Pedogenesis in an Archaeological Dark Earth – Mulatto Earth Catena over Volcanic Rocks in Western Amazonia, Brazil

Abstract

Archaeological Dark Earth (ADE) pedogenesis and pre-Columbian history are fundamental for understanding the biodiversity and pedodiversity of the Neotropical rainforest in the Amazon region. This study aimed to evaluate the morphological, physical, chemical, and mineralogical properties as well as NaOH-extractable organic matter [OM(NaOH)] in ADE and Mulatto Earth (ME) overlying volcanic rocks along a toposequence (four soil profiles) in western Amazonia, Brazil. The soil profiles show anthropic A horizons over an argic horizon (Bt) in the ADE (Humic, Pretic Luvisols) and Bi in the ME (Clayic, Dystric Cambisols). The soil-forming processes in all of the profiles are associated with organic matter accumulation, such as humification and melanization, besides the formation of organometallic complexes. Calcium, Mg, P, and organic carbon contents were higher in ADE compared to ME. High-activity clays are derived from parent volcanic material, distinguishing the soils studied from Amazonian soils (Tertiary Plateau, Terra Firme) and most Amazonian anthropic soils. The anthropic horizons generally have a large contribution from OM(NaOH), predominantly humin and humic acids associated with Ca, Mg, and poorly crystalline Al hydroxides. The results suggest that the anthropic driving-forces caused greater differences in pedogenesis than the soil location in the landscape.

Characterization and classification of soils from an Amazonic Biome in western Pará

“…This predominance of basic cations is the main responsible for the higher pH values in these profiles, close to 6.0 in almost all horizons, which explains the null values of Al 3+ , especially in P3 and P6. Differing from the patterns observed by Santos et al (2013) and Santos et al (2018a) in areas of Archaeological Black Earth, the K + values were considered as very low in all studied soils, having a maximum content of 0.10 cmolc kg -1 in Au1 of P3.…”

“…Even though there are soils with low natural fertility, some discontinuous patches of anthropic soils of high natural fertility are distributed throughout the Amazon territory, having high contents of P, Ca 2+ , Mg 2+ , stabilized organic matter and high biological activity, (Santos et al, 2018a;Batistão et al, 2020). These soils are mainly associated with the "Argissolos" (Oxisols) and "Latossolos" (Ultisols) classes in the Brazilian Soil Classification System (BSCS) .…”

“…In the Amazonian environment, the large territorial extension contributes to the difficulty in reaching many areas, thus hindering the advancement of knowledge about soils in this region (Sousa et al, 2018a). Soil surveys conducted in the region are in a small scale that does not allow the more detailed planning of agricultural and forestry activities, settlement areas, irrigation and drainage project, among others (Araújo Filho et al, 2013).…”

Avaliação da fertilidade de áreas de terra preta de índio no sul do Amazonas

“…O potássio trocável foi considerado muito baixo em todas as áreas, exibindo teores de 0,02 cmolc.kg -1 (área sob cultivo de cacau), 0,01 cmolc.kg -1 (área sob cultivo de café) e 0,02 cmolc.kg -1 (área sob cultivo de pastagem), podendo estar relacionado com manejo empregado nas áreas, sem a realização da queima, não receber aporte expressivo de K de outras fontes, bem como a elevada mobilidade deste nutriente no solo pode justificar seus baixos teores nas áreas estudadas, Santos et al, (2018) estudando gênese de TPI´s também verificaram teores de K muito baixos e em horizontes antrópicos e não antrópicos.…”