"I know about sodicity - that"s where all the soils run together and become as hard as hell. Water won"t get into it... The paddocks aren"t good when they"re worked in the wet - this leads to sodicity. Boron occurs on lower lying grounds, but I don"t know much about it - I only know what they tell us." - Victorian project reference group member
By Roger Armstrong
As the above quote suggests, many graingrowers on the neutral and alkaline soils that dominate the grain-growing regions of South Australia and Victoria are aware of sodicity and high boron in cropping paddocks. Recent research indicates that these "subsoil constraints" are often a major cause of poor and variable yields.
But despite research in the past few years increasing scientific knowledge and awareness of subsoil constraints, how can growers manage cropping soils with subsoil constraints?
A project comprising researchers and advisers from DPI Victoria, the South Australian Research and Development Institute (SARDI), the University of Adelaide, in partnership with farmer groups such as the Birchip Cropping Group and Wimmera Farming Systems (BCG) in Victoria, and the Eyre Peninsula Farming Systems (EPFS) and the Yorke Peninsula Alkaline Soils Groups (YPASG) in South Australia, hopes to answer this question.
Project leader Dr Roger Armstrong (DPI) believes that growers try to maximise the yield potential of their system as determined by rainfall, by either ameliorating the subsoil to overcome the factor/s limiting crop growth and water use; or they can "live with the problem" and adjust inputs to better match the real production potential of the soil, and thus maximise their profitability (rather than total production).
The DPI"s Kate Nichols will play a key part in the project. Ms Nichols will assess the extent to which farmers achieve an increase in their knowledge of subsoil constraints and, most importantly, translate this knowledge into improved profitability of their cropping practices. The evaluation involves activities including a large-scale longitudinal survey of growers (in conjunction with the Birchip Cropping Group/Wimmera Farming Systems annual members" survey) as well as in-depth interviews with grower/adviser reference groups conducted at the beginning and end of the project.
Preliminary results from the evaluation have been enlightening and have already influenced how we are approaching extension activities. The initial evaluation revealed that some growers know more about the "hell" of subsoil constraints than we first anticipated (see above quote). Farmer knowledge is far from uniform however, and this is what the project seeks to address.
Other key points revealed from the evaluation include:
Subsoil constraints to crop water-use and production may be akin to how Morpheus describes the Matrix to Neo: "Knowing there is something wrong ... where you can"t explain it ... but you can feel it, like a splinter that drives you mad."
Dr James Nuttall, of DPI Horsham, says: "Alkaline soils by their very nature possess multiple physical and chemical constraints, often occurring simultaneously." This makes it difficult to identify causal relationships between a particular subsoil property and crop production. Knowing what is limiting the crop is necessary in order to identify possible solutions.
In unravelling this question, Dr Nuttall, along with Damien Adcock, of the University of Adelaide, is conducting an extensive survey of the linkage between crop production and soil characteristics in a large number of farmer-sown paddocks. This link is being established by using specialised statistical methods, which are specifically designed to analyse data where strong correlation exists between the potential soil constraints.
This technique has been successfully used for wheat growth and alkaline soils in the Birchip region, where sodicity and salinity, rather than boron toxicity as previously believed, were the main soil factors limiting cereal yields. The project survey extends across several major soil types used for cropping in north-west Victoria and South Australia and covers a wide range of crops including wheat, barley, canola, lentil and chickpea.
Large-scale trials on farmers" paddocks will be used to evaluate and demonstrate the effectiveness of strategies to manage subsoil limitations to crops. These trials will provide a platform to simultaneously ascertain why, and under what circumstances, these amelioration strategies will work, or whether the nature of the particular subsoil constraint is so severe that cost-effective management options are not feasible.
Four trial sites have been established to begin in the 2004 season: at Birchip (southern Mallee) and Lubeck (southern Wimmera) in Victoria and Darke Peak (Eyre Peninsula) and Stansbury (Yorke Peninsula) in South Australia. These four sites cover environments ranging from 350 millimetres to 500mm rainfall and neutral sands to highly alkaline/sodic clay soils.
A key aspect of these core evaluation sites is input by a local reference group, drawn from the membership of the local farmer and TopCrop groups.
The reference group will assist the project team with both site and treatment selection and help provide guidance on site management. It will also help to champion the trials and assist with communicating findings.
Treatments such as deep ripping/calcium injection; application of composted organic matter and deep nutrient treatment will be compared to a district practice control. While all of these treatments have been demonstrated to be effective in improving crop growth in some environments (for example, team member Dr Nigel Wilhelm has demonstrated the large yield responses to deep nutrient placement on the Yorke Peninsula), the project aims to assess the potential of these management strategies across a much greater range of soil and crop types.
A more novel treatment being used in the Victorian trials is the use of Sulla, a biannual legume, as a "primer plant". In addition to providing value as a pasture legume, the "primer plant" will hopefully create biopores into dense clay subsoils, which can then be exploited by following crops.
It is anticipated that as new varieties specifically bred for tolerance to specific subsoil constraints, such as boron- and salt-tolerant lentils, become available for large scale plots, they will also be tested in the trial.
The impact of subsoil constraints can vary markedly with soil and crop type, therefore a key output of the project will be the development of a user-friendly decision support tool to empower growers to assess the likely impact of subsoil constraints and potential management options for their paddocks.
This tool will rely heavily on information gained in the survey and core trials and subsequent economic analysis, as well as using information on subsoil constraints developed by other projects throughout Australia.
Diagnostic schools will be conducted to enhance the skills of growers and advisers to understand the nature of the interaction between various subsoil constraints and crop performance, as well as developing the skills needed to identify potential constraints in the field. These schools will be complemented with more traditional extension strategies such as presentations at targeted field days, Farming Systems Groups events such as the BCG, YPASG and Minnipa Agricultural Centre field days and soil pits, as well as more modern communication strategies such as web links.
Growers and their advisers will also be able to assess for themselves the effectiveness of selected amelioration treatments through a series of on-farm testing activities coordinated by regional agronomists such as Tony Fay (DPI) in Victoria and Sam Doudle (EPFS) in South Australia.
Ultimately, economics (dollars) will determine the particular strategy adopted by growers.
The project economist, Fiona Best of the Birchip Cropping Group, is compiling historic profiles of selected enterprises. Her analysis will include a number of factors that influence the comparative costs of different management - amelioration strategies, including capital requirements, transport costs of ameliorants, residual value of treatments and options for changing crop types.
This latter point will be important as many growers in the target area currently do not grow high-value pulses and oilseeds. A key aim of the project is to determine whether overcoming particular subsoil constraints will also help reduce the risks associated with these crops. When collated, this information will be used to develop a gross margin analysis, including a sensitivity analysis that accounts for different yield-response scenarios.
For further information:
Victoria: Dr Roger Armstrong, 03 5362 2336, firstname.lastname@example.org
Dr C. Bell, BCG, Birchip, 03 5492 2787
South Australia: Dr N. Wilhelm, SARDI Adelaide, 08 8303 9353
Dr A. McNeill, University of Adelaide, Roseworthy, 08 8303 7879.
GRDC Research Code: DAV 00049