Clay trials on dryland dairy pasture improving nutrient retention

Our latest farm trials using clay as a soil amendment are starting to show positive results in improved nutrient retention. 

Inspecting root growth in the South Coast clay-incorporation trial with farmer Andrew Jenkins and his agronomist

Dr Brad Degens, senior soil scientist at the Department of Water and Environmental Regulation said that adding clays to pasture soils can improve water retention and help build organic matter, with potential benefits for reducing nutrient losses to waterways.

Brad has been working with dairy farmers Brad and Cherie Boley and agronomist Brooke Anderson to trial different rates of clays top-dressed or mixed with soils under pasture production. The Boleys provided the clays from two pits on their farm.

“The soils with clays added are starting to show improvements in nutrient retention and these vary depending on the clay properties,” said Brad.

“We haven’t yet seen any changes to pasture productivity. While clays can have immediate effects on improving some aspects of soils, we expect that other effects such as improving storage of organic matter will take several seasons to show up.” 

Spreading subsoil clay with high P retention to mix into sandy soils

Brooke Anderson, who manages the clay mixing trial for Western Dairy, said the application of orange clay at 150 tonnes per hectare (t/ha) had the dramatic effect of completely breaking water repellence. It also reduced the phosphate that could be leached by improving phosphorus retention capacity.

Top-dressing of this clay at lighter rates (less than 50 t/ha) had similar effects but only in the surface few centimetres of the soils.

During the winter-spring growing season we will continue to collect pasture growth measurements to assess the effects of the clay application over time and follow up with another round of soil sampling next summer.

Taking plant samples to measure pasture growth at the clay trials

The trials are funded through Healthy Estuaries WA – a State Government initiative to improve the health of our South West estuaries.The trials have been implemented in partnership with host farmers, the Lower Blackwood Land Conservation District Committee, and Western Dairy.