Allotments yield healthier soil, study finds

Its authors, who include Professor Kevin Gaston, Director of the Environment and Sustainability Institute (ESI) at the University of Exeter’s Penryn Campus, say planners and policy makers should increase the number of allotments available in light of the findings.

One of the greatest challenges facing the growing human population is meeting rising demand for food without undermining the soils on which food production – and other services such as carbon storage, flood mitigation and locking up pollutants – depend.

Intensive farming often results in significant declines in organic carbon stocks in soil, as well as reducing the ability of soils to store water and nutrients and damaging soil structure, which can lead to soil erosion.

The researchers took soil samples from 27 plots on 15 allotment sites in Leicester, also sampling soils from local parks, gardens and surrounding agricultural land.

They measured a range of soil properties, including soil organic carbon levels, total nitrogen, and the ratio between carbon and nitrogen (which are all directly related to the amount and quality of organic matter in the soil) as well as soil bulk density, an indicator of soil compaction.

Compared with local arable fields, the allotment soil was significantly healthier: allotment soil had 32% more organic carbon, 36% higher carbon to nitrogen ratios, 25% higher nitrogen and was significantly less compacted.

Professor Gaston said: “These results have important implications for land use planning and management decisions across much of the UK and beyond. They are particularly important for those regions, such as Cornwall, that have recognised the vital importance not simply of maintaining but of increasing their natural assets, such as carbon stocks and local food production.”

Allotment holders are able to produce good food yields without sacrificing soil quality because they use sustainable management techniques. For example, 95% of allotment holders compost their allotment waste, so they recycle nutrients and carbon back to their soil more effectively.

As well as being good news for urban soils, the results underline the value of allotments. There are around 330,000 allotment plots in the UK, covering more than 8000 hectares, and demand is growing, with more than 90,000 people currently on allotment waiting lists in the UK.

However, the heyday for allotments was during World War Two, when 10% of the UK's food came from less than 1% of its cultivated land thanks to the expansion of own-growing under the Dig for Victory campaign.

As well as protecting soils and boosting food security, own-growing offers other health benefits. Dr Jill Edmondson from the University of Sheffield, who did much of the work for the study, said: “Using urban land, including domestic gardens, allotments and community gardens for own-growing is an important and often overlooked way of increasing productivity whilst also reconnecting urban dwellers with food production.

“As well as improving food security, studies show that own-growing has direct physical and mental health benefits, and can provide access to sustainably produced fruit and vegetable crops without the associated food miles.”

The ESI is working with businesses and enterprises across all sectors of the economy in Cornwall, the Isles of Scilly and beyond to translate research and expertise into innovative business practices, products and services in order to respond to the challenges of environmental change. It has been funded by the European Regional Development Fund Convergence Programme (£22.9M) and the South West Regional Development Agency (£6.6M), with significant support from the Higher Education Funding Council for England.