Investigating acidity in sub-surface soils

Father and son duo Neil and Charlie Vallance are farming in the high rainfall, high yielding region of Western Victoria. Purchasing this farm in April 2018, it was previously managed as an Australian phalaris pasture system with no history of lime addition for pH management or fertiliser inputs.

Following on from surface lime applications in 2018, Neil and Charlie wanted to investigate potential variation in pH down through the soil profile, in particular what was happing in the sub-surface layers.

Kirsten Barlow from Precision Agriculture explained that paddocks were initially grid sampled (0-10cm) in 2018, followed by a Variable Rate (VR) lime application. The paddocks were then re-sampled (using the same GPS referenced locations) in 2021. These grid soil sampling results are summarised in GRID SOIL MAPPING HELPS NEW FARM DEVELOPMENT – Southern Farming Systems (sfs.org.au)

Following the remapping, additional soil samples were collected from 3 paddocks in January 2022. These segmented samples were divided into 0-5 cm, 5-10 cm, 10-15 cm, and 15-20 cm intervals.

“This sampling strategy is recommended for detection and monitoring of acid throttles and sub-surface acidity. The samples were tested for pH CaCl2 and were strategically selected across the paddock based on the change in pH between samplings and the variation in Cation Exchange Capacity (CEC) of the topsoil,” said Kirsten.

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