April 1, 2021

Apex Yield Trials Take Wheat to the Next Level

Our Apex yield trials show just how important balanced early nutrient availability is, if growers are to capitalise on ever improving varieties.

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Corrigin apex yield trial site - July 2020.

In 2019 we established the first of our Apex Yield series trials. These trials are aimed at providing a range of nutrient treatments at the high end of the scale to determine the yield response potential of popular wheat varieties, often selected for their farm use based on National Variety Trial yields.

The results so far have been quite extraordinary and show just how important balanced, early nutrient availability is if growers are to capitalise on ever improving varieties. It's clearly not just about addressing deficiencies if you want to achieve the biggest rewards.

Results to date show that in 2019 on a highly productive soil at Dandaragan, Scepter wheat yield did not 'top out', even when 190 kg N/ha was applied for the season (see Figure 1, full trial report available here). This trial also builds on the evidence that early in-season N application (in this case applied between 4 and 8 weeks after emergence) produced a significant yield advantage over later applications (8 and 12 weeks).

Figure 1: Comparison of early and late in-season nitrogen application on yield and grain protein accumulation at Dandaragan 2019.

In 2020 the Apex Yield series continued, including a site near Corrigin. Soils at this site were moderate in P status and showed marginal surface K that increased with depth. This trial design incorporated N, P and K rates, with N in-particular applied to a high rate of 240 kg/ha. Despite challenging conditions post seeding and a decile 2 growing season rainfall of 188 mm (64 mm below average - Figure 2) individual plots of Scepter wheat in this trial achieved yields of up to 4.9 t/ha.

Figure 2: Rainfall (above) and wheat yield (above right) at the 2020 Corrigin Apex Yield trial site. NB: Data from treatments with nil K applied.
Figure 3: Soil nutrient test results for the 2020 Corrigin site.

The value of establishment P providing a foundation for in-season N to push yield higher was clear, as maximum yields stepped up progressively through P application of 0, 8, 16 and 24 kg/ha.

While increasing rates of P and N to such high levels achieved striking yield gains, the Corrigin site also showed how supplementary K can have an important supporting role. Applying 20 kg K/ha along with the banded P boosted yield by an additional 400 kg/ha (Figure 4).

Figure 4: Additive effect of K at the Corrigin Apex Yield site to assist uptake from the soil K pool as high N and P rates encourage rapid growth rates.

It is important to maintain a balance of all nutrients especially if rapid growth rates are encouraged by other management practice, such as applying high P and N rates.

View the trial Corrigin trial report here.

Importantly, optimising nutrition will dramatically increase rainfall use efficiency . The poorest treatment in the Corrigin trial, the nil control, achieved yield of 13 kg/mm of growing season rainfall. Applying 180 kg of N/ha only improved this to 16.5 kg/mm. However, if the optimum trial treatment of 16 kg P, 20 kg K and 240 kg N/ha is selected, rainfall use efficiency jumps to almost 24.5 kg/mm.

The rainfall use efficiency achieved at the Corrigin site was extraordinary, demonstrating the value and resilience of breeding lines adapted to the evolving WA climatic conditions.

These results provide further support for the need to select the most appropriate combination of nutrient rates to take full advantage of both site and genetic potential, rather than rely on N alone.