Pulse trials aim to optimise brown manuring

Key points

  • MoravaPBR logo vetch sown in mid-April was an effective option for weed control by brown manuring
  • Field pea varieties sown in mid-May were suitable for both brown manuring and crop-topping
  • Crop-topping is the application of a non-selective herbicide before harvest when the target weed (often ryegrass) is at flowering
  • Lupins produced the least biomass and were less competitive against annual ryegrass

Brown manuring of pulses has shown potential for controlling chemical-resistant weeds and boosting soil nitrogen.

A GRDC-funded project is working to expand the area sown to pulses in the southern grain-growing region through the use of improved management. A major aim of the project is to narrow down best practices in pulse manuring.

Research in 2012, which is being repeated this year, focused on how growers can optimise results when it comes to new variety selection, time of sowing and maximising biomass production.

A 2012 trial at Wagga Wagga, New South Wales, evaluated the performance of a range of pulse varieties in a brown manure system and their role in the crop sequence.

The trial was conducted by the NSW Department of Primary Industries (DPI) in partnership with the Victorian Department of Environment and Primary Industries, the South Australian Research and Development Institute, CSIRO and FarmLink.

This research compared three sowing dates (20 April, 9 May and 2 June) and six pulse varieties (Morgan PSE 23PBR logo, PBA PercyPBR logo and PBA HaymanPBR logo field peas; MoravaPBR logo vetch; and RosettaPBR logo albus and MandelupPBR logo angustifolius lupins). 

The varieties were assessed for their total biomass production, grain yield and contribution to soil nitrogen (Tables 1 to 3).

NSW DPI research agronomist Luke Gaynor says there is a clear choice to make when brown manuring – either spray out the legume in early spring at the very early flat pod growth stage or wait until plants reach peak biomass to help maximise nitrogen fixation.  

Photo of plant life

NSW DPI research agronomist Luke Gaynor ran a trial looking at pulse sowing dates at this Wagga Wagga trial site last year. He says pulses should be brown manured by either spraying out in early spring, at the very early flat pod growth stage, or waiting until plants reach peak biomass to maximise nitrogen fixation.

PHOTO: Deanna Lush

“This can mean the difference between two and five tonnes of biomass per hectare, and therefore more nitrogen fixation,” he says.

If targeting the control of early flowering weeds such as wild oats, Mr Gaynor says early brown manuring is critical. 

“Growers must aim to kill the crop according to the flowering [phenology] of the weed to gain maximum weed control,” he says. “If chasing annual ryegrass, which flowers later than wild oats, crop-topping is a viable alternative but a suitable, early-maturing field pea should be used.”

Using the approximate rule of thumb of 25 kilograms of nitrogen fixed per tonne of dry matter, Mr Gaynor says the most effective treatments in this trial have potentially fixed more than 300kg N/ha.

He says biomass levels at the flat pod stage were highest in April-sown MoravaPBR logo vetch at 10t/ha. But then volumes decreased with each delay in sowing.

“Field pea varieties tested did not show a large variation in biomass across all varieties and sowing dates, although the May-sown Morgan PSE 23PBR logo and April-sown PBA PercyPBR logo were statistically higher.

“Lupin biomass was lower at all sowing dates, but the April-sown plot was unfairly disadvantaged by hare grazing.” 

When the biomass of mature plants was assessed, May-sown PBA PercyPBR logo field peas produced the most biomass, followed by April-sown and May-sown MoravaPBR logo vetch and April-sown PBA HaymanPBR logo field peas.

The trials showed that sowing on 2 June was too late to maximise biomass for all varieties.

Other results included the following. 

  • Field peas – all varieties tested were suitable for mid-May sowing for either brown manuring or crop-topping. Yields increased with each delay in time of sowing under conditions at the trial site, which included plenty of stored subsoil moisture at the start of the season, but below-average growing-season rain and a dry finish. Mr Gaynor says all three varieties sown on 20 April had ascochyta and/or bacterial blight in early winter, which reduced biomass, but plants recovered as the season progressed. Early sowing of field peas is considered risky, especially if the season is wet. Disease reduced grain yield.
  • Vetch – MoravaPBR logo vetch was the best choice for mid-April sowing, particularly if brown manuring for early weed control was the objective. Early desiccation stopped seed set and prevented hard-seeded vetch growing in following crops. 
  • Lupins – hares grazed the early-sown lupins, while the June-sown crop was too late to achieve yield potential. May-sown lupins had significantly higher yield than the June planting. Despite damage to some plots, lupins produced the least biomass of all the pulse crops in the trial, even when damage was not a factor. Poor lupin plant competition with annual ryegrass during early growth further restricted biomass production.
TABLE 1 Effect of sowing time on grain yield, brown manure trial, Wagga Wagga 2012 (t/ha)
Sowing date MandelupPBR logo Angustifolius lupins RosettaPBR logo Albus lupins MoravaPBR logo vetch Morgan PSE 23PBR logo field pea PBA HaymanPBR logo field pea PBA PercyPBR logo field pea
20-Apr 0.90 1.33 1.59 1.43 1.03 1.48
9-May 1.73 2.26 1.58 1.95 1.43 2.44
2-Jun 1.08 1.39 1.44 2.00 1.84 2.39
TABLE 2 Crop dry matter anthesis/early pod fill (t/ha)
Sowing date MandelupPBR logo Angustifolius lupins RosettaPBR logo Albus lupins MoravaPBR logo vetch Morgan PSE 23PBR logo field pea PBA HaymanPBR logo field pea PBA
PercyPBR logo field pea
20-Apr 3.22 4.34 10.18 6.16 6.10 7.76
9-May 5.71 6.06 7.47 8.03 7.01 6.41
2-Jun 3.46 5.18 4.16 5.38 6.44 6.93
TABLE 3 Brown manure pre-harvest dry matter cut (t/ha)
Sowing date MandelupPBR logo Angustifolius lupins RosettaPBR logo Albus lupins MoravaPBR logo vetch Morgan PSE 23PBR logo field pea PBA HaymanPBR logo field pea PBA PercyPBR logo field pea
20-Apr 8.62 4.55 12.31 11.83 12.75 10.58
9-May 9.39 6.53 12.31 11.67 10.83 13.64
2-Jun 6.28 5.00 7.56 10.19 8.39 10.06

More information:

Luke Gaynor
02 6938 1999,
luke.gaynor@dpi.nsw.gov.au

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