Subsoil acidity trial work is underway at Rokewood in south-west Victoria at a site where soil acidity is affecting the soil depth to 30cm. The trial reflects many soils across south west Victoria where the pH varies with depth and the acidity affects the 10 to 20 cm depth, where previous lime applications have not reached.
The soil pH (Ca) across the trial site at the 10-20 cm depth averages 4.1, the topsoil at 5.1 reflecting the use of previous applications of lime and the 20-30 cm depth, 4.7. A soil pH above 5.5 in the top 0-10cm is desirable for allowing deeper lime movement and for removing yield constraints.
Deep ripping and surface application of lime will indicate what acidity penalties are incurred from sub-surface acidity and if deep ripping is worth the expense rather than applying high rates of lime to saturate alkalinity to allow it to move into the deeper layers.
Lisa Miller, research and extension officer at Southern Farming Systems said: “Superfine lime from NSW has been used in the trial and it will be interesting to see how quickly it works compared to the coarser south-west lime product that has been applied to the rest of the paddock.”
The paddock was also low in potassium and strips of potassium have been applied by the farmer, Andrew Whitlock, to explore responses. Lisa Miller said, “Potassium responses in crops are generally not seen but we have found in many trials that if acidity is limiting production then you will rarely see fertiliser responses.”
Lisa explained that fertiliser doesn’t substitute for lime and vice versa, both are needed if they are below critical levels for plant growth. Organic amendments of lucerne pellets have also been deep ripped into the acid soil as a lime alternative that is expected to raise pH due to its alkalinity. This trial is part of a network of GRDC funded trials sown across NSW and Victoria and is led by NSW Department of Primary Industries in collaboration with farming groups in the hunt for alternative liming products and solutions to subsoil acidity.