A pressing challenge facing poor farmers is how to maintain yields in swidden-fallow systems when confronting growing land scarcity and declining soil fertility. The objective of this research is to document the innovative use of biochar and biochar-rich kiln soils on charcoal kiln sites by Amazonian peasant farmers for annual and perennial crop production as part of their swidden-fallow agroforestry cycle. The study was undertaken in a riverside community near Iquitos, Peru, where the availability of primary forest land has decreased significantly over the past 30 years. Charcoal production is a long-standing, near ubiquitous local activity, drawing on wood primarily from secondary forest fallows. Data were collected in 2011 through household interviews (n = 36) and an extensive survey of upland kiln sites (n = 500). Results indicate this innovation, dubbed “kiln site agriculture” (KSA), evolved endogenously within the study community as an adaptation to growing land scarcity. Current landholdings were found to negatively correlate with both the number of crops households (n = 32) cultivated per kiln site (r = −0.3483, p = 0.0254) and the proportion of those sites cultivated with manioc, the local staple crop (r = −0.5441, p = 0.0006), suggesting that land-poor households rely on KSA harvests to supplement subsistence. This study provides evidence charcoal production need not be a rapacious forest use and can, through KSA and biochar, offer an affordable opportunity to peasant farmers who practice swidden-fallow agroforestry where new land in primary forest is scarce and the productivity of their weathered soils is falling.