Increasing nutrient efficiency with new organic amendments

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 will determine how new ‘nutrient balanced’ organic amendment products affect NUE in the field compared to traditional fertiliser inputs. It will resolve the mechanisms that drive NUE, using a combination of field and controlled-environment studies with locally available manure and treated (composted or thermally treated) manure sources.

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.