Optimising nitrogen (N) inputs can dramatically improve the profitability of wheat crops. Many growers are weighing up different N application options, for instance, retaining some of the N inputs until after establishment for risk management or for better seeding efficiency. A series of research trials aimed to revisit tactical nitrogen applications with the varieties Mace and Hydra at four low rainfall sites (Ballidu, Merredin, Lake Grace and Ogilvie) and Mace and Trojan at three medium-high rainfall sites (Broomehill, Cunderdin, Mingenew). The results of the Ballidu trial are presented here.
To determing the impact of different nitrogen rates and application time on the grain yield and quality of wheat production systems.
Yellow sandy loam
pH (CaCl2): (0-10cm) 5.5, (10-20cm) 4.7; (20-30cm) 4.5
Nitrate (mg/kg): (0-10cm) 17, (10-20cm) 10; (20-30cm) 5
Ammonium (mg/kg): (0-10cm) <1: (10-20cm) 3; (20-30cm) 5
N in profile (0-30cm): 60kg/ha
|Crop||Wheat varieties - Mace and Hydra|
|Treatments||See Table 2|
|Replicates and plot size||Three and 10m x 1.78m|
|Sowing date||26 May 2015|
|Seeding rate||target 120 plants/m2|
|Fertiliser||80kg/ha Super CMZ drilled at seeding|
|Total N (kg/ha)||N (kg/ha) at seeding||N (kg/ha) at Z21||N (kg/ha) at Z31|
The 2015 season at East Ballidu had 71mm summer rainfall in February and March. There was adequate soil moist to establish the crop in late May with follow up rains in mid-June. The season finished sharply with a very dry September and October. There were extended dry periods without rainfall followed by several rainy days, thus while monthly rainfall recorded at East Ballidu seem reasonable, the crop experienced intermittent stress. Canopy temperatures recorded at the nearby wheat NVT site included a -1.0°C frost event on 2 September which may have affected yields. However, high temperatures were more prevalent during grain-filling: with six days >30°C and one day >35°C in September; and 21 days >30°C in October of which 16 days were >35°C and four days >40°C .
The mean yield of the site was 1.4t/ha, with no difference between Mace and Hydra. There was a significant difference (F prob. <0.001) between N treatments; however, there was no significant interaction between variety and N treatment, thus yield data is presented as the mean of both Mace and Hydra for a given N rate. The trial site was N responsive (unlike some of the other 2015 trials) with the nil N treatment producing 1.0t/ha and the highest N treatments (total 70N) producing 1.6t/ha (see attachments). Treatments receiving 30N either at sowing or as a split application were not significantly different (all ~1.4t/ha). The same occurred for the 50N (~1.5t/ha) and 70N (1.6t/ha) treatments. The NVT treatment only received 23N upfront and its yield was significantly different to both the10N and 30N upfront treatments.
A typical grain protein response was observed: protein content increasing with additional N after yield plateaued; however, protein content remained quite low as has occurred in much of central wheatbelt in 2015. Even applying 70N did not achieve the 10% protein content required to meet APW classification. While the protein response was statistically significant, it was unlikely to be economically worthwhile, especially with the low premium paid for protein in recent times. Some growers have asked whether the large rainfall events leached the N below the root zone. Given the yield and protein responses were different between N rates but not timing, this suggests that leaching was not a major contributing factor. Results for screenings and grain weights were not available at time of publishing.
Of the six tactical N trials in 2015, Ballidu was the most N responsive; however, it was also the lowest yielding site (mean 1.4t/ha). The intermittent dry spells, particularly early in the growing season limited tiller survival and this likely constrained yield. The effect of N timing was less importance in this trial than N rate. However, all applications were before first node appearance (Zadok 31) which is considered a key development stage for yield response to applied N. Future studies in the project will seek to clarify potential cut-off times for N applications.
DAFWA colleagues Bob French and Brenda Shackley for trial development. The Grain Crop Agronomy Reference group (managed by GRDC), for their support with research development in 2015. Kalyx for trial management and DAFWA’s Bruce Haig for technical support with nitrogen application, data collection and management. This project Tactical wheat agronomy for the west (DAW00249) is funded by GRDC and DAFWA.