Challenge of transition: the history of a case study involving tropical fruits polyculture stimulated by humic acids and plant-growth promoting bacteria

Background: Innovative technologies are required in agricultural production to eliminate the environmental risk generated by the intensive use of fertilizers and pesticides. Soil organic matter is a keystone for the transition towards sustainable production. However, it is not an easy task to increase soil organic matter in highly weathered soils without considerable resources and energy. Here, we highlighted the role of biological inputs in plant adaptation to low fertility and water scarcity. The direct use of humic acids and plant growth-promoting bacteria on plants can modify the root architecture systems, including surface area and roots length, thus allowing greater soil exploration. Material and methods: Within a socio-historical perspective of concepts and research methods, a case study is presented on the effects of humic acids applied together with plant-growth promoting bacteria, as an efficient tool for supporting the transition to more suitable production system. We implemented this natural ecological approach onto a polyculture system with different tropical fruits (banana, passion fruit, papaya and pineapple) and evaluated crop yields. Results: We observed increases of around 50 and 90% in banana and papaya yield, respectively, and 25% in passion fruit productions, with significantly greater yields maintained over four production cycles. No effect was observed in ananas production probably due to the large shading level in the area. Conclusion: The biostimulant formulated with endophytic diazotrophic bacteria and humic acids represents a low-cost technology that enhances crop yields and can play an important role in promoting a transition process towards sustainable agriculture. Graphical Abstract: [Figure not available: see fulltext.]