Dark Earths and manioc cultivation in Central Amazonia: a window on pre-Columbian agricultural systems?

Abstract

Many commentators highlight the fertility of Anthropogenic Dark Earths (ADE), emphasizing their potential for sustainable agriculture. Some scholars believe that terra mulata (the less fertile, more extensive form of ADE) was created by means of agricultural practices used by large settled populations of pre-Columbian farmers. But what was it that these Amerindian farmers were growing? Until recently, scholarly consensus held that manioc does not perform well on ADE. New research on the middle Madeira River is showing, however, that this consensus was premature. In this region, the most common crop in ADE fields is bitter manioc. Farmers there have various landraces of manioc that they believe yield particularly well on ADE, and logically plant more of these varieties on ADE. Aspects of the behaviour and perception of manioc cultivation among 52 farmers at the community of Barro Alto were measured quantitatively on four terra firme soil types (Terra Preta, Terra Mulata, Oxisols and Ultisols). These farmers plant different configurations of landraces in different soils, according to their perception of the suitability of particular landraces and their characteristics to certain soil types and successional processes. This, in turn, shapes selective pressures on these varieties, as new genetic material incorporated from volunteer seedlings is more likely to contain traits present in the most prevalent landrace(s) in each soil type. Owing to localized population pressure at Barro Alto, manioc is under more intensive cultivation systems, with shorter cropping periods (5-10 months) and shorter fallow periods (1-2 years). The outcome of these processes is different co-evolutionary dynamics on ADE as opposed to non-anthropogenic soils. Further anthropological study of manioc swiddening in one of the richest agricultural environments in Amazonia can fill a gap in the literature, thus opening an additional window on the pre-Columbian period.Keywords: Anthropogenic soils. Dark Earths. Agricultural Intensification. Manioc. Central Amazonia. Madeira River.Resumo: Muitos comentaristas realçam a fertilidade da Terra Preta de Índio (TPI), enfatizando seu potencial para uma agricultura sustentável. Alguns estudiosos acreditam que Terra Mulata (uma forma menos fértil, porém mais comum de TPI) foi criada por meio de práticas agrícolas usadas por grandes populações sedentárias na época pré-colombiana. Mas o que estes agricultores ameríndios cultivavam? Até recentemente, o consenso acadêmico era de que mandioca não se adaptava bem em TPI. Novas pesquisas no Médio Rio Madeira estão demostrando, porém, que este consenso era prematuro. Nesta região, a colheita mais comum em roças de TPI é mandioca amarga. Os agricultores têm diversas variedades crioulas (raças primitivas) de mandioca, que eles acreditam render especialmente bem em TPI e, logicamente, plantam mais destas variedades em TPI. Aspectos do comportamento e da percepção do cultivo de mandioca entre 52 agricultores da comunidade de Barro Alto foram observados quantita...

The role of Amazonian anthropogenic soils in shifting cultivation: learning from farmers’ rationales

“…2). The high weed pressure on ADE has also been reported in other studies with a focus on the current cultivation of these soils (German 2003b, Major et al 2003, 2005, Fraser and Clement 2008, Fraser 2010a, b, Junqueira et al 2016). This aspect of ADE is very salient in farmers' reasoning and influences many decisions about opening swiddens, their cultivation practices, and the cultivation cycle.…”

Phytolith Assemblages Along a Gradient of Ancient Human Disturbance in Western Amazonia

“…Palms are well known to be important sources of food and building material for indigenous and local people (Clement, 1988(Clement, , 2006Sosnowska et al, 2015). Increased densities of both useful and non-useful palm species have been reported at other archeological sites, especially those containing terra pretas (Fraser and Clement, 2008;Fraser et al, 2011;Junqueira et al, 2011). The lasting signature of ancient palm enrichment that has occurred over the last 1500 years was clearly documented in the phytolith assemblages from Teotônio (Figure 3), providing a baseline to compare with other regions of unknown human history.…”

Origin and Domestication of Native Amazonian Crops

“…Once produced, seeds become part of the soil seed bank, and seedlings sprout among the vegetatively propagated varieties in the plots [25,[29][30][31]. Many smallholders let these volunteers grow, either unconsciously or consciously [32,33]. At the time of harvest, they decide if a given volunteer is worth including among the plants that will be vegetatively propagated [25,32,34,35].…”

“…This also makes them well adapted to human modified niches in the landscape, such as dump heaps that later became home gardens [145] and incipient horticultural systems. Manioc was also selected for growth in anthropogenic soils (terra preta de í ndio), some of which also originated as dump heaps [150], and floodplain soils [33], although most landraces are well adapted to nutrient poor upland soils. It is probable that the other root and tuber crops also had some varieties adapted to floodplain soils, but they may have been lost in the post-conquest wave of genetic erosion that accompanied population decline [1].…”