Nutrient benefits of clay the next step
GroundCover™ Issue: 113 | Author: Melissa Williams
- It is estimated that three million hectares of water-repellent, sandy-textured soils in Western Australia and South Australia could benefit from clay application
- Clay spreading in WA is economical if the clay source is within half a kilometre of the area where it is to be applied
- Pre-application tests of both soil and clay are important to determine clay rates and manage post-clay crop nutrition
Clay spreading is an effective ameliorant for many of the constraints that occur on water-repellent deep sands and sandy duplex soils in Western Australia and South Australia.
But at a cost of $700 to $900 a hectare (or more in some areas) the expense can be prohibitive and often results in only small areas being treated in any given year.
Delving of subsoil clay to the surface is a cheaper option, but is only suitable if the subsoil clay is within 60 centimetres of the surface.
Researchers estimate about 160,000ha of sands with water-repellent topsoil in WA and SA have by now been treated with clay-rich subsoil.
David Hall, Department of Agriculture and Food, Western Australia (DAFWA) senior research officer at Esperance, says long-term trials show clay spreading will invariably boost the productivity of water-repellent sands.
He says these trials have shown consistent yield increases due to claying over the past 14 years.
Mr Hall says claying achieves yield increases by overcoming constraints that include:
- uneven distribution of soil moisture leading to poor or staggered emergence of crops and weeds;
- low nutrient-holding capacity;
- potassium deficiencies; and
- wind erosion.
“There is no doubt there are big crop production benefits to be had from spreading clay or delving subsoil clay,” he says.
But the next frontier of GRDC-funded research through the More Profit from Crop Nutrition (MPCN) initiative is to explore the potential for improved crop nutrition management after clay application.
Mr Hall says this is a new area of research and there may be benefits from increasing nutrient retention and availability, reducing nutrient leaching, and gradually raising crop yield potential and soil organic matter levels.
Mr Hall says that through the MPCN project, initial sampling of 43 WA paddocks treated with clay showed some had a high phosphorus retention index (PRI), which makes phosphorus less available to crops in the short term.
He says other clays were able to supply enough potassium and/or sulfur to change the soil from deficient to adequate for these nutrients.
No major toxic – salt or boron – properties were found in the clays tested (but high levels can often be found in low-rainfall mallee soils).
Based on these preliminary findings, DAFWA is recommending claying material be tested prior to spreading and that tests include standard nutrients, percentage of clay and boron, and PRI. These tests can be carried out by all major soil-testing laboratories.
Mr Hall says 10 to 20 per cent of the WA clay samples assessed through the MPCN project had a high PRI (greater than 100 millilitres per gram), which affects phosphorus availability and highlights the need to adjust phosphorus rates in the first few years after claying.
“Also, because claying has increased crop yield potential, there may be a need for extra nutrients – including nitrogen – to meet the higher demand,” he says.
“An experiment at Dalyup, near Esperance, is testing this out in 2014.”
MPCN field and laboratory research in the next two years will further investigate the relationships between clay rates and types and incorporation methods on nutrient availability and crop nutrient uptake on a range of sands across WA.
Mr Hall says researchers will also revisit long-term clay trial sites and study the paddocks of growers who have been using clay for long periods to assess how crop nutrition management has changed post-treatment.
“We want to develop soil fertility trends and produce more robust recommendations for growers about how to adjust nutrient strategies after clay enhancement and cultivation of sandy soils,” he says.
“If clay sources contain enough of some nutrients to meet crop needs, it could represent big savings for growers.”
08 9083 1111
Dr Richard Bell, MPCN Murdoch University
08 9360 2370
DAFWA – Claying to ameliorate soil water repellence:
Delivering solutions for water repellent soils:
GRDC Project Code UMU00042