There are an estimated 160,000ha of soils on Lower Eyre Peninsula that have known soil constraints that negatively impact on agricultural production that can be addressed through current soil modification techniques. These include soils with poorly structured subsoils and sandy soils with low water holding capacity and poor fertility.
In the past 2 or 3 decades research organisations and farmers have conducted trials and have applied various soil modification techniques in an attempt to address these constraints. There has been limited review of the success or otherwise of these operations in the long term. As a result there is little understanding of the benefit of treatments or of their longevity. Responding to increasing levels of interest in soil modification by group members the Lower Eyre Peninsula Agricultural Development Association (LEADA) developed a project to undertake a review of soil modification in the district. The outcome was to develop some guidelines to support farmers in making decisions on which soils can be modified, the best treatments and likely benefits. Funding was obtained from the Eyre Peninsula Natural Resource Management Board to assist in this work.
Summary of Results and Key Messages
(refer Case studies for more detailed analysis)
- The soils most at risk of a changing climate also offer the greatest opportunity to increase agricultural production through better use of the available soil moisture and this can be increased through soil specific modifications
- Current crop water use efficiency is the greatest indicator of the likely response to implementation of soil modification treatments – crops with low water use efficiency are more likely to provide the greatest response
- The greatest benefits to production have resulted where amelioration of the major constraint in the subsoil has been achieved
- The deep incorporation of organic matter accelerates changes to soil properties following claying of sandy soils
- Shallow mixing of ameliorants delivers some benefits only where constraints are also shallow
- Clay application increased soil pH and exchangeable cation exchange capacity
- Spading delivers mixed results depending on the nature of the soil and the amount of mixing of soil horizons involved in the spading process. Changes to soil chemical properties may not persist and the major constraints and the depth of influence needs to be understood prior to implementing spading programs. However, spading is a cheap option to mix soil horizons addressing low soil carbon in bleached A2 layers and potentially water repellence in the short term.