INCREASING seeding rates and sowing wheat varieties earlier were identified as strategies for success in a shallow stony soil trial conducted for the past two seasons in the northern Mallee.
Supported by Wunkar Agricultural Bureau and funded by the SA Murray-Darling Basin Natural Resources Management board and the National Landcare Program, Loxton-based agronomist Chris McDonough conducted the trial on Wunkar farmer Peter Heinrich’s property.
Mr McDonough said the trial’s purpose was to evaluate management strategies that growers could utilise on shallow stony soil areas, such as seeding times, seeding rates and targeting short versus mid-season varieties, to maximise yields and minimise risk in seasons with higher moisture stress.
“Shallow stony soils are a large percentage of SA cropping soils and it has low plant available water holding capacity. This means that crops and pastures are highly vulnerable to periods of moisture stress throughout the growing season,” Mr McDonough said.
The trial sites were sown with early wheat variety Emu Rock, and later maturing wheat varieties Yitpi in 2016 and Estoc in 2017.
In 2016, trial areas were sown on May 12 and May 27, and in 2017 wheat varieties were sown on May 20 and July 7, because of the late season opening rainfall.
Mr McDonough said it was previously thought that a lower number of plants a square metre on stony soils would result in reduced soil water demand from crops, and preserve more moisture into spring when the soil type was most vulnerable to moisture deficit.
But the trial found plots sown at a lower seeding rate of 40 kilograms a hectare to 50kg/ha compensated by growing more tillers, leading to a similar level of stems and heads as the higher seeding rate plots going into spring.
“In the wet 2016 season, the higher seeding rate plots averaged 10 per cent higher yielding,” Mr McDonough said.
“The dry finish in 2017 led to higher head abortion in the low seeding rate plots and the plots with a higher seeding rate, at 60-75kg/ha, had more primary stems with fuller heads, and less tillers,” he said.
Increased salt levels revealed
Third-generation farmer Peter Heinrich, Wunkar, has battled the challenges of cropping on shallow stony soil for more than 30 years, so was eager to help conduct a trial on his property to find solutions.
Mr Heinrich said there had been limited research conducted on stony soils in low rainfall regions receiving less than 300 millimetres a year.
Mr Heinrich is a conventional farmer and crops about 2600 hectares, and also runs 1400 Merino ewes.
“We sow at about 55 kilograms a hectare to 60kg/ha but the higher sowing rate in the trial was at about 70kg/ha and that is just too high for us because of the risk,” he said.
The trial area also exhibited large bare patches that did not grow any crop during the two seasons.
Soil tests revealed that these patches had up to five times the salinity levels in the top 10 centimetres of soil when compared with the surrounding crop growing areas.