Legume Soil Health Project

Current trial site status

Krui Plains, NSW. Winter trial plots of Faba beans, field peas and chick peas were sampled in August 2015. A LabLab green manure trial was planted in late September to investigate if an effective cover crop can be established and terminated prior to a summer grain planting. Lack of rainfall did not allow canopy closure and the trial was utilised as cattle feed.

Coondarra, Qld. Barley oversown over previous trial areas and winter trial plots of Faba beans, field peas and chick peas were sampled in October 2015. A LabLab green manure trial was planted in late September with a similar aim to the Tulloona planting. The crop achieved good canopy closure by the end of 2015.

Project Background

Darryl Bartelen, Chairman of Project Advisory Council, believes the positive effects of incorporating legumes into cropping rotations should be considered across an extended cropping cycle.

“The anecdotal evidence from my legume cropping experience indicates that the benefits from nitrogen fixing and organic matter contributions can show up when not expected; often under particular seasonal conditions. The trials will try to quantify some of these benefits.”

legume tulloona field day sep 2015

Presentation of trial findings at the Tulloona Field Day September 2015

The use of legumes to improve soil health is not new, but the issue is what legume to plant, when and what tradeoffs will need to be made. The Conservation Farmers Inc. Legume Soil Health project is testing a range of summer and winter legumes as both grain crops and manure crops. The project has been run on three different sites over the last two years.

 General Rules for Nitrogen Fixation

  • As a general rule legumes can fix between 15- 25kg of Nitrogen for every tonne of shoot dry matter accumulated.
  • Legumes provide Nitrogen residues after decomposition of soft plant tissue. This Nitrogen is estimated to be available for the following crop at 100-120kg of Nitrogen fertiliser/ha/yr.
  • The actual amount of Nitrogen fixed will depend on the species, the season, the site, the effectiveness of inoculation and how well the legume grows.
  • Typically the Nitrogen fixation increases with biomass production, but is reduced by high levels of soil nitrate.

Observations from Winter Legumes

Winter 2014 saw the first trials planted. At Killarney on the eastern Darling Downs faba bean, field pea and chickpea plots were established. The legume plots were terminate at 90 days, by which time the faba beans and field peas had produced 1.6t/ha biomass with an estimated Nitrogen fixation of between 24 and 38kg N/ha. Chickpeas produced 1.0t/ha and an estimated 15 to 25kg N/ha.

Despite these differences in biomass, no observed yield differences were found between the legumes in the following sorghum crop. Yield measures in the following sorghum crop suggested that the legumes contributed Nitrogen at a level equivalent to 50% of the rate applied by the grower.

Additionally the yield results suggest that a reduction in soil moisture following mechanical incorporation of the legumes reduced the sorghum yield compared to terminating the legumes with a herbicide.

In northern NSW at Tulloona, the 2015 winter trial plots planted in April were sampled for biomass production at 120 days after planting. The faba beans produced the most biomass, but used more than half the plant available soil moisture.

biomass measurements jimbour winter legumes

The plots were terminated using either mechanical incorporation or brown kill (glyphosate). Further soil moisture and yield assessments will be made to determine if there are any longer term differences between these two approaches.


Observations from Summer Legumes

The summer legumes trialled included guar, lab lab, mung bean and soya beans. The 2014-15 summer trials at Jimbour on the central Darling Downs were planted in December and terminated at 46 days after planting. There was evidence of weed suppression from good canopy closure by all species. The plots were terminated using either glyphosate or with a combination of glyphosate and mechanical crimping/rolling.

biomass measurements jimbour summer legumes

The mung beans produced the largest biomass but it depleted the soil profile more than the other species. All cover crops depleted more than half of the plant available soil water. Guar and lab lab showed very similar water use patterns although lab lab produced more biomass.

Emerging Findings

The data collected to date indicates that there will be benefits and trade-offs from the use of green manure legumes in crop rotations. The benefits from Nitrogen fixation and legume decomposition will be balanced with possible reductions in soil moisture. Importantly the technique chosen for crop terminations will influence the soil moisture availability for following crops.

Growers will need to develop planting regimes which enable them to adjust planting and crop termination to maximise potential to refill the soil moisture profile for the following crop. For example, the use of rapidly establishing summer legumes during late winter and early spring is likely to enable growers to produce good biomass and terminate the crop before the early summer rainfall. The challenge will be establishing the legume so that it produces good biomass and aids in the suppression of weeds.

The use of legumes such as faba beans will give growers greater flexibility. In seasons where rainfall is below average growers may find carrying the legume crop to harvest more beneficial than manuring it.

The Legume Soil Health Project is nearing completion and a full report will be prepared summarising the findings.

Three farmers: Darryl Bartelen, Tulloona NSW, St John Kent, Jimbour Qld. and Scott Petersen, Killarney Qld., are trial co-operators for the project.


Comparing chickpeas and Faba beans


Faba beans in Dalby


Summer legumes field day at Jimbour


Field Day Handouts

Legume Soil Health Project

Field Day Legume Handout