- Spreading or delving involves incorporating a clay-based subsoil into a sandy topsoil that usually has less than five per cent clay content.
- It can significantly improve the productivity of light sandy soils by ameliorating unwanted effects of sandy soils on crop growth.
- Yields on soils that have had clay spread or have been correctly delved have increased by up to 130 per cent.
- Benefits include eliminating water repellence, improved weed control, reduced erosion potential and increased nutrient and water-holding capacity.
- Using the correct clay spreading and delving process is critical for success and to avoid any adverse impacts on productivity.
SARDI trials looking into the effects of soil amelioration on crop performance at Brimpton Lake, South Australia.
PHOTO: David Davenport
Primary Industries and Regions South Australia (PIRSA) soil and land management consultant David Davenport, from the department’s Rural Solutions SA division, says there are at least one million hectares of land in SA alone that would benefit from amelioration of sandy soils.
“Sandy soils have several known constraints including water repellence, compaction, low fertility and low water-holding capacity,” he says.
“We are finding that bleached, sandy subsoils, as opposed to topsoils, are particularly low in fertility and can be compacted.”
Mr Davenport says there are a range of different amelioration options that growers can use to overcome one or more of these constraints including spading, deep nutrition, incorporation of organic matter and the addition of clay.
GRDC-funded research in Western Australia has demonstrated significant benefits from the addition of clay to sandy soils. In soils with low soil organic carbon of less than one per cent, clay addition to produce a clay content of three per cent converted a non-wetting soil into one that wets uniformly. The average yield increase at this trial in Dalyup, WA, was 52 per cent over 15 years following the addition of 300 tonnes of clay per hectare.
A survey of WA growers found 87 per cent of respondents achieved yield increases between 0.25 and 3t/ha in cereals after claying.
“Adding clay will increase the cation exchange capacity, which is the ability of the sand grains to hold and exchange nutrients,” Mr Davenport says.
“This increases fertility and the clay particles in the soil increase the water-holding capacity and reduce repellence. This effect has been seen to last for more than 20 years.”
Incorporating organic matter also provides nutrients and may support increased soil biological activity. This may lead to improved soil structure and an increase in plant-available water.
PIRSA’s New Horizons trials at Brimpton Lake, Karoonda and Cadgee in SA have shown significant benefits from incorporation of mineral nutrients, organic matter and clay to 30 centimetres deep.
“All of the treatments improved yields; however, the best performers in 2014 and 2015 have been the incorporation of lucerne hay and/or mineral nutrients. Clay addition had mixed results, with deep incorporation significantly better than shallow incorporation,” Mr Davenport says.
“Based on these results, as well as growers’ experiences, growers who are dealing with particularly difficult sands can potentially double their wheat yields through amelioration.”
While research has been underway in WA for several years, new GRDC research in the 2016-17 External Investment Plan will look further into adapting these practices to south-eastern soils in the new project ‘Increasing production on sandy soils in low and medium rainfall areas of the southern region’.
David Davenport, PIRSA,
0427 201 956,
Ground Cover Supplement – 'Soil Constraints'
Clay spreading and delving Fact Sheet
Spread, delve, spade, invert (a best pracice guide to the aiddition of clay to sandy soils)
Watch nutrient levels following dry year
Take-no-prisoners approach to resistance ryegrass
GRDC Project Code