Complex agroforests have been promoted as apotential solutions to address trade-offs between environmental conservation effortsand the need for increased agricultural productivity for smallholder farmers inthe tropics. However, the effects of tree diversification on soil fertility intropical agroforests remain unclear. In this study, we examine whether treediversification in cocoa plantations is associated with soil fertility benefitsand can contribute to soil restoration after deforestation. We tested forpositive associations between increasing tree species diversity and increasedsoil aggregation, soil nutrients and microbial communities across a diversity gradientranging from cocoa monocultures to complex cocoa agroforests. Secondary forestsand primary forests were used as reference ecosystems. Increase in treediversity within cocoa plantations did not increase soil fertility parametersin topsoil layers or cocoa yields. Mean soil C contents were 8% lower, meanweight diameter of aggregates 48% lower and total bacterial biomass 35% lowerin cocoa plantations than in primary and secondary forest systems, whereas soilP content was 22% higher. Across all land-use systems, microbial biomass wasgreater in sites with higher soil carbon contents and soil aggregation. Thissuggests soil function restoration in terms of microbial communities, soil Cand aggregate stabilization in secondary forests. However, in cocoa plantationstree diversification alone may not be an effective solution to mitigate soildegradation after deforestation. Rather, preserving remaining forests orpromoting farming approaches that allow for secondary forest regeneration (e.g.implementing forest strips and regular fallow rotations) might have a moresubstantial impact on soil health. |
