THE importance of timing in-crop nitrogen applications to wheat crops in the high-rainfall cropping zone of southern Australia has been confirmed in a GRDC-funded Fast Track Project last season.
It has found that applying nitrogen at stem elongation (GS32) puts the nutrition into yield and a later application at head emergence (GS55) pushed up protein levels.
GS70 (the end of anthesis) was too late to impact grain protein, even with a liquid fertiliser.
The project, led by Southern Farming Systems in collaboration with a number of farming systems groups including MacKillop Farm Management Group, involved eight wheat crops in SA, Vic, NSW and Tas.
Four timings of nitrogen application GS32 (stem elongation), GS 39 (flag leaf), GS55 (50 per cent head emergence) and GS70 (end of anthesis) and three forms of nitrogen (UAN, liquid urea and urea) were evaluated. Two different rates 25 kilograms a hectare and 50kg/ha at each timing were also tested.
International Plant Nutrition Institute regional director for Australia and New Zealand Robert Norton, who provided technical expertise to the Southern Farming Systems project, said late nitrogen decisions should be made as the season unfolded to meet yield potential but also to deliver acceptable grain receival standards for protein concentration
He said the project results reinforced current best-practice management although the key timing to influence yield, GS39 (flag leaf) was slightly later than the recognised standard of GS32 (stem elongation).
Applications after GS39 increased yield - as expected - in some cases but were more likely to start having a greater effect on grain protein.
The protein of the grain was significantly increased with a treatment at GS55 at five of the eight sites.
The mean response overall was 0.29t/ha and a protein increase of 0.5pc but responses varied up to 2pc protein levels.
He said that two SA sites -Conmurra and Wolseley - were among the eight sites evaluated.
At Conmurra there was a small effect of adding extra nitrogen on yield over the control crop but no significant differences were seen in the timing, rate or type of nitrogen on yield or screenings.
Protein concentration of the Revenue wheat was only weakly affected by the timing, with the highest protein of 12.33pc at GS55.
Wolseley was the only site where there was no effect of the additional nitrogen on either yield or protein.
The crop was sown relatively late compared with the other sites but suggested that for Axe, sown in mid-June, with 90kg nitrogen/ha applied pre-GS32, the yield potential had already been achieved.
Each season, growers and agronomists needed to make tactical decisions in their overall nitrogen management, and while early nitrogen established a platform for higher yields there was a range of other factors including soil moisture and seasonal conditions, and even luck needed.
* Full report in Stock Journal, June 26, 2014 issue.