Take home message

• In 2021 and 2022 trials, for each tonne of above ground biomass (greater than ~1.2 t/ha), nitrogen fixation averaged 31 kg/ha
• Nitrogen fixation differences between species were largely driven by differences in biomass
• Faba beans and (where well drained) lupins had the highest biomass and hence the highest nitrogen fixation
• Grain nitrogen concentration ranged from about 6% in albus lupin, down to 3.2% in chickpea. Nitrogen removal per tonne of grain harvested (or hay cut for vetch) was ranked from albus lupin > narrow-leaf lupin > vetch > lentil = faba bean = field pea > chickpea > vetch hay.

Introduction

In 2021 GRDC initiated a project focused on ‘Best Practice Pulse Agronomy’ that brought together a unique group of organisations including Frontier Farming, Grain Orana Alliance, FAR Australia and AgGrow Agronomy. Led by Brill Ag it established two major themes of research activity:

1. Maximising economic yield and nitrogen (N) fixation in regional environments.
2. Developing locally relevant research knowledge on limitations to pulse production and productivity. Research to date has focused on plant density, disease management, nutrition management, inoculation strategy, phenological development, and herbicide tolerance.

This paper reports on the findings from Theme 1 above for the 2021 and 2022 seasons.

Materials and methods

Trials were conducted at seven sites across southern and central NSW in 2021 and five sites in 2022 (Table 1). Sites were selected to be regionally relevant with challenges (both perceived and real e.g., low pH, sodic and/or poorly drained soils) that may restrict the use and production of pulses in the rotation. The research is not designed to compare the performance of pulses in a benign situation but is focused more on determining the performance of pulse species for yield and N fixation performance in the local environment where adapted species may thrive, but less adapted species may struggle. This paper is reporting on ten of these twelve sites where N fixation analysis has been completed.

Table 1. Site description of ten pulse agronomy research sites from 2021 & 2022

¹Faba beans, vetch and lupins sown at earlier sowing date; field peas, lentils and chickpeas sown at later sowing date.

N fixation was determined by collecting biomass samples at peak biomass (i.e., mid-podding stage and before leaf drop) and analysed using the ¹⁵N natural abundance technique (Unkovich et al., 2008) to determine what proportion of the N in the biomass was derived from the atmosphere (NDFA). Once the quantity of NDFA in above ground biomass was calculated (peak biomass * N content of biomass * NDFA%), total N fixation (N-fix) was calculated by multiplying a co-efficient that estimates the root contribution which was 1.5 for faba beans, field peas, lentils, lupins and vetch; and by 2.0 for chickpeas. These figures (1.5 and 2.0) are known as ‘root factors’ and are described by Swan et al. (2022). The root factor calculation makes an allowance for below ground N (e.g. in roots and nodules) so an improved estimate of total N fixed can be provided. Finally, the N balance is calculated by subtracting the N removed in grain from total N fixed.

Results

Total nitrogen fixation

Total N fixed by the pulse species across the ten sites in 2021 and 2022 was closely related to crop biomass. For each tonne of biomass >1.2 t/ha, total N fixation was ~31 kg N/ha (Figure 1). Some crop biomass figures were very high in 2021 and 2022 due to high rainfall. The species most consistently able to achieve these very high biomass levels was faba bean as it handled intermittent waterlogging relatively well. Lupins had very high biomass in some trials (e.g. Canowindra 2021 & Barellan 2022) but had low biomass where waterlogging was an issue (e.g. Parkes 2021, Trundle 2022). Overall lentils had the lowest biomass and the lowest N fixation.

Figure 1. Relationship between peak biomass of pulses and total N fixed (N-fix) across 10 trials in 2021 and 2022.

Nitrogen removal

Nitrogen concentration in the grain was highest in albus lupin and lowest in chickpea, with albus lupins having approximately double the grain N concentration of chickpeas (60 kg N/tonne for albus lupins versus 33 kg N/tonne for chickpeas). Narrow-leaf lupins had the second highest grain N concentration (52 kg N/ tonne) with faba beans, field peas and lentils all within 40–45 kg N/tonne of grain (Figure 2). Vetch hay (from nearby trials) had an average N removal of 27 kg N/tonne of hay (data not shown). Site variation for grain N concentration was less significant than the differences between species.

Figure 2. Average Grain (and hay) N concentration of pulse species in 2021 and 2022 in trials in southern and central NSW.

Nitrogen balance

N balance is simply a measure of how much N is harvested in grain (or removed in hay) subtracted from total N fixation. With >50 species*site combinations assessed in 2021 and 2022, the N balance was always positive ranging from 2 kg/ha to 402 kg/ha. Due to their low biomass production, the N balance of lentils was <100 kg N/ha in eight of nine trials where lentils were included. In contrast, faba beans had an N balance >100 kg N/ha in eight of ten trials where they were included (Tables 2 & 3). In general, higher biomass crops had higher grain yield and higher nitrogen balance. Pulse agronomy (for example sowing date, species selections, seeding rate) should focus on maximising biomass to increase both crop biomass (and N fixation) and grain yield.

Table 2. Peak biomass, total N fixed (N-fix), grain yield, N removed in grain and N balance of pulse species at research sites in NSW in 2021.

Table 3. Peak biomass, total N fixed (N-fix), grain yield, N removed in grain and overall N balance of pulse species at research sites in NSW in 2022.

Discussion and conclusion

The above average rainfall in 2021 and 2022 led to some very high biomass and grain yields being achieved across the project region, most consistently with faba bean. Other pulses such as lupin, lentil and chickpea had more variable yield responses. Field pea and vetch (for grain) performed consistently across sites and seasons, only occasionally being the best performer but also rarely being the poorest performer. This trait of lowish but stable yield may be appealing to some growers that wish to manage potential downside risks in pulse production. In addition to their excellent grain yield performance, faba bean had an average N balance of 180 kg N/ha.

The work from this project on pulse crop suitability to local environments and tactical agronomy couples well with GRDC Farming Systems research to gain a full understanding of the role of pulses in regional farming systems.

Caragabal 2023

The Caragabal trials in 2023 were sown on a soil with a silty loam topsoil (pH 5.9 0–10 cm, 107 kg available N/ha) overlying clay at depth. The trials were sown into moist soil with a full moisture profile after a wet 2022 and above average rains in March 2023. The season turned very dry from mid-July with 40 mm total rainfall recorded from mid-July to mid-October. There were also several days with temperature above 30°C in September. Winter growth was excellent, and crops set up high yield potential, but the dry and hot finish limited yield.

Three separate sowing date trials were sown for faba beans, lupins and vetch with sowing dates of 19 April and 19 May. Early sowing of the faba bean varieties FBA Ayla and PBA Nasma had the highest yield in this trial set at 2.8 and 2.9 t/ha respectively. Yield of these two varieties was approximately double the yield of PBA Amberley and PBA Samira when sown early (Table 4).

In the lupin trial, narrow-leaf lupin varieties Mandelup and PBA Bateman yielded 2.0 t/ha from early sowing, 600–700 kg/ha higher than the albus lupin varieties despite producing less biomass (Table 5).

In the vetch trial, highest yields were from later sowing of Timok and Rasina and Morava at either sowing date. The vetch was ungrazed and the early sowing led to the development of mould in the canopy in winter which especially penalised the quickest variety, Volga (Table 6).

Table 4. Grain yield and peak biomass of four faba bean varieties sown at two sowing dates at Caragabal in 2023.

Table 5. Grain yield and peak biomass of four lupin varieties sown at two sowing dates at Caragabal in 2023.

Table 6. Grain yield and peak biomass of four vetch varieties sown at two sowing dates at Caragabal in 2023.

Three separate trials for field peas, lentils and chickpeas were sown at the later sowing date. There were some issues with lentil seed so results of that trial are not reported here. An extra treatment of 100 kg N/ha (as urea early post crop emergence) was added to one variety in each trial.

Yield of chickpeas averaged 1.7 t/ha (Table 7), with CBA Captain and PBA Slasher the highest. Nitrogen application did not affect grain yield of CBA Captain but did increase its biomass.

Field pea grain yield ranged from 1.9 t/ha for APB Bondi down to 1.1 t/ha for Sturt (Table 8). Nitrogen application had no effect on grain yield or biomass of field peas.

Table 7. Grain yield and peak biomass of chickpeas at Caragabal in 2023.

Table 8. Grain yield and peak biomass of field peas at Caragabal in 2023.

The peak biomass samples from Caragabal and other sites in 2023 have been sent for analysis to determine nitrogen fixation and nitrogen balance to add to the data from 2021 and 2022.

Discussion and conclusion

The above average rainfall in 2021 and 2022 led to some very high biomass and grain yields being achieved across the project region, most consistently with faba bean. Other pulses such as lupin, lentil and chickpea had more variable yield responses. Field pea and vetch (for grain) performed consistently across sites and seasons, only occasionally being the best performer but also rarely being the poorest performer. This trait of lowish but stable yield may be appealing to some growers that wish to manage potential downside risks in pulse production. In addition to their excellent grain yield performance, faba beans had an average nitrogen balance of 180 kg N/ha.

There was a good start to the season in 2023 but late winter and spring turned warm and dry. Yield potential was generally lower than previous years but faba beans – specifically early sowing of the northern faba bean varieties FBA Ayla and PBA Nasma – still performed well at Caragabal with yield just below 3 t/ha. With high nitrogen fixation and consistent yield over the three years of the project, they are proving their worth as part of farming systems in medium to high rainfall zones.

The work from this project on pulse crop suitability to local environments and tactical agronomy couples well with GRDC Farming Systems research to gain a full understanding of the role of pulses in regional farming systems.

Acknowledgements

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 author would like to thank them for their continued support.

Thanks to grower co-operators Jeff Savage (Barellan), Dennis Tomlinson (Buraja), Daybreak Farming (Caragabal), Stephen Cooper (Caragabal), Chris Berry (Trundle), Viridis Ag (Canowindra), Angus Maurice (Wellington), Trentham Estate (Gol Gol), Nathan Border (Parkes).

Further reading

NSW Pulse Agronomy Development and Extension Project – 2021 summary of field trial results. https://grdc.com.au/resources-and-publications/all-publications/publications/2022/nsw-pulse-agronomy-development-and-extension-project

References

Unkovich M, Herridge D, Peoples M, Cadisch G, Boddey R, Giller K, Alves B. and Chalk P (2008) Measuring plant-associated nitrogen fixation in agricultural systems – Part 4. https://www.aciar.gov.au/publication/books-and-manuals/measuring-plant-associated-nitrogen-fixation-agricultural-systems

Swan T, Dunn M, Kirkegaard J, Goward L, Leighton E, Sandral G, Hunt J, Bullock M, Pumpa R, Fiske K, Woodford-Smith A, Reardon D, Barry M and Burns H (2022) What is the N legacy following pulses for subsequent crops and what management options are important to optimise N fixation? 2022 Wagga Wagga GRDC Update. https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2022/02/what-is-the-n-legacy-following-pulses-for-subsequent-crops-and-what-management-options-are-important-to-optimise-n-fixation2

Contact details

Rohan Brill
Brill Ag
Ganmain, New South Wales
Mobile: 0488 250 489
Email: rohan@brillag.com.au

Date published

August 2024

Varieties displaying this symbol are protected under the Plant Breeders Rights Act 1994.

GRDC Project Code: BRA2105-001RTX,