Researchers from the University of Plymouth, alongside colleagues from the Universities of and and industry partners at the , are investigating whether artificially made soils can be used as a sustainable solution against soil degradation, whilst reducing the quantity of waste sent to landfill.
The year-long experiment, led by Professor Mark Fitzsimons, measured the amount of nutrients the soil lost due to the movement of water through it. ‘Leachate’ is the term used for the nutrient-bearing water, after it has passed through the soil. The researchers tested the chemical content of the leachate, as a measure of how well the artificial soil could retain nutrients.
Specifically, the focus of the study was on the ability of the soil to retain nitrogen, especially once carbon quantity in the soil becomes low (limited). This is important as British soil is losing 0.6 per cent of its carbon annually due to climate change related processes. Whether the soil is appropriate for use in projects, ranging from urban landscaping to farming depends heavily on how well it retains nitrogen.
The economic and environmental impacts of topsoil loss, in the UK and throughout the world, are significant. Across the UK, rainwater is washing soil from the land into rivers, lakes and seas; this process is ‘soil erosion’. Under natural conditions, soil erosion occurs very slowly, however, farming requires the clearing of forests and woodlands, resulting in a lack of plants to anchor soil to the ground. This speeds up soil erosion; the speed of soil loss dramatically outpaces the accumulation of new soil.
The fabricated soil samples, composed entirely from waste materials, contained:
During the experiment, soil was compacted into four, one metre tall opaque tubes with a sandy layer at the bottom. As artificial rainwater dripped continuously onto the soil, the water flowed through the soil and reached the base to be collected as leachate. At weeks 26 and 48, the team added a common agricultural fertiliser, made of Nitrogen, Phosphorous and Potassium (NPK), to two of the samples.
The quantity of lost soil nitrogen was determined by measuring the nitrogen content in the leachate over time. Ideally, the soil would retain most of its nutrients; this is required for healthy plant growth. Additionally, if the soil retains nitrogen poorly it would potentially pollute local water sources, through a process called ‘’. Nitrogen-rich leachate could fertilise local water sources, forcing algae to bloom on the surface; this blocks sunlight and damages ecosystems below.
These results highlight the need for careful management of fertilised soils, by adding carbon rich materials before carbon becomes limited.
Artificial soil has potential as a sustainable solution for mitigating soil erosion problems, and reducing the quantity of waste sent to landfill. However, in order to be environmentally beneficial in the longer term, the carbon component of the soil may require attention to reduce water pollution, especially when used in the agricultural industry.
