Soils ain’t soils, even in one paddock

By Rick Bayne

SOILS AIN’T necessarily soils, even within the confines of one paddock.

And knowing the soil profile will allow farmers to optimise soil performance and smart fertiliser applications.

Andrew Whitlock from Precision Ag Services told WestVic Dairy’s Dairy Innovation Day, held in Warrnambool last month, how the soil profile on farms can vary from one extreme to the other, even within single paddocks.

Mr Whitlock farms near Rokewood south of Ballarat, with 1600 hectares of permanent pastures that support a merino sheep base plus 400 ha of cropping.

While what happens on his farm might not necessarily apply to a dairy farm, Mr Whitlock said most farmers of all persuasions are surprised by the variability of their soils.

“I’ve done work with dairy farms and found enormous variability in nutrient levels across paddocks,” he said.

“Pretty much everywhere we map people are surprised by the level of variation in paddocks. It’s crazy not to address it. There’s technology out now that can easily manage it through variable rate spreading, spraying or seeding.”

Mr Whitlock said his farm had processes in place to manage soil acidity through grid pH mapping, associated variable rate lime application maps, lab-based grid samples and phosphorous samples.

He also told the innovation day about using EM38 soil conductivity maps for mapping soil textural zones and different soil types across paddocks and then building variable gypsum application rate maps and linking that with elevation data from GPS to build surface drainage plans.

“It’s all done by contractors. I get someone else to do it and get the benefits. The only thing I need to do is load the map into my tractor to do the spreading, which is easy,” he said.

“The mapping itself is quite expensive but it pays for itself by allowing smart fertiliser applications.”

“With my variable rate lime and gypsum, the savings I get with those products alone pays for the mapping service plus leaves me cash-flow positive. I can save 30–40 per cent on my lime application bills by going down the path of mapping.”

Mr Whitlock said farmers need to know if they have an issue with their soils and then be able to manage it properly.

“I want the right data for each management action,” he said.

His farm has soils ranging from deep sands to clays and paddock sizes much larger than dairy farms.

“It’s tricky to get a variable rate application map in dairy with small paddocks; but we need to start with our eyes open and see what variability we have and understand nutrient loads and then if the pay-off is high enough a solution will follow.”