A classification of eroded Cuban soils, based on changes· in humus content in the A and B1 horizon, is proposed. Slightly eroded soils are soils that have lost up ...
UDC632.125 .·
. Translated from: Pochvovedeniye, 1990, No. 8:118-123
CLASSIFICATION AND IDENTIFICATION OF ERODED CUBAN SOILS G.L. SHCHEPASHCHENKO, M.O. SOKA, and M.R. RIVEROL', Dokuchayev Soil Institute A classification of eroded Cuban soils, based on changes· in humus content in the A and B1 horizon, is proposed. Slightly eroded soils are soils that have lost up to 25 percent of their humus content, moderately eroded soils-25-50 percent, severely eroded soils-50-75 percent, and very severely eroded soils, more than 75 percent of their humus content. Models of eroded and noneroded soils are formulated, which facilitates their identification and mapping. Identification of eroded soils is usually accomplished by comparing them. In recent years, however, a wide range of discussions has centered on how and where to select a field standard. Some investigators maintain that it is necessary to use actual profiles from plains as a standard, because all soils on slopes are eroded [7, 8]. Others assume that field standards should be found on slopes, since soils of plains differ . significantly from those of slopes not only in horizon thickness but also in soil properties [15]. A third group leans toward the opinion that it is necessary to rule out field standards altogether, since it is impossible to find plots with noneroded soils in a zone of intensive farming. In searching for a resolution to this situation, some investigators suggest that, instead of using an individual profile, extensive tables be used which represent mean data for certain soil properties, such as the thickness of genetic horizons, which serve as diagnostic indices in determining the extent of soil erosion [3, 14]. Even though this method is not without its drawbacks, it is, in our opinion, more valid, enabling one to obtain mean soil data and a sense of the variability in soil indices and properties, which inevitably occur when natural conditions vary. This method of creating a standard for measuring soil erosion was also used for our studies of eroded Cuban soils. In the course of these studies, standards models for measuring the degree of erosion were developed for those common soil types that are wisely used in agricultural production and are susceptible to erosion: Humus-calcareous soils on limestones and marls, Cinnamon-Brown calcareous soils on calcareous loams and clays, Cinnamon-Brown noncalcareous soils on neutral rocks, Gray Cinnamon-Brown soils on granodiorites, Yellow Pseudopodzolic .soils on binary deposits, Yellow lessive soils on sandy deposits, and Red ferritic soils on weathering crusts of serpentinites. . · . · . In the first phase of these studies, a diagnostic index was selected whereby eroded soils could be reliably distinguished from noneroded soils. Mter reviewing many soil characteristics (thickness of genetic horizons, depth of efferves59
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Table 1 Thickness of the humus layer of Cinnamon-Brown soils on different relief elements Thickness of humus layer, em
..
'
Soil type
Cimiamon-Brown calcareous Cinnamon-Brown noncalcareous Gray Cinnamon-Brown
Flat plain
50±3 50±2 49±2
Slope portion
'
Upper
Middle
Lower
40±2 42±3 34±5
50±3 51±2 49±3
65±4 69±5 71±6
cence, ·depth of occ~rrence of concretions, stoniness, etc.), one diagTiostic index was selected that is peculiar to all the soils, stable in all soilsites, and measurable in the field. This index is the thickness of the humus layer (A + B1 horizon). The other indices could not be used in identifying eroded soils, since most of them occurred only in 2 or 3 soil types. The thickness of the A1 horizon was not used because this horizon does not exist in severely eroded ,soils. Next, the pattern of variation for this diagriostic index was studied under different· environmental conditions. It was established that relief has the strongest influence on this index (Table 1). Variation in the thickness of the indicated soil layer, on different relief elements was so great that it was impossible to use a mean thickness as a leading index of standard measurement. Noneroded soils on flat, undifferentiated plains and on middle-slope portions, under natural grassy and woody-shrub vegetation, were more or less uniform in thickness, whereas on· lower-slope portions, and at the foot of the slopes, it was considerably thicker. On the other hand, on watersheds and on upper-slope portions, the thickness of the humus layer was considerably smaller than on plains (Table 1). This is evidently due to ·greater wetting of the soil profile on lowerslope portions and at the food of the slopes, due to redistribution of precipitation by the relief and· by the related, more intensive weathering and soil formation here than on middle- and, especially, upper-slope portions. · In studies of the effect ofvegetation on variation of the diagTiostic index, pro'files· were taken under natural grassy and woody vegetation as well as under sugar cane. It was found that the difference between the thickness of the humus layer under sugar cane and natural vegetation was insigTiificant. Under other kinds of agricultural crops, noneroded soils could not be found: · .
,
I
'·
. 'The former classification of Cuban soils was structur~d so that almost all of the studied soil types occur on the same parent material. As a result, it seemed impossible for us to determine how variations in parent material affect the thickness of the humus layer in soils of the same type. Nonetheless, a comparison of the thickness of the studied layer belonging to genetically similar. soil types, formed on different materials, indicates that the thickness of the humus layer is sigTiificantly dependent on parent material type (Table 2). Therefore in ... 60
Table 2 Thickness of the A + Bl layer (em) standardized models of noneroded soils in Cuba Mean value
"
Soil type
.Error of the . mean
52 '
Humus-calcareous Cinnamon-Brown calcareous Cinnamon-Brown noncalcareous Gray Cinnamon-Brown Yellow Pseudopodzolic Yellow lessive · Red ferritic
1.7 . 1.4
53· 51
..
49 49 54
71
1.9 ..
..
1.7 1.5 2.0. 1.8
Coeffici- Interval ent of of variavariation tion 10 8 11 18
48-{56
50-56 47--55 45-03
12·
46-52
11 10
50-08
67-75
selecting profiles for the purpose of developing standards models, each soil type was studied on a specific parent material. A study of the variation in the thickness of the humus layer of major Cuban soil types, under different environmental conditions, showed that profiles taken under natural vegetation and sugar cane on plains and middle-slope portions can be used in developing standard soil models. Based on this requirement, about 200 profiles were sampled in which the thickness of the A and Bl horizon was measured and samples were analyzed. Mathematical processing of the data obtained made it possible to calculate mean values and intervals of natural variation in the thickness of the diagnostic layer at the 0.95 probability level (Table 2). .
'
'
After. standardized models of non eroded soils were .designed, studies were made on areas where erosion was widespread. More than 400 profiles were taken, which provided the basis for the development of a classification of eroded soils. · · Until recently, a classification of eroded soils proposed by Sobolev [12] for the European USSR was used in Cuba. However, in our opinion, in its original form this classification cannot be used in Cuba, since its gradations do not correspond well to changes in the productivity levels of soils, which occur on different erosion phases. An example is the decrease in humus content in CinnamonBrown calcareous soils during erosion (Table 3). Soil in which 11 out of 22 em of the A horizon is eroded is, according to Sobolev's classification, slightly eroded; This soil loses about 60 metric tons of humuslha--:-the principal nutrient source, which is more than 30 percent of its total humus content in the A+ B1 horizon, taken together. Such soil can hardly be called slightly eroded. A similar disproportion is observed for other erosion phases. '·
.
"
. In· our opinion,· the extent of erosion should be determined by the level of remaining productivity. Many investigators have made similar proposals. At the same time, various other criteria have been proposed for separating soils according to the extent of erosion. Some authors used soil morphological features 61
Table 3 Humus content in Cinnamon-Brown calcareous soils of Cuba on various erosion phases [12] ·Horizon thickness, em . Erosion .. . phase
.....
c
A
B1
Humus content, ·metric tonslha
A+B1
Humus losses, %
..
r
Noneroded Slightly eroded ~oderately eroded Severely eroded Very· severely eroded
zz·
31 31 ' 31 • 16 0
11
0 0
o·
53 42
31 16 0
.~
-
179.35 119.92 73.32 27.55 .. - 0.00
' '
33 59 ..
84 100
!
'
.'
Table 4 Humus content (metric tonslha) in noneroded soils. of Cuba · .
Soil type
Mean value
Error of the mean
··184.89 179.35 148.08 142.69 79.36' 65.29 143.72
4.20. 3.63 3.55 3.78 2.47 1.70 4.08
•'
Humus-calcareous Cinnamon-Brown calcareous Cinnamon-Brown noncalcareous Gray Cinnamon-Brown Yellow Pseudopodzolic .. Yellow lessive Red ferritic
.
Coef-· Standard ficient deviation of variation, % '
'
16.27 14.06 13.75 14.63 . 9.56 6.58 15.81
'
.. 9 8 9 10 12·
10 11 .
.
for this. purpose [4, 14]; others used analytical data: content of micronutrients in the soil [9, 10], amount of aggregates larger than 1 mm in diameter [13], qualitative composition of humus [1, 2, 11]; a third group combined soil morphological features with analytical data [6]. However, most investigators assume that data on soil humus eontent could also be used with other indices in classifying eroded soils. . · ! \ ' .'
As early as the 1960s, Zaslavskiy [4] suggested using, in a classification of soils according to the extent of erosion, the decrease in thickness of the soil layer having a humus content greater than 1 percent, as well as the decrease in humus content in the 0- to 50-cm layer. Somewhat later, he [5] suggested using, along with other indices, the content of humus in the 0- to 50- or O--to 30-cm layer de-
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Table 5 Thickness of the A+ Bl ,layer (em) of models of eroded soils of Cuba
I
Soil type
Humus-calcareous Cinnamon-Brown cal-· careous Cinnamon-Brown noncalcareous Gray Cinnamon-Brown Yellow Pseudopodzolic Yellow lessive Red ferritic
Very severely eroded
Noneroded
Slightly eroded
Moderately · eroded
48-56 50--56
41-47 42-49
'·32-41
18-29 : 20-31
2)
47-55
49-46
31-39
20-30
2)
. 45-53 46-52 50-58 67-75
38-44 40-45 42-49 60-{)6
29-37 32-39 32-41 51-59
17-28 20-31 ' 19-31. 39-50
30-40
Severely eroded
18
17 ,2)
19
ro
pending on the thickness of the studied soils. Non eroded soils were soils which had lost up to 10 percent of their humus content, slightly eroded soils-10-20 percent, moderately eroded-20-50 percent, severely eroded soils:-50-70 percent, and very severely eroded soils more than 70 percent of their humus content in the 0- to 50-cm layer. Bakhirev [1] and Gubaydulin [2] proposed similar classifications. Those classifications, in our opinion,· have two weak points. First, soils which had lost up to 10 percent of their humus content were classed with the noneroded soils. Naturally the variability of soil humus content is observed in non eroded soils but this is due not to erosion but to diversity in the conditions of soil formation. Hence these variations can hardly be called losses. Second, the criteria of the various phases in the abovementioned classifications differ. Slightly eroded soils are soils that have lost only 10 percent of their humus content, moderately eroded soils-:-30 (50-20 percent), severely eroded soils-20 percent, and very severely eroded soils-again 30 percent. In our opinion, it is better to have a uniform scale of humus loss for delineating the process of erosion. ' . Considering the above discrepancies between soil productivity in Cuba and the extent of soil erosion, and the results from previous studies in developing a classification of eroded soils, we suggest using the humus content of A' and B1 horizon as a basis for classification. Previous studies have shown that the humus content· in this layer varies only slightly within a given soil type (Table 4). Hence. this property may serve as a diagnostic index in determining the extent of erosion. At the same time, slightly eroded soils should be soils which have lost up to 25 percent of their humus content, moderately eroded soils-25-50 percent, severally er'oded soils-50-75 percent, and very severely eroded soils more than 75 percent of their humus content. In this case, the classification will have five erosion phases, which is quite sufficient for both scientific and production purposes. Each of the delineated phases will be characterized by a specific level of productivity whose index is the humus content in the A+ Bl layer. '
'
'
. Most of the above proposals aimed at developing a classification of eroded soils have, unfortunately, not been widely used in mapping because of problems 63
associated with identifying the erosion extent in the field. The point is that the extent of erosion can be determined from the content and qualitative composition of humus or from other elements only after analyses have been performed in the laboratory. However, by this time, as a rule, a field map has already been con. structed from a classification based on thickness of genetic horizons. Of course, the compiled map can be corrected based on the results of analyses obtained, but this can be done only with unbroken contours, since it would also be necessary to take a large number of profiles and to perform analyses to change the boundaries. · Standardized models of eroded soils may resolve this problem. These models should have diagnostic indices whereby they could be easily determined in the field, but at the same time they should be based on data reflecting the productivity of the soils. The thickness of the remaining humus layer of soil may serve as such an index: By using data on the humus content of the A and B1 horizon of noneroded soils, as well as the profile distribution of humus, in conjunction with the above-adopted parameters, we calculated the minimum and maximum thickness of the remainder of the humus layer of the studied soils for the different erosion phases (Table 5). The basis for such calculations were the data on the content of humus in Cuban soils obtained from 410 profiles taken under different environmental conditions. The proposed classification of eroded soils differs from the traditional one in that it reflects more accurately the decrease in soil productivity during the course of erosion, while standardized models provide a means for identifying and mapping soils without a further search for field standards .. · BIBLIOGRAPHY BAKHIREV, G.I. 1972. Determination of the extent of erosion in Sod-Podzolic soils according to humus content. In Voprosy metodiki pochvennoerozionnogo kartirovaniya (Problems associated with methods of soil erosion mapping). Moscow, MGU. . · 2. GUBAYDULIN, S.A. 1972. Experiment in mapping eroded soils according to their humus content. In Voprosy metodiki pochvenno-erozionnogo kartirovaniya (Problems associated with methods of soil erosion mapping). Moscow, MGU. ·. . ·· . 3. GUBAYDULIN, S.A. 1976. Problem of determining the extent of soil erosion~ In Zakonomernosti proyavleniya erozionnykh i ruslovykh protsessov v razlichnykh prirodnykh usloviyakh (Patterns of erosion and channel processes under different natural conditions). Moscow, MGU. 4. ZASLAVSKIY, M.N. 1962. Some problems in the classification and map. ping of eroded soils. Voprosy erozii i povysheniya produktivnosti sklono· , · vykh zemel' Moldavii, No. 11. 5. ZASLAVSKIY, M.N. 1969. Some problems ,in soil erosion mapping. Pochvovedeniye, No. 10. . · . 6. ZASLAVSKIY, M.N. 1979. Eroziya pochvy (Soil erosion). Moscow, Mysl'. 7. KIRYUKHINA, Z.P., G.A. LARIONOV, and L.S. SAMODUROVA. 1977. Diagnostic indices of erosion of Sierozems and their variation (based on soils of the Karshi and Dzhizak steppe). In Tez. dokl. na respubl. konf. . , "Aktual'nyye problemy okhrany okruzhayushchey sredy i ratsional'nogo ispol'zovaniya prirodnykh resursov" (Abstracts of reports presented at the union republic conference "Topical problems in environmental conservation and the efficient use of natural resources"). Tashkent. 8. MORYAKOVA, L.A., and Z.V. PATSUKEVICH. 1976. Some methodical problems in the selection of standard resources for determining soil ero1.
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sion. In Zakonomernosti proyavleniya erozionnykh i ruslovykh protsessov v raznykh prirodnykh' usloviyakh (Patterns of erosion and channel processes under different natural conditions). Moscow, MGU. 9. PATSUKEVICH, Z.V. 1973. Character of distribution of some micronutrients in soils on different relief elements. In Otsenka i kartirovaniye erozionnoopasnykh i deflyatsionnoopasnykh zemel' (Appraisal and mapping of erosion- and deflation-prone lands). Moscow, MGU. 10. PATSUKEVICH, Z.V. 1973. Micronutrients as an index of soil erosion. In Otsenka i kartirovaniye erozionnoopasnykh i diflyatsionnoopasnykh zemel' (Appraisal and mapping of erosion- and deflation-prone lands) . ·... , •. . . . ...•.. , . .. . Moscow,MGU, · 11.. POLUEKTOV, Ye·.v. 1978. Agroproizvodstvennaya kharakteristik·a erodirova~~ykh chernozemov i 'effektivnost' protivoerozion_nykh priyemov: p0 ukl).odu za. c~istym. parom v Rostovskoy oblasti (Indexes of agricultural produetivity in· eroded Chernozerns and the effectiveness of erosion control measures to maintain clean fallow in the Rostov Oblast). Author's abstract of Candidate's dissertation. Kishinev. · · ' · 12. SOBOLEV, S.S. 1948. Razvitiye erozionnykh protsessov na territorii yevropeyskoy chasti SSSR i bor'ba s nimi. Tom 1 (Development of erosion processes in the European USSR and erosion control me.asures. Vol. 1). Moscow, lzd. AN SSSR. . · · . ·. . · · 13. TANASIYENKO, A.A. 1975. Vliyaniye vodnoy erozii na svoystva chernozemov Kuznetskoy kotloviny (Effect of water erosion on properties of Chernozems of the Kuznetsk Basin). Author's abstract of Candidate's dissertation: Baku. · · 14. KHYRKHYROVA, M.M. 1972. Problems associated with determining the extent of soil erosion. In Voprosy ·metodiki pochvenno-erozionnogo kar. tirovaniya (Problems associated with· methods 'of soil erosion mapping). · Moscow, MGU: 15. CHUYAN, G.A., V.V. YERMAKOV, and S.l. CHUYAN. 1987. Agrochemical properties of Typical Chernozern in relation to slope exposure. Pochvovedeniye, No. 12. · · I
Received 9 March 1989
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