Land cover effects on soil infiltration capacity measured using plot scale rainfall simulation in steep tropical lowlands of Central Panama

Understanding land use/land cover (LULC) effects on tropical soil infiltration is crucial for maximizing watershed scale hydro-ecosystem services and informing land managers. This paper reports results from a multiyear investigation of LULC effects on soil bulk infiltration in steep, humid tropical, and lowland catchments. A rainfall simulator applied water at measured rates on 2 x 6 m plots producing infiltration through structured, granulated, and macroporous Ferralsols in Panama's central lowlands. Time-lapse electrical resistivity tomography (ERT) helped to visualize infiltration depth and bulk velocity. A space-for-time substitution methodology allowed a land-use history investigation by considering the following: (a) a continuously heavy-grazed cattle pasture, (b) a rotationally grazed traditional cattle pasture, (c) a 4-year-old (y.o.) silvopastoral system with nonnative improved pasture grasses and managed intensive rotational grazing, (d) a 7 y.o. teak (Tectona grandis) plantation, (e) an approximately 10 y.o. secondary succession forest, (f) a 12 y.o. coffee plantation (Coffea canephora), (g) an approximately 30 y.o. secondary succession forest, and (h) a >100 y.o. secondary succession forest. Within a land cover, unique plot sites totalled two at (a), (c), (d), (e), and (g); three at (b); and one at (f) and (h). Our observations confirmed measured infiltration scale dependency by comparing our 12 m(2) plot-scale measurements against 8.9 cm diameter core-scale measurements collected by others from nearby sites. Preferential flow pathways (PFPs) significantly increased soil infiltration capacity, particularly in forests greater than or equal to 10 y.o. Time-lapse ERT observations revealed shallower rapid bulk infiltration and increased rapid lateral subsurface flow in pasture land covers when compared with forest land covers and highlighted how much subsurface flow pathways can vary within the Ferralsol soil class. Results suggest that LULC effects on PFPs are the dominant mechanism by which LULC affects throughfall partitioning, runoff generation, and flow pathways.