Soil texture derived from topography in North-eastern Amazonia

Figures & data

Figure 1. Regional geological context, adapted from Kotschoubey et al. (2005b).

Figure 2. The tree top layers of the geological profile: the bottom of duricrust is columnar while the top of duricrust is nodular; the Belterra clay layer is thin in this area near the convex edge of the plateau (coordinates: −2.9686°/+47.3665°), the common profile observed.

Figure 3. Topographical pattern of the Grajaú region, from Kotschoubey et al. (2005b).

Table 1. Inference rule for texture depending on the difference in elevation to the modelled Paleogene duricrust surface.

Elevation with respect to the modelled duricrust surface	Texture
< −20 m	Loamy sand
−20 to −5 m	Mottled clay
−5 to +5 m	Duricrust
> +5 m	Belterra clay

Figure 4. Flow chart of field observations and spatial analysis used to compile the map of soil texture.

Figure 5. Difference in elevation between the observation points and the interpolated surface of the duricrust.

Table 2. Confusion matrix between observations (columns) and map (rows).

	Belterra clay	Duricrust	Mottled clay	Loamy sand
Belterra clay	83	6	2	15
Duricrust	16	142	7	11
Mottled clay	6	9	15	19
Loamy sand	2	1	13	67

Table 3. Results of the spatial overlay of the soil texture map (columns) on the Embrapa soil map (rows), in km².

	Belterra clay	Duricrust	Mottled clay	Loamy sand
Plinthosols	0.1	4.8	0.3	71.5
Gleysols	–	8.8	0.7	125.8
Ferralsols (medium texture)	308.4	993.2	271.2	4768.9
Ferralsols (pisolotic)	234.3	242.5	83.8	350.9
Ferralsols (clayey)	5380.6	1838.6	1113.2	948.1
Acrisols	95.2	251.0	63.5	347.3
Arenosols	26.0	168.1	19.9	689.8
Non classified	–	7.9	–	928.3

Kotschoubey, B., Truckenbrodt, W., & Calaf, J. M. C. (2005b). Evolução geologica da porção meridional da Província bauxitífera de Paragominas durante o Néogeno/Pleistoceno (Noroeste da Bacia do Grajaú, nordeste do Pará e extreme oeste do Maranhão) [Geological evolution of the southern part of Paragominas bauxite province during the Neogene/Pleistocene (North-western of the Grajaú Basin, North-eastern of Pará and far west of Maranhão)]. Rev. Bras. Geoc., 35, 263–272.

 Google Scholar