Soil structure and organic carbon dynamics from agroforestry and conventional coffee systems in a clayey Oxisol

Agroforestry systems can enhance C retention in soils, nutrient cycling, and biodiversity, helping offset soil and water degradation commonly associated with monocultures. However, impacts of agroforestry on soil organic carbon and water retention are variable and remain largely understudied for tropical soils and coffee ( Coffea arabica L.) systems. This study assessed soil organic C (SOC), soil structure, and particulate organic matter C (POM-C) in a gibbsitic Oxisol under conventional coffee (CC), coffee + macadamia [ Macadamia integrifolia Maiden & Betche (CM)] agroforestry, no-till (NT) soybean [ Glycine max (L.) Merr.]-corn ( Zea mays L.), and a secondary forest succession (SF) as a control. After 10 years, CM had 24 % lower bulk density and 18 % greater soil porosity than CC, resulting in 20 % greater water storage to a 0–40 cm. CM enhanced macroaggregate stability compared to CC, likely owing to greater litter inputs and root activity. Soil organic C stocks were relatively high (87–100 Mg C ha −1 at the 0–40 cm layer), due to clayey soil texture and abundant Fe and Al oxides, being higher under secondary forests but similar across agricultural land use systems ( p > 0.05). Particulate organic matter C was unaffected by land use systems, comprising approximately 11 % of total SOC at 0–5 cm, suggesting a steady state in organic matter turnover and accumulation after 10 years. Integrating macadamia trees into coffee plantations improves water storage relative to CC and preserves SOC, thus supporting natural resource conservation programs, ecosystem services’ markets, and enhancing income diversification and rural development in tropical regions. • Soil organic C and structure were assessed in tropical agroforestry coffee system. • Agroforestry had lower bulk density and higher porosity than conventional coffee (CC). • Leaf and root inputs likely enhanced soil aggregation in the agroforestry system. • Agroforestry and CC had similar soil organic matter levels after 10 years. • Agroforestry conserves soil C and enhances water retention by 20 % relative to CC.