Soil quality indicators under five different cacao production systems and fallow in Alto Beni, Bolivia

Cacao can be cultivated either as a monoculture or within diverse agroforestry systems, which differ, among others, in the choice of shade tree species, tree density, and whether conventional or organic management is applied. Agroforestry can improve ecosystem services in comparison to cacao monocultures, but the effect of different systems on soil quality, a main driver of the whole ecosystem´s health, needs further investigation. We analysed soil samples from a long-term trial in Bolivia that compares conventional and organic monocultures, conventional and organic agroforestry, successional agroforestry, and fallow plots. We measured chemical parameters (pH, organic carbon, available phosphorous), microbial parameters (microbial biomass carbon and phosphorous, microbial activity), and enzymatic activity (phosphatase, β-glucosidase, urease and protease activities). Plant inputs to soil were also quantified in the different systems. Soil organic matter and enzymatic activities were higher in fallow plots than in monocultures. Agroforestry showed intermediate values, not significantly higher than monocultures. Management type (organic versus conventional) had minimal impact on most parameters. Plant matter input quantity did not affect soil properties, suggesting that quality and diversity of plant inputs might have stronger effects than the quantity. Moderate to strong spatial variability was observed for all studied parameters. For microbial and biochemical properties, sampling season also caused strong variation. Our study contributes to highlighting that the characteristics of specific plants, such as those that grow in the fallow plots, could have a higher impact on soil quality than the sheer quantity of fresh plant material incorporated into the soil.