Improving soils with organic waste

Nutrients and organic matter from urban and agricultural wastes are increasingly being used on arable land as fertilisers and for improving soil quality. It is unclear, however, what environmental impact this waste management process has, from the energy required to recycle waste to emissions and benefits to the environment.

The EU-funded project SOILWASTEBENEFITS (Integrated assessment of soil quality, environmental emissions and agronomic benefits from land application of organic waste products) used life-cycle assessment (LCA) to study the impact of applying organic wastes to land.

While standardised LCAs integrate environmental impacts of many waste management processes, current models do not take into account the effects of organic wastes on soil quality. SOILWASTEBENEFITS combined biogeochemical characterisation of soil organic matter in long-term field experiments with agro-ecosystem modelling to improve LCAs of organic waste.

Researchers first analysed the chemical composition of different organic waste products applied to soil, including the fraction of organic carbon that is available for microorganisms. They then looked at the changes in soil organic carbon content after repeatedly applying organic waste products to soil in field experiments spanning 11 years.

They found that applying compost results in fuel savings of up to 25 % with the highest application rate of composted municipal solid waste, due to reduced soil resistance for soil tillage, a benefit not usually considered.

After adding this parameter to their LCA model however, they concluded that the fuel savings are negligible for the global warming impact, when compared with energy usage and production along the entire waste life cycle (composting vs. incineration).

Integrating other environmental effects of recycling waste may further improve the LCA model and allow researchers to accurately compare different waste treatment options. For example, waste recycling by composting compared with incineration may lead to less soil erosion, or enhanced activity of soil microbes that recycle nutrients.

By quantifying the environmental effects of applying differently treated organic wastes to soil, this project's outcomes will be useful for soil researchers, farmers and policymakers alike.