DAV00149 - 2016.05.07 Understanding the amelioration processes of the subsoil application of amendments in the Southern Region
Most cropping soils in the Southern Grains region contain one or more subsoil physicochemical constraints such as high boron or sodicity that can limit root growth and hence water and nutrient use by crops. As a result, grain yields are significantly reduced, resulting in major financial penalties for growers and poor environmental outcomes such as severe waterlogging and nutrient loss to ground water. A range of management practices including deep ripping, applying gypsum, or use of ‘primer-crops’ have been tested to overcome subsoil constraints, usually with variable impacts on grain yields and often resulting in net financial losses to growers. Due to this uncertainty, many growers have opted instead to reduce variable inputs or restrict crop choice to protect profitability rather than chasing higher yields.
Research dating back to the 1990’s demonstrated that spectacular improvements in grain yields on soils containing physicochemical constraints could be achieved by placing organic matter and nutrients at depth. La Trobe University extended this research to develop the ‘subsoil manuring’ concept. Subsoil manuring can produce large (up to 70%) improvements in grain yields lasting several years after applying large quantities (20 t/ha) of organic matter in slots at depth in dense clay soils (Gill et al 2008).
Despite the potentially step change in crop yields that can be achieved by subsoil manuring, practice change by the grain industry to date has been limited due to several key constraints (Nicholson et al 2015) such as a paucity of in depth economic assessments of these major intervention approaches and fine tuning of the approaches to improve logistics and reduce upfront costs. This project aims to develop the knowledge and agronomic practices required to overcome these constraints so that growers can reliably achieve the significant potential crop responses to subsoil manuring whilst reducing the associated financial risk and other logistical constraints currently limiting the uptake of this practice.
Specifically this project will:
- review current knowledge about organic matter application to soils and how they can boost crop yields (from Australia and overseas) and use this knowledge to guide future R,D&E; and
- continue to monitor existing field trials to assess the long term residue value of applying organic matter on grain yields and use a series of new field and controlled environment trials to develop a better understanding of the soil chemical, physical and biological properties and crop processes underpinning improvements in crop performance following the application of organic matter to subsoils. This component will also optimise combinations of organic matter source, rate and depth of incorporation needed to increase crop yields on different soil types and environments in medium and high rainfall zones of South Australia, Victoria, southern NSW and Tasmania.
The project will
- undertake a scoping study of machinery design needed to apply different sources of organic matter to subsoil to guide the development of future commercial equipment; and
- undertake an analysis to identify the most financially attractive scenarios (soil type and environment/yield potential) for subsoil amelioration by accounting for the impact of seasonal variation, different input costs such as organic matter sources, commodity prices and the residual value of treatments based on data obtained from the field trials and simulation modelling using long-term climate records.
Ultimately the project will provide valuable information for grain growers in south eastern Australia to significantly improve their farm productivity by producing management guidelines for ameliorating subsoil constraints.
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