Soil multifunctionality in tropical agroecosystems through agroforestry and biochar-based management

Abstract

tSoil degradation compromises the sustainability of tropical agroecosystems by reducing the capacity of soils to sustain productivity and provide essential ecosystem services. This thesis evaluated soil multifunctionality and the provision of soil ecosystem services in two contrasting contexts: the transition from pastures to agroforestry systems in the Colombian Amazon and the use of biologically activated biochar in Andean coffee systems. In the first study, paired systems of primary forest, pasture, and cacao-based agroforestry were evaluated. Soil physical, chemical, and biological indicators, measured down to 1.0 m depth, were integrated into ecosystem service indices. Primary forest showed the highest overall functionality, whereas pastures exhibited functional simplification and lower integrated service provision. Cacaobased agroforestry systems partially restored soil multifunctionality, especially functions related to climate regulation, acidity control, and fertility, indicating their potential as a functional recovery strategy in degraded Amazonian landscapes. In the second study, conducted in acidic soils of the Andean coffee region, the effects of application rates of biologically activated coffee wood biochar were evaluated in combination with mineral fertilizer reduction and different application methods. The most consistent responses occurred in soil chemical attributes, with increases in pH, exchangeable bases, organic carbon, and available phosphorus, along with reduced aluminum saturation. These changes were partially reflected in foliar nutrition and coffee productivity. Activated biochar combined with a 25% reduction in mineral fertilization maintained or increased productivity in some treatments, whereas surface application was generally more favorable than incorporation. Overall, the results show that the restoration of soil multifunctionality in tropical agroecosystems can occur through complementary strategies at different scales. At the landscape scale, agroforestry systems contribute to recovering functions lost after forest-to-pasture conversion. At the plot scale, biologically activated biochar acts as a regenerative soil conditioner, improving soil fertility and favoring more efficient fertilizer use. Thus, this thesis demonstrates that integrated soil indicators can guide regenerative management strategies aimed at recovering ecosystem services in Colombian agricultural landscapes.