GroundCover™ Issue: 34
"It would be hard to design a better legume than butterfly pea," is Stuart Coaker's verdict. He's the Central Queensland grower who persevered with the colourful pasture pea when no-one else was too interested.
Now its value as a fertility-building rotation and an excellent grazing legume is generally recognised, thanks to its adoption by the Central Queensland Sustainable Farming Systems Project.
A suite of development sites across the central Queensland grainbelt has demonstrated in less than three years that butterfly pea (Clitoria ternatea) is the northern ley legume to match the subclovers and lucerne of southern Australia. More than 30,000 hectares are planted, indicating that growers have readily incorporated the legume into their rotation. And none too soon.
The answer to fertility decline?
Concerns about declining soil fertility levels drive a good deal of the current research effort for the 800,000 hectares of Central Queensland cropping country. The Open Downs and Brigalow scrub soils have shown over 25 years organic carbon and N declines of up to 40 per cent.
According to the farming systems project principal technical officer, Maurie Conway, some 700 legume contenders from around the world have been considered without outstanding success. "There's nothing much left in the cupboard that's adapted to clay soils. And I don't think there will be either."
Butterfly pea, however, has been proving its worth. Says project leader and Queensland Department of Primary Industries agronomist John Doughton, "one of the farmers working with us in the project demonstrated the weight gains cattie could achieve on butterfly pea. These were 0.91 kg/day, returning $194/ha from 89 days grazing. That farmer has planted 520 hectares of butterfly pea since."
Despite such advantages, butterfly pea didn't excite much interest in its first century in Australia following its introduction by Chinese miners during the gold rushes of the 19th century.
The breakthrough started when butterfly pea was evaluated on heavy clay soils in Central Queensland, under the Meat Research Corporation's 'legumes for clay soils' project and GRDC's 'ley legumes' project, with continued development and planting by Stuart Coaker at 'Lindley Downs'.
|Site||Soil total N 0-10cm (kg/ha)||Site comments|
|1. Queensland bluegrass||1027||Not disturbed — original total N level|
|2. Fallowed||470||40 years cultivation — total N has declined|
|3. Perennial grass pasture, planted 1992||683||Total N has risen slightly after 7 years of grass only|
|4. Butterfly pea, planted 14 Apr 1993||924||Total N after 6 years of butterfly pea|
|5. Butterfly pea, planted 23 Jan 1995||1092||Total N after 4 years of butterfly pea|
|6. Butterfly pea, planted 10 Mar 1996||659||Total N after 3 years of butterfly pea. Initial establishment was poor and plant population remained low.|
|7. Butterfly pea and grass, planted 13 Feb 1997||1081||Total N after 2 years of butterfly pea.|
|8. Butterfly pea, planted 10 Feb 1998||997||Total N after 13 months of butterfly pea|
Changes in soil nitrogen (total N) in eight paddocks with various aged butterfly pea pastures, grasses and continuous cropping (the fallow site) on 'Lindley Downs' measured in March 1999
"We originally trialed butterfly pea on 'Lindley Downs' as a ley legume that provided a natural source of nitrogen without the cost of synthetic fertilisers," Mr Coaker says.
Mr Coaker says he has tried most other legumes and finds that lab lab, lucerne and leucaena are excellent legumes in the right situation, but had their faults for use in the 'Lindley Downs' legume program.
High plant production key to nitrogen
"We were just looking for something to build the soil nitrogen up. We didn't intend on grazing it, but we were so impressed with its forage value we decided to harvest the seed and go into an expansion program," he says.
The benefits to soils of butterfly pea are easily seen from the table on p14, which shows the surface soil nitrogen levels from eight paddocks on 'Lindley Downs'. The first site has never been farmed, and this shows the 'natural' nitrogen levels, against which all the other nitrogen levels should be compared.
The soil nitrogen measurements clearly show the importance of high plant production in building up soil nitrogen,
rather than just the length of time that the plant is growing.
"You can see from the lower nitrogen levels at site 6, where a dry season gave poor establishment and low plant numbers, that a stand with a good plant population growing for a short time will capture more nitrogen in a soil then a poor stand, even if it is there for a long time," says Mr Conway.
The on-farm trials have developed best-practice establishment techniques in row spacing, plant populations and weed control.
Butterfly pea has now been adopted through the farming systems project as a possible ley legume for all of central Queensland, including on lighter soils, with the credibility and resources of the Queensland DPI and the other agencies backing it.
Mr Coaker's work in pioneering the development and extension of Milgarra butterfly pea has been recognised by industry and he was awarded the Tropical Grassland Society — Meat and Livestock Australia Pasture Award for development and extension of innovative pasture technology in April 2000. One-third of his property is currently planted to butterfly pea.
Contact: Mr Stuart Coaker 07 4984 6152