The little legume that could
Chickpeas can mine that vital phosphorus
AUSTRALIA boasts some of the Earth’s most ancient soils, with much of its phosphorus locked away.
But new research from the University of Western Australia has shown that chickpea, known for its nitrogen-fixing capabilities, also has some varieties that can efficiently make phosphorus available to crops.
Some early clues came from looking at some species of banksia, capable of producing elaborate flowers on seemingly quite poor soils suggesting something was occurring at a chemical level, and also around root structure, that was unlocking bound phosphorus, which led to exploring traditional cropping species like chickpea.
Hackett Professor Kadambot Siddique, of the UWA Institute of Agriculture and Environment, said his team has been exploring a genetic core collection of chickpea that represent all major genetic lines of the crop, to find the lines most adept at unlocking phosphorus within soil.
The insight could potentially change agricultural fertilising processes worldwide, including for intensive, broadacre farmers.
“Australia has very ancient and weathered soils in many parts, so generally speaking, the phosphorus has been very low, so when the first white settlement came in we tried many types of things, many crops: wheat, barley, canola,” Prof Siddique said.
“And when we got these crops, largely from England, they were poorly adapted, and we started breeding our own varieties.
“But one of the problems is the soil is very poor, so when we first started clearing the land, we got some respectable yields at that time, but soon it declined because of lack of nitrogen, phosphorus, micronutrients.
“Farmers then started to apply phosphorus to the soil: because wheat and canola and all those crops need a lot of phosphorus. Based on analysis, a lot of that phosphorus is bound in the soil.”
For every 100kg of phosphorus applied to a crop, very little of that is available to the crop. A cycle of repeat applications would result in a high total phosphorus content in the soil, but still very little available.
And it’s more complex than simple soil pH in making that phosphorus bioavailable.
It’s an interesting chemical process that some plants,
❝can Chickpea mobilise the phosphorus bound in soils by exuding carboxylates... — Prof Kadambot Siddique
such as chickpea, can trigger.
“Chickpea can mobilise the phosphorus bound in soils by exuding carboxylates such as malonate from the root system, which are particularly important for phosphorus acquisition in low phosphorus conditions,” Prof Siddique said.
While it is difficult to measure the presence of this in the soil, as part of the research the team found that its presence could be measured through the manganese concentration in mature leaves. The chickpea varieties that have been most effective in unlocking phosphorus have a bushier root zone (rhizosphere) and efficient transpiration.
Professor Siddique said this research would have a big impact in global legume production through the development of more phosphorus efficient chickpea cultivars.
“Chickpea fits in well to farming systems, where soil-bound phosphorus can be mobilised and made available for succeeding cereal and oilseed crops,” he said.
The new information will offer benefits for rotational broadacre cropping and intercropping systems.