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Effect of post-emergent solid and liquid nitrogen on grain yield and quality of bread and durum wheats

Shahajahan Miyan1, Stephen Loss2 and Wal Anderson3

1 Centre for Cropping Systems, Department of Agriculture and Food, Northam, WA 6401; Email:
CSBP Limited, PO BOX 345, Kwinana, WA 6966; Email:
Department of Agriculture and Food, 444 Albany Highway, Albany, WA 6330; Email:


A field experiment was conducted in 2006 on a loamy soil at York, Western Australia to investigate responses to ‘in-crop’ nitrogen application on the grain yield and protein content of wheat. The treatments were nitrogen rate (0, 21 or 42 kgN/ha), source (solid urea or liquid urea ammonium nitrate ‘Flexi-N’), timing (early booting and/or anthesis) and variety (durum wheat cv. Kalka and bread wheat cv. EGA Bonnie Rock). Growing season rainfall was below normal and average yields were 1.76 t/ha for EGA Bonnie Rock and 1.24 t/ha for Kalka. No significant differences in grain yield were recorded between any of the nitrogen treatments tested and this may have been due to the relatively dry conditions and the high recovery of nitrogen applied at sowing. The mean grain protein level of durum wheat was 1.4% higher (P<0.05) than the bread wheat. Compared to the control treatment with no post-emergent nitrogen, the application of 21 or 42 kgN/ha at booting and/or anthesis using either fertiliser source generally increased grain protein by 0.9 to 3.8% (P<0.05). The exception was urea applied at anthesis where there was no significant response, most likely due to a lack of rainfall after application to make this nitrogen available to plants. The highest grain proteins (14.9 to 16.2%) recorded in this experiment were achieved by applying 42 kgN/ha either as solid urea or Flexi-N at early booting and these treatments would have attracted premium prices in grain markets.

Key Words

Flexi-N, urea, post-emergent timing, rate, grain protein


Many regions of Western Australia (WA) produce wheat (Triticum aestivum) with low a protein content, especially in wet years when nitrogen (N) applied at seeding is lost through leaching and yields are not limited by water deficit during spring. Protein content can often be increased with the late application of urea, however benefits are highly dependent on rainfall after application (Palta et al. 2003). Flexi-N (urea ammonium nitrate solution, 32% N w/w) is an alternative N fertiliser that can be absorbed directly by leaves, suggesting that it could be a more reliable means of increasing grain protein content. In the United Kingdom and elsewhere, late applications of liquid N are often applied to wheat between the head emergence and soft dough growth stages for this purpose (Gooding and Davies 1992).

From 2000 and 2005, CSBP conducted a series of trials investigating the ability of Flexi-N applied between the flag leaf and flowering growth stages to increase the protein content of bread wheats (Loss 2005; Loss and Appelbee 2006). Dry seasonal conditions at some sites resulted in low yields and high protein contents, and in these cases there was generally little benefit from late applications of Flexi-N. Nonetheless, significant increases in grain protein and profits were recorded at three sites from late applications of Flexi-N where grain yields exceeded 3 t/ha (Loss 2005).

Both durum and Australian Hard wheat attract a price premium for high grain protein contents as reflected by the AWB Golden Rewards prices scheme (AWB 2008). Apart from the initial trial work by CSBP, little information has been generated to reliably manipulate the protein content of wheat by applying liquid nitrogen fertilisers during the growing season. The aim of this study was to investigate the effect of liquid and solid N fertilisers applied at booting and/or anthesis on the grain yield and protein content of durum and bread wheats in WA.


The field trial was conducted near York, WA in a paddock sown to wheat in the previous season. The clay loam soil had a topsoil pH(CaCl2) of 5.5, organic carbon content of 1.02% and the electrical conductivity was 0.11 ds/m. A completely randomised, factorial design was used with three replicates and the plot size was 1.44 by 20 m. The treatments were fertiliser type (urea or Flexi-N), rate (0, 21 or 42 kgN/ha), timing (early booting - Zadocks 41 and/or anthesis - Zadocks 65) and wheat variety (durum cv. Kalka and bread cv. EGA Bonnie Rock). Further details on N rates and the timing of applications are provided in Table 1.

Sowing occurred on the 8th June 2006, with seeding rates adjusted for seed weight and germination to achieve a target plant density of 200/m2. Basal fertiliser was applied to all plots at a rate of 14kg/ha P and 14 kgN/ha banded 3 cm below seed, plus a further 46 kgN/ha top dressed as urea. Flexi-N was applied using a small hand-held boom and urea was top dressed manually. Weeds and pests were controlled using appropriate pesticides as per label recommendations.

Machine harvested grain yield and grain protein content are presented here. Protein content data was obtained by near infrared reflectance calibrated against the standard Kjeldahl test. All data were analysed with ANOVA using Genstat 10th edition.

Results and Discussion

The growing season rainfall (April to October) of 161 mm was well below the long term average of 392 mm for this site. No rain fell during October after the anthesis N fertiliser applications and only 12 mm fell during November. This resulted in relatively low yields for this site with mean grain yields being 1.76 t/ha for EGA Bonnie Rock and 1.24 t/ha for Kalka (Table 1).

Table 1. Effect of liquid Flexi-N and solid urea nitrogen (N) fertilisers on grain yield (t/ha) and protein content (%) at York in 2006. Treatments indicate N fertiliser type, with the first and second number indicating the rate of N/ha applied at booting and anthesis, respectively.


(kg N/ha)

Grain yield


Grain protein



Bonnie Rock


Bonnie Rock


Control N 0-0





Flexi-N 21-0





Flexi-N 0-21





Flexi-N 21-21





Flexi-N 42-0





Flexi-N 0-42





Urea 21-0





Urea 0-21





Urea 21-21





Urea 42-0





Urea 0-42





LSD (P=0.05)



*n.s. denotes not significant at P=0.05.

No significant responses in grain yield were recorded in response to the application of any rate of Flexi-N or urea in either wheat variety. This is attributed to the dry season and consequently relatively low grain yields and the moderate basal N rate applied at sowing. Average grain yields with post emergent applications of Flexi-N and urea were virtually the same in both wheat varieties which is consistent with previous studies in WA on wheat and canola (Loss and Appelbee, 2006).

The mean grain protein content of durum wheat was 1.4 % higher (P=0.05) than the bread wheat. Compared to the control, protein content generally increased with post-emergent nitrogen applications, especially when applied at early booting and this trend was largely consistent across the two products and varieties (Table 1). Significant increases in grain protein also occurred in response to the application of liquid Flexi-N at anthesis, although the magnitude of this increase was generally less than that the equivalent N rate applied as single application at early booting or split between booting and anthesis. The application of solid urea had no significant effect on grain protein when applied at anthesis and this is attributed to dry conditions preventing this N from reaching the root zone in a suitable form for uptake. In contrast, the relative effectiveness of applying Flexi-N at anthesis may have been due to the N uptake directly through the leaves. At least in this experiment, there was no significant increase in grain protein by exceeding 21 kgN/ha when applying Flexi-N at anthesis.

Australian hard and durum wheats attract a price premium for grain high protein content under the AWB Golden Rewards payment system. Current recommendations from the fertiliser company CSBP based on their trial work suggest that growers can increase the protein contents of cereals by applying 14-21 kg N/ha as Flexi-N late in the season as where yields are likely to be high (Loss 2005). The results reported here support this recommendation and suggests that in at least some cases, grain protein can also be increased in crops yielding less than 2 t/ha of grain.


In this experiment, the post-emergent application of 21 or 42 kgN/ha as solid urea or liquid Flexi-N had little effect on grain yield, but it did significantly increase the grain protein content of durum and bread wheat, especially when applied at early booting. Under the dry conditions, there was no response to solid urea applied at anthesis. Compared to no post-emergent N, grain protein did increase significantly when liquid Flexi-N was applied at anthesis, although the magnitude of this increase was lower than for the same rate of N applied at booting using either product. These results support current recommendations of applying up to 21 kgN/ha as Flexi-N late in the season to increase grain protein, especially where no N is applied at booting. In this experiment was no advantage in increasing the rate of Flexi-N applied at anthesis to 42 kgN/ha. Further work is required to reliably predict grain protein responses to post-emergent N applications over a range of environments.


AWB (2008). ‘Golden Rewards Launched.’ Australian Wheat Board. Accessed Feb 2008.

Gooding MJ and Davies WP (1992). Foliar urea fertilisation of cereals: a review. Fertiliser Research 32 (2), 209-22.

Loss S (2005). The impact of fertiliser placement , timing and rates on nitrogen-use efficiency. In “2005 Crop Update Proceedings – Cereals” pp. 37. Western Australian Department of Agriculture..

Loss S and Appelbee M (2006). Agronomic performance and adoption of liquid fertilisers in Western Australia. Proceedings of the 13th Australian Society of Agronomy Conference, Perth, Australian Society of Agronomy.

Palta J, Bowden W and Asseng S (2003). Timing of late applications of N fertiliser and season on grain yield and protein in wheat. Proceedings of the 11th Australian Society of Agronomy Conference, Geelong, Australian Society of Agronomy.

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