Unlocking crop potential

By Chris Gazey, Bill Porter, Jim Dixon, Bob Gilkes, Mohammed Hamza, Linda Leonard and Cameron Weeks

A five-year project is being undertaken between the Department of Agriculture Western Australia and the University of Western Australia to help in the management of subsoil constraints to lift productivity and improve environmental outcomes for the agricultural land in the state"s south-west.

A large group of natural resource management professionals, agricultural and soil scientists, economists and extension experts, in collaboration with grower groups, will develop:

This project is based in the areas used for winter cereal grain production, including the higher rainfall zone. The winter dominant rainfall ranges from 750 millimetres near the west coast to 300mm a year at the eastern edge of the wheatbelt.

In conjunction with two other WA based projects in the SIP08 initiative, this work covers a wide range of soil and landscape systems.

A large component of this work will be to raise awareness among growers of the importance of good subsoil condition which, in the drier parts of WA, allows roots to access moisture at the end of the growing season (when it is often limiting) and thus makes a substantial contribution to yield and profit.

In wetter areas, better subsoil conditions assist root growth through minimising waterlogging.

The project has two major focus areas. We will be working with the Mingenew Irwin Group (MIG) and Corrigin Farm Improvement Group (CFIG) to determine the information growers need, and to rigorously test the usefulness of the information produced.

Once the two key groups, which are both members of the Grower Group Alliance in Western Australia, have tested the information products, the alliance network will be used to help disseminate the information.

We will maintain our close working relationship with growers in the Liebe group by continuing our subsurface acidity research and development work (GRDC Project DAW00014) and also our relationship with CFIG and other growers through the soil structure and compaction research in GRDC Project DAW00002.

This subsoil constraints project has just begun, with new research staff only recently appointed. The spatial analysis team has begun to develop initial maps of subsoil constraints.

This is achieved by interrogating the WA soils database and combining models with landscape position and other datasets.

The subsurface aluminium risk map for the south-west of Western Australia is an example. Aluminium toxicity is a major constraint in many sandy soils of WA, produced by low soil pH particularly in the 10 to 25 centimetre layer.

Several trials using different lime sources and tine spacing to investigate the rapid treatment of subsurface acidity by deep lime placement were established in 2003 and 2004. Up to 1.4 tonnes/hectare of liming material was incorporated using a modified airseeder and deep ripping bar.

The trials are large scale and the assistance of the collaborating growers is greatly appreciated.

In other work, Dr Mohamed Hamza at the Merredin Dryland Research Institute has confirmed that using a deep ripper with a shallow leading tine to break the surface reduces the energy required by 17 and 10 percent for clay and sandy soils respectively.

An unexpected bonus from this approach is that the soil clods are significantly reduced, which means more energy can be saved because seedbeds do not require further treatment. The system developed for this work will also be able to incorporate more than one ameliorant to different depths.

Project staff and invited experts have made a series of presentations to Regional Crop Updates and soils workshops to raise awareness of the importance of subsoil constraints.

A working list of constraints for WA has been developed, and for each constraint the risk that the subsoil is affected now, or will be in the future, needs to be determined.

Additionally, our understanding of how to manage or avoid the constraint developing will need to be determined.

Potential subsoil constraints are:

Deep ripping on sandplain soils to remove compaction pans in conjunction with tramline farming may further benefit from incorporated lime. The structure of heavier soils may also benefit from the incorporation of gypsum and other materials.

In the meantime, we strongly encourage growers to understand the chemical and physical constraints of their soils by taking soil samples from below 10cm and inserting a thin rigid rod into the soil as far as it will go when moist to give an indication of physical constraints.

Pits excavated in mature crops provide a direct indication of how effectively roots exploit soil resources. A good knowledge about the condition of their soils will enable growers to take the appropriate action to improve subsoils.

There are several WA-based projects in the GRDC initiatives on Combating Subsoil Constraints (SSC), Precision Agriculture (PA) and Nutrient Management Initiative (NMI). There are good signs that effective collaboration will develop between these projects.

To further develop synergies, more than 33 people working in these initiatives met in June to share information and project aims.

In addition, a representative from each of these initiatives sits on the WA Precision Agriculture Steering Committee and every effort will be made to ensure that appropriate PA techniques are used in research and development by the SSC and NMI projects.

For more information:
Chris Gazey, 08 9690 2000, cgazey@agric.wa.gov.au

Chris Gazey, Bill Porter, Jim Dixon, Mohammed Hamza and Linda Leonard are with the Department of Agriculture, Western Australia. Bob Gilkes is with the University of Western Australia and Cameron Weeks is with the Mingenew Irwin Group.

GRDC Research Code: UWA 00081