Some growers have been able to reduce N inputs for at least three years following the placement of manure into the subsoil. Trials in Victoria’s High Rainfall Zone by Southern Farming Systems are showing promising signs of multiple benefits from subsoil manuring.
Originally, subsoil manuring was primarily for improving the physical properties of heavy clay soils. Placement of manure at around 40 – 50 cm depth produces changes in the subsoil structure that increases the Plant Available Water Capacity, and therefore water limited yield potential for the paddock.
It turns out that subsoil manuring also seems to be an effective way to provide several years nitrogen (N) supply. The chicken manure used in the trial had a N content of 3.8%, and was applied in a deep band (accompanied with a deep ripping) at rates of 10 and 20 tonnes per ha. Some growers have been able to successfully reduce N inputs while achieving yield increases following subsoil manuring.
The practice of subsoil manuring is being extended in the HRZ this season (beyond the trials), with the introduction of custom machinery capable of working on a larger scale. South Australian trials are also underway at Kybybolite and Joanna.
An episode of Groundcover TV explains more about the treatments used and results seen in the subsoil manuring trial – GCTV12: Subsoil Manuring’s positive impact on crop yields
An economic analysis of the subsoil manuring trials: Amending sodic soils using sub-soil manure: economic analysis of crop trials in the high rainfall zone of Victoria, Peter Sale and Bill Malcolm, AFBM Journal Vol 12 – 2015.
Renick Peries, VIC DEDJTR, Roger Armstrong VIC DEDJTR & Chris Sounness, BCG.