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Soil chemical properties of a toposequence under primary rain forest in the Itacoatiara vicinity (Amazonas, Brazil)
GEODER~ ELSEVIER
Geoderma 72 (1996) 119-132
Soil chemical properties of a toposequence under primary rain forest in the Itacoatiara vicinity (Amazonas, Brazil) l Johannes Botschek a, Joao Ferraz b, Marcelo Jahnel c, Armin Skowronek a a Institutfiir Bodenkunde. Universit~t Bonn. Nuflallee 1 3 . 5 3 1 1 5 Bonn. Germany b I N P A - C P S T . C.P. 478. 69011-370 Manaus - - AM. Brazil c E S A L Q / U S P . C.P. 9. 13418-900 Piracicaba - - SP. Brazil
Received 22 June 1995; accepted 13 March 1996
Abstract
Nine soil profiles of a typical toposequence under primary rain forest of the Amazon area were investigated, distinguishing between Geric Ferralsols (Xanthic Kandiudox) in the upper and middle parts of the slope and Geri-Haplic Arenosols (Oxyaquic Quartzipsamments) in the lower ones. Generally, the soils are strongly acid with very high AI contents and show extremely low nutrient contents. In spite of this conformity, significant differences were found referring to the agricultural suitability along the toposequence. The decrease of soil potentials from the top to the lower positions is mainly due to the variation of texture.
1. I n t r o d u c t i o n
Since the mid-1960s, ambitious projects have been set in motion in the Brazilian Amazon region to promote its industrial, and in particular, its agricultural evolution (Kohihepp, 1976). Counteracting those plans, the agricultural suitability of large areas of the A m a z o n basin is strongly restricted by soil chemical properties. According to Silva Madeira Neto et al. (1982) the soils belong to the " p r o b l e m s o i l s " of Brazil. Irion
In memoriam Prof. Dr. Heinrich Zakosek. 0016-7061/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved P l l SO016-7061(96)00026-2
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J. Botschek et al. / Geoderma 72 (1996) 119-132
(1978) doubts their agricultural suitability. However, completely renouncing the use of the acid infertile soils means giving up about 75% of the Amazon area (Sanchez et al., 1982a). This does not appear realistic considering the increasing regional and worldwide food gap. Increasing pressure to use land leads to shortened fallow periods in some Amazon regions. Under the current circumstances ecological damage occurs where previous shifting cultivation practice was ecologically sound. According to Sanchez et al. (1982a), from an economic and ecological perspective it makes more sense to intensify agricultural production in certain areas. Van Wambeke (1978), on the other hand, doubts the profitability of massive fertilizer inputs for productivity increase due to the tendency of the Amazon low-fertility soils to degrade. He recommends paying more attention to natural land-use potential and the diversity of soils. A decisive prerequisite for effective fertilizer application as well as for area-specific land use is a precise knowledge of the distribution of soils and their properties. Pedological studies undertaken near Manaus (Klinge, 1965; Lucas et al., 1984; Chauvel et al., 1987; Bravard and Righi, 1988) show a variety of soils within short distances. In this study, soil chemical properties of a catena near Itacoatiara are described and the agricultural suitability of these soils is evaluated.
2. Material and methods 2. I. Areal site and soils The study site is part of the Fazenda Aruana in Itacoatiara municipality, Amazon state. The fazenda is situated at 3°04'S and 58°45'W, 54 km west of Itacoatiara north of highway AM-010 (Manaus-Itacoatiara). The toposequence is 840 meters long and consists of 9 soil profiles (Fig. 1, lower part). The convex-concave slope has a relief of 50 meters with a gradient of up to 16%. All soils were analyzed and five representative profiles were selected for presentation in this study. The Manaus area is covered with Tertiary fluvio-lacustrine deposits, the so-called Barreiras formation (Chauvel et al., 1987), a sediment derived from the deeply weathered Precambrian Guiana rocks and from the Brazilian shield. It consists of fine-textured sandstones and kaolinitic clays (Journaux, 1975). The undulating relief of the plateaux is strongly dissected by V-shaped valleys. During the Pleistocene, concretions and iron crusts were added by solution transport as well as colluvial and alluvial deposits at the valley bottom. During the Holocene, fluvio-marine sediments were deposited in lacustrine depressions and talwegs. The climate (Am after KiSppen, 1931) is characterized by a mean annual temperature of 25.9°C, an average annual rainfall measured at Itacoatiara station of ca. 1,900 mm and a potential evapotranspiration of about 1,600 mm (Ministerio da Agricuitura, 1990). The short dry season comprises three months (September, October, November) with less than 50 mm of rainfall, six months have less than 100 mm. The natural semi-deciduous terra-firme (terrain free of floods) forest is enriched with Brazil-nut (Bertholletia
J. Botschek et al. / Geoderma 72 (1996) 119-132
121
excelsa) and changes abruptly into a brush-rich campina forest at lower elevations. This change in vegetation is directly related to the presence of sandy soils in those positions. A general view of the areal distribution of soils in the region is given by Cochrane and Sanchez (1982). A more detailed soil survey taken along Highway AM-010 illustrates that the soils in the Itacoatiara vicinity can be basically identified as Yellow Latosols with differing texture, Humic Gleys, Hydromorphic Podzols and Regosols in accordance with the Brazilian soil classification scheme (IPEAN, 1969). Moreover, several authors (Klinge, 1965; Lucas et al., 1984; Chauvel et al., 1987; Bravard and Righi, 1988) found kaolinitic Latosols on the plateaux and sandy Podzols at lower elevations of slopes near Manaus. Profile pits were dug along the catena to represent the characteristics of upper, middle, and lower elevations. The profiles were described and classified in the field according to the Brazilian soil classification (Bennema, 1966; Camargo et al., 1987), the Soil Taxonomy (Soil Survey Staff, 1994) and the FAO-system (FAO-Unesco-ISRIC, 1990). Soil samples were taken from representative depths to the laboratory. 2.2. Soil analysis Air-dried samples were passed through a 2 mm sieve and analyses were undertaken using fine earth: Texture of the soils was analyzed by wet sieving (2000-63 tzm) and pipetting ( < 63 p.m) following treatment with 35% H20 _, (Gee and Bauder, 1986) and dispersion through overnight shaking with 0.1 M Na4P20 7. pH was measured potentiometrically in 1:2.5 suspensions (soil:l M KCI and soil:H20) using a glass electrode (McLean, 1982). The analysis of organic carbon was conducted spectrophotometrically by measuring reduced Cr 3÷ at 578 nm after wet ashing with acidified K2CrzO 7 (Nelson and Sommers, 1982). Total nitrogen was determined titrimetrically with 0.1 M NaOH after distillation of NH 3 of Kjeldahl digestion fraction (Bremner and Mulvaney, 1982). Exchangeable cations were extracted by 0.05 M NH4CI at soil pH according to the Triiby and Aldinger (1989) method. The cations Ca, Mg, K, and Na were measured spectro-photometrically. H ÷ and AI 3÷ were measured simultanuously by potentiometric titration with 0.04 M NaOH using a titroprocessor (METROHM E 636XTriiby, 1989). The Effective Cation Exchange Capacity (ECEC) was calculated as the sum of exchangeable cations at soil pH. ECEC is the basis for the calculation of Base Saturation and AI saturation. Potential Cation Exchange Capacity (CECpH82) was measured according to the Mehlich method at pH 8.2. Available phosphorus was extracted by 0.03 M acidic (0.025 N HCL) NH4F (Bray and Kurtz, 1945) (Bray I) and analyzed spectrophotometrically at 578 nm. The Zero Point of Net Charge (ZPNC) was calculated by analyzing the exchange capacity for anions and cations depending upon the pH value (Marcano-Martinez and McBride, 1989). Pedogenic oxides were analyzed by extraction of Fe and AI with Na-dithionite (Fe d, A! d) and NH4-oxalate (Fe o, AIo) according to Jackson (1958) and Schwertmann (1964).
122
J. Botschek et al. / Geoderma 72 (1996) I 19-. 132
3. Results and discussion
3. I. Soil properties All soils of the toposequence are free of coarse components ( > 2 mm). The profiles of the higher elevations show high clay contents sometimes above 80% (Fig. 1, lower part; Table 1). At the lower elevations the clay contents significantly decrease in favour of sand and finally make up only 1-2% at the toot of the slope. Besides this horizontal textural differentiation of the toposequence there is a vertical textural change in the profiles. The soils are strongly or very strongly acid, with the lowest pH in the topsoils (Table 2). The negative ApH (pHKc I - p H u , o) in all investigated horizons indicate that negative charges prevail (Keng and Uehara, 1974). However, there are some topsoils in the catena with ApH values near zero. This may be due to the variable charges of the organic material and of the free oxides. All mineral soils are covered by organic layers between 2 and 5 cm thick. The highest organic carbon contents are tbund in the mineral topsoils in the upper part of the toposequence. Downslope they decrease to 0.34% C at the foot slope. In contrast to Klinge (1962) and Bravard and Righi (1991) the C / N ratios are higher at the higher elevations than in the other soils of the catena. This indicates lower degrees of N incorporation in the humic structure. Available P is low in all profiles. Only in some topsoils the P content exceeds 2 mg/kg. The Effective Cation Exchange Capacity (ECEC) is very low. With the exception of only two topsoil horizons in profile I the ECEC does not reach 30 m m o l J k g (Table 3). The very low Base Saturation (BS~tcEc) corresponds with the low pH whereas the potential acidity (AI 3+ + H* ) occupies between 89 and 100% of the ECEC. At the upper and middle parts of the catena exchangeable AI fills up the main portion of the ECEC. The AI saturation decreases on the lower slope and finally disappears in the last profile of the toposequence (Fig. 1, upper part). There only H + is detected. The comparison of ECEC at soil pH with the potential Cation Exchange Capacity (CECpHs2) indicates a pool of electric charges available in case of an increase in pH (Table 3). But even an enormous pH value increase up to 8.2 could only raise the exchange capacity of the topsoils significantly because of the variable charge of the organic matter. In the other horizons the CEC remains below 100, mostly < 50 mmolc/kg. The charge characteristics can be determined by measuring the cation and anion adsorption as a function of pH (Fig. 2). The Zero Point of Net Charge (ZPNC) of the topsoil of profile I lies in the strongly acid pH range wheras the ZPNC of the subsoil is between pH 3 and 4. Profiles III and VII also show this tendency but to a lesser degree which may be due to lower humus contents (Keng and Uehara, 1974). However, soil solution pH is higher than ZPNC in all profiles which confirms the ApH calculation. Anion adsorption is particularly found in the profiles at the higher and middle elevations. Besides the aforementioned high clay contents there are also the highest contents of free oxides, especially of Fe oxides (Table 1), with anion sorption capacities
J. Botschek et al. / Geoderma 72 (1996) 119-132
Profile 4
o.
.
I
Profile
.
III
Profile 8
8
.
4
Profile 8
o.._
50 ~
'oo
:
150
150
150
ev
o
4
O4
G8
o
,
0
04
08
Profile
VII
l 50. ioo
1"30
150
\
04
08
0" 50
100
'00
• 5O •
150 50
o 50
1 o0
0
"°[i':'
04
08
\ /7F%
"\
I
Aid
15o 5C
~00
50 c
ICO
o
5c
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100
% C otg
!oo
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100
8
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3
IX
4
8
oI
'00.
~4
V
123
gO
Io o %
AI saturation
~00
• 50
.c
3
50
1GO
150
50
ico
I. . . . .
I
(D o
::r ~
J5o
Fig. 1. The soil toposequence with clay distribution and some soil chemical properties of selected profiles.
124
J. Botschek et al. / Geoderma 72 (I 996) 119-132
Table I Soil texture and free metal oxides of selected profiles Profile Horizon Depth(cm) % fine earth
mg/kg
Sand Silt Clay Fe,, (2-0.063 mm) (0.063-0.(X}2 mm) ( < 0.002 mm)
F%
AI,,
AI,j
Ah AB BI B2 B3
0-6 6-18 18-35 35-60 60-120
16.4 14.9 87 6.1 6.3
24.3 7.7 12.9 15.8 14.7
59.3 77.4 78.4 781 79.0
1166 1519 1068 328 114
12151 18257 19317 21425 19667
1478 1350 1400 1194 1183
5953 6041 6104 6522 6156
111
Ahl Ah2 BI B2 B3
0-9 9-27 27-42 42-87 87-135
128 96 9.8 8.6 7.9
15.6 15.8 2.8 7.3 10.3
716 74.6 87.4 84.1 81.8
1548 1104 496 405 136
19769 19420 21111 21171 21049
1465 1415 1295 1325 1313
5971 5886 6127 6276 6316
V
Ahl Ah2 BI B2 B3
0-3 3-38 38-62 62-9(} 90-145
4(}.5 22.1 18.1 16.4 17.3
8.5 102 5.7 8.7 7.6
51.1} 67.7 76.2 74.9 75.1
1178 1174 371 210 I(X)
10529 1361}3 13750 13216 131)47
840 1224 1079 1056 1056
3151} 4348 4439 4234 4188
VII
All BI B2 B3
0-7 7-48 48-90 90-141)
74.9 58.4 50.6 48.9
4.9 7.8 4.9 5.4
20.2 33.8 445 45.7
694 1183 187 92
IX
Ah AB Bgl Bg2
0-15 15-45 45-95 95-160
96.5 95.1 96.3 97.9
2.0 2.7 19 1.3
1.5 2.2 1.8 0.8
5 39 57 9
4307 408 1685 6861 921 2550 8574 575 2783 8563 571 2647 71 174 353 87
26 117 212 387 519 646 14 143
under acid conditions. F r o m the higher to the l o w e r elevations the absolute contents o f Fe oxides decrease in c o r r e s p o n d a n c e with the net charge curves (Fig. 2). In contrast, the activity o f Fe and AI oxides ( F e o / F e d and A I o / A ! d in Fig. I, upper part) is significantly higher at the bottom of the slope which is also reported by Bravard and Righi (1989). The mineralogical c o m p o s i t i o n o f the soils can be derived from the E C E C calculated per kg o f clay (Table 3) particularly in subsoils with low organic matter contents. Apart from profile IX the low values in the subsoils indicate high kaolinite portions. The differing e x c h a n g e capacities per clay o f profile IX may be due to another clay type or higher amounts o f a m o r p h o u s metal oxides in the clay fraction. Bravard and Righi (1988) found kaolinite as the d o m i n a n t clay mineral in clayey and sandy soils of a c o m p a r a b l e t o p o s e q u e n c e near Manaus. 3.2. Pedogenesis and soil classification C l a y - r i c h soils on plateaux and d e c r e a s i n g clay contents along the slopes of the A m a z o n basin are described by several authors. Klinge (1965) regards the sandy
J. Botschek et al. / Geoderraa 72 (1996) 119-132
125
Table 2 Soil acidity, organic carbon, total nitrogen, and available phosphorus of selected profiles Profile
Horizon
Depth (cm)
pH 1 M KCI
H20
ApH
C,,fg (%)
N, (%)
C/N
P (mg/kg)
I
Ah AB BI B2 B3
0-6 6-18 18-35 35-60 60-120
3.2 3.6 4.1 4.3 4.4
3.4 4.0 4.5 4.7 4.6
-0.2 -0.4 -0.4 -0.4 -0.2
8.52 3.23 1.13 0.50 0.36
0.37 0.16 0.08 0.05 0.02
23 20 14 10 18
1.6 3.1 0.6 -
111
Ahl Ah2 BI B2 B3
0-9 9-27 27-42 42-87 87-135
4.2 4.3 4.3 4.3 4.4
4.5 4.7 4.7 4.8 5.0
-0.3 -0.4 -0.4 -0.5 -0.6
1.27 095 0.70 0.54 0.35
0.I0 0.07 0.01 0.03 0.02
13 14 70 18 18
1.4 1.9 1.4 1.0 0.6
V
Ahl Ah2 BI B2 B3
0-3 3-38 38-62 62-90 90-145
3.9 4.2 4.3 4.4 4.4
4.1 4.7 4.7 4.9 4.9
-0.2 -0.5 - 0.4 -0.5 -0.5
2.06 0.87 0.57 0.36 0.23
0.13 0.04 0.03 0.02 0.02
16 22 19 18 12
3.1 1.9 1.6 1.2 1.0
VII
Ah BI B2 B3
0-7 7-48 48-90 90-140
3.7 4.4 4.4 4.5
4.3 4.8 4.9 5.2
-0.6 -0.4 -0.5 -0.7
1.99 0.57 0.21 0.13
0.13 0.03 0.01 -
15 19 21 -
3.1 1.0 1.8 0.8
IX
Ah AB Bgl Bg2
0 -15 15-45 45-95 95-160
3.5 3.7 4.7 5. I
4.4 4.5 5.0 5.3
-0.9 - 0.8 -0.3 - 0.2
0.34 0.26 0.25 0.04
0.02 0.02 -
17 13 -
1.6 1.6 0.6 0.4
- = undetectable amounts.
substrata at the bottom of the slope of a similar toposequence near Manaus as non-autochthonous. He considers them fluvial deposits which are significantly different from the finer textured substrata of the higher situated Barreiras formation. Journaux (1975) explains such textural distribution with climatically induced erosion and land slides. These, in turn, have created so-called facette slopes. Chauvel et al. (1987) and Bravard and Righi (1988, 1989), on the other hand, view the Barreiras formation as the parent material for all soils of such toposequence. In these studies the distribution of textures is explained by lateral clay eluviation and selective erosion of clay. The significance of quarternary tectonics and of climatic changes for the geomorphogenesis, the stratigraphy of sediments, and the soils in the Amazon basin (Mousinho de Meis, 1971; Tricart, 1975; Irion, 1976; Bibus, 1983) is not taken into consideration. Consequently, the soils must originate from differently textured slope deposits and not from a homogeneous parent rock. The applied soil classification systems (Brazilian/Soil Map of the World/Soil Taxonomy) divide the toposequence into two sections (Table 4). Profiles I-VII of the upper and middle parts of the slope (Fig. 1) show diagnostic
126
J. Botschek et al. / Geoderma 72 (1996) 119-132
Table 3 Exchangeable cations, cation exchange capacities, and base saturation of selected profiles Profile Horizon Depth (cm) mmol,/kg fine earth Ca Mg K
Na AI
BSEcEC ECEC H
ECEC CECptix 2 (%)
(mmol c / k g clay)
Ah AB BI B2 B3
0-6 6-18 18-35 35-60 60-120
2.3 -
2.3 1.0 0.6 28.9 209 0.8 2.3 0.5 24.2 13.8 0.4 - 0.1 17.2 OI 12.8 13.1 --
56.0 41.6 17.7 12.9 13.1
253.3 157.7 672 46.1 37.3
I1.1 8.7 2.8 0.8 --
94.4 53.8 22.6 16.5 16.6
Ill
Ahl Ah2 BI B2 B3
0-9 9-27 27-42 42-87 87-135
0.1 1.2 2.5 1.0 -
0.1 0.1 0.2 13.0 0.1 9.8 0.1 - 0.1 8.9 0.1 4.8
8.8 9.6 8.6 9.1 I0.1
22.3 20.7 20.2 15.0 10.1
71.8 58.7 48.8 43.7 35.9
2.2 6.3 13.4 7.3 --
31.2 27.5 23.1 17.8 12.4
V
Ahl Ah2 BI B2 B3
0-3 3-38 38-62 62-90 90-145
- 0.2 0.4 0.4 0.2 0.1 0.1 0.2 0.2 -- 0.1 0.3 0.1 0.3 0.1 - 0.1
10.6 10.2 10.2 8.6 9.1}
28.8 21.3 10.8 13.6 9.5
972 54.2 41.4 36.6 32.6
3.5 2.8 5.6 0.7 5.3
56.5 31.5 14.2 18.2 12.7
VII
Ah BI B2 B3
0-7 7-48 48-90 90-140
0.3 0.6 0.6 0.6 14.3 0.1 0.1 0.6 0.6 0.6
9.4 25.8 9.1 9.9 9.4 I0.0 9.0 9.6
77.3 44.2 23.0 21.4
8.1 8.1 6.0 6.3
127.7 29.3 22.5 19.7
IX
Ah AB Bgl Bg2
0-15 15-45 45-95 95-160
-
8.3 8.2 9.8 9.5
26.1 38.1 32.2 9.5
1.2
560.0 372.7 544.4 1187.5
-
.
17.2 10.5 4.9 -
0.1 .
.
.
.
.
8.4 8.2 9.8 9.5
-
= undetectable amounts.
p r o p e r t i e s c o n n e c t e d to i n t e n s e w e a t h e r i n g , thus n a m e d L a t o s o l s / F e r r a l s o l s / O x i s o l s . The sandy, w e a k l y d i f f e r e n t i a t e d p r o f i l e s VIII and IX at the b o t t o m o f the s l o p e are called Q u a r t z o s e S a n d s / A r e n o s o l s / E n t i s o l s
and Q u a r t z i p s a m m e n t s , r e s p e c t i v e l y . Pro-
file IX s h o w s s o m e gleyic p r o p e r t i e s in the l o w e r subsoil w h i c h is d e s c r i b e d by three additional soil t e r m s ( H y d r o m o r p h i c / G l e y i c / O x y a q u i c ) .
Brazilian c l a s s i f i c a t i o n and
Soil T a x o n o m y s p e c i f y the texture o f all soils as well as the soil c o l o r o f L a t o s o l s and O x i s o i s . R e f e r e n c e is also m a d e to the textural c h a n g e in the O x i s o l s (Kandi-). T h e low cation e x c h a n g e c a p a c i t y o f the soils is i n d i c a t e d by all c l a s s i f i c a t i o n s y s t e m s ( l o w clay a c t i v i t y / G e r i c / k a o l i n i t i c ) w h e r e a s the b a s e saturation and high Al saturation is only c o n s i d e r e d by the Brazilian s y s t e m ( D y s t r o p h i c , Allic, Epiallic). A K C I - e x t r a c t a b l e Al c o n t e n t o f m o r e than 20 m m o l c / k g
o f fine earth c o u l d also be c o n s i d e r e d for O x i s o l s
(allic). T h e m a i n p h a s e s o f p r i m a r y v e g e t a t i o n are i n c l u d e d in the soil class n a m e as c l a s s i f i e d by the Brazilian s y s t e m . O t h e r soil and land c o n d i t i o n s i n f l u e n c i n g land use, e.g. the relief, can be a d d e d to the Brazilian soil class n a m e w h e r e a s soil m o i s t u r e r e g i m e and soil t e m p e r a t u r e r e g i m e are b o t h e c o l o g i c a l l y i m p o r t a n t data w h i c h are i n c o r p o r a t e d into the Soil T a x o n o m y n o m e n c l a t u r e .
127
J. Botschek et al. / Geoderma 72 (1996) 119-132 3.3. Agricultural suitability of soils and soil potentials
The acidity of all soils investigated may be an important factor impeding in the cultivation of most crops whereas the primary rain forest develops well under the conditions of the aforementioned acidity. The Fertility Capability Soil Classification System (Sanchez et ai., 1982b) enables grouping the major soil constraints, commonly associated with soil acidity in the tropics, into five classes: acid, aluminium toxic, low CEC, high P fixation, and low K availability. According to this system, P fixation cannot play an important role in the catena soils because there are no high free oxide contents. In addition, P availability is very low. The other constraints mentioned above are present in the catena in different combinations. The pH values range mostly between 4 and 5, and the AI saturations reach, or even exceed, the critical percentage of 60 (Kamprath, 1970) in several profiles. The ECEC is extremely low with less than 40 mmolc/kg of fine earth. It is mainly occupied by acid cations and the exchangeable K lies generally below 2 m m o l J k g of fine earth indicating low K reserves (Sanchez et al., 1982b). Agricultural suitability is often affected by Ca deficiency ( < 0.2 mmol~/kg of fine earth, after Ritchey et al., 1982) found in many horizons; others also show marginal values. In addition, the poor nutrient status is illustrated by the M g / K ratio. Rosolem et al. (1984) suggest an adequacy value of 0.6 for Brazilian Oxisols. This value was found to be higher only in the topsoils.
-100
-
Profile I
Ah .'
-80
•
-60 E E G
m
•
-40
~. ,
2
9
V ,=;-__~Tr_,
4
-80 • -60
•
m ....
'3
"~ "O "5
E E
B1
-20 o
$ z
-100 -
"
.H
2o
'
40[ 20
;: --
40'
m -80 -
u
E
Profile VII
I
_
-20 ~
z
i
i
40 ~
0 t ....... 2 20 f
40
Ah
I ~,,BI..,
3
4
...
" 5-
60
~:
°
E ~"-_
2ot
40
-100 T
Ah2 .eB1
.
0
5
Profile III
.
.
.
.
.
.
5 pH .
!
Fig. 2. Net electricchargesof selectedprofilesand horizons.
128
J. Botschek et a l . / Geoderma 72 (1996) 119-132
Table 4 Identification of selected catena profiles in three classification systcms Profile
Brazilian (Camargo et al.. 1987)
Soil Map of the World (FAO-Unesco-ISRIC, 1990)
Soil Taxonomy (Soil Survey Staff. 1994)
1
Yellow Latosol Allic, very fine clayey; semi-deciduous rain lbrest, plateau phase
Geric Ferralsol
Xanthic Kandiudox. very fine. kaolinitic, allic. isohyperthermic
Ill
Yellow Latosol Epiallic Dystrophic. very fine clayey; semi-deciduous rain forest, gentle slope phase
Geric Ferralsol
Xanthic Kandiudox, very fine. kaolinitic. isohyperthermic
V
Yellow Latosol Epiallic Dystrophic. very fine clayey; semi-deciduous rain forest, slope phase
Geric Ferralsol
Xanthic Kandiudox. very fine. kaolinitic. isohyperthermic
VII
Yellow Latosol Epiallic Dystrophic. medium; semi-deciduous rain forest, slope phase
Geric Ferralsol
Xanthic Kandiudox. fine. mixed, isohyperthcrmic
IX
Quanzose Sand Hydromorphic Dystrophic, sand>',low activity clay; tropical semi-evergreen rain li)rest. rich in palms, lower slope
Geri-Gleyic Arenosol
Oxyaquic Quarlzipsamment. sandy. siliceous, isohyperthermic
The soils investigated have low permanent negative charges which emphasizes the importance of organic matter and free oxides for the charge characteristics. With soil pH values significantly above the Zero Points of Net Charge the surface horizons rich of humus have in most cases higher cation exchange capacities as well as a better supply of cation nutrients in contrast to the subsoils of the catena. The organic material is known to play a fundamental role for most of the functional processes occurring in forest soils (Gosz et al., 1976). In the case of cultivation the land clearing method determines the decrease of C,,r.~ and other soil deteriorations during the first months after deforestation. Seubert et al. (1977) for the Amazon jungle of Peru prefer the traditional slashing and burning method which retards the decomposition of organic matter, increases the supply of exchangeable bases and available soil phosphorus, and decreases aluminium saturation. Yield responses are high in contrast to bulldozed lands suffering from severe soil compaction. Moreover, the bulldozed lands do not receive additional nutrients and they remain high in aluminium saturation levels. Even after successful land clearing the agricultural productivity of these acid soils is low and declines rapidly. There is need for special management techniques as summarized by Phiri et al. (1994) for acid soils in Africa: Lime applications aim at lowering acidity and reducing the toxicity of AI ~+ (Evans
J. Botschek et al. / Geoderma 72 (1996) 119-132
129
and Kamprath, 1970) as they are soil constraints restricting the cultivation of demanding crops. Experiments with different crops demonstrated the effects of liming on exchangeable Ca and AI and on crop yields on a Xanthic Hapludox near Manaus, Brazil (Smyth and Cravo, 1992). The application of inorganic fertilizers permits continuous production of annual crops even on Oxisols of the Amazon basin (Melgar et al., 1991; Smyth and Cravo, 1992). But both inorganic fertilizer use and liming are expensive and therefore inaccessible for most of the region's farmers. Another means to enhance fertility, alleviate element toxicity, and provide soil protection is the addition of organic matter such as crop residues and green manures, respectively. Organic additions without chemical inputs havc produced up to 90% of the yields with complete inorganic fertilization and liming on Ultisols of the Amazon basin (Wade and Sanchez, 1983). Smyth et al. (1991) showed the fertilizer-N substitution value of legume residues to succeeding corn crops on an Oxisol near Manaus. Thus, the use of on-farm generated organic fertilizers appears to be attractive tor a sustainable agriculture on the soils investigated. In contrast to management systems which try to raise the soil potential by organic or inorganic additions the use of acid-tolerant cultivars keeps the soil in its acid state (Sanchez and Benites, 1987) or leads to long-term improvements of acid soil conditions (Kirk and Zeigler, 1994). This reduces the need for expensive inputs and improves the applicability of that technique. However, the wide range of textures throughout the catena indicates varying soil potentials for the profiles along the slope. The change of the natural vegetation from terra-firme tbrest on the higher elevations with high clay contents to brush-rich campina forest on the lower slope with sandy textures was also described by Klinge (1965). This verifies the variation of ecological conditions consequently provoking different responses to agricultural management measures taken. The agricultural suitability of the sandy soils of the lower part of the catena (profile VIII and IX) is not only reduced by the soil chemical properties but also by the poor soil physical conditions. The high water table in profile IX possibly balances the low water holding capacity of the sands but high leaching rates are likely to occur on both soils as demonstrated for N leaching on an Entisol near Manaus (Melgar et al., 1992). The soils on the steep part of the slope (profile IV to VII) have higher clay contents which make them susceptible to soil erosion if no soil conservation measures are provided. Considering the soil physical properties and the erosion risks on the slope the soils of the higher elevations (profile I to III) have the highest potentials for agricultural use though their soil chemical properties are also very poor.
4. Conclusions
The soils investigated represent a typical toposequence in the area. All soils are extremely poor with high acidity and low exchange capacities although there are considerable differences pertaining to the soil potentials. Although very low in fertility the clay-rich soils of the upper part of the toposequence are best suited for crop
130
J. Botschek et al. / Geode rma 72 (1996) 119-132
production. The steep positions on the middle slope are endangered by erosion which decreases their agricultural sustainability. In contrast, the sandy texture heavily constrains soil fertility at the bottom of the slope. The physical and chemical differences of the soils are determincd by-and-large by deviating textures. Though the genesis of the textural distribution on the investigated slope remains unclear the wide spectrum of resulting soil properties necessitates the selection of appropriate technologies on each kind of soil. Considering the socio-economic conditions in the Amazon basin, low-input systems (Sanchez and Salinas, 1981) appear to be most appropriate for that region. Such systems require firm knowledge of soil properties, however.
Acknowledgements We thank the Agropecuaria Aruan~, Ings. S. Verguciro and G. de Paula Neto for their support to the field work. We are also grateful to M. D~iumer for reviewing the English text.
References Bennema, J., 1966. Report to the government of Brazil on classification of Brazilian soils. Report No. 2197, FAO, Rome, 83 pp. Bibus, E., 1983. Die klimamorphologische Bedeutung yon stone-lines und Decksedimenten in mehrgliedrigen Bodenprofilen Brasiliens. Z. Geomorphol. N.F., Suppl.-Bd 48: 79-98. Bravard, S. and Righi, D.. 1988. Characteristics of clays in an OxisoI-Spodosol toposequence in Amazonia (Brazil). Clay Miner., 23: 279-289. Bravard, S. and Righi, D., 1989. Geochemical differences in an OxisoI-Spodosol toposequence of Amazonia, Brazil. Geoderma, 44: 29-42. Bravard. S. and Righi, I).. 1991. Characterization of fulvic and humic acids from an OxisoI-Spodosol toposequence of Amazonia, Brazil. Geoderma, 48:151 - 162. Bray, R.H. and Kurtz, LT.. 1945. Determination of total, organic, and available forms of phosphorus in soils. Soil Sci., 59: 39-45. Bremner, J.M. and Mulvaney, C.S., 1982. Nitrogen-total. In: A L . Page, R.H. Miller and D R . Keeney (Editors), Methods of Soil Analysis, 11. A S A / S S S A , Madison, WL pp. 595-615. Camargo, M.N. Klamt, E. and Kauffman. J.H, 1987. Soil classification as used in Brazilian soil surveys. Annual report 1986, ISRIC, Wageningen. Chauvel, A., Lucas, Y. and Boulet, R., 1987. On the genesis of the sod mantle of the region of Manaus. Central Amazonia, Brazil. Experientia, 43: 234-241. Cochrane, T.T. and Sanchez. P.A.. 1982. Land resources, soils and their management in the Amazon region: A state of knowledge report. In: S. Hecht (Editor), Amazonia: Agricuhurc and Land Use Research: Proceedings, CIAT. Cali (Columbia), pp. 137-209. Evans, C.E. and Kamprath, E.J., 1970. Lime response as related to percent AI saturation, solution AI. and organic matter content. Soil Sci. Soc. Am. Proc., 34: 893-896. FAO-Unesco-ISRIC, 1990. Soil map of the world. Revised Legend. Reprinted with corrections. World Soil Resources Report, 60, FAO, Rome, 119 pp. Gee, G.W. and Bauder, J.W., 1986. Particle-size analysis. In: A. Klute (Editor), Methods of Soil Analysis, 1. 2n ed. A S A / S S S A . Madison. WI, pp. 383-41 I. Gosz, J.R., Likens, G E . and Bormann, F.H., 1976. Organic matter and nutrient dynamics of the forest floor in the Hubbard Brook Forest. Oecologia (Berlin). 22: 305-320.
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IPEAN (lnstituto de Pesquisas e Experimentac~o Agropecufirias do Notre), 1969. Os solos da firea ManausItacoatiara. 1PEAN, S6rie Estudos e Ensaios, I, 117 pp. irion, G , 1976. Die Entwicklung des zentral- und oberamazonischen Tieflands im Sp~it-Pleistoz~ und im HolozS.n. Amazoniana, 6: 67-79. lrion, G., 1978. Soil infertility in the Amazonian rain forest. Naturwis~nschaften, 65: 515-519. Jackson, ML., 1958. Soil Chemical Analysis. Prentice-Hall, Englewood Cliffs, N J, pp. 391-396. Joumaux, M.A.. 1975. G6omorphologie des bordures de I'Amazonie br~silienne: Le module des versants: essai d'6volution pal~oclimatique. Bull. Assoc. G6ogr. Fr., 52: 5-19. Kamprath, E.J., 1970. Exchangeable aluminum as a criterion for liming leached mineral soils. Soil Sci. Soc. Am. Proc., 34: 252-254. Keng, J.C.W. and Uehara, G , 1974. Chemistry, mineralogy, and taxonomy of Oxisols and Ultisols. Soil Crop Sci. Soc. Fla. Proc., 33: 119-126. Kirk, G.J.D. and Zeigler, R.S., 1994. The use of adapted cultivars in acid-soil improvement. In: Trans. 15th World Congr. Soil Sci., 5a, Commission IV, Acapulco (Mex.), pp. 567-578. Klinge, H., 1962. Beitffige zur Kenntnis tropischer BiSden. V. Uher Gesamtkohlenstoff und Stickstoff in B6den des brasilianischen Amazonasgebietes. Z. Pflanzenem~ihr. Bodenkd, 97: 106-118. Klinge, H., 1965. Podzol soils in the Amazon basin. J. Soil Sci., 16: 95-103. K/Sppen, W., 1931. Grnndril?~ der Klimakunde. Walter de Gruyter and Co., Berlin and Leipzig, 388 pp. Kohlhepp, G . 1976. Stand und Problematik der brasilianischen Entwicklungsplanung in Amazonien. Amazoniana, 6: 87-104. Lucas, Y., Chauvel, A., Boulet, R., Ranzani, G. and Scatolini, F., 1984. Transiq,5o latossolos-podz6is sobre a forma~:~.o barreiras na regiao de Manaus, Amaz6nia. R. Bras. Ci. Solo, 8: 325-335. Marcano-Martinez, E. and McBride, M.B., 1989. Comparison of the titration and ion adsorption methods for surface charge measurement in Oxisols. Soil Sci. Soc. Am. J., 53: 1040-1045. McLean. EO., 1982. Soil pH and lime requirement. In: A L Page, RH. Miller and DR. Keeney (Editors), Methods of Soil Analysis, II. ASA/SSSA, Madison, WI, pp. 199-224. Melgar, R.J., Smyth, TJ., Cravo, MS. and Sanchez, P.A., 1991. Doses e t~poca.s de aplica~,5o de fertilizante nitrogenado para milho em latossolo da Amaz6nia Central. R. Bras. Ci. Solo, 15: 289-296. Melgar, R.J., Smyth, T.J., Sanchez, PA. and Cravo, M.S., 1992. Fertilizer nitrogen movement in a Central Amazon Oxisol and Entisol cropped to corn. Felt. Res., 31:241-252. Ministerio da Agricultura, 1990. Balanco hidnco de Itacoatiara entre os anos 1961 e 1990. Primeiro Distrito Metereologico, I. l)isme. Mousinho de Meis, M.R., 1971. Upper quarternary process changes of the Middle Amazon area. Geol. Soc. Am. Bull., 82: 1073-1078. Nelson, I).W. and Sommers, L.E., 1982. Organic carbon. In: A.L Page, R.H. Miller and DR. Keeney (Editors), Methods of Soil Analysis, II. ASA/SSSA, Madison, WI, pp. 570-571. Phin, S., De Pauw, E. and Mapiki, A., 1994. The management of acid soils in Africa. An assessment of constraints, management solutions and research approaches through a case study from Northern Zambia. In: Trans. 15th World Congr. Soil Sci., 5a, Commission IV, Acapulco (Mex.), pp. 551-566. Ritchey, K.D., Silva, JE. and Costa, U.F., 1982. Calcium deficiency in clayey B horizons of savanna oxisols. Soil Sci., 133: 378-382. Rosolem, C.A.. Machado, JR. and Brinholi, O., 1984. Efeito das relaq6es Ca/Mg, C a / K e M g / K do sol() na produ~:~o de sorgo sacarino. Pesq. Agropec. Bras., 19: 1443-1448. Sanchez, P.A., Bandy, D.E., Villachica, J.H and Nicholaides, J.J., 1982a. Amazon basin soils: management for continuous crop production. Science, 216: 821-827. Sanchez, P.A. and Benites, JR., 1987. Low-input cropping for acid soils of the humid tropics. Science, 238: 1521-1527. Sanchez, P.A., Couto, W. and Buol, S.W., 1982b. The Fertility Capability Soil Classification System: interpretation, applicability and modification. Geoderma, 27: 283-309. Sanchez, P.A. and Salinas, J.G., 1981. Low-input technology for managing Oxisols and Uhisols in tropical America. Adv. Agronomy, 34: 279-406. Schwertmanm U., 1964. Differenziernng der Eisenoxide des Bodens dutch Extraktion mit AmmoniumoxalatL6sung Z. Pflanzenern?ihr. Bodenkd., 105: 194-202.
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Seuben, C.E., Sanchez, P.A. and Valverde, C., 1977. Effects of land cleanng methods on soil properties of an ultisol and crop performance in the Amazon jungle of Peru. Trop. Agric. (Trinidad). 54: 307-321. Silva Madeira Neto, J. da, Macedo. J. and Guimar~es de Azevedo, L.. 1982. Brazilian problem soils: distribution, characteristics and utilization. Trop. Agric. Res. Set., 15: 1-20. Smyth, T.J. and Cravo, M.S., 1992. Aluminum and Calcium constraints to continuous crop production in a Brazilian Amazon Oxisol. Agron J., 84: 843-850. Smyth, T.J., Cravo, M.S. and Melgar, R.J., 1991. Nitrogen supplied to corn by legumes in a Central Amazon Oxisol. Trop. Agric. (Trinidad), 68: 366-372. Soil Survey Staff, 1994. Keys to Soil Taxonomy. USDA Soil Conservation Service. 6th e d Pocahontas Press, Blacksburg, VA, 524 pp. Tricart, J.. 1975. Influence des oscillations climatiques r~,centes sur le modcl6 en Amazonie Orientale (Region de SantarEm) d'apr~s les images radar latt~ral. Z. Gcomorphol. N.F., 19: 140-163. Triiby, P.. 1989. Eine Titrationsmethode zur simultanen Bestimmung wm H" und Alumin|um in NHaCIBodcnextrakten. Z. Pflanzenern~.ihr. Bodenkd., 152: 297-300. Triiby, P. and Aldinger, E., 1989. Eine Methode zur Bestimmung austauschbarer Kationen in WaldbiSden. Z. Pflanzenern~hr. Bodenkd., 152: 301-306. Van Wambeke, A., 1978. Properties and potentials of soils in the Amazon basin, lnterciencia, 3: 233-241. Wade, M.K. and Sanchez, P.A., 1983. Mulching and green manure applications for continuous crop production in the Amazon basin. Agron. J., 75: 39-45.
Geoderma 72 (1996) 119-132
Soil chemical properties of a toposequence under primary rain forest in the Itacoatiara vicinity (Amazonas, Brazil) l Johannes Botschek a, Joao Ferraz b, Marcelo Jahnel c, Armin Skowronek a a Institutfiir Bodenkunde. Universit~t Bonn. Nuflallee 1 3 . 5 3 1 1 5 Bonn. Germany b I N P A - C P S T . C.P. 478. 69011-370 Manaus - - AM. Brazil c E S A L Q / U S P . C.P. 9. 13418-900 Piracicaba - - SP. Brazil
Received 22 June 1995; accepted 13 March 1996
Abstract
Nine soil profiles of a typical toposequence under primary rain forest of the Amazon area were investigated, distinguishing between Geric Ferralsols (Xanthic Kandiudox) in the upper and middle parts of the slope and Geri-Haplic Arenosols (Oxyaquic Quartzipsamments) in the lower ones. Generally, the soils are strongly acid with very high AI contents and show extremely low nutrient contents. In spite of this conformity, significant differences were found referring to the agricultural suitability along the toposequence. The decrease of soil potentials from the top to the lower positions is mainly due to the variation of texture.
1. I n t r o d u c t i o n
Since the mid-1960s, ambitious projects have been set in motion in the Brazilian Amazon region to promote its industrial, and in particular, its agricultural evolution (Kohihepp, 1976). Counteracting those plans, the agricultural suitability of large areas of the A m a z o n basin is strongly restricted by soil chemical properties. According to Silva Madeira Neto et al. (1982) the soils belong to the " p r o b l e m s o i l s " of Brazil. Irion
In memoriam Prof. Dr. Heinrich Zakosek. 0016-7061/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved P l l SO016-7061(96)00026-2
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(1978) doubts their agricultural suitability. However, completely renouncing the use of the acid infertile soils means giving up about 75% of the Amazon area (Sanchez et al., 1982a). This does not appear realistic considering the increasing regional and worldwide food gap. Increasing pressure to use land leads to shortened fallow periods in some Amazon regions. Under the current circumstances ecological damage occurs where previous shifting cultivation practice was ecologically sound. According to Sanchez et al. (1982a), from an economic and ecological perspective it makes more sense to intensify agricultural production in certain areas. Van Wambeke (1978), on the other hand, doubts the profitability of massive fertilizer inputs for productivity increase due to the tendency of the Amazon low-fertility soils to degrade. He recommends paying more attention to natural land-use potential and the diversity of soils. A decisive prerequisite for effective fertilizer application as well as for area-specific land use is a precise knowledge of the distribution of soils and their properties. Pedological studies undertaken near Manaus (Klinge, 1965; Lucas et al., 1984; Chauvel et al., 1987; Bravard and Righi, 1988) show a variety of soils within short distances. In this study, soil chemical properties of a catena near Itacoatiara are described and the agricultural suitability of these soils is evaluated.
2. Material and methods 2. I. Areal site and soils The study site is part of the Fazenda Aruana in Itacoatiara municipality, Amazon state. The fazenda is situated at 3°04'S and 58°45'W, 54 km west of Itacoatiara north of highway AM-010 (Manaus-Itacoatiara). The toposequence is 840 meters long and consists of 9 soil profiles (Fig. 1, lower part). The convex-concave slope has a relief of 50 meters with a gradient of up to 16%. All soils were analyzed and five representative profiles were selected for presentation in this study. The Manaus area is covered with Tertiary fluvio-lacustrine deposits, the so-called Barreiras formation (Chauvel et al., 1987), a sediment derived from the deeply weathered Precambrian Guiana rocks and from the Brazilian shield. It consists of fine-textured sandstones and kaolinitic clays (Journaux, 1975). The undulating relief of the plateaux is strongly dissected by V-shaped valleys. During the Pleistocene, concretions and iron crusts were added by solution transport as well as colluvial and alluvial deposits at the valley bottom. During the Holocene, fluvio-marine sediments were deposited in lacustrine depressions and talwegs. The climate (Am after KiSppen, 1931) is characterized by a mean annual temperature of 25.9°C, an average annual rainfall measured at Itacoatiara station of ca. 1,900 mm and a potential evapotranspiration of about 1,600 mm (Ministerio da Agricuitura, 1990). The short dry season comprises three months (September, October, November) with less than 50 mm of rainfall, six months have less than 100 mm. The natural semi-deciduous terra-firme (terrain free of floods) forest is enriched with Brazil-nut (Bertholletia
J. Botschek et al. / Geoderma 72 (1996) 119-132
121
excelsa) and changes abruptly into a brush-rich campina forest at lower elevations. This change in vegetation is directly related to the presence of sandy soils in those positions. A general view of the areal distribution of soils in the region is given by Cochrane and Sanchez (1982). A more detailed soil survey taken along Highway AM-010 illustrates that the soils in the Itacoatiara vicinity can be basically identified as Yellow Latosols with differing texture, Humic Gleys, Hydromorphic Podzols and Regosols in accordance with the Brazilian soil classification scheme (IPEAN, 1969). Moreover, several authors (Klinge, 1965; Lucas et al., 1984; Chauvel et al., 1987; Bravard and Righi, 1988) found kaolinitic Latosols on the plateaux and sandy Podzols at lower elevations of slopes near Manaus. Profile pits were dug along the catena to represent the characteristics of upper, middle, and lower elevations. The profiles were described and classified in the field according to the Brazilian soil classification (Bennema, 1966; Camargo et al., 1987), the Soil Taxonomy (Soil Survey Staff, 1994) and the FAO-system (FAO-Unesco-ISRIC, 1990). Soil samples were taken from representative depths to the laboratory. 2.2. Soil analysis Air-dried samples were passed through a 2 mm sieve and analyses were undertaken using fine earth: Texture of the soils was analyzed by wet sieving (2000-63 tzm) and pipetting ( < 63 p.m) following treatment with 35% H20 _, (Gee and Bauder, 1986) and dispersion through overnight shaking with 0.1 M Na4P20 7. pH was measured potentiometrically in 1:2.5 suspensions (soil:l M KCI and soil:H20) using a glass electrode (McLean, 1982). The analysis of organic carbon was conducted spectrophotometrically by measuring reduced Cr 3÷ at 578 nm after wet ashing with acidified K2CrzO 7 (Nelson and Sommers, 1982). Total nitrogen was determined titrimetrically with 0.1 M NaOH after distillation of NH 3 of Kjeldahl digestion fraction (Bremner and Mulvaney, 1982). Exchangeable cations were extracted by 0.05 M NH4CI at soil pH according to the Triiby and Aldinger (1989) method. The cations Ca, Mg, K, and Na were measured spectro-photometrically. H ÷ and AI 3÷ were measured simultanuously by potentiometric titration with 0.04 M NaOH using a titroprocessor (METROHM E 636XTriiby, 1989). The Effective Cation Exchange Capacity (ECEC) was calculated as the sum of exchangeable cations at soil pH. ECEC is the basis for the calculation of Base Saturation and AI saturation. Potential Cation Exchange Capacity (CECpH82) was measured according to the Mehlich method at pH 8.2. Available phosphorus was extracted by 0.03 M acidic (0.025 N HCL) NH4F (Bray and Kurtz, 1945) (Bray I) and analyzed spectrophotometrically at 578 nm. The Zero Point of Net Charge (ZPNC) was calculated by analyzing the exchange capacity for anions and cations depending upon the pH value (Marcano-Martinez and McBride, 1989). Pedogenic oxides were analyzed by extraction of Fe and AI with Na-dithionite (Fe d, A! d) and NH4-oxalate (Fe o, AIo) according to Jackson (1958) and Schwertmann (1964).
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3. Results and discussion
3. I. Soil properties All soils of the toposequence are free of coarse components ( > 2 mm). The profiles of the higher elevations show high clay contents sometimes above 80% (Fig. 1, lower part; Table 1). At the lower elevations the clay contents significantly decrease in favour of sand and finally make up only 1-2% at the toot of the slope. Besides this horizontal textural differentiation of the toposequence there is a vertical textural change in the profiles. The soils are strongly or very strongly acid, with the lowest pH in the topsoils (Table 2). The negative ApH (pHKc I - p H u , o) in all investigated horizons indicate that negative charges prevail (Keng and Uehara, 1974). However, there are some topsoils in the catena with ApH values near zero. This may be due to the variable charges of the organic material and of the free oxides. All mineral soils are covered by organic layers between 2 and 5 cm thick. The highest organic carbon contents are tbund in the mineral topsoils in the upper part of the toposequence. Downslope they decrease to 0.34% C at the foot slope. In contrast to Klinge (1962) and Bravard and Righi (1991) the C / N ratios are higher at the higher elevations than in the other soils of the catena. This indicates lower degrees of N incorporation in the humic structure. Available P is low in all profiles. Only in some topsoils the P content exceeds 2 mg/kg. The Effective Cation Exchange Capacity (ECEC) is very low. With the exception of only two topsoil horizons in profile I the ECEC does not reach 30 m m o l J k g (Table 3). The very low Base Saturation (BS~tcEc) corresponds with the low pH whereas the potential acidity (AI 3+ + H* ) occupies between 89 and 100% of the ECEC. At the upper and middle parts of the catena exchangeable AI fills up the main portion of the ECEC. The AI saturation decreases on the lower slope and finally disappears in the last profile of the toposequence (Fig. 1, upper part). There only H + is detected. The comparison of ECEC at soil pH with the potential Cation Exchange Capacity (CECpHs2) indicates a pool of electric charges available in case of an increase in pH (Table 3). But even an enormous pH value increase up to 8.2 could only raise the exchange capacity of the topsoils significantly because of the variable charge of the organic matter. In the other horizons the CEC remains below 100, mostly < 50 mmolc/kg. The charge characteristics can be determined by measuring the cation and anion adsorption as a function of pH (Fig. 2). The Zero Point of Net Charge (ZPNC) of the topsoil of profile I lies in the strongly acid pH range wheras the ZPNC of the subsoil is between pH 3 and 4. Profiles III and VII also show this tendency but to a lesser degree which may be due to lower humus contents (Keng and Uehara, 1974). However, soil solution pH is higher than ZPNC in all profiles which confirms the ApH calculation. Anion adsorption is particularly found in the profiles at the higher and middle elevations. Besides the aforementioned high clay contents there are also the highest contents of free oxides, especially of Fe oxides (Table 1), with anion sorption capacities
J. Botschek et al. / Geoderma 72 (1996) 119-132
Profile 4
o.
.
I
Profile
.
III
Profile 8
8
.
4
Profile 8
o.._
50 ~
'oo
:
150
150
150
ev
o
4
O4
G8
o
,
0
04
08
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VII
l 50. ioo
1"30
150
\
04
08
0" 50
100
'00
• 5O •
150 50
o 50
1 o0
0
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04
08
\ /7F%
"\
I
Aid
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~00
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ICO
o
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o 50
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~4
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123
gO
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~00
• 50
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1GO
150
50
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I
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Fig. 1. The soil toposequence with clay distribution and some soil chemical properties of selected profiles.
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J. Botschek et al. / Geoderma 72 (I 996) 119-132
Table I Soil texture and free metal oxides of selected profiles Profile Horizon Depth(cm) % fine earth
mg/kg
Sand Silt Clay Fe,, (2-0.063 mm) (0.063-0.(X}2 mm) ( < 0.002 mm)
F%
AI,,
AI,j
Ah AB BI B2 B3
0-6 6-18 18-35 35-60 60-120
16.4 14.9 87 6.1 6.3
24.3 7.7 12.9 15.8 14.7
59.3 77.4 78.4 781 79.0
1166 1519 1068 328 114
12151 18257 19317 21425 19667
1478 1350 1400 1194 1183
5953 6041 6104 6522 6156
111
Ahl Ah2 BI B2 B3
0-9 9-27 27-42 42-87 87-135
128 96 9.8 8.6 7.9
15.6 15.8 2.8 7.3 10.3
716 74.6 87.4 84.1 81.8
1548 1104 496 405 136
19769 19420 21111 21171 21049
1465 1415 1295 1325 1313
5971 5886 6127 6276 6316
V
Ahl Ah2 BI B2 B3
0-3 3-38 38-62 62-9(} 90-145
4(}.5 22.1 18.1 16.4 17.3
8.5 102 5.7 8.7 7.6
51.1} 67.7 76.2 74.9 75.1
1178 1174 371 210 I(X)
10529 1361}3 13750 13216 131)47
840 1224 1079 1056 1056
3151} 4348 4439 4234 4188
VII
All BI B2 B3
0-7 7-48 48-90 90-141)
74.9 58.4 50.6 48.9
4.9 7.8 4.9 5.4
20.2 33.8 445 45.7
694 1183 187 92
IX
Ah AB Bgl Bg2
0-15 15-45 45-95 95-160
96.5 95.1 96.3 97.9
2.0 2.7 19 1.3
1.5 2.2 1.8 0.8
5 39 57 9
4307 408 1685 6861 921 2550 8574 575 2783 8563 571 2647 71 174 353 87
26 117 212 387 519 646 14 143
under acid conditions. F r o m the higher to the l o w e r elevations the absolute contents o f Fe oxides decrease in c o r r e s p o n d a n c e with the net charge curves (Fig. 2). In contrast, the activity o f Fe and AI oxides ( F e o / F e d and A I o / A ! d in Fig. I, upper part) is significantly higher at the bottom of the slope which is also reported by Bravard and Righi (1989). The mineralogical c o m p o s i t i o n o f the soils can be derived from the E C E C calculated per kg o f clay (Table 3) particularly in subsoils with low organic matter contents. Apart from profile IX the low values in the subsoils indicate high kaolinite portions. The differing e x c h a n g e capacities per clay o f profile IX may be due to another clay type or higher amounts o f a m o r p h o u s metal oxides in the clay fraction. Bravard and Righi (1988) found kaolinite as the d o m i n a n t clay mineral in clayey and sandy soils of a c o m p a r a b l e t o p o s e q u e n c e near Manaus. 3.2. Pedogenesis and soil classification C l a y - r i c h soils on plateaux and d e c r e a s i n g clay contents along the slopes of the A m a z o n basin are described by several authors. Klinge (1965) regards the sandy
J. Botschek et al. / Geoderraa 72 (1996) 119-132
125
Table 2 Soil acidity, organic carbon, total nitrogen, and available phosphorus of selected profiles Profile
Horizon
Depth (cm)
pH 1 M KCI
H20
ApH
C,,fg (%)
N, (%)
C/N
P (mg/kg)
I
Ah AB BI B2 B3
0-6 6-18 18-35 35-60 60-120
3.2 3.6 4.1 4.3 4.4
3.4 4.0 4.5 4.7 4.6
-0.2 -0.4 -0.4 -0.4 -0.2
8.52 3.23 1.13 0.50 0.36
0.37 0.16 0.08 0.05 0.02
23 20 14 10 18
1.6 3.1 0.6 -
111
Ahl Ah2 BI B2 B3
0-9 9-27 27-42 42-87 87-135
4.2 4.3 4.3 4.3 4.4
4.5 4.7 4.7 4.8 5.0
-0.3 -0.4 -0.4 -0.5 -0.6
1.27 095 0.70 0.54 0.35
0.I0 0.07 0.01 0.03 0.02
13 14 70 18 18
1.4 1.9 1.4 1.0 0.6
V
Ahl Ah2 BI B2 B3
0-3 3-38 38-62 62-90 90-145
3.9 4.2 4.3 4.4 4.4
4.1 4.7 4.7 4.9 4.9
-0.2 -0.5 - 0.4 -0.5 -0.5
2.06 0.87 0.57 0.36 0.23
0.13 0.04 0.03 0.02 0.02
16 22 19 18 12
3.1 1.9 1.6 1.2 1.0
VII
Ah BI B2 B3
0-7 7-48 48-90 90-140
3.7 4.4 4.4 4.5
4.3 4.8 4.9 5.2
-0.6 -0.4 -0.5 -0.7
1.99 0.57 0.21 0.13
0.13 0.03 0.01 -
15 19 21 -
3.1 1.0 1.8 0.8
IX
Ah AB Bgl Bg2
0 -15 15-45 45-95 95-160
3.5 3.7 4.7 5. I
4.4 4.5 5.0 5.3
-0.9 - 0.8 -0.3 - 0.2
0.34 0.26 0.25 0.04
0.02 0.02 -
17 13 -
1.6 1.6 0.6 0.4
- = undetectable amounts.
substrata at the bottom of the slope of a similar toposequence near Manaus as non-autochthonous. He considers them fluvial deposits which are significantly different from the finer textured substrata of the higher situated Barreiras formation. Journaux (1975) explains such textural distribution with climatically induced erosion and land slides. These, in turn, have created so-called facette slopes. Chauvel et al. (1987) and Bravard and Righi (1988, 1989), on the other hand, view the Barreiras formation as the parent material for all soils of such toposequence. In these studies the distribution of textures is explained by lateral clay eluviation and selective erosion of clay. The significance of quarternary tectonics and of climatic changes for the geomorphogenesis, the stratigraphy of sediments, and the soils in the Amazon basin (Mousinho de Meis, 1971; Tricart, 1975; Irion, 1976; Bibus, 1983) is not taken into consideration. Consequently, the soils must originate from differently textured slope deposits and not from a homogeneous parent rock. The applied soil classification systems (Brazilian/Soil Map of the World/Soil Taxonomy) divide the toposequence into two sections (Table 4). Profiles I-VII of the upper and middle parts of the slope (Fig. 1) show diagnostic
126
J. Botschek et al. / Geoderma 72 (1996) 119-132
Table 3 Exchangeable cations, cation exchange capacities, and base saturation of selected profiles Profile Horizon Depth (cm) mmol,/kg fine earth Ca Mg K
Na AI
BSEcEC ECEC H
ECEC CECptix 2 (%)
(mmol c / k g clay)
Ah AB BI B2 B3
0-6 6-18 18-35 35-60 60-120
2.3 -
2.3 1.0 0.6 28.9 209 0.8 2.3 0.5 24.2 13.8 0.4 - 0.1 17.2 OI 12.8 13.1 --
56.0 41.6 17.7 12.9 13.1
253.3 157.7 672 46.1 37.3
I1.1 8.7 2.8 0.8 --
94.4 53.8 22.6 16.5 16.6
Ill
Ahl Ah2 BI B2 B3
0-9 9-27 27-42 42-87 87-135
0.1 1.2 2.5 1.0 -
0.1 0.1 0.2 13.0 0.1 9.8 0.1 - 0.1 8.9 0.1 4.8
8.8 9.6 8.6 9.1 I0.1
22.3 20.7 20.2 15.0 10.1
71.8 58.7 48.8 43.7 35.9
2.2 6.3 13.4 7.3 --
31.2 27.5 23.1 17.8 12.4
V
Ahl Ah2 BI B2 B3
0-3 3-38 38-62 62-90 90-145
- 0.2 0.4 0.4 0.2 0.1 0.1 0.2 0.2 -- 0.1 0.3 0.1 0.3 0.1 - 0.1
10.6 10.2 10.2 8.6 9.1}
28.8 21.3 10.8 13.6 9.5
972 54.2 41.4 36.6 32.6
3.5 2.8 5.6 0.7 5.3
56.5 31.5 14.2 18.2 12.7
VII
Ah BI B2 B3
0-7 7-48 48-90 90-140
0.3 0.6 0.6 0.6 14.3 0.1 0.1 0.6 0.6 0.6
9.4 25.8 9.1 9.9 9.4 I0.0 9.0 9.6
77.3 44.2 23.0 21.4
8.1 8.1 6.0 6.3
127.7 29.3 22.5 19.7
IX
Ah AB Bgl Bg2
0-15 15-45 45-95 95-160
-
8.3 8.2 9.8 9.5
26.1 38.1 32.2 9.5
1.2
560.0 372.7 544.4 1187.5
-
.
17.2 10.5 4.9 -
0.1 .
.
.
.
.
8.4 8.2 9.8 9.5
-
= undetectable amounts.
p r o p e r t i e s c o n n e c t e d to i n t e n s e w e a t h e r i n g , thus n a m e d L a t o s o l s / F e r r a l s o l s / O x i s o l s . The sandy, w e a k l y d i f f e r e n t i a t e d p r o f i l e s VIII and IX at the b o t t o m o f the s l o p e are called Q u a r t z o s e S a n d s / A r e n o s o l s / E n t i s o l s
and Q u a r t z i p s a m m e n t s , r e s p e c t i v e l y . Pro-
file IX s h o w s s o m e gleyic p r o p e r t i e s in the l o w e r subsoil w h i c h is d e s c r i b e d by three additional soil t e r m s ( H y d r o m o r p h i c / G l e y i c / O x y a q u i c ) .
Brazilian c l a s s i f i c a t i o n and
Soil T a x o n o m y s p e c i f y the texture o f all soils as well as the soil c o l o r o f L a t o s o l s and O x i s o i s . R e f e r e n c e is also m a d e to the textural c h a n g e in the O x i s o l s (Kandi-). T h e low cation e x c h a n g e c a p a c i t y o f the soils is i n d i c a t e d by all c l a s s i f i c a t i o n s y s t e m s ( l o w clay a c t i v i t y / G e r i c / k a o l i n i t i c ) w h e r e a s the b a s e saturation and high Al saturation is only c o n s i d e r e d by the Brazilian s y s t e m ( D y s t r o p h i c , Allic, Epiallic). A K C I - e x t r a c t a b l e Al c o n t e n t o f m o r e than 20 m m o l c / k g
o f fine earth c o u l d also be c o n s i d e r e d for O x i s o l s
(allic). T h e m a i n p h a s e s o f p r i m a r y v e g e t a t i o n are i n c l u d e d in the soil class n a m e as c l a s s i f i e d by the Brazilian s y s t e m . O t h e r soil and land c o n d i t i o n s i n f l u e n c i n g land use, e.g. the relief, can be a d d e d to the Brazilian soil class n a m e w h e r e a s soil m o i s t u r e r e g i m e and soil t e m p e r a t u r e r e g i m e are b o t h e c o l o g i c a l l y i m p o r t a n t data w h i c h are i n c o r p o r a t e d into the Soil T a x o n o m y n o m e n c l a t u r e .
127
J. Botschek et al. / Geoderma 72 (1996) 119-132 3.3. Agricultural suitability of soils and soil potentials
The acidity of all soils investigated may be an important factor impeding in the cultivation of most crops whereas the primary rain forest develops well under the conditions of the aforementioned acidity. The Fertility Capability Soil Classification System (Sanchez et ai., 1982b) enables grouping the major soil constraints, commonly associated with soil acidity in the tropics, into five classes: acid, aluminium toxic, low CEC, high P fixation, and low K availability. According to this system, P fixation cannot play an important role in the catena soils because there are no high free oxide contents. In addition, P availability is very low. The other constraints mentioned above are present in the catena in different combinations. The pH values range mostly between 4 and 5, and the AI saturations reach, or even exceed, the critical percentage of 60 (Kamprath, 1970) in several profiles. The ECEC is extremely low with less than 40 mmolc/kg of fine earth. It is mainly occupied by acid cations and the exchangeable K lies generally below 2 m m o l J k g of fine earth indicating low K reserves (Sanchez et al., 1982b). Agricultural suitability is often affected by Ca deficiency ( < 0.2 mmol~/kg of fine earth, after Ritchey et al., 1982) found in many horizons; others also show marginal values. In addition, the poor nutrient status is illustrated by the M g / K ratio. Rosolem et al. (1984) suggest an adequacy value of 0.6 for Brazilian Oxisols. This value was found to be higher only in the topsoils.
-100
-
Profile I
Ah .'
-80
•
-60 E E G
m
•
-40
~. ,
2
9
V ,=;-__~Tr_,
4
-80 • -60
•
m ....
'3
"~ "O "5
E E
B1
-20 o
$ z
-100 -
"
.H
2o
'
40[ 20
;: --
40'
m -80 -
u
E
Profile VII
I
_
-20 ~
z
i
i
40 ~
0 t ....... 2 20 f
40
Ah
I ~,,BI..,
3
4
...
" 5-
60
~:
°
E ~"-_
2ot
40
-100 T
Ah2 .eB1
.
0
5
Profile III
.
.
.
.
.
.
5 pH .
!
Fig. 2. Net electricchargesof selectedprofilesand horizons.
128
J. Botschek et a l . / Geoderma 72 (1996) 119-132
Table 4 Identification of selected catena profiles in three classification systcms Profile
Brazilian (Camargo et al.. 1987)
Soil Map of the World (FAO-Unesco-ISRIC, 1990)
Soil Taxonomy (Soil Survey Staff. 1994)
1
Yellow Latosol Allic, very fine clayey; semi-deciduous rain lbrest, plateau phase
Geric Ferralsol
Xanthic Kandiudox. very fine. kaolinitic, allic. isohyperthermic
Ill
Yellow Latosol Epiallic Dystrophic. very fine clayey; semi-deciduous rain forest, gentle slope phase
Geric Ferralsol
Xanthic Kandiudox, very fine. kaolinitic. isohyperthermic
V
Yellow Latosol Epiallic Dystrophic. very fine clayey; semi-deciduous rain forest, slope phase
Geric Ferralsol
Xanthic Kandiudox. very fine. kaolinitic. isohyperthermic
VII
Yellow Latosol Epiallic Dystrophic. medium; semi-deciduous rain forest, slope phase
Geric Ferralsol
Xanthic Kandiudox. fine. mixed, isohyperthcrmic
IX
Quanzose Sand Hydromorphic Dystrophic, sand>',low activity clay; tropical semi-evergreen rain li)rest. rich in palms, lower slope
Geri-Gleyic Arenosol
Oxyaquic Quarlzipsamment. sandy. siliceous, isohyperthermic
The soils investigated have low permanent negative charges which emphasizes the importance of organic matter and free oxides for the charge characteristics. With soil pH values significantly above the Zero Points of Net Charge the surface horizons rich of humus have in most cases higher cation exchange capacities as well as a better supply of cation nutrients in contrast to the subsoils of the catena. The organic material is known to play a fundamental role for most of the functional processes occurring in forest soils (Gosz et al., 1976). In the case of cultivation the land clearing method determines the decrease of C,,r.~ and other soil deteriorations during the first months after deforestation. Seubert et al. (1977) for the Amazon jungle of Peru prefer the traditional slashing and burning method which retards the decomposition of organic matter, increases the supply of exchangeable bases and available soil phosphorus, and decreases aluminium saturation. Yield responses are high in contrast to bulldozed lands suffering from severe soil compaction. Moreover, the bulldozed lands do not receive additional nutrients and they remain high in aluminium saturation levels. Even after successful land clearing the agricultural productivity of these acid soils is low and declines rapidly. There is need for special management techniques as summarized by Phiri et al. (1994) for acid soils in Africa: Lime applications aim at lowering acidity and reducing the toxicity of AI ~+ (Evans
J. Botschek et al. / Geoderma 72 (1996) 119-132
129
and Kamprath, 1970) as they are soil constraints restricting the cultivation of demanding crops. Experiments with different crops demonstrated the effects of liming on exchangeable Ca and AI and on crop yields on a Xanthic Hapludox near Manaus, Brazil (Smyth and Cravo, 1992). The application of inorganic fertilizers permits continuous production of annual crops even on Oxisols of the Amazon basin (Melgar et al., 1991; Smyth and Cravo, 1992). But both inorganic fertilizer use and liming are expensive and therefore inaccessible for most of the region's farmers. Another means to enhance fertility, alleviate element toxicity, and provide soil protection is the addition of organic matter such as crop residues and green manures, respectively. Organic additions without chemical inputs havc produced up to 90% of the yields with complete inorganic fertilization and liming on Ultisols of the Amazon basin (Wade and Sanchez, 1983). Smyth et al. (1991) showed the fertilizer-N substitution value of legume residues to succeeding corn crops on an Oxisol near Manaus. Thus, the use of on-farm generated organic fertilizers appears to be attractive tor a sustainable agriculture on the soils investigated. In contrast to management systems which try to raise the soil potential by organic or inorganic additions the use of acid-tolerant cultivars keeps the soil in its acid state (Sanchez and Benites, 1987) or leads to long-term improvements of acid soil conditions (Kirk and Zeigler, 1994). This reduces the need for expensive inputs and improves the applicability of that technique. However, the wide range of textures throughout the catena indicates varying soil potentials for the profiles along the slope. The change of the natural vegetation from terra-firme tbrest on the higher elevations with high clay contents to brush-rich campina forest on the lower slope with sandy textures was also described by Klinge (1965). This verifies the variation of ecological conditions consequently provoking different responses to agricultural management measures taken. The agricultural suitability of the sandy soils of the lower part of the catena (profile VIII and IX) is not only reduced by the soil chemical properties but also by the poor soil physical conditions. The high water table in profile IX possibly balances the low water holding capacity of the sands but high leaching rates are likely to occur on both soils as demonstrated for N leaching on an Entisol near Manaus (Melgar et al., 1992). The soils on the steep part of the slope (profile IV to VII) have higher clay contents which make them susceptible to soil erosion if no soil conservation measures are provided. Considering the soil physical properties and the erosion risks on the slope the soils of the higher elevations (profile I to III) have the highest potentials for agricultural use though their soil chemical properties are also very poor.
4. Conclusions
The soils investigated represent a typical toposequence in the area. All soils are extremely poor with high acidity and low exchange capacities although there are considerable differences pertaining to the soil potentials. Although very low in fertility the clay-rich soils of the upper part of the toposequence are best suited for crop
130
J. Botschek et al. / Geode rma 72 (1996) 119-132
production. The steep positions on the middle slope are endangered by erosion which decreases their agricultural sustainability. In contrast, the sandy texture heavily constrains soil fertility at the bottom of the slope. The physical and chemical differences of the soils are determincd by-and-large by deviating textures. Though the genesis of the textural distribution on the investigated slope remains unclear the wide spectrum of resulting soil properties necessitates the selection of appropriate technologies on each kind of soil. Considering the socio-economic conditions in the Amazon basin, low-input systems (Sanchez and Salinas, 1981) appear to be most appropriate for that region. Such systems require firm knowledge of soil properties, however.
Acknowledgements We thank the Agropecuaria Aruan~, Ings. S. Verguciro and G. de Paula Neto for their support to the field work. We are also grateful to M. D~iumer for reviewing the English text.
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