Researchers have discovered that lifting soil pH above a critical threshold of 4.8, in combination with deep cultivation, can significantly improve yields on Western Australia’s non-wetting forest gravel soils.
This is one of the findings from research in recent years aimed at improving crop germination and productivity on these soil types, which are estimated to account for about 2.4 million hectares of the State’s farming area.
“Trials have explored opportunities to reduce the impact of non-wetting and soil acidity and their effect on phosphorus availability,” Department of Agriculture and Food (DAFWA) researcher Derk Bakker told Perth’s 2014 Agribusiness Crop Updates earlier this year.
The research has been funded largely by the Grains Research and Development Corporation (GRDC) project Delivering agronomic strategies for water repellent soils in Western Australia, led by DAFWA.
Trials have also been supported by the GRDC’s Regional Cropping Solutions Networks, the South West Catchments Council and the Shire of West Arthur.
“Non-wetting soils – caused by the presence of waxy surfaces on the sand particles - can be a major impediment to crop germination and thus productivity in many WA soils, including forest gravels,” Dr Bakker said.
“In addition, many forest gravels tend to ‘hold on’ to phosphorus, which limits the availability of this nutrient to crops, despite high soil test phosphorus levels.”
Dr Bakker said non-wetting and soil nutrition trials at Darkan, initiated by former DAFWA researcher Bill Bowden, had found that soil pH had the greatest impact on yield and availability of phosphorus at seeding time.
He said the pH level 4.8 had been found to be critical and levels below this had a very detrimental effect on crop yields.
“This ‘cliff face’ effect in forest gravels appears to be different from the effect of soil acidity in other WA soil types where there seems to be a more gradual reduction in yields with declining pH,” Dr Bakker said.
He said adding lime and improving the soil pH from 4.3 to at least 4.8 had a big impact on crop yields, even when no phosphorus fertiliser was applied.
“Yield improvements were even greater when soil cultivation also occurred,” Dr Bakker said.
“We hope that the combined beneficial effects of lime and cultivation will be sufficient for growers to overcome phosphorus deficiencies, although phosphorus may still need to be applied in some years.”
The type of cultivation used in the Darkan trials was a one-way, three disc plough that mixed rather than inverted the soil.
“While this plough did not greatly improve the wettability of the soil, the cultivation facilitated root growth and improved water penetration, which would have enhanced the accessibility of phosphorus to crops,” Dr Bakker said.
He said research had shown that wetting agents applied to forest gravels were sometimes effective and economical.
“Timing of application in relation to rainfall appears to be important and best results were achieved when wetting agents were applied just before rainfall,” he said.
Derk Bakker, DAFWA
08 9892 8444
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
Caption: DAFWA researcher Derk Bakker after digging in a ‘flume’ to measure water run-off and making channels across the trial plot to trap the water.
GRDC Project Code
West, North, South