Take Home Messages
- Wheat yields in 2024 were not affected by lentil end-use treatments imposed in 2023.
- Brown manure field peas in 2023 and 150kg/ha urea treatments in 2024, resulted in a higher wheat yield in 2024.
- Best 2-year partial GM ($/ha) was lentil grain yr 1/wheat yr 2 and field pea grain yr 1/wheat yr 2, rather than brown manure/hay in year 1/wheat yr 2.
Aim
To measure the legacy effect of different lentil and field pea end-uses on soil mineral N and water for the following cereal crop.
Background
There are many recorded benefits from including a pulse phase in a cereal-based farming system, such as: (i) a weed and disease break, (ii) nitrogen (N) fixation, and (iii) conservation of soil moisture (Swan, 2023). However, it is not well understood how in-season agronomic decisions relating to pulse crop end-use for instance brown manure, hay or harvesting for grain, affect the yield and quality of the following cereal crop (Hunt, 2023) For instance, which pulse phase and end use contributes the most towards the next seasons wheat crop. Grain legumes provide some, but often insufficient levels, of N for following cereal crops at the current intensity of cereal crops grown in cropping rotations (Finger, 2023). Given the importance of legumes in cereal-based cropping rotations, it’s critical to understand how end-use affects following cereal crops. Pulse crops all fix different amounts of N, this is due to inherent differences such as crop productivity, shoot to root ratio, biomass production and N fixation capacity (Farquharson, 2023).
In this instance lentils were used as they have been grown in the region and also trialled in previous BCG experiments. BCG have observed some growers trialling lentils purely for the purpose of brown manuring. For this reason, it allows growers to work with seed on hand or available to them. Field peas have also shown to be a suitable option for the North Central region, in previous BCG trials, this is why field peas were chosen to be included in this experiment.
For further information about pulse end-use effects, ‘Vetch end‑use and its legacy effect on wheat’ on page 240 presents results from the two-year research in the Mallee. These trials highlight there is a still a need to conduct further research on these different pulse crops on their end-use impact for the following seasons crop.
Paddock Details
Location: Pyramid Hill
Previous year rainfall (Nov 2022 – Oct 2023): 379 mm
GSR (Apr–Oct 2023): 250 mm
Crop year rainfall (Nov 2023 – Oct 2024): 428 mm
GSR (Apr–Oct 2024): 169 mm
Soil type: Clay loam
Paddock history: Oats (2022)
Trial Details
Crop type/s: Lentils var. GIA Thunder (2023), Field Peas var. PBA Butler (2023), Wheat var. Scepter (2024)
Treatments: See Table 1
Target plant density: 130 plants/m²
Seeding equipment: Knife point, press wheels, 30 cm row spacing
Sowing date: 25 May 2023 (lentil, field pea), 7 May 2024 (wheat)
Replicates: Four
Harvest date: 6 December 2024
Trial Inputs
Fertiliser: Granulock Supreme Z + Flutriafol (400 mL/100 kg) @ 60 kg/ha at sowing. See Table 1 for in season urea application rates.
Weeds, pests and diseases were managed as per best practice.
Method
Two replicated field trials were sown using a complete randomised block trial design in 2023 to lentils and field peas at Pyramid Hill. Three different end-uses for field pea (brown manure, hay and grain), and two for lentil (brown manure and grain) were implemented.
In 2024 all plots were sown to Scepter wheat. The first grain treatment relied on residual legume N in soil and no urea was applied; the second grain treatment received 150kg/ha urea (70 kg N/ha) in 2024.
Assessments included crop biomass, grain yield and quality. The trial plots were soil sampled on 2 April 2024 for soil available N and water to a depth of 1m. Urea was top dressed over one lentil and one field pea (27 June) treatment in 2024, the rates were determined based on starting soil nitrogen and calculated using Yield Prophet®.
Results & Interpretation
Lentil and field pea biomass and yield results 2023
Biomass was measured at flowering for both lentil and field pea crops on 19 September 2023 (Table 2). Brown manure treatments were terminated on the same date. Data are presented as an average for each crop across all treatments as in-season management was consistent across treatments, with the exception of the end-use.
Soil Mineral N & PAW
Baseline soil N sampling was conducted at the commencement of the trial. In 2023 the site had 105kg/ha of starting soil N (combined ammonium and nitrate) (sampled 22 May 2023).
At the end of 2023, soil sampling on a plot-scale revealed a trend of higher soil mineral N following the brown manure and hay treatments for both lentils and field peas (Table 3). However, the levels of soil N between treatments were not significantly different. This may be due to 150mm of summer rainfall occurring prior to soil sampling in January 2024, potentially influencing soil N and water dynamics, and masking differences between treatments. Similarly, soil chemistry and moisture data collected in March 2024 also showed minimal differences (non-significant) between the treatments.
Wheat biomass
Data collected from biomass cuts taken from the wheat crop in 2024 showed that previous end-use treatment for both lentil and field pea produced no differences in terms of wheat biomass production at flowering (data not shown).
Wheat grain yield and protein
The effects of 2023 pulse end-use on 2024 wheat grain yield and protein are presented in Table 4. Wheat yield and protein content were generally consistent across treatments, and no significant differences for either variable were observed. This suggests minimal influence of previous lentil end‑use and N application on the following wheat.
In contrast, the field pea brown manure and 150kg/ha urea treatments produced higher yields (0.5t/ha and 0.6t/ha, respectively) than the field pea hay and no additional N treatment (p = 0.016, LSD = 0.39). A significant grain protein difference was also observed between the four field pea treatments, with the 150kg/ha urea treatment (applied in 2024, producing the highest grain protein at 10.2% (p = 0.006, LSD = 0.6).
Commercial Practice and On Farm Profitability
The partial gross margin (PGM) for lentils showed that Grain 1, where 0kgN/ha was applied to the wheat, had the highest PGM (Table 5). This is due to the absence of cost for urea, as there were no differences in the wheat yield following the three different lentil treatments, i.e., the only difference in the PGM between the 100kgN/ha treatment is the cost of the urea. The brown manure treatment had the lowest PGM as this treatment did not generate an income in 2023.
The highest PGM for the field pea treatments was field pea grain, that received 150kgN/ha in the subsequent wheat crop. The additional N which resulted in extra wheat yield had an $833/ha higher PGM, largely due to no return in 2023 from the brown manure. High summer rainfall may have negated any possible differences in soil water and N, where in some years a benefit (in the following wheat crop) may be observed from brown manuring a pea crop (Browne, 2012).
Wheat yields following field peas was highest when either 150kgN/ha was applied to the wheat, or the field peas were brown manured (Table 3). The three different lentil end-uses resulted in no differences in the following years wheat yields, even with the addition of N. Lentils typically fix less N in the first place, than field peas due to their low amount of above ground biomass (Seymour N. 2018).
The outcome of these cropping and end-use choices is highly seasonally dependent as in this instance large amounts of summer rain negated many benefits. Crop end use choice should remain selected based on seasonal conditions, to maximise profitability (i.e. cut for hay in drier year) (Browne 2012).
References
Swan T., 2023, Calculating the nitrogen benefit from legume crops, GRDC GroundCover. <https://groundcover.grdc.com.au/agronomy/soil-and-nutrition/calculating-the-nitrogen-benefit-fromlegume-crops>
Hunt J., 2023, A systems approach to nitrogen management, GRDC Update papers. <https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2022/02/a-systemsapproach-to-nitrogen-management>
Finger K., 2023, 2023 BCG Season Research Results ‘Managing N in variable paddocks: Application of N bank strategies part 2 ‘ pp 78–85.
Farquharson L., (2023) Inoculating legumes: Practice and Science, GRDC. <https://grdc.com.au/__data/assets/pdf_file/0023/400865/Inoculating-Legumes-Guide_FA_May23_online.pdf>
Seymour N., 2018, How much nitrogen is fixed by pulse crops and what factors affect fixation? GRDC Update paper. <https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2018/03/how-much-nitrogen-is-fixed-by-pulse-crops-and-what-factors-affectfixation#:~:text=The%20amount%20of%20nitrogen%20(N,spacing%2C%20plant%20population%20 and%20variety>
Browne, C., (2012), 2012 BCG Season Research Results, ‘Break Crops pay in the Mallee ’, pp 42–48. <https://www.bcg.org.au/research-article/break-crops-pay-in-the-mallee/>
Acknowledgements
This research was funded by the Grains Research and Development Corporation (GRDC) and Agriculture Victoria as part of the Southern Pulse Agronomy project (DJP2105-006RTX) and supported by the Birchip Cropping Group (BCG), Southern Farming Systems (SFS), Field Applied Research (FAR) Australia and Frontier Farming Systems (FFS) in 2023.
From 2024 this project was funded by the Grains Research and Development Corporation (GRDC) as part of the ‘RiskWi$e’ project (BCG AGR001-NRMI-RTX).
Thank you to Harm van Rees, Cropfacts, for providing a technical review of this article.
