Science e-newsletter: Breaking down subsoil acidity
Author: Toni Somes | Date: 08 Aug 2017
Recognising that subsoil acidity is a significant barrier to both crop and pasture performance, particularly in high rainfall environments (500 to 800mm annual rainfall), the Grains Research and Development Corporation has invested in an innovative research program investigating how to manage subsoil acidity.
Led by the New South Wales Department Primary Industries principal research scientist, Dr Guangdi Li, the project is researching changes in soil acidity at depth from application of varying soil amendments via deep ripping at different depths in the soil profile.
Surface application of lime is commonly used to manage topsoil acidity, however the slow movement of lime down the soil profile tends to lessen the benefit of lime on managing acidity in the subsoil.
A number of field experiments have been established to monitor crop growth and soil chemical, physical and biological processes in response to varying soil treatments across different soil and climate conditions in southern NSW and northern Victoria.
The data will improve understanding of the soil-plant interactions, which factors drive the differences in crop response to the various soil treatments and the residual value of the soil amendments.
Soil amendments tested include a range of inorganic amendments, such as lime, magnesium silicate, reactive phosphate rock, calcium nitrate, dolomite, gypsum; and organic amendments, such animal litters and manures, composts, lucerne pellets, crop residues.
Field trials are investigating the impact of surface liming and application of organic amendments in the subsoil at 10 to 30cm depth, in combination with deep ripping under different crops.
A customised built ripping machine, known as the 3-D, delivers soil amendment at dual depths and provides the ability to place lime and other soil amendments at depths from 10 to 30cm in the subsoil.
The 3-D ripping machine, constructed from a Grizzly Ripper, features dual boxes to hold two different types of soil amendments with associated dual feeding systems to deliver up to 4 t/ha of lime and up to 20t/ha of organic amendment product.
Deep ripping and soil amendments
Initial data from field experiments undertaken over the past two years showed a great crop response to deep ripping and application of soil amendments in wheat, barley and canola at seedling and flowering stages.
Deep ripping with lucerne pellets produced more seedling dry matter than surface liming in the first year.
“We did not expect a huge crop response from deep placement of soil amendments in the first one to two years as soil amendments would take years to ameliorate subsoil acidity,” Dr Li said.
“The unexpected crop response to deep ripping of lucerne pellets in the first year is likely due to availability of crop nutrients rather than changes to subsoil acidity. We are planning to undertake more tests in the glasshouse to distinguish crop response from nutrients or changes to subsoil acidity with application of lucerne pellets.
“Observations of the application of novel materials such as magnesium silicate and calcium nitrate in improving subsoil acidity look promising in the first year, but we need to collect longer term data before drawing any conclusions for field recommendations.”
The research team is particularly interested in understanding the residual effects of the soil amendments and how they improve crop productivity, such as improving efficiency of nutrient and water use.
The GRDC project is led by NSW DPI, in collaboration with La Trobe University and Charles Sturt University, CSIRO, Farmlink Research, Holbrook Landcare, Riverine Plains and Southern Farming Systems.
Project Code: GRDC DAN00206
Dr Guangdi Li, Principal Research Scientist, DPI,
02 6938 1930