Figure 2. Northampton trial site in 2023. Twenty-one main plots (rotations) per replicate, split plot for fertiliser nitrogen rate, with three row and column replicates (latinised) (Photo: Boyce, DPIRD 2023)

Within each trial most of the rotations are phased, with several plots of each rotation in different phases each year. Nitrogen fertiliser treatments were determined based on the amount of nitrogen required to replace nitrogen exported in grain of cereals and canola in a decile 2 and decile 7 rainfall season at each site. Legumes received a small amount of starter fertiliser N (~10 kg/ha) applied versus no N applied. Hence, at all sites two levels of fertiliser nitrogen were tested (Table 1). Additionally, at Merredin, a third treatment of nil nitrogen was included across all rotations. The rationale for a strip or spit plot design was to increase the power of statistical analysis of the rotation x nitrogen interaction. The effect of high and low fertiliser regimes on legume performance is of particular interest, with the expectation that legumes will be well adapted to low soil nitrogen conditions and have a competitive advantage over other plants in these conditions. Extensive measurements of soils, weather, nitrogen dynamics, weeds, soil pathogens, yield and quality are being taken at each site to assess a wide range of production constraints. Additional satellite trials and bio-economic modelling is also being undertaken within the WAFS project; see https://www.agric.wa.gov.au/wa-farming-systems-project for more details.

Table 1. Nitrogen applied per site for high (H), low (L) and zero (Z) nitrogen by species

Preliminary results

Yields at Merredin and Northampton in 2023 were low due to decile one rainfall, with timely sown wheat averaging 0.85 t/ha and 1.6 t/ha respectively. At Lake Grace, a decile three season yielded 3.3 t/ha for timely-sown wheat. In 2024, Lake Grace had a decile three year, Merredin decile four and Northampton decile ten, with growing season rain of 212mm, 200mm and 517mm respectively.

Yield of cereals in 2024 was affected by rotation, nitrogen rate and their interaction with sites differing in responsiveness to both rotation and fertiliser nitrogen (Figures 3 & 4).

At Northampton, wheat yields were highest after a legume, lupin, serradella or brown manured vetch, with a large reduction in yield under continuous wheat. At Merredin, wheat yields were highest after fallow from 2023 and legumes provided a small yield boost compared to continuous wheat. At Lake Grace, there were large increases in cereal yield compared to continuous barley, with barley after pasture yielding the most, followed by wheat after brown manured lupin and oats after fallow.

The response to nitrogen was greater at Northampton than the other sites, with large increases in wheat yield with higher nitrogen, even after legumes. This is likely because it was a decile 10 rainfall season and nitrogen leached from the site. At Merredin, the response to nitrogen was much smaller, with no nitrogen effect after fallow and brown manured vetch even when no fertiliser nitrogen was applied. At Lake Grace, there was a classical effect where cereals grown after legumes were not as responsive to fertiliser N, with large reductions in yield at the low nitrogen rate for cereal grown after cereal or oilseed.

Figure 3. Yield of wheat in 2024 after various land uses in 2023 at Northampton and Merredin
C = canola, F = fallow, L = lupin, SP = Serradella, Vm = Vetch brown manure, W = Wheat, Ck = Chickpea, Ms = Multispecies, P = Pasture (Medic and Sub clover mixed)

Figure 4. Yield of cereals in 2024 after various land uses in 2023 at Lake Grace
B = barley, C = canola, W= Wheat, O = oat, F = Fallow, L = lupin, Lm = Lupin brown manure, P = sub clover.

Gross margin analysis

In Northampton, the GM of wheat grown in 2024 was lowest after wheat and highest after legume crop/pasture (Figure 5). Wheat with the high nitrogen treatment performed better regardless of what was grown in previous year. On the overall rotation for the first two years, wheat-lupin rotation with low N input had the highest average GM of $428/ha/year followed by canola-wheat rotation with high N input at $391/ha/year (not shown). However, it is still too early to make any conclusions.

In Lake Grace, cereal followed by legume performed better than other rotations. When legume was grown or fallow was practised the previous year, the GM of cereal grown with low nitrogen was either the same or more than the GM of cereal with high nitrogen. However, when cereal was grown the previous year, the rotational GM of cereal/cereal with higher nitrogen was higher (Figure 5).

In Merredin, the GM of cereal following fallow was the highest while cereal after multispecies and pasture was the lowest (Figure 6). There were mixed results between GM of the low and zero nitrogen treatments; however, GM of the high nitrogen treatment in cereal was consistently lower.

Figure 5. Gross margin of cereals in 2024 after various land uses in 2023 at Northampton and Lake Grace B = barley Bd = Barley delay sowing, C = canola, O = oat, F = Fallow, L = lupin, Lm = Lupin brown manure, P = sub clover, W = Wheat, Wd = Wheat Delay sowing.

Figure 6. Gross margin of cereals in 2024 after various land uses in 2023 at Merredin
B = barley, C = canola, O = oat, F = Fallow, Vm = Vetch brown manure, P = sub clover, W = Wheat, Wd = Wheat Delay sowing, Ck = Chickpea.

Conclusion

Three complex farming systems trials have been successfully implemented. Initial results are already showing the impact of rotations, fertiliser nitrogen and the interactions of these on yield. With the comprehensive set of data being measured from these trials there will be capacity to investigate which parameters are impacting yield and quality. The trials will continue to assess water and nitrogen use efficiency, risk and profit of these systems.

Acknowledgments

Thanks to the Western Australian Farming Systems project team; Aman Kaur, Balwinder Singh, Brenda Shackley, Bob French, Dion Nicol, Grace Williams, Imma Farre, Karyn Reeves, Klaudia Vizi, Kristy Hunter, Lea Obadia, Mark Seymour, Marty Harries, Megan Abrahams, Naomi Simpson, Rachel Mason, Rod Bowey, Steph Boyce, Sud Kharel, Vanessa Stewart-McGinniss, and Waseem Ashfaq. We thank the DPIRD Geraldton and Merredin Field Research Operations teams and Living Farm for managing these trials. Also, to farmers, consultants on regional advisory groups and trial hosts Jess Horstman and Kevin Naisbitt and Merredin Research Station.

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC; the authors would like to thank them for their continued support. This research is supported by the DPIRD/GRDC co-investment – “Western Australian Farming Systems” project – DAW2204-003RTX.

Contact details

Martin Harries 
DPIRD 
20 Gregory Street Geraldton WA 6530 
0428942682 
martin.harries@dpird.wa.gov.au