spring irrigated crops or dryland crops with good rainfall springs, the rule of thumb for soil N mineralisation is 110kgN/ha (240kgurea/ha).
At tillering, cereal crops with less than 450-500 tillers/m2 should be topdressed at the first node, or the moment that any light greening is observed from N deficiency.
Canola is different. It needs as much biomass and ground cover as possible from topdressed or pre-sowing N fertiliser before the start of the optimum flowering date on July 26.
Apply first topdressing at the 3-4 leaf stage and the second at early elongation.
The 2021 record dryland crops were topdressed with 45-200kg urea/ha, mainly in June.
The second topdressing was zero to 100kg urea/ha in July.
In 2020, for the higher yields, the first topdressing of 50-150kg/ha urea or 50-120kg/ha SOA was May 13 to May 30.
The second topdressing of 75-200kg/ha urea was June 18 to July 2.
The 2021 dryland, record yielding group farmer season was also a late emergence for many wheat and barley crops.
The first urea wheat topdressings of the higher yields was 100-150kg/ha from June 1 to August 22.
In 2020, the first topdressing of the highest yields was 75-180kg/ha urea from July 7 to 25.
The 2021 second topdressings were based on great June, July, moderate August, great September rainfall, and moderate October rainfall.
The topdressing was mainly zero to 100kg urea/ha from August 10 nto September 3.
In 2020, the second topdressing was earlier with range 75-150kg/ha urea of the higher yields from July 29 to August 17.
Topdressing needs to be carried out at least a week before the optimum wheat flowering date on September 25, with close follow-up rains needed in warmer months to reduce potential for volatilisation.
In 2021, most crops’ grain quality was ASW (Australian Standard White) because the unexpected high yields diluted the grain protein.
In 2020 most crops were AH (Australian Hard) from similar nitrogen rates as 2021.
If the season progresses and farmers - particularly irrigated farmers - are thinking of a late topdressing to increase grain protein, the urea must be topdressed or water run by the head emergence stage at least a week before flowering.
You will recall I have produced several topdressing gross margin profit tables, including urea cost over the years, and can easily reproduce one for 2025 at say $900/tonne urea if needed.
We can talk more about topdressing or any other issue at the future discussion group meeting crop walkabouts.
~ John Lacy is an independent agricultural consultant, based in Finley.
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