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Soil solution chemistry in the profiles of forest and arable light textured soils, S.E. Poland
Applied Geochemistry,
Vol. 11,pp. 81-85, 1996 Copyright 0 1996Elsevier Science Ltd
Printed in Great Britain. All rights reserved 0883-2927/96 $15.00+0.00
0883-2927(95)00095-X
Soil solution chemistry in the profiles of forest and arable light textured soils, S.E. Poland Halina Smal and Modest Misztal Institute of Soil Science and Environment Management, Agricultural University Leszczynskiego 7, 20-069 Lublin, Poland Abstract-Soil solution composition and solution speciation of Al(III), Fe(III), Mn(I1) in forest and arable sandy soil profiles were studied. Contents of ions were typically below 1.Ommol dmm3.Generally, amounts of Ca, K, Mg, and Cl, NO,, PO4 were higher in solutions of the arable soil as compared to the forest soil, Contents of Mn, Fe, Al and SO4 were higher in forest soil solutions. The model GEOCHEM predicted a wide range of free Al’+ and Mn*+ between horizons as well as between arable and forested sites. The model also predicted a substantial percentage of Al-SO, species, especially in forest solutions and high a percentage of Mn-humus acid complexes. Copyright 0 1996 Elsevier Science Ltd
The objectives of the research were: (i) to compare soil solution composition in profiles of sandy soils under arable cultivation or forest and (ii) to investigate speciation of Fe, Al, Mn in the solutions.
INTRODUCTION Soil solution is the medium in which most soil chemical reactions occur. It is the mobile phase that is responsible for redistributing solutes within the soil, and hence controls and reflects the differentiation of the soil profile. It provides water and nutrients for plants and is the phase in which potential pollutants move through the soil profile. Hence, the study of the soil solution chemistry can provide a valid measure of the nutrient status of a soil (Adams and Odom, 1985; Kabata-Pendias, 1975; Khasawneh, 1971; Pearson, 1971). In addition, it can be useful for monitoring the effects of various soil amendments (Simard et al., 1988; Hirsch and Banin, 1990; Jarvis, 1987), and provide data for soil mineral weathering studies (Kittrick, 1971; Manley et al., 1987). Among the considerable amount of literature data on the soil solution published, there are no comprehensive chemical data sets on the soil solution for soil profiles and soils of the same genesis, but with different land uses.
MATERIALS AND METHODS Sites characteristic and soil sampling Four locations of podzolic sandy soils in the Lublin region (Southern-Eastern Poland) were chosen for the study. Each location was chosen so that natural forest and arable land (under long term cultivation) were in close proximity (ca. 3& 50 m). The four soils chosen for study are representative of podzolic soils in the region. Their general properties are shown in Table 1. Soil samples were taken in the autumn during the period when fields were fallow after harvesting and unfertilized to avoid direct fertilization and vegetation effects. The cropping system in each location was typical for the light textured soils in the region i.e. potatoes, ray, oats and cereals. In the year of soil sampling, potatoes were grown in one site and cereals in the three others.
Table 1. Selected mean physical and chemical properties of four forest and four arable soil profiles Particle size distribution
Horizon
km1
(1Mp:Cl) 2-0.05
0.05-0.002
Total C (%)
CEC* [mol Kg-‘]
Water content at -9.8 KPa [% by weight]
1.67 0.37 0.09
7.41 4.23 2.20
32.50 19.60 14.30
0.95 0.21 0.07
4.50 3.22 2.49
22.2 15.7 11.5
i 0.002 pm
WI Ah Bs C
O-18 1845 >45
77 78 86
22 21 13
1 1
1
forest profile 3.70 4.10 4.50
AP Bs C
O-26 26-56 > 56
76 79 89
23 19 10
1 1 1
arable profile 4.60 4.60 4.80
* CEC: cation exchange capacity measured using 1M NH&l 81
82
H. Smal and M. Misztal
Detailed information on rate of the fertilizer application in the past is unknown, as the chosen fields were owned by farmers with small size farms with no fertilization records. Generally, every fourth year for potatoes 2.5 ton per ha of manure has been applied, supplying about 100-150 kg N, 7& 100 PzOs, 100-l 50 KzO. For cereal crops about 100 kg per ha per year of NPK have been applied as inorganic fertilizer. Forest profiles studied were located in stands of at least 100 a old). Two sites were coniferous (dominated by pine) and two mixed (dominated by pine and spruce, with some oak). The forests had not received any fertiliztion. Soils were sampled from each horizon, using cylinders of undisturbed soil for the field capacity moisture content determination (three per horizon, nine per profile). For soil solution analysis, one composite sample (about 10 kg of soil) from each horizon (three per profile) was collected.
Soil solution extraction The soil solution
was obtained
by centrifugation.
Air dried and sieved soil samples were moistened to field capacity. They were then incubated for 48 h at room temperature in darkness (Qian and Wolt, 1990). Soil solution extractions were carried out using a centrifuge assembly made of plexiglass and consisting of two tubes. On the perforated cover of the bottom tube a filter disc was placed to prevent the transfer of fine particles to the extracted soil solution. Centrifugation was performed over 20 minutes with a speed of 3500 r.p.m. On average between 58 to 76% of the soil solution was recovered.
Soil solution analysis
Determination of total concentrations of cations and anions in the soil solutions were made as follows: Ca, K, Na by flame photometry, Mg, Fe, Mn by atomic absorption spectrophotometry (AAS). Various calorimetric methods were used for the determination of Al, NH4, NOs, and PO4 (Hermanowicz et al., 1976) Aluminium was determined by the eriochrome cyanine method, NH4 by direct nessleritation,
NO3 with phenoldisulphonic acid and PO4 with ammonium molybdate. Chlorides and sulphates were determined by titration (Hermanowicz et al., 1976) and Total Dissolved Organic (DOC) by a modified Turin’s method (ArinuSkina, 1961). In this paper the range of values and means for the different horizons from the four forest and four cultivated soil profiles are presented. The GEOCHEM chemical equilibria model (Sposito and Mattigod, 1979) was used to estimate the speciation of ions. The concentration of the FUL ligand needed as an as input to the program was calculated from DOC content assuming that it constituted humic materials that behaved like fulvic acids and that their complexing capacity was equal to 2 mmol DOC g-‘C (Buffle, 1988). Modelling was performed using the mean chemical composition of soil solution for one representative of each forest and arable soil profiles.
RESULTS AND DISCUSSION
The composition of the soil solutions are shown in Table 2. In the forest profiles the pH of solutions varied from 4.05 in humus horizon to 5.25 in the C horizon. In the arable soil profile the lowest value of 4.50 occurred in the Ap horizon and the highest (6.40) in the C horizon. Generally, soil solution pH in the forest soil profiles was lower than in the arable soil profiles and in both cases increased with depth. DOC concentration varied in both the forest and arable soils. In both cases it was the highest in humus horizons and decreased with depth. The range and average concentrations of DOC in forest soil horizons was considerably higher in comparison to comparable horizons in the arable soil. The concentration of Ca, Mg, Na, K, NH4 in all solutions was low and typically did not exceed 1 mmol dme3. However in several cases higher concentrations were measured than this and in one case the Na
Table 2. Soil solution composition of different horizons of forest and arable soils PH
DOC
Range Mean Range Mean Range Mean
4.05-4.50 4.25 4.15-4.60 4.36 4.25-5.25 4.60
10.56-25.13 19.69 3.10-22.60 12.07 1.30-7.50 3.14
Range Mean Range Mean Range Mean
4.50-6.05 4.60 4.65-S. 18 4.85 4.90-6.40 5.20
8.08-18.53 12.30 0.90-3.70 2.50 0.70-3.60 1.68
horizon Ah Bs C
AP BS C
Na
K
NH4
forest soil profile 0.214.33 0.31-0.61 0.26 0.44 0.15-0.35 0.33-0.88 0.26 0.49 0.060.28 0.154.67 0.18 0.44
0.1 la.16 0.14 0.15-2.48 0.76 0.11-1.07 0.41
0.20-0.67 0.48 0.1 l-O.93 0.35 0.094.76 0.27
0.59-1.12 0.75 0.44-0.72 0.55 0.13-0.82 0.40
arable soil profile 0.19-0.57 0.59-0.89 0.39 0.81 0.17-0.32 0.47-l .06 0.25 0.73 0.10-0.39 0.54-0.98 0.21 0.75
0.12-0.20 0.15 0.16-1.08 0.52 0.18-0.54 0.29
0.31-1.41 0.69 0.2W.77 0.51 0.13-0.99 0.54
0.50-0.97 0.76 0.35-0.88 0.54 0.15-0.81 0.43
Ca
Mg
[ mmol dm-‘1
Soil solution chemistry in the profiles of forest and arable light textured soils, S.E. Poland
concentration in the Bs horizon of a forest soil was 2.48 mmol dm-3. The concentration of cations were found to be lower (with the exception of K) than those found in a similar cultivated arable podzolic soil (Simard et al., 1988). The range and average values of Ca, Mg, Na and K in humus horizons of arable soils were substantially higher than in related horizons of the forest soils. This was due mainly to fertilizer inputs, however the observed differences between the soil solution chemistry of soils were as large as suspected. This could result from the following: (a) soil sampling was carried out in late autumn when soil solution concentration in arable soils is lower compared to the other seasons (Campbell et al., 1989; Wiklander and Andersson, 1974). (b) rates of fertilization were low at these sites, and (c) the soil had a low sorptive capacity. Manganese showed a wide range of concentration in solution extracted from both forest and arable soils. In forest soils, Mn concentration ranged from 6.37 mmol dm-’ (C horizon) to 318.52 mmol dme3 (Bs horizon). Manganese concentration in forest and arable soils was highest in the humus horizons and decreased with depth. A comparison of the average concentration of Mn shows that these were higher amounts in forest soils than in arable soils. Compared to Mn, the concentrations of Al and Fe in soil solutions were lower. However, Al and Fe were present in higher concentrations in the humus horizons and low concentrations in the C horizons. Moreover, the range and average values of Al and Fe in horizons of forest soils were (except for Fe in C horizons) substantially higher than related values in arable soils. The main anions measured, Cl and SO*, were present in similar concentrations in the soil solution compared to the concentrations of the main cations (Table 3).
83
Chloride content varied more in the forest soils (0.08 mmol dm-3 in C horizon to 2.35 mmol dm-’ in Bs horizon) compared to the arable soils (0.11 mmol dmp3 in Ap horizon to 1.83 mmol dm-3 in Bs horizon). The average concentrations of Cl were higher in solutions extracted from the arable soils compared to those extracted from the forest soils. In contrast the SO4 concentration of soil solutions from forest soils was higher than those from arable soils. Among the anions, the lowest concentrations were found for P04; from 0.002 to 0.024 mmol dm-’ in the forest soils and from 0.002 to 0.057 mmol dm-3 in the arable soils. In the case of both NO3 and P04. concentrations were higher in all horizons of the arable soils compared to the related solutions of the forest soils. Nitrate concentrations were highest in the Ap horizon of the agricultural soils. In general, soil solutions extracted from both the arable and forest soils contain low concentrations. The sum of the concentration of ions in solution of the cultivated soil profile was higher than in the forest soil; this is reflected in the ionic strength (Table 4). Distribution of Fe and Al species predicted by the GEOCHEM program, as expected, was dependent on the pH of the soil solutions, and in the case of Mn. on DOC content (Table 4). Percentages of free A13+ varied from 59 to 42% of the total Al in solutions within the pH range from 4.3 to 4.6 (forest soils solutions). Increasing the solution pH up to 5.2 (arable soil solution) caused a decrease in the free Al3 + content to 9% and an increase in Al-OH species to 88%. Species of Al-SO4 were also present in substantial amounts, especially in forest soil solutions where they constituted 25 to 31% of the total aluminium. Iron was almost fully bound with OH‘ (75%-99%) and POd3- (l-25%) ligands. Species of Fe-SO4 were present at very low percentages. Manganese was strongly complexed by fulvic acids
Table 3. Soil solution composition of different horizons of forest and arable soils (contined) Mn horizon
Ah Bs C
AP Bs C
Al [pmol dme3]
Fe
Cl
Not
so4
PO4
[mmol dm-3]
Range Mean Range Mean Range Mean
9.10-172.90 103.07 14.46318.52 112.62 6.37-172.92 57.11
12.4617.50 15.45 5.6620.91 14.31 0.22-15.57 8.03
forest soil profile 15.21-44.76 0.314.75 27.08 0.54 0.90-8.06 0.24-2.35 4.03 0.95 0.17-3.58 0.08-l .44 1.43 0.50
0.58-0.79 0.71 0.64-1.81 0.96 0.36-l .55 0.87
0.09-0.39 0.26 0.02-0.28 0.11 0.02-0.26 0.09
0.003-0.019 0.025 0.003-0.024 0.012 0.0024.008 0.003
Range Mean Range Mean Range Mean
36.40-172.91 81.68 9.1Gl72.00 56.42 0.90-163.81 55.06
0.7e14.35 5.81 0.12-I 1.27 4.54 0.12-1.26 0.55
arable soil profile 0.89-19.69 0.11-1.46 6.94 0.79 0.17-7.52 0.49-I .83 2.41 1.41 0.17-7.52 0.71-1.63 2.19 1.11
0.32-0.71 0.47 0.43-1.14 0.64 0.38-0.86 0.64
0.81-3.56
0.047-0.057 0.054 0.004-0.012 0.076 0.002-0.008 0.005
1.59 0.05-2.18 0.73 0.07-1.50 0.76
84
H. Smal and M. Misztal
Table 4. Ionic strength of the soil solutions and Percentage speciation of free ions and complexes of Fe, Al and Mn, as calculated by GEGCHEM Profile Horizon
Al’+ AI-SO4
AlaH
Ah
Forest Bs
Arable c
AP
Bs
C
3.9
Ionic strength [x IO-‘] 4.7 3.1
5.3
5.1
4.7
59.4 21.5 13.1
Species [% of total content] Al 53.0 42.3 30.6 24.5 16.4 33.3
50.2 13.3 36.5
29.5 10.9 59.6
8.7 3.3 88.1
Fe Fe’+ Fe--SO4
Fe-PO4 Fe-OH Mn*+ Mn-SO4 Mn-FUL
Mn-Cl
0.2 0.5 21.0 78.3
0.1 0.5 11.5 87.9
0.0 0.2 2.3 91.5
0.0 0.0
0.0 0.0
0.0 0.0
25.4 74.5
2.8 97.1
0.9 99.1
20.7 1.6 77.6 0.0
34.3 3.4 62.2 0.1
Mn 59.6 5.1 34.6 0.0
40.3 1.8 57.1 0.1
74.0 4.7 21.0 0.3
19.1 5.1 14.8 0.3
in soil solutions of humus horizons (78 and 58%). Less complexation of Mn with in fulvic acid occured in the deeper horizons e.g. 35 and 15% for forest and arable soils respectively. Thus, the percentage of free Mn*+ was the lowest in solutions extracted from the surface horizons and increased with depth, possibly associated with a decrease in DOC concentration.
CONCLUSIONS
The study showed substantial differences between forest and arable soil profiles with respect to the chemical composition of the soil solution. The main conclusions are:(a) contents of Ca, K, Mg, Na, were higher in solutions extracted from arable soils in comparison to forest soils, (b) DOC, Al, Fe concentrations in solutions of all horizons in forest soils were higher than in solutions from related horizons in arable soils, (c) Cl was the dominant anion in solutions from arable soils (with the exception of the Ap horizon) and in forest soils the dominant anion solutions was SO4, and (d) both NO, and PO4 contents were higher in solutions of all horizons in arable soils, compared to forest soils. GEOCHEM calculations showed that for the forest soils with a solution pH of ca. 4.5, about 50% of the total Al was present as free A13+.
Acknowledgements-Study financed by Committee for Scientific Research within the grant project Nr 551299203 in years 1992-1994
REFERENCES Adams J.F. and Odom J.W. (1985) Effect of pH and phosphorus rates on soil-solution phosphorus and phosphorus availability. Soil Science 140,202-205. ArinuSkina E.B. (1961) Rukovodstvo po chimiceskomu analizu pocv. Izdatielstvo Moskovskogo Universiteta, 130-139. Buffle J. (1988). Complexation reactions in aquatic systems: An analytical approach. Ellis Horwood, Chichester. Chap. 6. Campbell D.J., Kinniburgh D.G. and Beckett P.H.T. (1989) The soil solution chemistry of some Oxfordshire soils: temporal and spatial variability. J. Soil Sci. 40, 321-339. Hermanowicz W., Dozanska J., Dojlido J. and Koziorowski B. (1976). Physico-chemical investigations of water and sewage. Warsaw, “Arkady”, 118 pp. Hirsch D. and Banin A. (1990) Cadmium speciation in soil solutions. J. Environ. Qual. 19, 366312. Jarvis S.C. (1987) Laboratory studies of effects of lime on soluble Al, Ca, Mg and Mn in a pelostagnogley soil. J. Soil Sci. 38, 443-151. Kabata-Pendias A. (1975) Influence of chemical composition of soil solution on macro- and micronutrient content in cereals. Roczniki Gleboznawcze (Soil Sci. Ann.) 3, 7588.
Khasawneh F.E. (1971) Solution ion activity and plant growth. Soil Sci. Sot. Amer. Proc. 35, 426-436. Kittrick J.A. (1971) Soil Solution Composition and Stability of Clav Minerals. Soil Sci. Sot. Amer. Proc. 35. 450-454. Manley E.P., Chesworth W. and Evans L.J. (J987) The solution chemistry of podzohc soils from the eastern Canadian shield: a thermodynamic interpretation of the mineral phases controlling soluble A13+ and H4Si04. J. Soil Sci. 38, 39-51.
Soil solution chemistry in the profiles of forest and arable light textured soils, S.E. Poland Pearson R.W. (1971) Introduction to Symposium-The Soil Solution. Soil Sri. Sot. Amer. Proc. 35, 417-420. Qian P. and Wolt J.D. (1990) Effects of drying and time of incubation on the composition of displaced soil solution. Soil Science 6, 367-373. Simard R.R., Evans L.J. and Bates T.E. (1988) The effects of additions of CaC03 and P on the soil solution chemistry of a podzolic soil. Can. J. Soil Sci. 68, 41-51.
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Sposito G. and Mattigod S.V. (1979) GEOCHEM; a computer program for the calculation of chemical equilibria in soil solutions and other natural water systems. Department of Soil and Environmental Science, University of California, Riverside. Wiklander L. and Andersson A. (1974) The composition of the soil solution as influenced by fertilization and nutrient uptake. Geoderma 11, 157-166.
Vol. 11,pp. 81-85, 1996 Copyright 0 1996Elsevier Science Ltd
Printed in Great Britain. All rights reserved 0883-2927/96 $15.00+0.00
0883-2927(95)00095-X
Soil solution chemistry in the profiles of forest and arable light textured soils, S.E. Poland Halina Smal and Modest Misztal Institute of Soil Science and Environment Management, Agricultural University Leszczynskiego 7, 20-069 Lublin, Poland Abstract-Soil solution composition and solution speciation of Al(III), Fe(III), Mn(I1) in forest and arable sandy soil profiles were studied. Contents of ions were typically below 1.Ommol dmm3.Generally, amounts of Ca, K, Mg, and Cl, NO,, PO4 were higher in solutions of the arable soil as compared to the forest soil, Contents of Mn, Fe, Al and SO4 were higher in forest soil solutions. The model GEOCHEM predicted a wide range of free Al’+ and Mn*+ between horizons as well as between arable and forested sites. The model also predicted a substantial percentage of Al-SO, species, especially in forest solutions and high a percentage of Mn-humus acid complexes. Copyright 0 1996 Elsevier Science Ltd
The objectives of the research were: (i) to compare soil solution composition in profiles of sandy soils under arable cultivation or forest and (ii) to investigate speciation of Fe, Al, Mn in the solutions.
INTRODUCTION Soil solution is the medium in which most soil chemical reactions occur. It is the mobile phase that is responsible for redistributing solutes within the soil, and hence controls and reflects the differentiation of the soil profile. It provides water and nutrients for plants and is the phase in which potential pollutants move through the soil profile. Hence, the study of the soil solution chemistry can provide a valid measure of the nutrient status of a soil (Adams and Odom, 1985; Kabata-Pendias, 1975; Khasawneh, 1971; Pearson, 1971). In addition, it can be useful for monitoring the effects of various soil amendments (Simard et al., 1988; Hirsch and Banin, 1990; Jarvis, 1987), and provide data for soil mineral weathering studies (Kittrick, 1971; Manley et al., 1987). Among the considerable amount of literature data on the soil solution published, there are no comprehensive chemical data sets on the soil solution for soil profiles and soils of the same genesis, but with different land uses.
MATERIALS AND METHODS Sites characteristic and soil sampling Four locations of podzolic sandy soils in the Lublin region (Southern-Eastern Poland) were chosen for the study. Each location was chosen so that natural forest and arable land (under long term cultivation) were in close proximity (ca. 3& 50 m). The four soils chosen for study are representative of podzolic soils in the region. Their general properties are shown in Table 1. Soil samples were taken in the autumn during the period when fields were fallow after harvesting and unfertilized to avoid direct fertilization and vegetation effects. The cropping system in each location was typical for the light textured soils in the region i.e. potatoes, ray, oats and cereals. In the year of soil sampling, potatoes were grown in one site and cereals in the three others.
Table 1. Selected mean physical and chemical properties of four forest and four arable soil profiles Particle size distribution
Horizon
km1
(1Mp:Cl) 2-0.05
0.05-0.002
Total C (%)
CEC* [mol Kg-‘]
Water content at -9.8 KPa [% by weight]
1.67 0.37 0.09
7.41 4.23 2.20
32.50 19.60 14.30
0.95 0.21 0.07
4.50 3.22 2.49
22.2 15.7 11.5
i 0.002 pm
WI Ah Bs C
O-18 1845 >45
77 78 86
22 21 13
1 1
1
forest profile 3.70 4.10 4.50
AP Bs C
O-26 26-56 > 56
76 79 89
23 19 10
1 1 1
arable profile 4.60 4.60 4.80
* CEC: cation exchange capacity measured using 1M NH&l 81
82
H. Smal and M. Misztal
Detailed information on rate of the fertilizer application in the past is unknown, as the chosen fields were owned by farmers with small size farms with no fertilization records. Generally, every fourth year for potatoes 2.5 ton per ha of manure has been applied, supplying about 100-150 kg N, 7& 100 PzOs, 100-l 50 KzO. For cereal crops about 100 kg per ha per year of NPK have been applied as inorganic fertilizer. Forest profiles studied were located in stands of at least 100 a old). Two sites were coniferous (dominated by pine) and two mixed (dominated by pine and spruce, with some oak). The forests had not received any fertiliztion. Soils were sampled from each horizon, using cylinders of undisturbed soil for the field capacity moisture content determination (three per horizon, nine per profile). For soil solution analysis, one composite sample (about 10 kg of soil) from each horizon (three per profile) was collected.
Soil solution extraction The soil solution
was obtained
by centrifugation.
Air dried and sieved soil samples were moistened to field capacity. They were then incubated for 48 h at room temperature in darkness (Qian and Wolt, 1990). Soil solution extractions were carried out using a centrifuge assembly made of plexiglass and consisting of two tubes. On the perforated cover of the bottom tube a filter disc was placed to prevent the transfer of fine particles to the extracted soil solution. Centrifugation was performed over 20 minutes with a speed of 3500 r.p.m. On average between 58 to 76% of the soil solution was recovered.
Soil solution analysis
Determination of total concentrations of cations and anions in the soil solutions were made as follows: Ca, K, Na by flame photometry, Mg, Fe, Mn by atomic absorption spectrophotometry (AAS). Various calorimetric methods were used for the determination of Al, NH4, NOs, and PO4 (Hermanowicz et al., 1976) Aluminium was determined by the eriochrome cyanine method, NH4 by direct nessleritation,
NO3 with phenoldisulphonic acid and PO4 with ammonium molybdate. Chlorides and sulphates were determined by titration (Hermanowicz et al., 1976) and Total Dissolved Organic (DOC) by a modified Turin’s method (ArinuSkina, 1961). In this paper the range of values and means for the different horizons from the four forest and four cultivated soil profiles are presented. The GEOCHEM chemical equilibria model (Sposito and Mattigod, 1979) was used to estimate the speciation of ions. The concentration of the FUL ligand needed as an as input to the program was calculated from DOC content assuming that it constituted humic materials that behaved like fulvic acids and that their complexing capacity was equal to 2 mmol DOC g-‘C (Buffle, 1988). Modelling was performed using the mean chemical composition of soil solution for one representative of each forest and arable soil profiles.
RESULTS AND DISCUSSION
The composition of the soil solutions are shown in Table 2. In the forest profiles the pH of solutions varied from 4.05 in humus horizon to 5.25 in the C horizon. In the arable soil profile the lowest value of 4.50 occurred in the Ap horizon and the highest (6.40) in the C horizon. Generally, soil solution pH in the forest soil profiles was lower than in the arable soil profiles and in both cases increased with depth. DOC concentration varied in both the forest and arable soils. In both cases it was the highest in humus horizons and decreased with depth. The range and average concentrations of DOC in forest soil horizons was considerably higher in comparison to comparable horizons in the arable soil. The concentration of Ca, Mg, Na, K, NH4 in all solutions was low and typically did not exceed 1 mmol dme3. However in several cases higher concentrations were measured than this and in one case the Na
Table 2. Soil solution composition of different horizons of forest and arable soils PH
DOC
Range Mean Range Mean Range Mean
4.05-4.50 4.25 4.15-4.60 4.36 4.25-5.25 4.60
10.56-25.13 19.69 3.10-22.60 12.07 1.30-7.50 3.14
Range Mean Range Mean Range Mean
4.50-6.05 4.60 4.65-S. 18 4.85 4.90-6.40 5.20
8.08-18.53 12.30 0.90-3.70 2.50 0.70-3.60 1.68
horizon Ah Bs C
AP BS C
Na
K
NH4
forest soil profile 0.214.33 0.31-0.61 0.26 0.44 0.15-0.35 0.33-0.88 0.26 0.49 0.060.28 0.154.67 0.18 0.44
0.1 la.16 0.14 0.15-2.48 0.76 0.11-1.07 0.41
0.20-0.67 0.48 0.1 l-O.93 0.35 0.094.76 0.27
0.59-1.12 0.75 0.44-0.72 0.55 0.13-0.82 0.40
arable soil profile 0.19-0.57 0.59-0.89 0.39 0.81 0.17-0.32 0.47-l .06 0.25 0.73 0.10-0.39 0.54-0.98 0.21 0.75
0.12-0.20 0.15 0.16-1.08 0.52 0.18-0.54 0.29
0.31-1.41 0.69 0.2W.77 0.51 0.13-0.99 0.54
0.50-0.97 0.76 0.35-0.88 0.54 0.15-0.81 0.43
Ca
Mg
[ mmol dm-‘1
Soil solution chemistry in the profiles of forest and arable light textured soils, S.E. Poland
concentration in the Bs horizon of a forest soil was 2.48 mmol dm-3. The concentration of cations were found to be lower (with the exception of K) than those found in a similar cultivated arable podzolic soil (Simard et al., 1988). The range and average values of Ca, Mg, Na and K in humus horizons of arable soils were substantially higher than in related horizons of the forest soils. This was due mainly to fertilizer inputs, however the observed differences between the soil solution chemistry of soils were as large as suspected. This could result from the following: (a) soil sampling was carried out in late autumn when soil solution concentration in arable soils is lower compared to the other seasons (Campbell et al., 1989; Wiklander and Andersson, 1974). (b) rates of fertilization were low at these sites, and (c) the soil had a low sorptive capacity. Manganese showed a wide range of concentration in solution extracted from both forest and arable soils. In forest soils, Mn concentration ranged from 6.37 mmol dm-’ (C horizon) to 318.52 mmol dme3 (Bs horizon). Manganese concentration in forest and arable soils was highest in the humus horizons and decreased with depth. A comparison of the average concentration of Mn shows that these were higher amounts in forest soils than in arable soils. Compared to Mn, the concentrations of Al and Fe in soil solutions were lower. However, Al and Fe were present in higher concentrations in the humus horizons and low concentrations in the C horizons. Moreover, the range and average values of Al and Fe in horizons of forest soils were (except for Fe in C horizons) substantially higher than related values in arable soils. The main anions measured, Cl and SO*, were present in similar concentrations in the soil solution compared to the concentrations of the main cations (Table 3).
83
Chloride content varied more in the forest soils (0.08 mmol dm-3 in C horizon to 2.35 mmol dm-’ in Bs horizon) compared to the arable soils (0.11 mmol dmp3 in Ap horizon to 1.83 mmol dm-3 in Bs horizon). The average concentrations of Cl were higher in solutions extracted from the arable soils compared to those extracted from the forest soils. In contrast the SO4 concentration of soil solutions from forest soils was higher than those from arable soils. Among the anions, the lowest concentrations were found for P04; from 0.002 to 0.024 mmol dm-’ in the forest soils and from 0.002 to 0.057 mmol dm-3 in the arable soils. In the case of both NO3 and P04. concentrations were higher in all horizons of the arable soils compared to the related solutions of the forest soils. Nitrate concentrations were highest in the Ap horizon of the agricultural soils. In general, soil solutions extracted from both the arable and forest soils contain low concentrations. The sum of the concentration of ions in solution of the cultivated soil profile was higher than in the forest soil; this is reflected in the ionic strength (Table 4). Distribution of Fe and Al species predicted by the GEOCHEM program, as expected, was dependent on the pH of the soil solutions, and in the case of Mn. on DOC content (Table 4). Percentages of free A13+ varied from 59 to 42% of the total Al in solutions within the pH range from 4.3 to 4.6 (forest soils solutions). Increasing the solution pH up to 5.2 (arable soil solution) caused a decrease in the free Al3 + content to 9% and an increase in Al-OH species to 88%. Species of Al-SO4 were also present in substantial amounts, especially in forest soil solutions where they constituted 25 to 31% of the total aluminium. Iron was almost fully bound with OH‘ (75%-99%) and POd3- (l-25%) ligands. Species of Fe-SO4 were present at very low percentages. Manganese was strongly complexed by fulvic acids
Table 3. Soil solution composition of different horizons of forest and arable soils (contined) Mn horizon
Ah Bs C
AP Bs C
Al [pmol dme3]
Fe
Cl
Not
so4
PO4
[mmol dm-3]
Range Mean Range Mean Range Mean
9.10-172.90 103.07 14.46318.52 112.62 6.37-172.92 57.11
12.4617.50 15.45 5.6620.91 14.31 0.22-15.57 8.03
forest soil profile 15.21-44.76 0.314.75 27.08 0.54 0.90-8.06 0.24-2.35 4.03 0.95 0.17-3.58 0.08-l .44 1.43 0.50
0.58-0.79 0.71 0.64-1.81 0.96 0.36-l .55 0.87
0.09-0.39 0.26 0.02-0.28 0.11 0.02-0.26 0.09
0.003-0.019 0.025 0.003-0.024 0.012 0.0024.008 0.003
Range Mean Range Mean Range Mean
36.40-172.91 81.68 9.1Gl72.00 56.42 0.90-163.81 55.06
0.7e14.35 5.81 0.12-I 1.27 4.54 0.12-1.26 0.55
arable soil profile 0.89-19.69 0.11-1.46 6.94 0.79 0.17-7.52 0.49-I .83 2.41 1.41 0.17-7.52 0.71-1.63 2.19 1.11
0.32-0.71 0.47 0.43-1.14 0.64 0.38-0.86 0.64
0.81-3.56
0.047-0.057 0.054 0.004-0.012 0.076 0.002-0.008 0.005
1.59 0.05-2.18 0.73 0.07-1.50 0.76
84
H. Smal and M. Misztal
Table 4. Ionic strength of the soil solutions and Percentage speciation of free ions and complexes of Fe, Al and Mn, as calculated by GEGCHEM Profile Horizon
Al’+ AI-SO4
AlaH
Ah
Forest Bs
Arable c
AP
Bs
C
3.9
Ionic strength [x IO-‘] 4.7 3.1
5.3
5.1
4.7
59.4 21.5 13.1
Species [% of total content] Al 53.0 42.3 30.6 24.5 16.4 33.3
50.2 13.3 36.5
29.5 10.9 59.6
8.7 3.3 88.1
Fe Fe’+ Fe--SO4
Fe-PO4 Fe-OH Mn*+ Mn-SO4 Mn-FUL
Mn-Cl
0.2 0.5 21.0 78.3
0.1 0.5 11.5 87.9
0.0 0.2 2.3 91.5
0.0 0.0
0.0 0.0
0.0 0.0
25.4 74.5
2.8 97.1
0.9 99.1
20.7 1.6 77.6 0.0
34.3 3.4 62.2 0.1
Mn 59.6 5.1 34.6 0.0
40.3 1.8 57.1 0.1
74.0 4.7 21.0 0.3
19.1 5.1 14.8 0.3
in soil solutions of humus horizons (78 and 58%). Less complexation of Mn with in fulvic acid occured in the deeper horizons e.g. 35 and 15% for forest and arable soils respectively. Thus, the percentage of free Mn*+ was the lowest in solutions extracted from the surface horizons and increased with depth, possibly associated with a decrease in DOC concentration.
CONCLUSIONS
The study showed substantial differences between forest and arable soil profiles with respect to the chemical composition of the soil solution. The main conclusions are:(a) contents of Ca, K, Mg, Na, were higher in solutions extracted from arable soils in comparison to forest soils, (b) DOC, Al, Fe concentrations in solutions of all horizons in forest soils were higher than in solutions from related horizons in arable soils, (c) Cl was the dominant anion in solutions from arable soils (with the exception of the Ap horizon) and in forest soils the dominant anion solutions was SO4, and (d) both NO, and PO4 contents were higher in solutions of all horizons in arable soils, compared to forest soils. GEOCHEM calculations showed that for the forest soils with a solution pH of ca. 4.5, about 50% of the total Al was present as free A13+.
Acknowledgements-Study financed by Committee for Scientific Research within the grant project Nr 551299203 in years 1992-1994
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