Key points
- Hyper-yielding faba bean crops in excess of seven tonnes per hectare are physiologically possible under irrigation
- Optimum plant populations under both surface and overhead irrigation are approximately 25 to 30 plants per square metre with late April sowing
Irrigated faba bean crops generate more grain per tonne of dry matter than dryland.
With two winter cropping seasons under its belt, a project that aims to optimise irrigated grains is already breaking the seven-tonne-per-hectare yield barrier in faba beans.
The four-year project led by Field Applied Research (FAR) Australia is exploring opportunities to improve crop-specific agronomic management practices and novel soil management technologies in irrigated environments, in collaboration with the Irrigated Cropping Council and with GRDC investment.
In faba beans, the focus is on crop structure under irrigation, the impact of sowing directly after soil amelioration on a red duplex soil, and a suite of agronomic measures such as disease control, rhizobium inoculants and plant growth regulation and its effects on plant architecture.
In canola, grain maize and durum wheat there is a major emphasis on nutrition, particularly the role of nitrogen fertiliser in driving high yields.
Irrigated crop performance is being directly compared under both surface and overhead irrigation (lateral), and indirectly compared with dryland crops.
Seven tonnes
Experimental plots of faba beans grown under irrigation at Finley, New South Wales, in 2021 yielded in excess of 7.5t/ha. For the first time in 2021, FAR’s dryland faba bean plots also yielded above 7t/ha in both the southern Victoria high-rainfall zone (HRZ) and north-eastern Victoria in 2021. While larger yields typically have a larger crop canopy, the trials comparing dryland and irrigated typically demonstrated that in irrigated crop canopies grain makes up a higher proportion of the dry matter – measured as harvest index in Table 1.
Table 1: A crop component analysis shows that irrigated PBA Amberley faba bean crops generate more grain per tonne of dry matter – measured as harvest index – than dryland.
Dryland | Irrigated | ||
|---|---|---|---|
Yield component | sown 29 April 2019 | sown 14 May 2020 | sown 28 April 2020 |
Plants/m2 | 19 | 20 | 20 |
Stems/m2 | 71 | 84 | 60 |
Pods/stem | 4.5 | 3.7 | 7.6 |
Pods/m2 | 320 | 308 | 453 |
Harvest dry matter (t/ha) | 7.3 | 8.7 | 13.6 |
Grain yield (t/ha) at 14% moisture | 2.3 | 3.8 | 7.5 |
Harvest index (%) expressed at 0% moisture | 27.6 | 37.7 | 47.4 |
Source: FAR Australia.
The irrigated canopy did not look very different in terms of stems per unit area. However, those stems and pods were larger, with better grain fill. Potential key metrics for improved yields and better harvest index – number of beans per pod or thousand-grain weight – is currently under analysis.
When faba bean crops have the potential to yield more than 7t/ha, some of the fundamental aspects of agronomy are magnified compared to dryland. Agronomic advice recommends avoiding overly thick faba bean crops to reduce the risk of disease and lodging and overly thin crops to limit weed populations.
Experiments comparing plant density under irrigation at Finley in 2020 and 2021 found that exceeding 30 plants per square metre had no impact on yield, but when density fell below 20 plants/m2 yield losses could exceed 1t/ha. Optimum plant populations under both surface and overhead irrigation are about 25 to 30 plants/m2 with late April sowing.
Disease risk
The larger crop canopies achieved under irrigation might put the crop at higher risk of disease, lodging and brackling. Brackling is similar to lodging but the stems bend higher up.
So, do bigger irrigated crop canopies show much greater responses to more disease management intervention? Using better resistance genetics in PBA Amberley, the trial revealed little additional yield response to higher fungicide input based on more-expensive chemistry under irrigation at Finley.
While irrigation increased the canopy size at Finley in 2021, the conditions for disease were not as conducive as those in the longer growing season of the southern Victoria HRZ near Geelong, despite similar yields (6 to 7t/ha).
Experimental plant growth regulators have reduced crop height and lodging pressure in these larger canopies but have not generated any significant yield advantage in the past two years of irrigated trials.
Once the 2022 trials are completed, the key lessons will be released as best management practice guidelines for maize, faba beans, chickpeas, canola, durum and barley under surface and overhead irrigation systems.
More information: Rachel Hamilton, 0428 843 456, rachel.hamilton@faraustralia.com.au