Innovative Organic Ameliorants

New organic-based amendments for enhanced nutrient use efficiency and soil carbon

Project Funder: Soil CRC
Project Lead: Southern Cross University, NSW DPI, NSW EPA
Project Code: 3.1.005
Project Duration: 2021-2024
Trial Location: Tallimba

Background

Many farmers have access to manures or other organic amendments, but transport and spreading costs along with uncertainty over crop responses and longer-term impacts on soils have limited their use. Crop responses can be inconsistent because organic amendments can have variable effects on soil nutrient cycling and longer-term soil carbon stores. This is due to the complex interactions between soil microbes and soil carbon, and the additional nitrogen, phosphorus, sulphur and carbon inputs from organic amendments.

When carbon, nitrogen, phosphorus or sulphur are added to soils, and one element is in short supply, soil microbes typically obtain the missing nutrient to sustain their growth by degrading existing soil organic matter to release the needed element. As a result of these processes, and following the death of soil microbes, crop plants may accumulate more of a given nutrient than was applied in the fertiliser or amendment. This is often simplistically seen as ‘enhanced nutrient use efficiency (NUE)’. However, while there may be some short-term nutrient gain, it comes at the expense of native soil organic matter degradation, and this will have longer term consequences for both soil processes and crop nutrition.

The project is examining the impact organic amendments, mainly manures, have on soil carbon levels and nutrient availability in the field and will determine the effectiveness of manures as phosphorus fertilisers compared to synthetic fertilisers. A range of soil health parameters will also be assessed to investigate whether manures have any effects on soil health compared to synthetic fertilisers. Ultimately the project will develop recommendations for the use of new organic amendment products to give growers confidence to replace or partially replace mineral fertiliser inputs with organic amendment products.