The soil living system is globally threatened

Soil is a complex system with many living organisms interacting within physico-chemical conditions. Soil biota is very diverse in terms of size and roles, and represent the key driver of soil main functions (carbon transformation, nutrient cycling, structure maintenance, pest regulation). Multiple threats such as urbanization, deforestation, or intensive management practices are currently jeopardizing soil health at a global scale. This situation leads to unfavorable degradation that limits soil functioning, such as erosion, carbon and nutrient depletion, or compaction. There is thus a need to monitor the impact of agrosystem management - such as tree crop plantations - on soil health. Soil health assessment in agriculture (Thoumazeau et al, 2019) aims at measuring how agricultural practices or land management can affect both soil biotic activities and functions.
          

Agroecological practices: a lever to improve soil health in plantations

In plantations, various practices may weaken soil health. For example, plantation installation and logging practices, fertilization and weeding management, heavy tillage, bare soils maintenance. The field implementation of agroecological practices provide key opportunities to combine plantation performance with the improvement of environmental components such as soil health protection. For example, the restitution of logging residues to the agricultural plots, the use of cover crops during immature planting stage, the recycling of organic matter (such as Empty Fruit Bunches in oil palm plantations) are key strategies to reinforce soil health. Such agricultural practices and changes need however to consider other agronomic, environmental and socio-economic performances to increase the efficiency of the overall cropping system. Socio-economic bottlenecks and local rationalities especially need to be considered for a successful agroecological transition.
         

The road to circular economy

Enhancing agroecosystem properties through the development and implementation of agroecological practices can generate high palm oil yields while reducing external inputs such as mineral fertilisers and pesticides (Bessou et al, 2017). It is of paramount interest to reduce such external inputs as much as possible, given the large environmental burdens they may carry along accounting for emissions and impacts both upstream the supply chain and in the field. The recycling of oil palm and palm oil co-products at both the plantation and mill stages makes it possible to reduce the amounts of mineral fertilisers without depleting the soil nutrient resources or stressing the palms. Our story about the impact of palm empty fruit bunches application on soil quality showed that the use of these coproducts, in particular on fragile soils, could help to maintain or improve soil nutrient resources, soil permeability or soil biological activity. At the same time, the recycling of coproducts reduces the polluting emissions and environmental impacts related to waste treatments. The co-composting of empty bunches together with palm oil mill effluent drastically reduces methane emissions during the conventional anaerobic effluent digestion.