AVOIDING soil degradation and reduction in crop and pasture growth associated with acidic soils is the major aim of a project using soil pH mapping.
Rural Solutions SA's Andrew Harding outlined the project - 'Innovative and cost effective solutions to the treatment of acid soils in SA' - at the 17th Symposium on Precision Agriculture in Australasia at West Lakes, Adelaide, last week.
The project is run through the Advisory Board of Agriculture with federal government funding.
"There are 1.9 million hectares of land susceptible to soil acidification in SA," he said.
"This includes land in the South East, Adelaide Hills, Kangaroo Island, east of Clare, from Laura to Melrose and on areas of the EP between Cummins and Port Lincoln.
"We are seeing a pH of below 5 in some paddocks."
He says the pH for optimal plant growth is at least 5.5. Much of the soil in acid-prone areas has a pH less than 5 in the top 0 to 10 centimetre layer and subsurface (10-20cm) soil acidity is also becoming an issue.
And there are fairly significant costs in overcoming issues with acidic soils.
"Lime has become more expensive in recent times and freight has also increased," he said. "There is a $45/t cost all up for lime, so a 2t/ha application equals a $90/ha cost."
By mapping the pH zones in paddocks, targeted applications of lime can be done, leading to input cost savings.
The project has been testing two soil pH mapping machines for SA soils and conditions.
"We have access to two soil mapping machines,'' Andrew said.
"The Veris pH detector is a commercially operated machine that measures soil in seven to 10 seconds. It was purchased from the United States in 2010 and can map 200ha to 300ha a day.
"The Veris pH manager is an on-the-go pH machine, and the only one of its type in Australia. It's on loan from the University of Sydney and samples soil pH every 25 metres. If the difference between two points is more than 0.5pH, then the machine discards the information because it could be gravel or straw it's picking up."
He has conducted an experiment to compare the machine's results with laboratory data.
"I looked at 24 soil samples that ranged from 4.5 to 7.5 pH,'' he said. "The correlation between the pH machine and the laboratory data was very good.
"The on-the-go machine correlation was slightly higher than the detector."
* Full report in Stock Journal, September 11, 2014 issue.
Paula Thompson
Stock Journal's markets editor.
Stock Journal's markets editor.
