Wenceslau Geraldes Teixeira

Amazonian Dark Earths: Wim Sombroek's Vision

1 Amazonian soils are almost universally thought of as extremely forbidding. However, it is now clear that complex societies with large, sedentary populations were present for over a millennium before European contact. Associated with these are tracts of anomalously fertile, dark soils termed terra preta or dark earths. ese soils are presently an important agricultural resource within Amazonia and provide a model for developing long-term future sustainability of food production in tropical environments. e late Dutch soil scientist Wim Sombroek (1934-2003) was instrumental in bringing the signifi cance of these soils to the attention of the world over four decades ago. Wim saw not only the possibilities of improving the lives of small holders throughout the world with simple carbon based soil technologies, but was an early proponent of the positive synergies also achieved in regards to carbon sequestration and global climatic change abatement. Wim’s vision was to form a multidisciplinary group whose members maintained the ideal of open collaboration toward the attainment of shared goals. Always encouraged and o en shaped by Wim, this free association of international scholars termed the Terra Preta Nova Group came together in 2001 and has fl ourished. is eff ort has been defi ned by enormous productivity. Wim who is never far from any of our minds and hearts, would have loved to share the great experience of seeing the fruits of his vision as demonstrated in this volume. William I. Woods Wenceslau G. Teixeira Johannes Lehmann Christoph Steiner Antoinette M.G.A. WinklerPrins Lilian Rebellato Editors Amazonian Dark Earths: Wim Sombroek‘s Vision W oods et al. ds.

Microbial Response to Charcoal Amendments of Highly Weathered Soils and Amazonian Dark Earths in Central Amazonia — Preliminary Results

The abundance of charcoal and highly aromatic humic substances in Amazonian Dark Earths (ADE) suggests that residues of incomplete combustion of organic material (black carbon, pyrogenic carbon, charcoal) are a key factor for the persistence of soil organic matter (SOM) in ADE soils which contain up to 70 times more black carbon than the surrounding soils (Glaser et al. 2001). 13C-NMR studies showed that the only chemical structures that appear to survive decomposition processes are mostly due to finely divided charcoal (Skjemstad 2001). Generally, in highly weathered tropical soils, SOM and especially charcoal play a key role in maintaining soil fertility (Glaser et al. 2001, 2002).

The domestication of Amazonia before European conquest.

During the twentieth century, Amazonia was widely regarded as relatively pristine nature, little impacted by human history. This view remains popular despite mounting evidence of substantial human influence over millennial scales across the region. Here, we review the evidence of an anthropogenic Amazonia in response to claims of sparse populations across broad portions of the region. Amazonia was a major centre of crop domestication, with at least 83 native species containing populations domesticated to some degree. Plant domestication occurs in domesticated landscapes, including highly modified Amazonian dark earths (ADEs) associated with large settled populations and that may cover greater than 0.1% of the region. Populations and food production expanded rapidly within land management systems in the mid-Holocene, and complex societies expanded in resource-rich areas creating domesticated landscapes with profound impacts on local and regional ecology. ADE food production projections support estimates of at least eight million people in 1492. By this time, highly diverse regional systems had developed across Amazonia where subsistence resources were created with plant and landscape domestication, including earthworks. This review argues that the Amazonian anthrome was no less socio-culturally diverse or populous than other tropical forested areas of the world prior to European conquest.

Distribution of throughfall and stemflow in multi-strata agroforestry, perennial monoculture, fallow and primary forest in central Amazonia, Brazil

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi-strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuacu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open-area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuacu monoculture and 3·1% in the fallow. With more than 20% of the open-area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright

Subsoil accumulation of mineral nitrogen under polyculture and monoculture plantations, fallow and primary forest in a ferralitic Amazonian upland soil

Central Amazonia is characterized by high and intensive rainfall and permeable soils. When rainforests are cleared for agricultural use, the efficient nutrient recycling mechanisms of the forests are disrupted and the nutrient availability in the topsoil is increased by fertilization, thereby increasing the potential for nutrient leaching. In this study, the distribution of mineral N in the upper two meters of a ferralitic upland soil was evaluated as an indicator for nutrient leaching and for the potential contribution of the subsoil to crop nutrition. A perennial polyculture system with four tree crops and a leguminous cover crop at two fertilization levels was compared with a monoculture plantation of peach palm (Bactris gasipaes), spontaneous fallow and primary rainforest. Mineral N accumulated principally as nitrate in the subsoil under all agricultural crops and also under the primary forest, although to a lesser extent. Within the polyculture system, there were significant differences in N accumulation between the tree crop species, and for one of the species (Theobroma grandiflorum) also between fertilization levels. The principal sources of subsoil N were mineral fertilizer and presumably N from the mineralization of leguminous biomass and soil organic matter. The N losses from the agricultural systems and the absence of yield responses of the tree crops to N fertilization indicated that agricultural production was not limited by N at this site, or that N was too rapidly leached to be taken up efficiently by the crops. None of the tree crop species seemed to be efficient in capturing leached N. Strategies are discussed for reducing N losses from agricultural systems with perennial crops, including the development of site- and species-specific fertilizer recommendations, closer tree spacing, and the encouragement of lateral and vertical tree root development.

Slash and Char: An Alternative to Slash and Burn Practiced in the Amazon Basin

The forested area in the tropics continues to decrease. It is a challenge to preserve large areas of tropical forest to counteract the accelerating climate change and loss of biodiversity. The cumulative deforested area (including old clearings and hydroelectric dams) in Amazonia up until 1991 reached 427,000 km2 or 11 % of the 4 million km2 original forested portion of Brazil’s 5 million km2 legal Amazon region (Fearnside 1997).

Soil Physical Characterization

1. INTRODUCTION Amazonian Dark Earths (ADE) normally show plaggic, terric or hortic horizons. These horizons are identified by the dark matrix colors of the top layers, and often by the presence of potsherds, lithic artifacts and charcoal pieces (Sombroek, 1966; Ranzani et al. 1970; Kern and Kampf, 1989). The more widely accepted theory about the origin of these epipedons is that they were improved by Amerindian populations in pre-Colombian Indian settlements. Human beings had a significant influence on these sites, as confirmed by the presence of high phosphorus (P) contents (Smith, 1980; Kern and Kampf, 1989; Lima et al., 2002) that are characteristic of anthropogenic horizons (Smith, 1980; McDowell, 1988). Despite the high amounts of P, calcium (Ca), magnesium (Mg) and micronutrients, textures are typically lighter in the top horizon than the deeper horizon and are also lighter relative to the surrounding soils. The top horizons on ADE sites show some differences in soil physical and hydraulic properties compared to the adjacent soils in the region. They have certain chemical characteristics and contain large amounts of charcoal and often ceramic pieces that require specific soil physical methods to characterize them. Their structure is typically granular (Sombroek, 1966; Silva et al., 1970; T. Cunha, unpubl. data) with slightly interlocking edges. The high amounts of soil organic matter (SOM) in ADE strongly influences the soil’s color, structure, and hydraulic properties. Bulk density values are commonly smaller in the top horizons in ADE than in adjacent soils near Belterra (Santarem), and are greater near Manaus. At most investigated sites, ADE displays soil physical properties that are advantageous for agricultural purposes. The workability of ADE is easier, and the drainage is usually very good. Because of this easy workability and ADE’s sustainability in relation to surrounding soils, the local population intensively uses these sites (M. Hiraoka, this issue). ADE seems to be a very resilient soil type, able to keep its good soil physical qualities when submitted to intensive soil management. A depletion of productivity of those highly fertile soils has been mentioned by many farmers and reported by Smith (1980) and German (2001). It is probably related to some soil physical degradation and changes in the fluxes of mass

Amazonian Dark Earth and Plant Species from the Amazon Region Contribute to Shape Rhizosphere Bacterial Communities

Amazonian Dark Earths (ADE) or Terra Preta de Índio formed in the past by pre-Columbian populations are highly sustained fertile soils supported by microbial communities that differ from those extant in adjacent soils. These soils are found in the Amazon region and are considered as a model soil when compared to the surrounding and background soils. The aim of this study was to assess the effects of ADE and its surrounding soil on the rhizosphere bacterial communities of two leguminous plant species that frequently occur in the Amazon region in forest sites (Mimosa debilis) and open areas (Senna alata). Bacterial community structure was evaluated using terminal restriction fragment length polymorphism (T-RFLP) and bacterial community composition by V4 16S rRNA gene region pyrosequencing. T-RFLP analysis showed effect of soil types and plant species on rhizosphere bacterial community structure. Differential abundance of bacterial phyla, such as Acidobacteria, Actinobacteria, Verrucomicrobia, and Firmicutes, revealed that soil type contributes to shape the bacterial communities. Furthermore, bacterial phyla such as Firmicutes and Nitrospira were mostly influenced by plant species. Plant roots influenced several soil chemical properties, especially when plants were grown in ADE. These results showed that differences observed in rhizosphere bacterial community structure and composition can be influenced by plant species and soil fertility due to variation in soil attributes.

Effect of five tree crops and a cover crop in multi-strata agroforestry at two fertilization levels on soil fertility and soil solution chemistry in central Amazonia

The spatio-temporal patterns of soil fertility and soil solution chemistry in a multi-strata agroforestry system with perennial crops were analysed as indicators for the effects of crop species and management measures on soil conditions under permanent agriculture in central Amazonia. The study was carried out in a plantation with locally important tree crop species and a leguminous cover crop at two fertilization levels on a xanthic Ferralsol. Soil fertility to 2 m soil depth was evaluated 3.5 years after the establishment of the plantation, and soil solution chemistry at 10, 60 and 200 cm soil depth was monitored over 2 years. Several soil fertility characteristics exhibited spatial patterns within the multi-strata plots which reflected the differing properties of the plant species and their management, including the fertilizer input. Significant differences between species could be detected to 150 cm depth, and between fertilization treatments to 200 cm depth. Favourable effects on nutrient availability in the soil were found for annatto (Bixa orellana) (P, K) and cupuaçu (Theobroma grandiflorum) (Ca, Mg) in comparison with peach palm (Bactris gasipaes) and Brazil nut (Bertholletia excelsa). Nutrient concentrations of the soil solution showed pronounced fluctuations in the topsoil, corresponding to fertilizer applications. Large nutrient concentrations in the soil solution were accompanied by increased concentrations of aluminium and low pH values, caused by exchange reactions between fertilizer and sorbed acidity and reinforced by the acidifying effect of nitrification. The soil solution under the leguminous cover crop Pueraria phaseoloides had relatively large N concentrations during periods when those under the tree crops were small, and this could partly explain why no yield responses to N fertilization were observed at this site.

Functional diversity of bacterial genes associated with aromatic hydrocarbon degradation in anthropogenic dark earth of Amazonia

The objective of this work was to evaluate the catabolic gene diversity for the bacterial degradation of aromatic hydrocarbons in anthropogenic dark earth of Amazonia (ADE) and their biochar (BC). Functional diversity analyses in ADE soils can provide information on how adaptive microorganisms may influence the fertility of soils and what is their involvement in biogeochemical cycles. For this, clone libraries containing the gene encoding for the alpha subunit of aromatic ring‑hydroxylating dioxygenases (α‑ARHD bacterial gene) were constructed, totaling 800 clones. These libraries were prepared from samples of an ADE soil under two different land uses, located at the Caldeirao Experimental Station - secondary forest (SF) and agriculture (AG) -, and the biochar (SF_BC and AG_BC, respectively). Heterogeneity estimates indicated greater diversity in BC libraries; and Venn diagrams showed more unique operational protein clusters (OPC) in the SF_BC library than the ADE soil, which indicates that specific metabolic processes may occur in biochar. Phylogenetic analysis showed unidentified dioxygenases in ADE soils. Libraries containing functional gene encoding for the alpha subunit of the aromatic ring‑hydroxylating dioxygenases (ARHD) gene from biochar show higher diversity indices than those of ADE under secondary forest and agriculture.