Soil constraints, which are responsible for significant yield losses globally, can be defined as any soil characteristic that limits crop growth and negatively impacts agricultural production. In Australia, ~75% soils have single or multiple constraints and cost farmers $2 billion/annum in forfeited grain yield. An extensive body of research has demonstrated that it is possible to improve crop growth in constrained soils by applying agricultural amendments such as lime, gypsum, sulphur, and organic matter. These amendments have shown the potential to improve soil structure and fertility and improve soil properties associated with constraints.

However, while it is relatively simple to apply amendments to treat constraints occurring at the surface of the profile, their application is more challenging when constraints are present in subsoil environments (>20-30 cm) (as commonly occurs across wide areas of Australian cropping land). Ameliorants applied at the surface of the profile are typically spread across the soil surface using modified fertilizer boxes with an agitator inside. Surface application can be followed by incorporation into the soil using equipment such as a disk harrow, although in no-till systems this may not occur. However, because of the low mobility of amendments in soil, surface spread material often fails to impact (or only slowly impacts) constraints occurring below the depth of application. The agricultural machinery capable of delivering these materials deeper into the subsoil is not widely available. In addition, these ameliorants typically need to be applied in large volumes to be effective (application rates can range from 1-20 t/ha depending upon the ameliorant). Placing large volumes of ameliorants at depth, particularly in higher clay content soils, is logistically challenging and expensive.

Clearly, improved techniques are required if farmers are to use ameliorants to effectively treat soil constraints present in subsoil environments. One promising research approach is to alter amendments to improve their flowability or ease of application. For products such as gypsum and lime, finer materials are typically found to be more effective due to improvements in solubility. In contrast, to apply organic materials, which are often bulky and take up large volumes, processing amendments into granular form or pellets can significantly increase the ease of ameliorant application. Research also indicates that combining different amendments (e.g., gypsum + organic material or organic material + nutrients) can provide multiple benefits and have a greater combined impact than applying either ameliorant alone.

A limited number of products are currently on the market that may be easier to apply to subsoil environments. These include products such as liquid nano-gypsum and -lime; ultra-fine preparations of gypsum and lime; granulated organic fertiliser; and combinations of granulated organic material + micronized gypsum. However, these types of ameliorants often have a relatively high cost and are not widely used in the agricultural sector to treat subsoil constraints. Greater research is required to identify the potential use of these, and other emerging approaches in materials research.

Continued research into the most efficient placement of ameliorants in subsoil environments is also required. Work has already begun to identify machinery solutions to place amendments in the subsoil. However, this work needs to be better linked to advances in materials research to ensure that the emerging machinery and emerging ameliorants are compatible and work together in the most efficient manner to improve subsoil conditions.

This consultancy will conduct a thorough assessment of the current state of research on soil ameliorants and the capacity of key research institutions in the field of material development. This will occur via a two-stage process whereby a thorough desktop review of the current state of research is conducted, followed by a gap analysis to assess research and development needs in this area. Details of the specific methodology to be followed are provided below.