SOIL COVER TRANSITIONS IN THE VRANCEA REGION

Transcription

1 Factori şi Procese Pedogenetice din Zona Temperată 9 S. nouă (2010) SOIL COVER TRANSITIONS IN THE VRANCEA REGION Ionut Vasiliniuc, Adrian Ursu, Lilian Niacşu University Al. I. Cuza, Faculty of Geography and Geology, Department of Geography, Iaşi, Carol I, no. 20A, , ursu_v_adrian@yahoo.com Tranziţii ale învelişului de sol în zona Vrancei Abstract In the study area, the soil cover generally respects the principles of horizontal and vertical zonality, with transitions from low plain Chernisols and Aluviosols toward the Preluvosols and Luvosols characteristic for the hilly Subcarpathian area and then to the mountain soils belonging to Cambisols, Spodisols and Umbrisols. Normally, this pattern is complicated by the presence of azonal and intrazonal soils such as Protisols and Anthrisols. Frequently, although the profile database was not too large, it can be seen that a part of the physical and chemical parameters respect these transitions. In what regards physical characteristics, can be seen a clear decrease in the fine sand content from the plain to the mountainous area, compensated by an increase in the percentages of silt and coarse sand. In the same direction bulk density decreases, while the soil and upper horizon depths decrease. In the case of chemical parameters, obvious differentiations occur in the case of mobile P content (decrease from Chernisols to Luvosols). Also the exchangeable bases sum and ph decrease, being compensated by an increase in hydrolytic acidity. Key words: soil cover, transitions, horizontal and vertical zonality, azonality INTRODUCTION The term of transition defines the passage (sudden or gradual) from a state / situation / idea to another, referring to something intermediary, transitory. Physicogeographical transitions may be approached from several viewpoints, yet the study is limited to passages only, in the attempt to see how these are manifested in the case of soils. Geographic regions present themselves as a system resulted from the interactions between natural and anthropic components on a certain area. Yet these components maintain close connections to the geospheres they are part of, thus frequently their limits are not clear. In this way are evidenced a series of transition areas between different territorial units, in which a clearer or more graded passage is made towards the neighboring units. 99

2 The physico-geographical units analyzed are Vrancea Mts., Vrancea s Subcarpathians (with the subdivisions Vrancea Depression, internal hills, Vidra Depression, external hills), the subcarpathian glacis, the piedmontan plain of Râmnic and the plain of Lower Siret River MATERIALS AND METHODS The first stage of the study consisted in georeferencing and vectorizing the soil map scale 1: (Focşani, Galaţi and Bacău sheets), and finally creating a digital soil map of the region. For this was needed the correction / redrawing of some soil polygons (with the help of terrain attributes obtained from the 10m-DEM and from aerial photos scale 1:5000), because in several situations the polygons soil mapping units from the printed map do not correspond to the surveyed field reality. A second operation needed has been the bringing up to date of the soil names, more precisely, the correlation from the old Romanian Soil Classification System (1980) to the new Romanian Soil Taxonomy System (2004). The statistical analyses were conducted on profiles obtained from the soil surveys from OSPA Focşani for the administrative territories entering the study area. The tables and final graphics include mean values for most of the parameters taken into account. RESULTS AND DISCUSSIONS The high diversity of the soil cover from the studied region can be seen from the obtained map. As it can be seen and in table 1, in the region, at this scale, have been identified seven soil classes, 13 soil types and 47 sub-types. The mentioned diversity can be seen in the transition from lowland soil types Chernisols to those representative for the hilly area Luvosols, and then to the specific soils of the mountainous region Cambisols, Spodisols and Umbrisols. The landscape, through its vertical development between 32.5 and 1724 m, is the main responsible for this general pedogeographic law: soil vertical zonality, consequence of the similar distribution of the zonal factors of soil formation climate and vegetation. This bended layout is disturbed by the presence of azonal and intrazonal soils, which belong to two large classes: Protisols and Anthrisols. In the analysis of the percentages occupied by different soil classes, it can be noticed a relatively expected aspect, more precisely a distribution in agreement with the surfaces occupied in the studied area by the different physico-geographical regions. Thus, the dominant class, with 34.01%, is that of Cambisols, representative for the mountainous area that occupies the largest part of the study region. The other soil classes specific for the mountainous area detain small percentages, being characteristic to higher altitudes. Thus, Spodisols detain 7.82% and Umbrisols only 0.20%, the later characterizing the highest altitudes, usually over 1800 m. 100

3 The main soil classes, types and subtypes in the studied area 1 Table 1 SOIL CLASS ha Soil type ha Soil subtype ha Litosol typical 7.19 typical 33.5 Regosol salinic 2.07 typical gleyic 1.79 PROTISOLS Aluviosol entic 7.14 typical cambic-vertic 1.76 cambic-marnic 0.91 cambic-gleyic 3.58 cambic argic Chernozem aluvic 1.01 typical CHERNISOLS Phaeozem greyic 4.32 vertic-stagnic 7.09 typical eroded typical stagnic Preluvosol skeletal 4.25 typical eroded typical stagnic skeletal 2.99 albic stagnic albic eroded LUVISOLS Luvosol albic CAMBISOLS typical eroded typical stagnic 5.40 skeletal molic-vertic 1.63 Eutric Cambisol litic 1.04 Dystric Cambisol umbric skeletal 0.74 umbric The soil class, type and subtype names are approximate translations from Romanian and not the WRB-SR correspondents. 101

4 SOIL CLASS ha Soil type ha Soil subtype ha typical skeletal litic prespodic typical skeletal Prepodzol litic 4.64 typical SPODISOLS Podzol skeletal UMBRISOLS 2.17 Nigrosol typical 2.17 typical 2.87 ANTHROSOLS 4.34 Erodosol cambic 1.47 The second class as percentage (28.44%) is that specific to the sub-carpathian area, namely of Luvisols. Covering a reduced surface of the studied region, the lowland plain area is thus weakly represented, Chernisols occupying only 10.77%. Here it must be mentioned that the piedmont glacis is remarked from the soil cover viewpoint as a transition area, making the passage from lowland Chernisols to hilly Luvisols sqkm Protisols Chernisols Luvisols Cambisols Spodisols Umbrisols Anthrisols Figure 1. Percentages of soil classes As it was mentioned, the soil cover is complicated by the occurrence of azonal soils, conditioned by a soil forming factor with a dominant action, most often of a petrographic or geomorphologic nature. Thus, Protisols are clearly remarked as presence through their 18.33%. 102

5 250 sqkm Litosols Regosols Aluviosols Chernozems Phaeozems Preluvosols Luvosols Eutric Cambisols Distric Cambisols Prepodzols Podzols Nigrosols Erodosols Figure 2. The participation of the soil types to the soil cover Continuing the analysis at the type level (fig. 2) should be noted the curiosity of the large surfaces covered by Protisols and in this class the dominance of Aluviosols. The explanation stands in the large development of Putna and its tributaries floodplains, but also in the dominance of alluvial deposits in the low plain and glacis areas. With their different subtypes, Aluviosols are also met on the lower river terraces. Regosols are on the second place in this class, overcoming Litosols, their presence being a consequence of one of the region s characteristics, namely intense erosion which does not allow soils on slopes to evolve. Despite all these, the main soil types from the region respect the order seen at the class level. Thus the most common soil is the Dystric Cambisol, consequence of the large development of the altitude class of m, characteristic to this soil type. It is followed at short distance by the Luvisol, specific to the subcarpathian perimeter. In a similar order to that of the classes, the previous are followed by Eutric Cambisols and Preluvosols, and only after by the Chernozems typical for the low plain region. The other soil types cover much more reduced surfaces, according to the specific of the plain, glacis, subcarpathic or mountainous regions. Characterization of the main soil classes, types and subtypes 1. In the low plain area, Chernisols are represented mainly by Chernozems (with different subtypes: typical, cambic, argic) and Phaeozems. 103

6 Typical Chernozems generally present a medium grain size distribution (sandy loams, loams, rarely clayey loams). The upper horizon (Am) is dark colored, with a granular structure. Carbonates occur in the transition area towards the parent material. Soil texture is generally not too differentiated on the profile, being medium. Bulk densities are relatively high, of g/cm 3. Total porosity is small, the compaction degree being moderate, while humus content is low and the reaction neutral. Characteristics of some low plain Chernozems Table 2 Horizons Typical Chernozem Cambic Chernozem Ap Am AC C Ap Am AB Bv 1 Bv 2 C Depth (cm) Coarse sand ( mm) % Fine sand ( mm) % Silt ( mm) % Clay (< 0.002mm) % Fine clay (< 0.01 mm) % ph Humus % Total N % Mobile P ppm 44 8 Mobile K ppm SB-me/l00g sol T-me/l00g sol V% Cambic Chernozems are weakly differentiated on the profile, having a medium to coarse grain size distribution. The upper horizon is brown, granular or blocky, loamy, porous and with frequent roots. The Bv horizon is also medium textured, brown or yellowish-brown, having a blocky structure. The clay quantity is usually between 29-33%, bulk densities being high and porosity medium. The humus content is medium and soil reaction slightly alkaline. Due to the diversity of local conditions, in this plain area occur also double subtypes of cambic Chernozems, the most frequent being the cambic-vertic (favored by the clayey texture) and the cambic-gleyic or cambic-stagnic (in the small depressions where water stagnates or the underground water level is close to the terrain surface). Argic Chernozems are formed in the more humid part of the plain, soil forming processes being more intense than in the previous cases. Usually they are more compacted and have a heavier texture. 104

7 According to local conditions, can be met and other subtypes of Chernozems, such as gleyic or stagnic, as well as vertic. According to the same specific conditions, besides zonal soils are met and azonal ones, linked especially to excess water or alluvial materials. Hydrisols occur in spots in the area of the piedmont and low plains, being mainly represented by Gleysols, where the reduced depth of the underground water determines soil s high humidity. Most common are saline Gleysols, due to the mineralization of the phreatic. Their texture is loamy to clayey, fact that helps a high capacity of water retention. Salsodisols (saline and alkalic soils) also have an island-type occurrence, being represented by Solonetzs and Solonchaks. These soils occur in low sectors of the divagation plain, where the close-to-surface underground water is strongly mineralized. Solonetzs occupy higher terrains, with deeper underground water. Protisols are represented in this unit mainly by Aluviosols, but also by Litosols. Aluviosols (table 3) have a large occurrence in the space of the low subsiding plain and at the contact between the piedmont glacis and the high plain. Their texture differs from an area to another, according to the nature of the alluvia on which they evolve. The upper horizon is yellowish brown, loamy, porous, frequently with high carbonate content. They have a small humus content and slight alkaline reaction. In the sectors where phreatic water is at low depths, Aluviosols are gleyic. In the confluence area between Putna and Siret are also met saline subtypes. Characteristics of some Aluviosols from the low plain glacis area Table 3 Horizons Typical Aluviosol Entic Aluviosol Ap Ao Ao 2 AC C Ao AC C C Depth (cm) Coarse sand ( mm) % Fine sand ( mm) % Silt ( mm) % Clay 2 (< 0.002mm) % ph Humus % Total N % Mobile P ppm Mobile K ppm CaCO Bulk density g/cm Entic Aluviosols (table 3) have very similar physical and chemical characteristic to the typical ones, only a less developed profile. They occupy spaces in 105

8 the floodplains of the main rivers in the area, with the largest extension in the convergence area of Putna, Milcov and Râmna. In the areas where underground water has low depths, they might present gleyic (at the confluence between Putna and Siret) or even salic subtypes. Other subtypes met in the plain area are the litic, gleyic, rarely molic or even molic-vertic ones. Litosols are developed on alluvial gravels, mainly on the old Putna riverbed. They lack structure, having a weakly developed A horizon (yellowish, sandy loam, only 10 cm), low humus content and a slightly alkaline reaction. 2. To the area of the piedmont glacis are still specific Chernisols, represented by cambic Chernozems and Phaeozems. They make the transition from eastern silvosteppe soils to those of the western subcarpathian forested area. The formation of Phaeozems is characterized by a more advanced weathering and levigation than in the silvo-steppe, with a moderate neoformation and migration of clay. Generally they have a loam texture, without a too clear differentiation between horizons. The presence of the Bt clayey horizon makes water percolation into the soil more difficult, leading to the occurrence of the stagnic subtype. Argic Phaeozems are characterized by a heavy texture due to the high clay content (35-50%). Thus their permeability is reduced and the internal drainage weak, favoring the same stagnogleyzation processes. Characteristics of some Phaeozems from the glacis area Table 4 Horizons Typical Phaeozem Calcaric Phaeozem Ap Ame AB Bt C Ap Ame AB Bv C Depth (cm) Coarse sand ( mm) % Fine sand ( mm) % Silt ( mm) % Clay (< 0.002mm) % ph Humus % Mobile P ppm Mobile K ppm Base sum SB-me/l00g sol T-me/l00g sol Hydrolytic acidity Base saturation V% Bulk density g/cm

9 Along Chernisols, in the glacis area occur soils of the Luvisols class, more precisely Preluvosols and Luvosols, whose maximum extension is reached in the subcarpathian region. 3. Thus, the subcarpathian region is clearly dominated by the class of Luvisols. The soil forming conditions in this area have been favorable for the occurrence of Preluvosols and albic and typical Luvosols. Specific for these soils is the Bt argic diagnosis horizon, with a diminished permeability, which leads to a high water retention capacity, a weak internal drainage and implicitly stagnogleyzation. On lacking vegetation inclined terrains, water surplus flows at the surface or inside the upper horizon, detaching soil particles. Preluvosols have a small percentage in the region, being defined by an argic horizon and an upper horizon depleted in clay and organic matter. The physical and mechanical properties are generally good. The texture is sandy-loamy, loam and clayloamy, in the Bt horizon being more clayey. Soil reaction is slightly acid, with a ph between 5.4 and 8.2. The humus and nitrogen contents in the first 50 cm are small to moderate, while the phosphorous and potassium contents are from extremely low to medium. The most common subtypes are the stagnic, luvic, molic and vertic ones. Characteristics of some Preluvosols from the subcarpathian area Table 5 Horizons Typical Preluvosol Stagnic Preluvosol At Ao AB Bt C At ABw Btw C/R Depth (cm) Coarse sand ( mm) % Fine sand ( mm) % Silt ( mm) % Clay (< 0.002mm) % Fine clay (< 0.01 mm) % ph Humus % Nitrogen index Mobile P ppm Mobile K ppm SB-me/l00g sol Hydrolytic acidity V% Bulk density g/cm Total porosity % Field capacity %

10 Luvosols are met on relatively plan or lowland surfaces, but also on slopes up to 25%. Due to a higher water quantity, soil formation is oriented towards the occurrence of elluvial-illuvial horizons. Because of a more intense migration of clay, sesquioxides and organic matter, under the A ochric horizon forms a light-colored El luvic horizon, enriched in silica and other resistant minerals. Soil texture is differentiated on the profile, being lighter in the upper horizons (loam) and heavier in the Bt. Physical properties are less favorable than in the case of Preluvosols. Soil reaction is slightly-moderate acid and the supply with nutrients is low, such soils needing amending. Albic Luvosols have formed due to an intensification in the elluviation processes, that have led to the occurrence of an Ea (eluvial albic) horizon, severely depleted in what regards clay, organic matter and sesquioxides. Also, the Bt horizon in this case has a higher clay content. Stagnogleyzation processes are more intense, soil reaction is moderately acid ( ), and the nutrient supply is poor, these soils needing fertilization. Characteristics of some Luvosols from the subcarpathian area Table 6 Horizons Stagnic Luvosol Albic-stagnic Luvosol Ap Aw Btw C Ap Eaw EBw Btw BCw Depth (cm) Coarse sand ( mm) % Fine sand ( mm) % Silt ( mm) % Clay (<0.002mm) % Fine clay (<0.01 mm) % ph Humus % Nitrogen index Mobile P ppm Mobile K ppm SB-me/l00g sol Hydrolytic acidity V% Bulk density g/cm Cambisols have a large distribution in the surveyed area, under the form of eutric and dystric types, the first being more characteristic to the subcarpathian region and the second to the mountainous one. Eutric Cambisols are characteristic to Vrancea Depression and to slopes with low and moderate inclination, yet they have also been identified on floodplains and lower terraces where the cambic horizon forms due to the young age of the landscape and the coarse parent material. The physical properties are 108

11 slightly more favorable than in the case of Luvisols. Soil reaction may be even neutral, while the other usual chemical parameters (organic matter, N, P, K) have low values. The most frequent subtype is the stagnic one, but skeletal-eutric Cambisols are also common. Dystric Cambisols occur on small surfaces in the subcarpathian area, at over 700 m altitude (Odobeşti and Răiuţ Hills). The reduced depth, high rock fragments content and light texture favor a good water circulation in these soils, but also a high erodability if they are not vegetated. From the class of Pelisols are encountered Vertisols, in the areas where the content of swelling clay is high, over 50%. These soils are characterized by a discrepancy between the unfavorable physical features (caused by the high clay content) and the good chemical characteristics. Stagnosols (Hydrisols class) are defined by a stagnic (W) horizon, whose upper limit is situated in the first 50 cm. They occupy a more representative area in the southern part of Vrancea Depression (NE of Nereju). The physical properties are poor, mainly due to the defective hydric regime determined by higher clay content. Soil reaction is acid to neutral ( ). The humus, phosphorous and potassium contents are low. Protisols include Litosols, Regosols and Aluviosols. Litosols are met on small, discontinuous surfaces, where the gravels or rocks are in the first 20 cm. They have a short ochric horizon followed by rocks or gravel. Having a low fertility and productive potential, are not used as arable terrains. Regosols are characterized by an incipient soil formation, consequence of erosion, and as such the profile is characterized only by a short A horizon followed by the parent material. They occupy important areas in the subcarpathian region. Aluviosols in this case have gleyic, but also coluvic subtypes (previously classified as Coluvisols). The later cover small surfaces, mainly at the slope contact with the valleys. The main characteristic is the presence of colluvial material with a thickness of over 50 cm. Texture is usually slightly differentiated, and the chemical properties are medium. Anthrosols class includes Erodosols and Anthrisols. The first are met on inclined landforms where erosion acts. When the process is intense, the upper horizons are eroded, and thus the soil can no longer be classified as a zonal one. These soils are representative for the region of the Vrancea s Subcarpathians, and in some cases the process is so severe that it has led to the occurrence of badlands. Besides typical, vertic and stagnic Erodosols, are quite frequent the eroded variants of other soil types, mainly Preluvosols and Luvosols. The Anthrosols are classified in the Romanian Soil Taxonomy System as soils from old orchards or vineyards, in which cases deep loosening works have been conducted, mixing the soil material on more than 50 cm. 4. In the limits of the Carpathian region, soil type diversity and complexity is different according on one side to the bio-climatic areas, being higher in the deciduous 109

12 forests and lower as one goes higher, and on the other to the more or less severe climatic conditions, the derived parent materials, the landforms and hydrologic conditions (Bălăceanu and Marian, 1985). Soils depend largely on the parent material, and because of this their diversity is quite high. It can be mentioned that on the dominant basic and ultrabasic flysch are largely developed Eutric Cambisols and even Luvisols, up to m altitude. On marls occur Rendzinas and molic-eutric Cambisols. In the limits of the same lower floor of deciduous forests, on the external flysch dominate oligo-mesobasic dystric Cambisols. Only on the Kliwa and sometimes on the Tarcău sandstones, dystric Cambisols become oligobasic or even criptospodic. To the upper limit of this floor become dominant the typical dystric Cambisols. On sandstones and conglomerates, even those with calcareous cement, dominate frequently litic dystric Cambisols. At higher altitudes, under associations of Nardus stricta and Festuca rubra, can occur Nigrosols. Beginning from the floor of the spruce forests, soil cover complexity decreases. Here dominate Prepodzols, which are reduced as proportion only due to the not so high altitudes in the area. In the high altitude pastures are met Spodisols, rarely Podzols. Well defined Podzols in this region occur only on acid conglomerates and sandstones. Cambisols group soils whose diagnostic horizon is the cambic Bv horizon, which indicates a less advanced evolution stage than in the case of the argic one, fact explained by the dominance of consolidated-compact rocks that are resistant to soil formation, and also by the fragmented relief that favors erosion, thus the soil being kept in a moderate stage of evolution (Barbu, 1987). In the lower and middle mountainous area, up to m, under deciduous and transition forests, dominate Cambisols (eutric up to 1000 m, dystric up to about 1300 m). On the siliceous rocks occur Spodisols, even at altitudes of m. Eutric Cambisols have a maximum occurrence at altitudes of m, with temperate mountainous climate, under deciduous forests (durmast, beech, rarely beechspruce forests) and pastures. The main element differentiating them from dystric Cambisols is the base content over 53%. The upper horizon is brown or grayish-brown, with a granular or blocky structure. The humus content is of 2-8%, the reaction weakly-moderately acid ( ). Base saturation and nutrient concentration is moderate to good. The Bv horizon has variable thickness, between 20 and 80 cm, a brown-yellowish color and a blocky structure. Among the subtypes, the most frequent are the molic, litic, gleyic and stagnic ones. Dystric Cambisols are specific to the upper part of the pedo-cambic floor, at altitudes between 1000 and 1300 m, being the soil type with the largest occurrence in the Carpathian area. In certain conditions of landscape aspect or rock, they go up to over 1500m, or may descend up to 800 m. Organic matter mineralization is slow, leading to the formation of an acid mull, mull moder or moder humus. The higher quantity of precipitations in combination with the presence of fulvic acids leads to an 110

13 intense weathering, with continuous liberation of silica and hydroxides, which are then combined in organo-mineral complexes. Characteristics of some soils from the mountainous area Table 7 Horizons Rezicalcaric Luvosol Molic Eutric Cambisol Ao E EB Bt1 Ap Ao AB BA Bv Depth (cm) Coarse sand ( mm) % Fine sand ( mm) % Silt ( mm) % Clay (<0.002mm) % Fine clay (<0.01 mm) % ph Humus % Nitrogen index Mobile P ppm Mobile K ppm SB-me/l00g sol V% Bulk density Density The A horizon has a depth of 5-20 cm, light brown color, granular or unstable blocky structure, low humus content (2-3%), low base saturation (V<53%) and strongly acid reaction ( ). The cambic Bv horizon has cm, is brownyellowish or yellowish, acid, having a blocky structure. The most frequent subtypes are the umbric, criptospodic, litic and stagnic ones. Spodisols include Prepodzols and Podzols, which make up the dominant soil cover over m altitude. This floor, corresponding to medium mountainous altitudes, has a lower soil typological diversity, due to the reduced surfaces and the bioclimatic tendency of homogeneity. The two soil types mentioned follow one another the first occupies a lower position, between 1300 and 1500 m, while podzols occur between 1500 and 1700 m (being specific to upper spruce forests and the small patches of subalpine pastures). Cambisols can also be found in small islands at the lower part, as can Nigrosols be met at the upper one (Barbu et al., 1995). These soils are less profound (40-90 cm), with a sandy to sandy loam texture and a reduced available volume, which determine an accentuated permeability and active internal drainage. The main diagnostic element is the presence of the spodic horizon of the Bs (accumulations of Fe and Al sesquioxides) and / or Bhs type (accumulation of sesquioxides and humus). The organic materials, slowly mineralized 111

14 due to the restrictive climate, lead to the formation of coarse humus, rich in fulvic acids, which contributes to silicate weathering and the elluviation of the resulting products. These soils have a low content of bases and nutritive substances, yet good physical properties. Prepodzols are the soils preceding Podzols, characterized by the presence of a Bs but the absence of the E horizon. In general are found under lower spruce forests or spruce-beech forests with Vaccinium. The chemical properties are medium, the physical ones being easily more favorable. Podzols occur at altitudes of over 1500m, under spruce forests with acid vegetation, but also under pastures with Festuca rubra or Nardus stricta. In this region they have more of an azonal distribution determined by the extreme acidity of siliceous Kliwa sandstones. The Ao horizon has low depths, is not structured, has a low humus content dominated by the fulvic fraction. It is strongly desaturated (V<20%) and acid (ph ). The Es horizon has a light color due to the migration of humus and sesquioxides and the residual accumulation of silica. It is destructured, desaturated and extremely acid. Texture is normally coarse to medium, but frequently includes large quantities of rock fragments. The most common types are the feriluvic, litic and skeletal. Umbrisols are represented by Nigrosols, which occupy an area in Zboina Frumoasă massif. Usually occur on small areas, at altitudes specific for dystric Cambisols. The main characteristic is given by the dark A umbric horizon, due to the evolution under a rich humid pasture vegetation. Besides the zonal soils, in the mountainous area occur azonal soils, conditioned mainly by parent material or by specific landforms. Among them are Litosols, Regosols, Aluviosols and Erodosols. CONCLUSIONS The soil, as an ecosystem component resulted from the interaction of the soil forming factors, is probably the best body able to reflect transitions between different regions. Thus, if we want to trace geological, geomorphologic, biotic and other transitions, many times this approach may be difficult, because different processes in nature tend to hide discontinuities (weathering deposits hiding geological strata, glacises covering the geomorphic contacts, transitions, inversions or alterations of the vegetal cover etc). The soil, resulting from the collaboration of these factors, is in a certain measure a mirror of them that also present images from the past. Thus, some properties that have resulted from the action of the soil forming factors processes soils triad do not easily modify, remaining proofs of previous conditions. With all these, the soil cover is frequently disturbed due to more obvious interferences of one or other soil forming factor. If in ideal conditions on one large area (as the present area of study) we would face the first pedo-geographical law that of soil cover zonality, this situation is never accomplished. This is because frequently occur penetrations of azonal and intrazonal soils, which lead sometimes to the 112

15 amalgamation of the soil cover. The clearest example in our study area is that already mentioned of the Aluviosols. Thus, Putna River occurs as a backbone of the region, disturbing horizontal and vertical zonality through the occurrence of typical and entic Aluviosols conditioned by the alluvial deposits (figure 3) Podzols Prepodzols Dystric Cam bisols Eutric Cambisols Luvosols Chernozems 5000 Preluvosols Phaeozems 0 Mountains Vrancea Depression Aluviosols Regosols Internal Hills Vidra Depression External Hills Glacis Plain Litosols Regosols Aluviosols Chernozems Phaeozems Preluvosols Luvosols Eutric Cambisols Dystric Cambisols Prepodzols Podzols Nigrosols Erodosols Figure 3. Transitions of soil types from the mountainous areas towards the low plain Table 8 Variations of mean, minimum and maximum values of some soil parameters in the different regions of the study area Zone / Plain Glacis Subcarpathians Mountains parameter med min max med min max med min max med min max Organic matter ph Potassium Base saturation Bulk density Phosphorous Base sum Hydrolytic acidity T Depth of upper horizon

16 Zone / Plain Glacis Subcarpathians Mountains parameter med min max med min max med min max med min max Soil depth Textural diff index Coarse sand Fine sand Silt Clay Fine clay Carbonates In relation to transitions, these are not manifested only under the form of soil types diversity, but also in the case of some physical, chemical and biological parameters. Analyzing the mean values of such parameters for the different types of zonal soils from the area of study, some variations can be seen. Maybe the best parameter to reflect transitions is grain size distribution, known being the fact that soil texture hardly changes (especially in comparison to some chemical parameters). Thus, from figure 4 can be seen a clear decrease in the fine sand content from the low plain soils to the mountainous ones, compensated by an increase in the percentages of silt and coarse sand. This variation is explained by the passage from fine-grained parent material (loams, loess-like deposits, fine alluvial deposits) towards the not so easy to weather hard rocks of the mountainous domain % Chernozems Phaeozems Preluvosols Luvosols Eutric Cambisols NG NF P A Linear (NF) Linear (A) Linear (P) Linear (NG) Figure 4. Textural transitions from low plain to mountain soils 114

17 Chernozems Phaeozems Preluvosols Luvosols Eutric Cambisols ph Pmob SB AH Linear (SB) Linear (Pmob) Linear (ph) Linear (AH) Figure 5. Transitions of chemical parameters from plain to mountain soils Chernozems Phaeozems Preluvosols Luvosols Eutric Cambisols Kmob V Poly. (V) Linear (Kmob) Figure 6. Variations of the potassium and base contents In the case of chemical parameters, the most obvious zonal differentiations are remarked in the case of mobile phosphorous content, which decreases abruptly from Chernozems to Luvosols. This tendency is similar in the case of exchangeable bases sum and soil reaction, being compensated by an increase in hydrolytic acidity. In this case can be seen an interesting aspect, namely that the eutric Cambisols from the mountainous area are evidenced through quite good chemical parameters, these soil not entering the general decreasing or increasing trends. Unfortunately, from our analysis 115

18 lack dystric Cambisols (being more frequent under forests, these areas do not enter the preoccupations of common soil surveys), which would have surely confirmed these tendencies. Slightly different variations are registered in the case of mobile potassium, which on the overall has a decreasing tendency from Chernisols to Cambisols. The base content does not have a clear tendency, the values being quite close Chernozems Phaeozems Preluvosols Luvosols Eutric Cambisols Humus IN Poly. (IN) Poly. (Humus) Figure 7. Variations in the humus content and nitrogen index A different pattern of variation and thus of transition is that of the humus content and nitrogen index. In the case of these two parameters are registered decreases from Chernozems to Phaeozems, followed by an increase in the case of Preluvosols, most probably given by the forest and pasture vegetation from the subcarpathian area, which leave high quantities of organic matter on soil. The decreasing tendency occurs again with Luvosols and eutric Cambisols. REFERENCES 1. BARBU N. (1988) - Regionarea pedogeografică a teritoriului României. Terra, XXXIX, Bucureşti 2. BARBU N., LUPAŞCU GH., RUSU C. (1995) - Sinteză pedogeografică preliminară asupra Carpaţilor Orientali. Factori şi procese pedogenetice din zona temperată, vol. II. Edit. Univ. "Al. I. Cuza" Iaşi, p , Iaşi. 3. BĂLĂCEANU V., MARIAN ELISABETA (1985) - Solurile Carpaţilor Româneşti. Lucr. Şt. ICPCP Măgurele Braşov, vol. X. (Pajiştile din Carpaţii României), Bucureşti. 116

19 4. HARTA SOLURILOR ROMÂNIEI, Foaia FOCŞANI, GALAŢI, L-35-XXII, XXIII, sc. 1: , Coordinators: Cernescu N., Florea N., Conea Ana; Redactori: Conea Ana, Gogoaşă T. 5. HARTA SOLURILOR ROMÂNIEI, Foaia BACĂU, L-35-XV, sc. 1: , Coordinator: Florea N.; Editors: Rîşnoveanu I., Rîşnoveanu Anişoara; Redactori: Barbu N., Lupaşcu Gh., Rusu C., Mară M. 117

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