Geoderma 262 (2016) 35–44 Contents lists available at ScienceDirect Geoderma j ourna l homepage: www.e lsev ie r .com/ locate /geoderma Characteristics of color and iron oxides of clay fraction in Archeological Dark Earth in Apuí region, southern Amazonas Renato Eleoterio de Aquino a, José Marques Jr. a, Milton César Costa Campos b,⁎, Ivanildo Amorim de Oliveira a, Angélica Santos Rabelo de Souza Bahia a, Luis Antônio Coutrim dos Santos c a Agrarian and Veterinarian Faculty, São Paulo State University, 14883-292 Jaboticabal, SP, Brazil b Institute of Education, Agriculture and Environment, Universidade Federal do Amazonas, 69800-000 Humaitá, AM, Brazil c Department of Soil, Center of Rural Sciences, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil ⁎ Corresponding author. E-mail addresses: aquino.rea@gmail.com (R.E. Aquino (J. Marques), mcesarsolos@gmail.com (M.C.C. Campos), iv (I.A. Oliveira), angelicasantosrabelo@yahoo.com.br (A.S.R. (L.A.C. Santos). http://dx.doi.org/10.1016/j.geoderma.2015.07.010 0016-7061/© 2015 Elsevier B.V. All rights reserved. a b s t r a c t a r t i c l e i n f o Article history: Received 9 February 2015 Received in revised form 20 June 2015 Accepted 12 July 2015 Available online 25 August 2015 Keywords: Anthropogenic horizon Anthropogenic soil Diffuse reflectance spectra Hematite Goethite One of the marks left by prehistoric man in the Amazonas landscape are the dark-colored soil stains, Archeological Dark Earth (ADE), which are rich in organic matter, phosphorus and calcium. The color in this soil is presented as an attribute of difficult interpretation on the horizon, and the studies towards a better iden- tification are important. In this sense, the objective of this study was to characterize the color and iron oxides of the ADE clay fraction in Apuí region in southern Amazonas. Six trencheswere opened, where these profiles were characterized morphologically, and also samples were collected per horizon for later performance of grain size analysis, flocculation, water clay dispersion and chemicals (pH inwater and potassium chloride, calcium,magne- sium, potassium, phosphorus, potential acidity, f, organic carbon and organicmatter) andmineralogical analyses. The datawere submitted to principal component analysis. Similar behavior in the studiedprofileswas found both in physical and chemical attributes. It was concluded that the hematite and goethite, determined by x-ray diffrac- tion and diffuse reflectance spectroscopy, besides not presenting significant variations between the studied soils, present similar characteristics to non-anthropogenic Brazilian soils. The color measured by diffuse reflectance spectroscopy proved efficient to indicate variations among the ADEs, proving to be an innovative technique, efficient and promising for indirect quantification of soil characteristics in a simple and low cost manner. The re- sults show that iron oxides demonstrate be sensitive indicators of pedoenvironmental conditions and pedogenic processes of Archeological Dark Earth. © 2015 Elsevier B.V. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2. Material and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.1. Physical and chemical attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.2. Mineralogy of iron oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.3. Color measurement and determination of hematite and goethite by XRD and DRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.4. Multivariate analysis — PCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 ), marques@fcav.unesp.br anildoufam@gmail.com S. Bahia), santoslac@gmail.com 1. Introduction Soils in Amazonas, known as Archeological Dark Earth (ADE), con- trast with no anthropogenic soils of the Amazonas region, mainly due to its natural fertility difference which is characterized by the wide http://crossmark.crossref.org/dialog/?doi=10.1016/j.geoderma.2015.07.010&domain=pdf http://dx.doi.org/10.1016/j.geoderma.2015.07.010 mailto:aquino.rea@gmail.com mailto:marques@fcav.unesp.br mailto:mcesarsolos@gmail.com mailto:ivanildoufam@gmail.com mailto:angelicasantosrabelo@yahoo.com.br mailto:santoslac@gmail.com Journal logo http://dx.doi.org/10.1016/j.geoderma.2015.07.010 http://www.sciencedirect.com/science/journal/00167061 www.elsevier.com/locate/geoderma 36 R.E. Aquino et al. / Geoderma 262 (2016) 35–44 availability of nutrients such as calcium (Ca), magnesium (Mg), zinc (Zn) and manganese (Mn) (Kern and Kämpf, 1989; Cunha et al., 2009) (Kern and Kämpf, 1989; Kern et al., 2003; Cunha et al., 2009), high organic matter (OM), high OM, intense biological activity, pH in water around 5.2 to 6.4; available phosphorus (P) in general above 250 mg dm−3, Zn and Mn above 200 and 450 mg kg−1, respectively (Lima et al., 2002). The anthropogenic horizons of ADEs are well drained, texture ranging from sandy to heavy clay and the presence of anthropogenic horizon A between 0.30 and 0.60 m depth (Campos et al., 2012; Santos et al., 2013). In terms of geographical distribution, German (2003) stated that the soils of the ADEs are distributed in the formof discontinuous spots throughout the Amazon. They are locat- ed in areas near watercourses (Centro de Pesquisa de Recursos Minerais — CPRM, 2010), in marginal elevations, upland and lowland areas (Teixeira and Martins, 2003; Macedo and Teixeira, 2009). Studies in ADE soils occur mainly for fertility purposes and on a smaller scale for studies of its genesis, its physical (Moreira, 2006; Kim et al., 2007; Santos et al., 2013) and microbiological attributes, where Navarrete et al. (2010) claim that the soil microbial community can be strongly influenced with the support of the black carbon present in ADEs. Researches oriented to the mineralogy of the ADEs is still incipi- ent, specifically for clay fraction oxides that are even scarcer. However, studies concerning the ADE iron oxides are required, taking into account the importance of oxides in tropical and subtropical soils, once they are characterized by being sensitive indicators of pedo-environmental con- ditions and pedogenic processes (Schwertmann and Taylor, 1989). Soil color is a property that is indicative of iron oxide presence or ab- sence, which varies according to the mineral type or proportions be- tween them, as well as their distribution over the soil, having an outstanding importance in the soil classification system of Brazil (Resende et al., 2007). However, this determination, used worldwide by pedologists, is based on visual perception, that is, subjective, and ac- cording to Campos and Demattê (2004), differences in color perception can result in classification errors. Color analysis with measuring instruments, such as the diffuse re- flectance spectroscopy (DRS), results in greater precision, given the con- trolled and not subjective conditions. Several authors (Torrent and Barron, 1993; Barrón et al., 2000; Viscarra Rossel and Webster, 2011; Bahia et al., 2014) have demonstrated the potential use of this tech- nique. The advantages of DRS over traditional methods are rapidity, cost savings, no use of reagents and being a non-destructive method (Brown et al., 2006; Viscarra Rossel et al., 2006). Therefore, the detailed characterization of DAEs can contribute to understanding its genesis and behavior in specific environments of the Amazon, allowing the establishment of hypotheses in the reproduction of artifacts of their main qualities. Moreover, the hypothesis of this study is that soil color characterization can be an important tool to esti- mate soil attributes, especially iron oxides. Given the above, the objec- tive of this study was to characterize soil color and iron oxides of clay fraction in Dark Archeological Earth within the region of Apuí, in the state of Amazonas. 2. Material and methods The study area is located in the southern Amazonas distributed in the Apuí region (Fig. 1). The climate is hot and humid with little pro- nounced dry season, “Am” type by the Köppen classification (1948). The average annual temperature varies between 25 °C and 27 °C, rela- tive humidity of 85%, and with rainfall above 2200 mm per year (Centro de Pesquisa de Recursos Minerais — CPRM, 2001). The geology of the Apuí region involves the geological domain formed by older rocks (Proterozoic and Paleozoic), inserted within Central Brazil Shield cratonic area with predominantly crystalline rocks (granites and gneisses, volcanic coverage and metasedimentary rocks) (Secretaria de estado do meio ambiente e desenvolvimento sustentável — SDS, 2004). Representative locations of the DAEs, as shown in Fig. 1 and Table 1, have an average of 10-year non-intensive agricultural exploration and use. In these places, trenches were opened and the soil profiles were characterized morphologically and collected by horizon according to Santos et al. (2005). Physical, chemical and mineralogical analyses were performed in the samples. Then, the soilswere classified according to criteria established by the Brazilian Society of Soil Science and Soil Taxonomy (Empresa Brasileira de Pesquisa Agropecuária — EMBRAPA, 2013; Soil Survey Staff, 1999). The particle size analyses were performed using a NaOH 0.1mol L−1 solution as chemical dispersant and mechanical stirring in high-speed apparatus for 15min. The clay fraction was separated by sedimentation using a pipette for its removal, the coarse and fine sand by sieving and the silt was calculated by difference. The water dispersed clay was de- termined and the degree of flocculation was calculated (Empresa Brasileira de Pesquisa Agropecuária — EMBRAPA, 1997). The pHwas determined potentiometrically using a 1:2.5 ratio of soil in water and KCl (Empresa Brasileira de Pesquisa Agropecuária — EMBRAPA, 1997). Contents of Ca, Mg, exchangeable K, available P, and potential acidity (H+Al)were extracted by ion-exchange resinmethod (van Raij et al., 1987). The total organic carbon (TOC) was determined by the Walkley–Black method modified by Yeomans and Bremner (1988). The OM was estimated based on organic carbon. Using results of chemical analysis, the sumof bases (SB), the cation exchange capacity (CEC) and the base saturation (V%) were calculated. To obtain the diffuse reflectance spectra (DRS), evaluations were made with the laboratory Perkin-Elmer Lambda 950 UV/Vis/NIR sensor (Perkin Elmer, United Kingdom), equipped with 80 mm integrating sphere. Approximately 0.5 g of fine air-dried soil (FADS) was ground in an agate mortar until constant color was obtained. The content was placed into a sample holder with a cylindrical space of 16 mm in diam- eter. The reflectance valueswere determined every 0.5 nmwith an inte- gration time of 0.2 s, performing a scanning at the range of 380–780 nm. After obtaining the diffuse reflectance spectra of the soil samples, the tristimulus values XYZ defined by the International Comisión de L'Eclairage were determined. From the XYZ coordinates, the Munsell Values (hue, value and chroma) and RGB (used for digital representa- tion of color) were deduced using theMunsell Conversion software ver- sion 6.4, according to Barrón et al. (2000). For the x-ray analysis diffraction (XRD), clay was separated from the soil sample by centrifugation method. Minerals from the clay fraction hematite (Hm) and goethite (Gt) were characterized by XRD in blades made with powdered material. The characterization of Hm and Gt oc- curred after treating clay fraction with NaOH 5 mol L−1 (1 g clay per 100 ml solution) for the concentration thereof, according to Norrish and Taylor (1961) method and modified by Kämpf and Schwertmann (1982). The ratio Gt / (Gt + Hm) was obtained after calculation of re- flection areas of Hm (012) and Gt (110), in the diffractogram reflec- tions; and in this case, the Gt (110) peak area was multiplied by 0.35 due to 35% of Hm (012) intensity (Kämpf and Schwertmann, 1998). The mean crystal diameter (MCD) was calculated from the width at half-maximum height (WHH) of the Hm (110 and 012) and Gt (110 and 111) reflections using the Scherrer equation (Klug and Alexande, 1974). The diffractometer used was the Mini-Flex Rigaku II, using copper cathode with nickel filter and kα radiation (20 mA, 30 kV). The scan speed was of 1° 2θ per minute with amplitude 23 to 49° 2θ for the Hm and Gt characterization. Procedures suggested by Schulze (1984) were used to calculate iso- morphic substitution (mol mol−1) of iron by aluminum in Gt, to which is proposed the following equation: molAl% ¼ 1730−572 � c ð1Þ where, c = 1 ∕ (1∕d1112 − 1∕d1102 )½. Fig. 1. Map showing location of soil profiles in Apuí region, southern of Amazonas state, Brazil. 37R.E. Aquino et al. / Geoderma 262 (2016) 35–44 As for the calculation of isomorphous substitution content (mol mol−1) of iron by aluminum in Hm, the equation proposed by Schwertmann et al. (1979) was used: molAl% ¼ 3098:8−615:12 � a0 ð2Þ where, a0 = 2 d110. The crystalline iron content was multiplied by the ratio Gt / (Gt + Hm) and by 1.59 to obtain estimates of Gt content. Yet for hema- tite, it was multiplied by 1.43, and then subtracting from this value the Table 1 Identification of profiles, coordinates, location, occupation, position. Profile Coordinate Location Occupation Position 1 S 07°6′32,8″ W 59°51′6,9″ 1Vic. Mariano Km 4 Corn Top down 2 S 07°6′54,9″ W 059°52′22,1″ Vic. Sulino Km 11 Orchard Top 3 S 07°7′9,1″ W 59°46′1,1″ BR 230 Km 17 Pasture Top 4 S 07°9′5,7″ W 059°42′52,1″ Vic. Fábio Lucena Km 26 Coffee Top 5 S 07°10′4,4″ W 59°42′55,4″ Vic. Fábio Lucena Km 28 Pasture hillside 6 S 07°12′28,4″ W 059°40′22,3″ Vic. Paredão Km 34 Capoeira Top 1 Vic. = Vicinal. amount of iron corresponding to the Gt (Dick, 1986), according to the equations: Gt=GtþHmð Þ½ � � Fed%−Feo%ð Þ ¼ %FeGt ð3Þ FeGt%� 1:59 ¼ FeOOH ¼ %Gt ð4Þ FeGt%− Fed%−Feo%ð Þ ¼ FeHm% ð5Þ FeHm%� 1:43 ¼ Fe2O3 ¼ Hm% ð6Þ Al and Fewere extracted from FADS by digestionwithH2SO4 1:1 and the Si by subsequent alkaline dissolution. The results were expressed as oxides (Al2O3, Fe2O3 and SiO2) according to Empresa Brasileira de Pesquisa Agropecuária — EMBRAPA (1979). The determination of dithionite iron (Fed) followed the methodology of Mehra and Jackson (1960), and the determination of the iron oxalate (Feo) followed the method of Camargo et al. (1986). The data were submitted to principal component analysis (PCA), with the aim of summarizing the values of the studied attributes at various en- vironments. For this purpose, the initial set of 32 variables has become characterized by two new latent variables (CP1 and CP2), which has en- abled the location in two-dimensional figures (ordering of accesses by principal components). The suitability of this analysis is verified by the total information of the original variables; it is retained in the main com- ponents that show eigenvalues superior or inferior to the unit, and not having relevant information. All multivariate statistical analyses were processed in the STATISTICA software version 7.0 (STATSOFT, Inc., 2004). 38 R.E. Aquino et al. / Geoderma 262 (2016) 35–44 3. Results and discussion 3.1. Physical and chemical attributes Regarding the DAE particle size fractions, it was noted silt and clay predominancewith a trend to increase in depth of clay fraction froman- thropogenic horizon to the subsurface one. Contrarily, the silt fraction had different behavior, except only for the P3, which presented domi- nance of silt fraction in anthropic and subsurface horizons (Table 2). The P5 presented a coarse sand fraction dominance, in which a clear variation in texture was verified due to DAE position within the relief, because of colluvial materials along the slope (Table 2). Silva et al. (2012) studied DAEs of Ultisols in Southwestern Amazon and observed sand fraction predominance in all horizons. The silt/clay ratio is used as an auxiliary index to indicate soil weathering degree; thus, the higher the value of this ratio, the smaller is the degree of weathering (Jacomine, 2005). The silt/clay ratio in the studied profiles showed higher values in the anthropic horizon than in the subsurface one for all profiles, what indicates the lower degree of Table 2 Physical attributes profiles of Archeological Dark Earth sites region of Apuí, southern of Amazonas state, Brazil. Hor.a Depth (cm) Gravel Fine sand Silt g kg−1 Clay Silt/clay WDCb DFc % P1—Typic Hapludox (Yellow Latosol dystrophic anthropic, clay texture) Ap1 0–15 120.38 35.42 513.14 331.07 1.55 170.2 48.59 Ap2 15–34 75.00 31.22 456.82 436.96 1.05 143.04 67.26 AB 34–63 54.20 26.59 339.89 579.32 0.59 252.72 56.37 BA 63–91 52.39 26.52 302.87 618.21 0.49 4.28 99.30 Bw1 91–117 48.52 26.01 275.89 649.57 0.43 3.44 99.47 Bw2 117–152+ 50.16 27.47 295.27 627.09 0.47 0.56 99.91 P2—Typic Paleudult (Yellow Argisol eutrophic typical, clay texture, A anthropic) Ap1 0–15 60.64 36.22 519.76 383.38 1.37 229.20 40.21 Ap2 19–30 56.83 33.08 397.21 512.88 0.78 318.96 37.81 AB 30–48 39.70 21.73 317.76 620.81 0.51 204.36 67.08 Bt1 48–66 21.03 18.09 278.94 681.95 0.41 492.04 27.84 Bt2 66–100 19.71 17.85 287.44 675.00 0.43 185.56 72.50 Bt3 100–130+ 18.38 14.89 285.73 681.00 0.42 604.68 11.20 P3—Typic Paleudult (Yellow Argisol dystrophic typical, silty texture, A anthropic) Ap1 0–21 25.70 60.43 585.58 328.25 2.51 37.32 94.10 Ap2 21–36 67.16 29.44 692.08 211.32 3.28 97.04 54.07 AB 36–58 61.56 29.91 655.21 253.32 2.60 85.4 66.28 Bt1 58–91 61.97 31.21 645.03 261.79 2.47 3.96 98.48 BCr 91–120+ 63.94 30.15 618.60 287.31 2.15 0.20 99.93 P4—Typic Paleudult (Yellow Argisol dystrophic typical, clay texture, A anthropic) Ap1 0–19 107.99 223.99 304.10 363.92 0.84 81.56 77.58 BA 19–41 155.72 104.15 266.59 473.53 0.57 31.36 93.37 Bt1 41–67 118.83 65.88 391.44 423.85 2.18 1.36 99.67 Bt2 67–104 107.75 59.15 233.90 599.20 0.39 0.44 99.92 Bt3 104–147+ 99.78 55.84 298.48 545.89 0.55 0.40 99.92 P5—Typic Udipsamments (Regolithic Neosol dystrophic typical, sandy medium texture, A anthropic) Ap1 0–18 484.09 296.22 139.63 80.05 1.74 1.04 98.70 Ap2 18–31 500.88 295.61 124.90 78.60 1.61 3.96 94.96 AC 31–49 519.28 304.18 94.50 82.04 1.15 19.44 76.30 C1 49–70 546.21 298.98 81.74 73.07 1.21 2.08 97.15 C2 70–90 542.55 278.75 64.21 114.49 0.57 12.24 89.30 C3 90–116 506.85 285.05 98.66 109.44 0.90 63.16 42.28 C4 116–135+ 477.50 270.72 70.60 181.19 0.39 119.00 34.32 P6—Typic Paleudult (Yellow Argisol dystrophic typical, clay texture, A anthropic) Ap1 0–15 220.76 140.69 355.11 283.44 1.25 92.52 67.35 AB 19–30 178.78 137.57 273.98 409.68 0.67 172.44 57.90 Bt1 30–48 125.15 80.26 240.14 554.45 0.43 208.28 62.43 Bt2 48–66 131.96 67.06 225.49 575.49 0.39 161.28 71.97 Bt3 66–100 124.38 73.53 265.84 536.24 0.50 408.04 23.90 Bt4 100–130+ 126.80 75.77 228.42 569.01 0.40 293.56 48.40 a Hor. = horizons. b WDC= water dispersible clay. c DF = degree flocculation. weathering, reinforcing its anthropogenic origin. The P3 showed values silt/clay high throughout the profile, indicating a lower degree of weathering when compared to the other profiles (Table 2). Water dispersible clay (WDC) presented for P1, P3 and P4 higher values in the first horizons. This behavior comes from the higher contri- bution of iron oxides at greater depths in themost weathered soils; and P2, P5 and P6 showed high values with increased depth; in this case, in- dicating greater movement of clay along the soil profile. The stability can be noted through DF for aggregates presented in P3, P4 and P5, in anthropic horizons, caused by the direct contribution of OM in this soil (Table 2). These results are in agreement with Lima et al. (2002) and Santos et al. (2013), who stated that severe weather conditions favor destruction of soil aggregates, although the organization state of the structure is highly developed. The Ca values in the anthropic horizon ranged from 11.0 to 122.0 mmol kg−1, with a decrease in depth in the subsurface horizons. The Mg varied from 4.0 to 15.0 mmol kg−1 in the anthropogenic hori- zon, in which values decrease with depth increases (Table 3). The P2 was the one with the highest Ca value; it is possibly due to the incorpo- ration of bones rich in Ca, or due to the higher affinity of Ca by the ex- change surfaces, resulting in lower leaching as highlighted by Barros et al. (2012). The other profiles that presented low value may be re- flexes of time variation and density of human occupation in these areas (Campos et al., 2012). The K contents were very low ranging from 0.10 to 1.70mmol kg−1. Falcão and Borges (2006) and Barros et al. (2012) also found such K values in DAEs. This may be a limiting element in crop production grown in DAEs. Considering that the appropriate average levels of Ca, Mg and K are 28mmol kg−1, 8 mmol kg−1, and 2.3 mmol kg−1, respec- tively, it can be inferred that low K values found in all the DAE profiles were greater or equal to 1.40 mmol kg−1, presenting high nutritional imbalance for plant growth and production. The pHprofiles of DAEs is acids,with values between5.6 to 4.10 con- nected to organic complexes that have provided this acidification through the release of H+ in the process of decomposition of organic matter. In this sense, noted that the Al3+ and consequently the satura- tion by aluminum (m%) are found in very low concentrations, indicating that these are complexed in compounds of organic matter. The acidity potential features and concentrations, are usually found in Amazonian soils (Santos et al., 2013). The CEC had high values for anthropogenic horizons, pointing out P1 and P2, which presented the highest ones. On the other hand, P5 pre- sented the lowest values (Table 3). It is important to emphasize the de- crease on CEC values with the increase in depth; this behavior can be justified by larger amounts of highly reactive organic matter originated from pyrogenic carbon in anthropogenic horizon of these soils (Glaser et al., 2000; Cunha et al., 2007). Liang et al. (2006) studying the Amazon DAE solos showed that the charge of CEC is much larger in relation to adjacent soils poor in the Amazon due to higher concentrations of or- ganic carbon. The highest percentages of V% were observed at P2, which is classi- fied as eutrophic, and the other profiles as dystrophic, implying in low fertility of these profiles. Campos et al. (2011) found profileswith eutro- phic characteristics among the DAE profiles in study; Santos et al. (2013) found profiles ranging from eutrophic to dystrophic,which rein- forces the idea of variation in anthropogenic soils. Concerning the P contents, P1, P2 and P3 showed elevated values that ranged between 84.0 and 173.0mg dm−3, whereas in P4, P5 and P6 they varies from 22.0 to 65.0 mg dm−3 (Table 3). In summary, these numbers are much higher than levels found in non-anthropogenic soils of the Amazonas, in which P concentrations typically lower than 5 mg kg−1 are observed (Rodrigues, 1996); indicating a decisive anthropogenic in- fluence in DAE formation. It is known that phosphorus presents organic origin, which may explain its higher concentrations in anthropic hori- zons, and transport to the subsurface horizon may still occur. Lima et al. (2002) justify this behavior with the occurrence of intense Table 3 Chemical attributes of profiles of Archeological Dark Earth sites in region of Apuí, southern of Amazonas state, Brazil. Hor. Depth cm pH H20 pH KCl Δ pH Ca Mg K SB Al H + Al CEC V m P TOC OM mmolc kg−1 % mg dm−3 g dm−3 P1 Typic Hapludox — (Yellow Latosol dystrophic anthropic, clay texture) Ap1 0–15 4.50 4.30 −0.20 48.00 7.00 1.30 56.30 0.40 109.00 165.30 34.10 2.26 166.00 37.70 65.00 Ap2 15–34 4.10 4.10 0.00 13.00 4.00 0.60 17.60 1.95 121.00 138.60 12.70 1.40 84.00 24.94 43.00 AB 34–63 4.10 4.10 0.00 6.00 2.00 0.50 8.50 2.05 98.00 106.50 8.00 1.92 94.00 10.44 18.00 BA 63–91 4.10 4.10 0.00 8.00 3.00 0.60 11.60 1.35 88.00 99.60 11.60 1.35 117.00 6.96 12.00 Bw1 91–117 4.40 4.20 −0.20 11.00 4.00 0.20 15.20 0.75 58.00 73.20 20.80 1.02 135.00 4.06 7.00 Bw2 117–152+ 4.40 4.20 −0.20 10.00 4.00 0.20 14.20 0.60 58.00 72.20 19.70 0.83 133.00 3.48 6.00 P2—Typic Paleudult (Yellow Argisol eutrophic typical, clay texture, A anthropic) Ap1 0–15 5.20 5.10 −0.10 122.00 15.00 1.30 138.30 0.00 58.00 196.30 70.50 0.00 144.00 32.48 56.00 Ap2 19–30 5.10 5.00 −0.10 92.00 14.00 1.00 107.00 0.00 58.00 165.00 64.80 0.00 173.00 18.56 32.00 AB 30–48 4.90 4.70 −0.20 62.00 13.00 0.90 75.90 0.00 52.00 127.90 59.30 0.00 159.00 9.28 16.00 Bt1 48–66 4.80 4.50 −0.30 52.00 8.00 0.90 60.90 0.00 52.00 112.90 53.90 0.00 143.00 5.22 9.00 Bt2 66–100 4.80 4.50 −0.30 47.00 6.00 1.50 54.50 0.00 47.00 101.50 53.70 0.00 152.00 4.64 8.00 Bt3 100–130+ 4.80 4.60 −0.20 42.00 6.00 1.70 49.70 0.00 42.00 91.70 54.20 0.00 157.00 3.48 6.00 P3—Typic Paleudult (Yellow Argisol dystrophic typical, silty texture, A anthropic) Ap1 0–21 4.50 4.20 −0.30 41.00 8.00 1.40 50.40 0.50 98.00 148.40 34.00 2.54 125.00 33.06 57.00 Ap2 21–36 4.50 4.30 −0.20 14.00 5.00 0.50 19.50 1.10 98.00 117.50 16.60 0.93 61.00 23.78 41.00 AB 36–58 4.40 4.20 −0.20 6.00 3.00 0.50 9.50 1.20 98.00 107.50 8.80 1.11 57.00 16.24 28.00 Bt1 58–91 4.40 4.30 −0.10 2.00 1.00 0.40 3.40 0.80 64.00 67.40 5.00 1.18 68.00 7.54 13.00 BCr 91–120+ 4.41 4.40 −0.01 2.00 1.00 0.30 3.30 0.80 64.00 67.30 4.90 1.18 68.00 6.38 11.00 P4—Typic Paleudult (Yellow Argisol dystrophic typical, clay texture, A anthropic) Ap1 0–19 4.30 4.10 −0.20 16.00 5.00 0.80 21.80 1.20 109.00 130.80 16.70 2.76 65.00 18.56 32.00 BA 19–41 4.20 4.00 −0.20 11.00 4.00 0.10 15.10 1.05 64.00 79.10 19.10 1.32 34.00 6.38 11.00 Bt1 41–67 4.20 4.10 −0.10 11.00 4.00 0.10 15.10 0.65 42.00 57.10 26.40 1.13 41.00 4.06 7.00 Bt2 67–104 4.25 4.20 −0.05 10.00 4.00 0.10 14.10 0.45 34.00 48.10 29.30 0.93 41.00 3.48 6.00 Bt3 104–147+ 4.30 4.20 −0.10 9.00 4.00 0.10 13.10 0.40 34.00 47.10 27.80 0.84 32.00 3.48 6.00 P5—Typic Udipsamments (Regolithic Neosol dystrophic typical, sandy medium texture, A anthropic) Ap1 0–18 5.30 4.30 −1.00 50.00 10.00 0.50 60.50 0.00 31.00 91.50 66.10 0.00 55.00 17.98 31.00 Ap2 18–31 5.30 4.40 −0.90 55.00 10.00 0.30 65.30 0.00 31.00 96.30 67.80 0.00 55.00 16.24 28.00 AC 31–49 5.50 5.20 −0.30 35.00 6.00 0.20 41.20 0.00 28.00 69.20 59.50 0.00 35.00 8.70 15.00 C1 49–70 5.30 5.20 −0.10 14.00 4.00 0.10 18.10 0.00 20.00 38.10 47.50 0.00 24.00 4.06 7.00 C2 70–90 5.30 5.20 −0.10 11.00 3.00 0.10 14.10 0.00 16.00 30.10 46.80 0.00 39.00 2.32 4.00 C3 90–116 5.15 5.10 −0.05 11.00 3.00 0.10 14.10 0.00 16.00 30.10 46.80 0.00 45.00 2.32 4.00 C4 116–135+ 5.10 5.00 −0.10 11.00 3.00 0.10 14.10 0.05 1800 32.10 43.90 0.15 52.00 2.32 4.00 P6—Typic Paleudult (Yellow Argisol dystrophic typical, clay texture, A anthropic) Ap1 0–15 5.60 5.50 −0.10 70.00 11.00 0.70 81.70 0.00 31.00 112.70 72.50 0.00 33.00 19.72 34.00 AB 19–30 4.90 4.70 −0.20 30.00 8.00 0.30 38.30 0.05 42.00 80.30 47.70 0.06 22.00 9.86 17.00 Bt1 30–48 4.80 4.60 −0.20 18.00 8.00 0.20 26.20 0.05 31.00 57.20 45.80 0.08 53.00 5.22 9.00 Bt2 48–66 4.00 4.60 −0.10 13.00 7.00 0.20 20.20 0.05 31.00 51.20 39.50 0.09 64.00 4.06 7.00 Bt3 66–100 4.20 4.10 −0.10 4.00 3.00 0.10 7.10 1.20 42.00 49.10 14.50 2.44 41.00 3.48 6.00 Bt4 100–130+ 4.20 4.10 −0.10 3.00 2.00 0.10 5.10 1.15 42.00 47.10 10.80 2.44 22.00 2.90 5.00 39R.E. Aquino et al. / Geoderma 262 (2016) 35–44 bioturbation in DAEs, which results in redistribution of P in profile, enriching subsurface horizons. Lehmann et al. (2003) claims that occur high levels of organic P available and retained on OM in soils of DAEs. Organic carbon and organic matter contents varied by depth, with higher levels in the anthropic horizon. P1, P2 and P3 showed decreasing values of organic matter in depth (Table 3), in agreement with the re- sults of Cunha et al. (2007). According to Campos et al. (2012), the high content of organic carbon in the areas of DAEs is attributed to an- thropogenic changes of which this soil has suffered along formation. 3.2. Mineralogy of iron oxides Sulfuric acid digestion revealed variation in Si, Fe andAl oxides of the DAE profiles. The Al contents were higher in P1, P2 and P3, showing the richness of oxides in these soils. Contrarily, P4 presented predominance of Fe; in P6, Si showed the highest values;while in P5, Si has prevailed in anthropogenic horizon, and Al had higher levels in the subsurface one (Table 4). Santos et al. (2013) observed a predominant presence of Al2O3 in studied profiles. The Fe2O3 content present in anthropogenic horizons ranged from 30.64 to 90.70 g kg−1 and in the subsurface horizons ranged from 45.55 to 124.36 g kg−1. These limits are higher than those found by Silva et al. (2011), studying man-made soils in the Amazon, they found values of Fe2O3 ranging from 42.9 to 99.3 g kg−1, in subsurface horizons, these values are considered low, but normally found in local soils. The free iron contents (Fed) predominated over the forms of low crystallinity iron (Feo) (Table 4). The ratio Feo/Fed indicates the proportion of pedogenic iron oxides that have low crystallinity, and its raise corresponds to a decrease in crystalline iron oxides (Schwertmann and Kämpf, 1985). Furthermore, the ratio Fed/Fet infers the proportion of iron already released by weathering of primary minerals and built into the pedogenic form of iron oxides, forming thus an indication of soil weathering degree. The ratio Feo/Fed presented higher values in P1, P2, P3 and P5, indicating a larger iron content of low crystallinity (N0.05) (Table 4), and it can be considered as an indicator of anthropogenic activities, especially burn- ing of materials at higher temperatures for a period. It is noteworthy that these soils also have higher organic carbon con- tents, which affects the Feo/Fed ratio, since organic matter inhibits crys- tallization during iron oxides formation (Meirelles et al., 2012). Another reason might be the large volume of rainfall in the Amazonas region, raising reducer microenvironments under undisturbed conditions, which would lead to iron oxide dissolution and leaching into deeper layers and neo-formation of new minerals (Kämpf and Curi, 2000; Silva Neto et al., 2008). High values in all profiles can be observed in the Fed/Fet ratio (Table 4). Table 4 Content of sulfuric attack oxides (SiO2, Fe2O3, Al2O3), oxide free extractedwith dithionite–citrate–bicarbonate (Fed) and low crystallinity oxide extracted by ammonium oxalate (Feo) and the relationship between them at sites profiles Archeological Dark Earth in region of Apuí, southern of Amazonas state, Brazil. Hor. Depth (cm) SiO2 Fe2O3 Al2O3 Feda Feob Kic Krd Feo/Fed Fed/Fete g kg−1 P1—Typic Hapludox (Yellow Latosol dystrophic anthropic, clay texture) Ap1 0–15 140.50 63.49 215.00 37.38 6.69 1.11 0.55 0.18 0.59 Bw2 91–117 294.50 77.40 255.00 42.08 16.80 1.91 0.97 0.40 0.54 P2—Typic Paleudult (Yellow Argisol eutrophic typical, clay texture, A anthropic) Ap1 0–15 20.50 90.70 210.00 51.47 11.26 0.17 0.08 0.22 0.57 Bt2 48–66 289.50 124.36 250.00 74.77 11.67 1.97 0.88 0.16 0.60 P3—Typic Paleudult (Yellow Argisol dystrophic typical, silty texture, A anthropic) Ap1 0–21 17.00 52.00 170.00 24.02 19.33 0.17 0.08 0.80 0.46 Bt2 58–91 30.50 45.55 150.00 24.38 16.56 0.35 0.17 0.68 0.54 P4—Typic Paleudult (Yellow Argisol dystrophic typical, clay texture, A anthropic) Ap1 0–19 131.00 54.22 90.00 32.87 5.79 2.47 1.05 0.18 0.61 Bt2 41–67 108.00 98.96 85.00 54.18 9.87 2.16 0.73 0.18 0.55 P5—Typic Udipsamments (Regolithic Neosol dystrophic typical, sandy medium texture, A anthropic) Ap1 0–18 13.50 30.64 35.00 17.52 2.28 0.66 0.25 0.13 0.57 C2 49–70 5.50 115.69 25.00 56.71 17.95 0.37 0.06 0.32 0.49 P6—Typic Paleudult (Yellow Argisol dystrophic typical, clay texture, A anthropic) Ap1 0–15 88.00 57.85 125.00 59.95 1.22 1.20 0.54 0.02 1.04 Bt2 30–48 56.50 81.02 200.00 39.37 4.08 0.48 0.22 0.10 0.49 a Feo = Fe2O3 extracted by ammonium oxalate. b Fed = Fe2O3 extracted by ditionite–citrate–bicarbonate. c Ki = relationship (%SiO2 × 1.7) / %Al2O3. d Kr = (%SiO2 × 1.7) / (%Al2O3 + %Fe2O3 × 0.64). e Fet = total iron on values Fe2O3. 40 R.E. Aquino et al. / Geoderma 262 (2016) 35–44 According to Resende and Santana (1988), Kr values lower than 0.75 define the soilwith oxidicmineralogical characteristics and, higher than 0.75 with kaolinitic ones, while values close to 1.0 emphasize a balance between these twominerals. Kr value in the anthropogenic horizon pre- sented oxidic characteristics, except for P4, had a balance between the two minerals (Table 4). Regarding the crystallinity degree and particle size, it is known that the larger the diffraction peak, the lower the crystal size and the worse the crystallinity degree. Crystallinity differences were observed be- tween the surface layers of each profile, as well as between profiles. The highest values of MCD was found on Hm 012, in Gt occurred Table 5 Crystallographic characteristics of iron oxides in Archeological Dark Earth sites profiles in regio Hor. Depth (cm) WHH WHH MCD MCD Gt 110 Gt 111 Hm 110 Hm 012 Gt 110 Gt 111 Hm 11 P1—Typic Hapludox (Yellow Latosol dystrophic anthropic, clay texture) Ap1 0–15 0.21 0.20 0.27 0.16 38.80 42.40 31.60 Bw2 91–117 0.37 0.32 0.32 0.15 22.40 26.80 26.90 P2—Typic Paleudult (Yellow Argisol eutrophic typical, clay texture, A anthropic) Ap1 0–15 0.27 0.41 0.16 0.14 30.60 21.00 52.90 Bt2 48–66 0.31 0.39 0.30 0.12 26.70 22.00 28.60 P3—Typic Paleudult (Yellow Argisol dystrophic typical, silty texture, A anthropic) Ap1 0–21 0.32 0.28 0.31 0.11 25.90 30.50 27.70 Bt2 58–91 0.49 0.54 0.35 0.09 17.10 16.00 24.60 P4—Typic Paleudult (Yellow Argisol dystrophic typical, clay texture, A anthropic) Ap1 0–19 0.18 0.34 0.35 0.09 45.30 25.20 24.60 Bt2 41–67 0.21 0.25 0.45 0.09 39.00 34.10 19.20 P5—Typic Udipsamments (Regolithic Neosol dystrophic typical, sandy medium texture, A anth Ap1 0–18 0.32 0.47 0.29 0.09 25.90 18.30 29.60 C2 49–70 0.31 0.46 0.65 0.51 26.70 18.70 13.30 P6—Typic Paleudult (Yellow Argisol dystrophic typical, clay texture, A anthropic) Ap1 0–15 0.29 0.28 0.29 0.13 28.50 30.50 29.50 Bt2 30–48 0.29 0.35 0.25 0.11 28.50 24.50 34.30 Hor = horizon, WHH= width at half-maximum height (°2θ), MCD = mean crystal diameter goethite, Hm = hematite, content (g kg−1). variation between the reflections from 16.00 to 45.30 nm (Table 5). Resende (1976) found for Gt in several Oxisols of Brazil, mean values from15 to 38 nm for d110 and d111 reflections, respectively. TheMCD re- sults of Gt in the DAE values exceeded the average of Brazilian soils. Interestingly for WHH, the results were inverse to the MCD, that is, where larger MCD values occurred (Table 5). According to the claims of Fitzpatrick and Schwertmann (1982), the highest degree of crystal- linity is evidenced by thehigherMCDand lowerWHH. In this case, it ap- pears that Hm is presented with a greater degree of crystallinity due to occurrence of higher values of MCD and lower of WHH in the profiles studied. There is a general trend for the Gt having smaller crystals n of Apuí, southern of Amazonas state, Brazil. SSA Is Gt / (Gt + Hm) Content 0 Hm 012 Gt Hm Gt Hm Gt Hm 51.30 59.31 46.92 24.29 21.40 0.55 31.20 23.40 55.00 106.34 51.53 24.68 50.94 0.65 31.30 15.10 74.20 76.70 28.92 16.27 12.14 0.69 74.40 30.50 68.20 88.60 46.95 18.94 55.16 0.74 99.00 31.00 74.20 91.55 47.37 30.95 4.72 0.60 2.70 1.60 89.90 141.19 50.75 21.07 29.20 0.63 17.80 9.40 89.90 50.15 50.75 30.95 21.40 0.65 31.60 15.10 89.90 59.03 63.03 17.45 29.66 0.71 59.40 21.60 ropic) 87.90 91.55 43.55 30.00 13.08 0.56 10.60 7.40 16.40 88.60 119.74 31.00 21.40 0.87 35.30 4.70 62.60 82.68 46.64 37.60 21.40 0.64 59.40 30.50 74.20 82.68 39.96 30.90 37.88 0.72 61.40 21.00 (nm), SSA = specific surface area (m2 g−1), Is = isomorphous substitution (mol%), Gt = 41R.E. Aquino et al. / Geoderma 262 (2016) 35–44 than the Hm (Resende et al., 2011), however, in ADEs profiles occurred presence of DMC Gt crystals larger than those of Hm. The values of the specific surface area (SSA) in Gt remained between 50.15 and 141.19 m2 g−1 and in the Hm between 28.92 and 119.74 m2 g−1 (Table 5). According to Cornell and Schwertmann (1996), the SSA influences the reactivity of iron oxide since the number of existing functional groups on the surface of theseminerals that inter- act with soluble species and gases depends on this attribute. Table 6 Color measurements by Munsell charts and diffuse reflectance spectra (DRS) profiles of Archeo Horizon Depth (cm) Munsell Hue Value Chroma P1- Typic Hapludox (Yellow Latosol dystr Ap1 0–15 10YR 2.00 1.00 Ap2 15–34 10YR 2.00 2.00 AB 34–63 10YR 3.00 2.00 BA 63–91 10YR 3.00 2.00 Bw1 91–117 10YR 5.00 6.00 Bw2 117–152 10YR 5.00 6.00 P2- Typic Paleudult (Yellow Argisol eutrop Ap1 0–15 10YR 2.00 1.00 Ap2 19–30 10YR 2.00 2.00 AB 30–48 10YR 3.00 3.00 Bt1 48–66 10YR 4.00 4.00 Bt2 66–100 10YR 5.00 6.00 Bt3 100–130 10YR 5.00 8.00 P3- Typic Paleudult (Yellow Argisol dystrop Ap1 0–21 10YR 2.00 1.00 Ap2 21–36 10YR 2.00 2.00 AB 36–58 10YR 3.00 3.00 Bt1 58–91 10YR 4.00 4.00 BCr 91–120+ 10YR 5.00 8.00 P4- Typic Paleudult (Yellow Argisol dystroph Ap 0–21 10YR 2.00 2.00 AB 21–36 10YR 4.00 3.00 Bt1 36–58 10YR 5.00 6.00 Bt2 58–91 10YR 5.00 8.00 Bt3 91–120+ 10YR 5.00 8.00 P5- Typic Udipsamments (Regolithic Neoso Ap1 0–18 10YR 2.00 1.00 Ap2 18–31 10YR 2.00 2.00 AC 31–49 10YR 4.00 3.00 C1 49–70 10YR 5.00 4.00 C2 70–90 10YR 5.00 6.00 C3 90–116 10YR 5.00 8.00 C4 116–135 10YR 5.00 8.00 P6- Typic Paleudult (Yellow Argisol dystr Ap1 0–5 10YR 2.00 2.00 AB 19–30 10YR 3.00 4.00 Bt1 30–48 10YR 4.00 4.00 Bt2 48–66 10YR 5.00 6.00 Bt3 66–100 10YR 6.00 6.00 Bt4 100–130 10YR 6.00 8.00 Mineral isomorphous substitution (Is) means exchange of elements without substantial alteration in its structure. In the DAE profiles of this study, the Is in Gt ranged from 16.27 to 37.60mol%, while the Hm ranged from4.72 to 55.16mol%. There is a greater isomorphic substitution rate in Hm (Table 5), with values above the average for Brazilian soils. In studies on Brazilian soils, Rezende (1980) observed variations on Gt values that ranged from 2 to 33mol%; while Kämpf et al. (1988) reported maximum values of 36 mol% for goethite and from 4 to 17 mol% for hematite. logical Dark Earth sites in region of Apuí, southern of Amazonas state, Brazil. DRS Colors Hue Value Chroma Colors ophic anthropic, clay texture) 9.99YR 4.47 3.33 0.24Y 4.72 3.58 9.92YR 5.65 4.53 9.88YR 6.29 4.99 0.01Y 6.75 5.88 0.05Y 7.01 6.00 hic typical, clay texture, A anthropic) 9.82YR 4.09 3.69 9.82YR 4.66 4.06 9.79YR 5.40 5.03 9.28YR 5.67 6.01 9.09YR 5.88 6.33 9.24YR 5.88 6.52 hic typical, silty texture, A anthropic) 9.54YR 3.46 3.66 9.78YR 3.94 3.80 9.85YR 4.47 4.27 9.95YR 5.73 5.54 0.03Y 6.08 6.02 ic typical, clay texture, A anthropic) 0.77Y 4.70 3.54 0.75Y 6.18 5.05 0.41Y 6.60 5.86 0.18Y 6.77 6.38 0.05Y 6.73 6.45 l dystrophic typical, sandy medium texture, A anthropic) 0.17Y 3.73 3.13 0.28Y 3.89 3.07 0.27Y 4.17 3.66 0.02Y 5.60 4.99 9.64YR 5.70 6.03 9.53YR 5.77 6.24 9.33YR 5.83 6.62 ophic typical, clay texture, A anthropic) 0.06Y 4.60 4.15 9.95YR 5.19 4.96 9.59YR 6.12 6.17 9.39YR 6.28 6.74 9.76YR 6.75 6.49 9.01YR 6.05 5.50 Unlabelled image 42 R.E. Aquino et al. / Geoderma 262 (2016) 35–44 The ratio Gt / (Gt +Hm) in the DAE profiles values above 50% in the surface and subsurface layers for all profiles, indicating a greater pres- ence of goethite. This statement is reinforced by Gt and Hm contents, where in all profiles; there is a predominance of Gt (Table 5). Gt preva- lence within these soils can be explained by OM accumulation along profiles as regards of the anthropogenic formation. As according to Schwertmann and Taylor (1989), organic matter favors Gt formation to the detriment of Hm, working on iron complexation and ferrihydrite inhibition, which is a Hm precursor (Curi and Franzmeier, 1984). 3.3. Color measurement and determination of hematite and goethite by XRD and DRS Colors observed by DRS and matched to a Munsell Color Chart, in which are determined hue (light wavelength), value (brightness or to- nality) and chroma (color intensity or pureness in relation to gray) pre- sented differences (Table 6). This is because Munsell Color Chart identification is based on visual perception; therefore, being subjective, in which the factors of greatest effect are non-objective (Melville and Atkinson, 1985; Post et al., 1993). On the other hand, color determina- tion by DRS is qualitative, that is, has greater precision due to its con- trolled conditions (Botelho et al., 2006). The hue identified by Munsell Chart presented 10YR color notation in all profiles, while DRS hue presented values close to those indicated by the Munsell Chart in profiles P1, P2, P3 and P6; and in P4 and P5, it presented measures ranging from 9.64YR to 0.02Y (Table 6). Organic matter promotes dark colors on surface horizons and some subsurface horizons (illuvial). Red, yellow and dark colors are attributed to the presence of iron oxides, while grayish colors are related to reduction and removal of iron oxides in hydromorphic conditions (Barrón and Torrent, 1986; Azevedo and Dalmolin, 2004; Botelho et al., 2006). Both theMunsell Chart and theDRS valueswere lower in the surface layers, in which the anthropogenic horizons are located, and increased with depth. This trend is related to organic matter high content in an- thropogenic horizons (Botelho et al., 2006). The chroma presented the highest variation in Munsell and DRS (Table 6) what may be related to visual toughness to evaluate chroma since shades of gray are not well discerned by eyes. There is a clear difference between Munsell Color Chart and DRS re- sults about hue, value and chroma. These results show the importance of more precise quantitative techniques, such as DRS, for interpreting soil color measurement, given its importance in Brazilian Soil Science. Barrón and Torrent (1986) reported that DRS is useful not only for color identification but also for quantification of iron oxide amounts, in particular Hm and Gt, once they are highly correlated with soil coloring. With the purpose of measure DRS technique accuracy in quantifying iron oxides indirectly, the levels of Hm and Gt, estimated by this meth- odology, were related to levels of these minerals determined by x-ray diffraction (XRD) (Fig. 2). The results show that there was a positive relation between the methods for Hm (r = 0.78; p b 0.01) and Gt (r = 0.98; p b 0.01), indicating that the DRS can be used in quantifying Fig. 2. Linear regressionmodels of hematite (Hm) and goethite (Gt) by themethod of x-ray diffr in Apuí region, southern of Amazonas state, Brazil. these iron oxides indirectly also in ADEs. The high R2 in Gt can be related to the stronger presence of this mineral in DAE profiles, evidenced in Table 6. The results above indicate that the DRS technique is a promising al- ternative to be used for indirect determination of soil attributes. This can be stated, since Hm and Gt are covariate minerals of soil processes, and therefore, are an auxiliary tool in the characterization of different envi- ronments in the Amazonas region. 3.4. Multivariate analysis — PCA In order to evaluate the interaction of physical, chemical and miner- alogical attributeswith the anthropogenic profiles was used to principal component analysis (PCA) (Fig. 3). The PCA has confirmed the results presented for the characterization of profiles (Tables 2, 3, 4 e 5). The first group was formed by P2 and P6, showing strong relationship with clay fraction and soil mineralogy, represented mainly by Hm, Gt and Fed. The second group was formed by P1, P3 and P4 and is linked to variables that indicate soil weathering. These profiles present soils with higher degree of development and are related to attributes and Ki, Kr, H + Al, m% and SiO2, which are attributes that characterize the soil evolution. This result agrees with the work of Santos et al. (2013) that found high degree of weathering in the Archeological Dark Earth profiles. Finally, the third group was formed by P5, related with the thicker fractions of the soil, prevalent in this profile (fine sand, gravel and DF). This result is justified mainly by the position of the profile in the relief, slope (Table 1). Campos et al. (2011), doing a study of characterization and classification of Archeological Dark Earth in the region of theMiddle Madeira River, Amazonas (Brazil) also found dominance of the sand fraction, influenced mainly by the position in the relief. In the layer of sub-surface horizons (diagnostic horizons) remained the same distribution of variables with the formation of three groups linked to the same profiles, indicating that the anthropogenic horizon is influencing directly on soil attributes even with increasing depth (Fig. 3). 4. Conclusions Hematite and goethite minerals determined by x-ray diffraction and diffuse reflectance spectroscopy, besides not presenting significant varia- tions between the soils, have similar characteristics to non-anthropogenic Brazilian soils. The color asmeasured by diffuse reflectance spectroscopyproved ef- ficient to indicate variations between the studied Archeological Dark Earth, proving to be an innovative technique, efficient and promising for indirect quantification of soil attributes in a simple and low cost manner. The results show that iron oxides are sensitive indicators of pedoenvironmental and pedogenic processes of Archeological Dark Earth. action (XRD) and diffuse reflectance spectra (DRS) profiles of Archeological Dark Earth sites Silt Clay Fine Sand Gravel WDC DF pH H2O pH KCl H+Al K Ca Mg P OM Al V m Fed Feo Al2O3 SiO2 Fe2O3 Ki Kr Gt Hm -1.0 -0.5 0.0 0.5 1.0 -1.0 -0.5 0.0 0.5 1.0 P1 P2 P3 P4 P5 P6 PC A 2 : 29 .0 6% PCA 1 : 41.70% Silt Clay Fine Sand Gravel WDC DF pH H2O pH KCl H+Al K Ca Mg P SB CEC OM Al V m Fed Feo Al2O3 SiO2 Fe2O3 Ki Kr Gt Hm -1.0 -0.5 0.0 0.5 1.0 -1.0 -0.5 0.0 0.5 1.0 PC A 2 : 36 .0 0% PCA 1 : 43.68% P3 P4 P5 P6P2 P1 A B Fig. 3. Principal component analysis of averages of attributes chemical, physical and mineralogical of the different sites of Archeological Dark Earth in Apuí region, southern of Amazonas state, Brazil. A = surface horizons; B = subsurface horizons. 43R.E. 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Introduction 2. Material and methods 3. Results and discussion 3.1. Physical and chemical attributes 3.2. Mineralogy of iron oxides 3.3. Color measurement and determination of hematite and goethite by XRD and DRS 3.4. Multivariate analysis — PCA 4. Conclusions Acknowledgments References