Soil health indicators, farmer concepts and carbon market standards in agroforestation of underutilized lands in West Sumatra (Indonesia)

We assessed soil health impacts in an externally supported program of farmer-led grassland agroforestation in the humid tropics of Sumatra (Indonesia). We documented local ecological knowledge and the existing policy environment, and collected data for a set of long-term soil-health indicators. Interviews with farmers clarified their concerns, values, perceived opportunities and actions. Views on earthworms vary from pest to soil improver. Combining farmer and policy concerns, we selected ten soil/land health indicators for further assessment. Eight land cover types were sampled in four replicates on higher elevation Andisols (1150–1630 m a.s.l.) and mid-elevation (500–835 m a.s.l.) Inceptisols in a virtual chronosequence of forests, open-field agriculture, Imperata/fern fallow grasslands, three stages in the agroforestation process (∼2, ∼5, >7 year after conversion) and mature multistrata ‘parak’ agroforestry. A principal component analysis of the data (60 metrics for 60 plots) confirmed the aboveground grouping; the two soil types were distinct in a number of properties. Agroforestation of Imperata /fern grasslands led to an initial decline of microbial biomass, earthworms, infiltration and soil organic carbon, followed by recovery during agroforestation. On a life-cycle timescale agroforestation is carbon neutral belowground and neutral in hydrological functions in a watershed health context. Increased carbon stock, microclimatic buffering and tree diversity are benefits expressed primarily above ground. The initial decline in measured ‘functions’ (including a 50 % reduction in microbial biomass N on Andisols in the first two years after conversion), a surprise in dominant restoration’ discourse, indicates a transition between two plant-soil interaction systems. • Global soil science collaboration can connect three types of soil knowledge. • Farmer-led agroforestation, with co-investment, can transform grass/fern fallows. • Changes in soil health during agroforestation involve and interface ten indicators. • Belowground changes are slower and more complex than aboveground restoration. • Decline and recovery of microbial biomass C and N indicates change in soil health.