What happens to the soil under permaculture?



The environmental and ecological limitations of conventional agriculture and market gardening are no longer to be demonstrated. While the planet is confronted to an environmental emergency (imbalances in biogeochemical and climatic cycles), many so-called "conservation" agriculture models are emerging among a significant number of farmers. Within these models, soil functioning plays a key role.

Interested by innovation in the agricultural sector, a research team from the Research Axis Water-Soil-Plant Exchanges of Gembloux Agro-Bio Tech (F. de Tombeur, V. Sohy, G. Colinet and J-T. Cornelis) and AgroParisTech (C. Chenu) studied the so-called "permaculture" market gardening model at the Bec Hellouin farm in Normandy (France). The purpose of the study is to understand the effects of permaculture practices on soil functioning and more specifically, on soil organic matter dynamics.

The Bec-Hellouin farm is a microfarm whose practices are inspired by the models of permaculture and bio-intensive microgardening; i.e. an intensive use of biological resources through the mimicry of the ecological functioning of ecosystems*. The practices are characterized by (1) an intensification of crops on small areas (2) the non-use of mineral fertilizers and agrochemical products (3) a reduced tillage (4) exceptionally high and localized inputs of organic matter (5) a very low mechanization and (6) a significant human working time per cultivated area. Permaculture soils have been studied in the light of soil properties in a pasture and a conventional agricultural system, in a similar geopedoclimatic context. 

The results showed that organic matter stocks in permaculture soils were up to 1.5 times higher than in pasture soils, and up to 6.5 times higher than in conventional soils. This increase is mainly controlled by the so-called "particulate" organic matter, non-associated with the soil mineral phases, and improves the physico-chemical properties of the soil. The decomposition processes of these high concentrations of organic matter under permaculture contribute to the increase of the phyto-available nutrient concentrations for vegetables.

However, these large stocks of organic matter are achieved through the availability of a large quantity of manure, amended on small cultivated areas. The study of the distribution and life cycle of carbon in agricultural landscapes affected by bio-intensive market gardening is therefore a major priority in order to better constrain the coherence of this agricultural model.

The study was published in the scientific journal Frontiers in Environmental Science

*Morel et al. (2018) Permaculture. Encyclopedia of Ecology, 2 ndedition, https://doi.org/10.1016/B978-0-12-409548-9.10598-6

 

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