In the high rainfall zone, problems lie beneath the surface

By Richard MacEwan

Plentiful rainfall means high potential for crop production in the high rainfall zone, but only if crops can make use of the water stored in the whole soil profile. The cropped area in this zone has been increasing over recent years due to shifting markets and changing land practices that have overcome one of the immediate and obvious problems - surface waterlogging.

However, there are deeper, hidden and varied problems in the subsoil. Understanding what these are, where they are, what impact they have on yield and profit and how they can be managed is crucial to maximising the production potential in these areas.

Consequently, researchers from the Department of Primary Industry (DPI) are undertaking a scoping study over the next two years to map out and assess the priorities for subsoil management research in the southeastern high rainfall zone.

The project will review the extent and significance of the dominant physical and chemical subsoil constraints affecting high rainfall grain production in the GRDC Southern Zone.

This will provide the basis for GRDC to make decisions on possible further R&D investment in this area.

The project has just started and will be completed by April 2006.

The scoping exercise will be conducted on four fronts - consultation, review, soil investigation and priority-setting.

The research team will work with four cropping groups to determine local perception and management of subsoil constraints (past and present) and to select local areas for more intensive study. The four groups are Farmlink (southern NSW), Riverine Plains Inc. (NSW, Vic), Southern Farming Systems (Vic, Tas) and Mackillop Group (south-east SA). From each group, the research team needs to know:

This will comprise a region-wide review of existing soil information (state government datasets and regional agronomists" experience) plus a literature review of past studies on subsoil management.

A broad overview of the distribution of major soil types across the GRDC Southern Zone will be compiled from Victorian, South Australian and NSW government sources. The cropping areas in this zone that have above-500 millimetres average annual rainfall will be the study areas for review of subsoil properties.

The study will concentrate on regions that already have a high level of farmer engagement and progressive farming practices.

Soil investigations will involve limited local, intensive surveys on selected paddocks (including any opportunity to use pre-existing paddock scale survey and yield data).

Fieldwork will be carried out at a paddock scale for at least one site with each group. We will deploy farm quad-bike mounted sensors (Electromagnetic Induction, EMI and Gamma Radio Spectroscopy, GRS) to determine the variability of some soil properties. Survey and sampling will be carried out as close to harvest as possible (ripe grain and no further soil water use).

Selected soil samples will be analysed using traditional laboratory testing methods and it is anticipated that all samples will be subject to mid infra-red (MIR) spectral analysis to provide surrogate estimates for a number of physical and chemical properties.

Reference pits will be excavated and sampled to provide more robust soil profile data than that collected with narrow soil cores. These will also be used as a focus for farmer group engagement.

Analysis of the issues to develop research priorities for GRDC will be based on consultation and some basic spatial and seasonal modelling.

The remotely sensed data and available grower paddock records will be used together with field data to analyse the seasonal effects of weather, and compare with theoretical potential yields and estimated subsoil restrictions to crop yields.

The priority constraints for further investment will be assessed on a spatial area basis, seasonal factors and potential for improved returns based on a rating of the likely effectiveness of any future management solutions generated by future research investment.

The results of this analysis will be presented back through the farmer groups to review and validate priorities for submission to the GRDC.

For more information:
Richard MacEwan, 03 5430 4326,

GRDC Research Code: DAV 00056

Region South, North