The challenge
On alkaline soils, chickpeas can produce an estimated 70 kilograms of fixed nitrogen per hectare. Given the benefit of this nitrogen to subsequent wheat crops, important agronomic, financial and environmental incentives exist to expand the cultivation of chickpea crops.
There is, however, one over-riding constraint to the broader adoption of this legume into cereal and canola crop rotations: acid soils. They present a dual challenge when it comes to cultivating chickpeas.
First, current cultivars require alkaline soils, which severely limits where chickpeas can be grown in Australia. Second, acid soils damage the plant root hairs that nitrogen-fixing rhizobia use to colonise the roots and form functioning nodules.
This pH sensitivity renders acid soils a constraint on both legume crops and rhizobia activity.
An urgent need was, therefore, identified for trait discovery work focusing on identifying chickpeas with acid soil tolerance capable of growing in acidic soil conditions.
The response
Over eight years starting in 2013, GRDC invested a total of $1.15 million in a project led by Murdoch University to identify chickpeas with acid tolerance to improve chickpeas’ adaptation to low pH soils. The project targeted both acid tolerance genetics in chickpea germplasm and in rhizobia activity.
Given the genetic bottleneck caused by the domestication of chickpeas, the project had a strong focus on wild chickpea material in order to access the genetic diversity needed for trait discovery work. This included targeting wild Cicer reticulatum and C. echinospermum species.
The success of the project also hinged on the development of viable assays to screen for tolerance to low pH and to manganese or aluminium toxicity. This involved the use of both controlled-growth conditions and field experiments. In addition, a hydroponic assay was developed that uses a solution of aluminium.
Up to 300 wild chickpea accessions were tested per year and ranked for tolerance to low pH and sandy soil conditions. In addition, rhizobia were also ranked for effectiveness on wild chickpeas in low pH, toxic aluminium and sandy soil conditions.
The impact
The project successfully identified sources of increased acid (aluminium and manganese) tolerance in wild chickpeas. It also identified rhizobia that are effective on this tolerant chickpea material.
Advances made in screening technology also proved valuable, with Chickpea Breeding Australia adopting the aluminium solution screening method for its own use. This will see tolerance to aluminium toxicity embedded in the breeding program.
The value to subsequent cereal crops of the extra nitrogen supplied by chickpeas has been estimated at $10.14 per hectare. When substituting for feed barley on acid soils, chickpeas stand to enhance farm profitability by an estimated $50/ha.
Economic analysis performed by Bob Farquharson & Associates found that the outputs from this project produced a net present value of $4.85 million. As such, the project will return $4.88 for every $1 spent over the next 25 years.
The project also contributed to international collaborations that are working to enhance chickpea tolerance to the most important abiotic and biotic stresses.
For example, it has built links with research groups at the University of California Davis, which also work on acid tolerance in chickpeas. The project also developed screening techniques for acid tolerance through a collaboration with the University of Nairobi. These techniques are being applied to screen chickpea cultivars grown by farmers on acid soils.
Looking forward, the project also identified a need for a more targeted search for acid-tolerant landraces and cultivars sourced from locations where chickpeas are an established crop on naturally acid soils, as occurs in Ethiopia and Kenya.
More information: view GRDC impact case studies.