Nutr Cycl Agroecosyst (2009) 83:39–50 DOI 10.1007/s10705-008-9197-8
RESEARCH ARTICLE
The Rengen Grassland Experiment: soil contamination by trace elements after 65 years of Ca, N, P and K fertiliser application Michal Hejcman Æ Jirˇina Szakova´ Æ Ju¨rgen Schellberg Æ Petr Sˇrek Æ Pavel Tlustosˇ
Received: 5 February 2008 / Accepted: 1 August 2008 / Published online: 20 August 2008 Ó Springer Science+Business Media B.V. 2008
Abstract The Rengen Grassland Experiment (RGE) was established in the Eifel Mts. (Germany) on a low productive Nardetum in 1941. Since then, the following fertiliser treatments have been applied along with a two cut system: unfertilised control, Ca, CaN, CaNP, CaNP–KCl and CaNP–K2SO4 with basic slag (syn. Thomas phosphate) as the only P fertiliser. The effect of long-term fertilisation on plant-available (extracted with 0.01 mol l-1 CaCl2), easilymobilisable (extracted with 0.05 mol l-1 EDTA), potentially-mobilisable (extracted with 2 mol l-1 HNO3) and total concentrations of trace elements
J. Szakova´ P. Tlustosˇ Department of Agrochemistry and Plant Nutrition, Czech University of Life Sciences, Kamy´cka´ 129, 165 21 Prague 6 – Suchdol, Czech Republic
(As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in the top 0–10 and 10–20 cm of soil were investigated in 2006. According to redundancy analysis (RDA), the effect of treatment on the concentrations of risk elements was significant and explained 82.3 and 90.6% of the variability in the data in the 0–10 and 10–20 cm soil layers, respectively. Basic slag supplied the soil with considerable amounts of As, Cr, Cu, Fe, Mn and Zn. Following 65 years of fertiliser application the concentrations of risk elements in the soil profile had increased substantially, especially with basic slag. However, threshold limits for total trace element concentration in soil permitted by Czech national legislation were exceeded only in the case of As. The increase in plant-available As concentrations was most critical as it increased the potential uptake of As by plants in plots fertilised with P. Although P treatments received more than 300 g of Cr ha-1 annually, no effect on plant-available Cr soil content was detected. This contrasted with the accumulation of total Cr in the 0–10 and 10–20 cm soil layers. Furthermore, plant availability of Cd, Fe, Mn and Zn was affected by soil pH and generally decreased with the application of quick lime. Plant availability of these elements was not correlated with amounts supplied by fertilisers.
J. Schellberg (&) Institute of Crop Science and Resource Conservation, University of Bonn, Katzenburgweg 5, 53115 Bonn, Germany e-mail:
[email protected]
Keywords Arsenic Chromium Heavy metals Long-term fertilisation Risk elements Mobility and accumulation Basic slag
M. Hejcman P. Sˇrek Department of Ecology and Environment, Czech University of Life Sciences, Kamy´cka´ 129, 165 21 Prague 6 – Suchdol, Czech Republic M. Hejcman P. Sˇrek Division of Plant Nutrition, Crop Research Institute, Drnovka´ 507, 161 06 Praha 6 – Ruzyne, Czech Republic
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Introduction Contamination of soil with trace elements (mainly heavy metals = risk elements) represents a serious risk for crop production, food quality and human health because of their high toxicity and bioaccumulation, high persistency in the environment and relatively high mobility (Mench 1998; Lehoczky et al. 2005; Lavado et al. 2007). While naturally occurring in the environment, risk elements may be introduced into agricultural soils, especially by anthropogenic activities. Atmospheric deposition and the use of mineral as well as organic fertilisers derived from sewage sludge and other wastes are the major sources of trace elements in agro-ecosystems (Sucharova´ and Suchara 2004; Guo and Zhou 2006; Greger et al. 2007; Kashem et al. 2007). Cadmium is of special interest because of its significant concentration in many P fertilisers which, if permanently applied, induce Cd accumulation in soils and an increase in the concentration in plant biomass (Mortvedt 1996; Gray et al. 1999; Taylor and Percival 2001; Ne´meth et al. 2002; Salviano et al. 2006; Chen et al. 2007). In addition to the direct application of risk elements by fertilisers, the effect of soil P concentration or pH on bioavailability of other elements must be taken into account. For example, arsenates, the dominant As compounds under oxidising soil conditions (McGeehan and Naylor 1994), compete with phosphates for the sorption sites on soil particle surfaces. Thus, P application can result in the enhancement of As mobility and increased As uptake by plants (Tao et al. 2006). It has also been found that Ca fertilisers decrease mobility and consequently also plant availability of Cd, Fe, Mn and Zn through pH alteration (Chowdhury et al. 1997; Gavi et al. 1997; Tlustosˇ et al. 2006). Although several long-term grassland fertiliser experiments are still under observation in Central and Western Europe (see Honsova´ et al. 2007 for details), no paper describing in detail the effect of fertilisation on concentration of risk elements in a soil has been published up to now. In the present paper, soils of the Rengen Grassland Experiment (RGE) were subjected to the analysis of trace elements after 65 years of Ca, N, P and K fertiliser application. These data will provide background information for future investigation of element uptake by vascular
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plants and bryophytes. The RGE is an unique experiment due to the continuous application of basic slag (syn. Thomas phosphate or Thomas slag), which is a P fertiliser with high P fertilising value, especially in acidic soils (Sinaj et al. 1994). Basic slag was produced by ironworks and frequently used in agriculture in the first half of the 20th century. In contrast to other P fertilisers, basic slag is characterised by low Cd concentration because the temperature during the production process leads to Cd evaporation. In addition to the total element concentrations in the soil, a detailed evaluation of the potential impact of these elements on plant production is necessary. Identification and quantification of element fractions associated with individual soil components can lead to better characterisation of plant-availability of potentially toxic elements and to an understanding of the behaviour of these elements in soils (Tlustosˇ et al. 2005). The plant-available fraction represents the mobile portion of risk elements that can easily be taken up by plants from the soil solution. Depending on the source of pollution and physico-chemical properties of the soil, various extraction procedures (using e.g. CaCl2, Ca(NO3)2, NaNO3, BaCl2 solutions) can be used (Moral et al. 2002). The most frequently used extractant in the Czech Republic is CaCl2 at a concentration of 0.01 mol l-1 (Menzies et al. 2007). The easily-mobilisable fraction extracted by organic acids or chelates represents the portion of elements in soil that are bound on the surface of oxides and in organic matter (Hickey and Kittrick 1984). For extraction, ethylenediaminetetraacetic acid (EDTA) is recommended by the Institute for Reference Materials and Measurements of the European Union (Quevauviller et al. 1993) and is the most frequently used extracting agent. The potentially-mobilisable concentration of risk elements represents elements that are tightly bound to the individual soil components, and which are immediately unavailable to plants. Only substantial changes in physico-chemical soil properties can lead to higher plant availability of these elements. For their extraction, strong acids such as HNO3 are usually applied (Boru˚vka et al. 1996; Sza´kova´ et al. 2000). The non-extractable portion of the elements represents the residual fraction that is strongly bound in the crystal lattices and consequently not releasable
Nutr Cycl Agroecosyst (2009) 83:39–50
41
to the environment (Navas and Lindhorfer 2003). Finally, the total concentration of trace elements represents all fractions together. The aim of this paper was to answer the following questions: is there any effect of long-term fertilisation on total, plant-available, easily- and potentiallymobilisable concentrations of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the top 0–10 and 10–20 cm soil layers on a typical mountainous hay meadow? We also considered whether the trace element concentrations could reach levels that might necessitate regulation of long-term fertiliser use.
Materials and methods Study site and treatments In 1941, the fertiliser experiment was set up at the Rengen Grassland Research Station of the University of Bonn in the Eifel mountains (Germany, 50°130 N, 6°510 E) at 475 m a.s.l. The experiment was arranged in a completely randomised block design with five fertiliser treatments (treatment B = Ca; C = Ca/N; D = Ca/N/P; E = Ca/N/P/KCl; F = Ca/N/P/K2SO4) and the same number of replicates (see Table 1 for details). In the RGE, the following fertilisers have been used: limestone ammonium nitrate (KAS 27), potassium chloride, quick lime, basic slag and potassium sulphate. The original aim of the experiment was to investigate the efficiency of N, P and K fertilisation under the same lime treatment and cutting system. Plots receiving only Ca were primarily considered as the control (treatment B). Control plots (treatment A) without any fertiliser input were added in 1998 on an adjacent area with the same soil properties that had never been fertilised but had been cut at the same time and with the same frequency as experimental plots B–F. For the last Table 1 Amounts of nutrients (kg ha-1) supplied annually to the treatments since 1941 (according to Schellberg et al. 1999)
List of fertilisers used is given in Table 3
Table 2 Results of basic soil chemical analyses of 0–10 cm layer performed in 2004 (mg 100 g of soil) Treatment
P
K
pH
N (%)
OM (%)
C/N
Mg
A
1.5
4.3
4.9
0.373
4.9
13.1
13.2
B
0.6
2.5
6.5
0.350
4.2
12.0
19.9
C
0.4
2.3
6.5
0.364
4.4
12.0
19.5
D
31.1
3.2
6.6
0.363
4.3
11.8
19.9
E
22.6
9.4
6.5
0.363
4.4
12.0
20.7
F
22.2
10.5
6.6
0.367
4.5
12.3
20.7
Numbers represent mean values of five replicates
45 years, all experimental plots have been cut twice a year in late June to early July and in mid-October. Further details of the location and the experimental design are given in Schellberg et al. (1999) and Hejcman et al. (2007). The results of basic chemical analysis performed following 63 years of fertiliser application are given in Table 2. All analyses were conducted in accordance with standardised methods of the Association of German Agricultural Analytical and Research Institutes. Soil pH was potentiometrically measured in a suspension with 0.01 M CaCl2. Plant-available P and K were extracted by a calcium–acetate–lactate solution and measured colorimetrically and photometrically, respectively. Magnesium was extracted with 0.01 M CaCl2 and measured with flame atomic absorbance spectrometry (AAS). Total C and N were quantified by elemental analyses (Carbo-Erba, Italy). Treatments had a considerable effect on Mg, K and P soil content. The large effect of quick lime application on soil pH is apparent in treatments B–F. Soil genesis and soil sampling The soils of the study site developed from Lower Devonian sandstones and clay slates. During the Mesozoic and Tertiary, the parent rock was deeply weathered and partially eroded. During the
Treatment abbreviation
Applied nutrients (kg ha-1)
A
Non fertilized control
0
B C
Ca = 715; Mg = 67 Ca = 752; N = 100; Mg = 67
Ca Ca/N
Nutrient
D
Ca = 936; N = 100; P = 35; Mg = 75
Ca/N/P
E
Ca = 936; N = 100; P = 35; K = 133; Mg = 90
Ca/N/P/KCl
F
Ca = 936; N = 100; P = 35; K = 133; Mg = 75
Ca/N/P/K2SO4
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Pleistocene, a thin loess cover accumulated. Subsequent erosion and mixing due to solifluction led to layered soils with silty topsoils and dense, stone-rich, often clayey subsoils. The reference soil profile at the edge of the experiment revealed 23% of sand, 54% of silt, and 23% of clay in the topsoil. The saturated hydraulic conductivity decreased from 256 cm per day in the topsoil to 4.6 cm per day in the subsoil. In consequence, stagnic properties occur, i.e. very wet conditions after rainfall and frequent drought during summer. According to the World Reference Base for Soil Resources, the soil is classified as a Stagnic Cambisol. Soil samples were taken in June 2006. In each plot, five separate samples were taken from 0 to 10 cm depth after removing plant residues and then amalgamated into one sample. The same procedure was used to take soil samples from the 10 to 20 cm soil depth. The soil samples were air-dried, ground in a mortar, and sieved to 2 mm after removal of living roots.
Nutr Cycl Agroecosyst (2009) 83:39–50
and N for HN03. The reaction mixtures were centrifuged at 3,000 rpm for 10 min and supernatants were kept at 6°C before measurement. Blank extracts representing 5% of the total number of extracts were prepared using the same batch of reagents and the same apparatus analysed at the same time and in the same way as soil extracts. All reagents used were of electronic grade purity (Analytika, Ltd., Czech Republic). Fertiliser analyses Samples of individual fertilisers were taken as a mixture of several sub-samples from the fertiliser store at the experimental farm. Two 2-g samples of each fertiliser were dissolved in 10 ml of aqua regia for 30 min at 110°C in 50 ml Teflon beakers. The digests were transferred to glass test-tubes and diluted with deionised water to 25 ml. The elements in the solutions were determined as described below. Determination of trace elements
Soil analyses The total concentrations of trace elements in the soils were determined in the digests obtained by the following two-step decomposition procedure. Exactly 0.5 g of a sample was decomposed by dry ashing in an Apion Dry Mode Mineraliser. The ash was then decomposed in a mixture of HNO3 and HF, evaporated to dryness at 160°C and dissolved in diluted aqua regia (Sza´kova´ et al. 1999). A certified reference material RM 7001 Light Sandy Soil was used for the quality assurance of analytical data. Subsequently, 0.5 g soil samples were extracted with a 0.01 mol l-1 CaCl2 aqueous solution in a ratio of 1:10 (w/v) for 6 h to determine plantavailable portions of the elements in the soil (Novozamsky et al. 1993). To determine easilymobilisable concentrations, additional 0.5 g soil samples were extracted with a 0.05 mol l-1 EDTA aqueous solution at pH 7 at a ratio of 1:10 (w/v) for 1 h (Quevauviller et al. 1993). Potentially-mobilisable concentrations of elements were determined by extraction of separate 0.5 g soil samples with a 2 mol l-1 aqueous solution of HNO3 at a ratio of 1:10 (w/v) at 20°C for 6 h (Boru˚vka et al. 1996). Abbreviations for individual elements include the method of extraction: Ca for CaCl2, E for EDTA
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The elements As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in soil digests and extracts were determined by optical emission spectroscopy with inductively coupled plasma (ICP-OES) with axial plasma configuration, Varian, VistaPro, equipped with an autosampler SPS-5 (Australia). Calibration solutions were prepared in corresponding extraction agents as follows: 5–50 lg l-1 for Cd, 50–500 lg l-1 for As, Cr, Cu, and Ni, and 1–10 mg l-1 for Fe, Mn, Pb and Zn. Operating measurement wavelengths for ICPOES were 189.0 nm for As, 214.4 nm for Cd, 324.7 nm for Cu, 238.2 nm for Fe, 205.6 nm for Cr, 259.4 nm for Mn, 231.6 nm for Ni, 220.4 nm for Pb and 206.2 nm for Zn. Measurement conditions were as follows: power 1.2 kW, plasma flow 15.0 l min-1, auxillary flow 0.75 l min-1, nebuliser flow 0.9 l min-1. Low concentrations of As in 0.01 mol l-1 CaCl2 and 0.05 mol l-1 EDTA extracts were determined by a continual hydride generation technique (HGAAS) using a Varian AA280Z (Varian, Australia) atomic absorption spectrometer equipped with a hydride generator VGA-77. A mixture of potassium iodide and ascorbic acid was used for prereduction of the sample and the extract was acidified with HCl before measurement. Two measurements were taken for each sample.
Nutr Cycl Agroecosyst (2009) 83:39–50
43
Data analysis
Results
A redundancy analysis (RDA) in the CANOCO 4.5 programme (ter Braak and Sˇmilauer 2002) was used to evaluate multivariate data. The RDA was used because data sets were sufficiently homogeneous and environmental variables (e.g. treatments) were in the form of categorical predictors. A Monte Carlo permutation test with 999 permutations was used to reveal if the tested explanatory variables (environmental variables in the CANOCO terminology) had a significant effect on the plant-available, easily and potentially-mobilisable concentrations of trace elements. Results of the multivariate analysis were visualised in the form of a bi-plot ordination diagram created by CanoDrawÓ software. The percentage of the explained variability in soil data induced by fertiliser treatments was used as a measure of explanatory power. All univariate analyses were performed using STATISTICA 5.0 software (StatSoft 1995). When RDA analysis demonstrated significance, a one-way ANOVA followed by post-hoc comparison using Tukey’s test was applied to identify significant differences between treatments for individual elements. A regression analysis was used to evaluate the relationship between the amount of applied trace elements in fertilisers and their concentrations in soil samples.
The mean concentrations of trace elements recorded in all applied fertilisers are given in Table 3. Concentrations of Pb and Zn were highest in limestone ammonium nitrate, concentrations of As, Cr, Cu, Fe and Mn were highest in basic slag and concentrations of Cd and Ni were negligible in all fertilisers. The mean amounts of trace elements supplied annually to the treatments calculated from fertiliser rates and relevant concentrations are given in Table 4. Treatments with limestone ammonium nitrate application (C–F) received elevated amounts of Pb and Zn in particular, and treatments with basic slag application (D–F) received considerable amounts of As, Cr, Cu, Fe and Mn. According to RDA, the effect of treatment on concentrations of trace elements was significant and explained 82.3 and 90.6% of the variability of the data in the 0–10 (F = 22.3, P = 0.001) and 10–20 cm (F = 46.3, P \ 0.001) soil layers, respectively. Both ordination diagrams clearly indicate the divergence between concentrations of many risk elements among treatments fertilised with P (D–F) in the 0–10 cm soil layer, shown on the left side of Fig. 1a, and those without P fertilisation (A–C), shown on the right side in the same diagram. In the 10–20 cm soil layer, the effect of basic slag application on concentrations of risk elements was the most remarkable among all applied fertilisers, with
Table 3 Concentration of trace elements in applied fertilizers (mg kg-1)
All fertilisers of the same chemical composition were used at least during the last 15 years
Table 4 Mean amounts of trace elements (g ha-1) supplied annually to the soil of various treatments during the last 15 years
The same approximate values probably were used since 1941
Fertilizer
As
Cd
Limestone ammonium nitrate (KAS 27)
0.6
0.2
Cr
Cu 0.7
Fe
Mn
5.3
392.4
90.7
Ni
Pb
Zn
1.5
29.5
25.3
Potassium chloride
0.2
0.1
3.0
4.3
153.4
3.0
2.5
1.0
3.4
Quick lime Basic slag
1.0 4.7
0.0 0.4
0.3 597.6
7.8 43.3
3.2 4578.5
0.2 1331.9
1.4 2.3
0.5 5.8
0.1 5.5
Potassium sulphate
0.2
0.0
0.1
8.8
10.3
2.3
0.3
0.9
5.8
Treatment
As
Cd
Cr
Cu
Fe
Mn
Ni
Pb
Zn
A
0
0
0
0
0
0
0
0
0
B
1.2
0.1
0.3
9.1
3.8
0.2
1.7
0.6
0.1
C
1.4
0.1
0.6
11.1
149.1
33.8
2.3
11.5
9.5
D E
4.0 4.0
0.3 0.4
319.3 320.5
34.2 35.9
2591.0 2652.3
744.1 745.3
3.5 4.5
14.6 15.0
12.4 13.7
F
4.0
0.4
319.3
37.0
2594.3
744.9
3.6
14.9
14.2
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44
Nutr Cycl Agroecosyst (2009) 83:39–50
Table 5 Results of regression analyses of trace elements concentration in the soil as a function of elements applied with fertilisers Indep. var. As
Cr
Fe
Mn
Pb
Zn
Depen. var.
R2
P-value
As (CaCl2)
0.57
\0.001
As (EDTA)
0.67
\0.001
As (HNO3)
0.64
\0.001
Cr (CaCl2)
0.02
0.451
Cr (EDTA)
0.76
\0.001 \0.001
Cr (HNO3)
0.98
Fe (CaCl2)
0.13
0.048
Fe (EDTA)
0.34
\0.001
Fe (HNO3)
0.88
\0.001
Mn (CaCl2)
0.14
0.042
Mn (EDTA) Mn (HNO3)
0.16 0.80
0.026 \0.001
Pb (CaCl2)
0.46
\0.001
Pb (EDTA)
0.26
0.004
Pb (HNO3)
0.07
0.159
Zn (CaCl2)
0.21
0.012
Zn (EDTA)
0.14
0.04
Zn (HNO3)
0.04
0.296
Abbreviations: Indep. var., independent variable, amount of applied risk elements by fertilisers; depen. var., concentration of risk elements in the 0–10 cm soil layer extracted by CaCl2 (plant available), EDTA (easily mobilisable) and HNO3 (potentially mobilisable) Significant results are faced in bold
Fig. 1 Ordination diagrams showing the result of RDA analysis of trace elements concentration in 0–10 cm (a) and in 10–20 cm (b) soil layers. Treatment abbreviations (A–F) are given in Table 1. Abbreviations of trace elements are
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treatments with P application located on the left side of the diagram and treatments without P application on the right side of the diagram, as in the 0–10 cm soil layer (Fig. 1b). In the same diagram, the length and direction of the vectors relating to the individual elements indicate the association of elements with their respective treatments. In the 0–10 cm soil layer for example, the concentration of plant-available Mn and Zn was highest in unfertilised treatment A on acid soil, but was lowest in treatment D. Concentrations of plant-available Mn and Zn were highly correlated (both vectors almost overlapped), but were negatively correlated with potentially-mobilisable concentrations of both elements (MnN and ZnN in the diagram) as indicated by the angle between vectors for MnCa and MnN or ZnCa and ZnN of more than 90°. The length of the vector is an indicator of the importance of a particular element. If the vector is long, big differences among treatments exist and the element has a strong effect on the results of the analysis, and vice versa. Ordination diagrams enable the visualisation of many soil chemical analyses together and clearly show the relations among the concentrations of all elements extracted by different methods. The average concentrations of individual elements in the 0–10 cm soil layer are given in Table 6.
supplemented by methods of extraction: Ca, CaCl2 (plant available); E, EDTA (easily mobilisable) and N, HNO3 (potentially mobilisable)
Nutr Cycl Agroecosyst (2009) 83:39–50 Table 6 Mean concentration of trace elements (mg kg-1) in 0–10 cm soil layer extracted by CaCl2 (plant available), EDTA (easily mobilisable), HNO3 (potentially mobilisable) and total concentration
Element
Extract
Treatment A
As
CaCl2 EDTA
Cd
Cr
Cu
Fe
Mn
Ni
Pb
Treatments with the same letter are not significantly different. Total concentrations (bold faced) were not statistically analysed
45
Zn
B
C
D
0.000a
0.000a
0.000a
a
a
a
0.019 a
0.008 b
0.030 b
E
0.004ab 0.139
b
bc
F
0.009bc c
0.099 bc
0.014c 0.076c
HNO3 Total
0.8 23.0
1.7 34.1
1.6 26.5
2.2 32.1
2.2 30.5
2.4c 34.3
CaCl2
0.044a
0.020b
0.011b
0.011b
0.010b
0.013b
EDTA
0.197
0.226
0.179
0.201
0.178
0.203
HNO3
0.249
0.305
0.257
0.313
0.303
0.339
Total
0.558
0.507
0.442
0.562
0.446
0.575
CaCl2
0.029
0.033
0.025
0.031
0.043
0.026
EDTA
0.1a
0.1a
0.1a
0.5b
0.3c
0.4bc
HNO3
2.0a
4.1a
3.4a
25.4b
25.0b
24.6b
Total
46.8
47.5
46.6
82.6
78.0
77.0
CaCl2
0.4
0.4
0.7
0.6
0.3
0.7
EDTA
4.4
4.6
3.9
4.4
3.8
3.0
HNO3
3.5
4.8
5.1
4.2
4.7
3.9
Total
28.6
26.5
34.5
24.7
23.6
22.6
CaCl2
5.2a
2.2b
1.7b
1.8b
1.3b
2.6b
EDTA
186.6a
222.5a
b
322.4ab
2581 11899
2550b 11545
4.6a
2.1b
2.2b
0.9a
3.0a
1.7b
EDTA
299.3
443.5
361.0
460.6
441.7
438.8
HNO3
602.5a
642.1a
631.4a
800.9b
810.3b
821.4b
Total
943
842
830
1174
1063
1162
CaCl2
0.3
0.4
0.4
0.3
0.3
0.3
EDTA
1.9
2.2
1.3
1.6
2.1
2.1
HNO3
3.6
4.4
3.6
4.5
5.6
3.9
Total
19.3
17.7
16.9
17.7
19.9
17.1
CaCl2
0.2ab
0.1a
0.3b
0.3b
0.3b
0.2ab
EDTA
11.3
11.0
9.8
10.1
8.7
9.0
HNO3
19.3
17.9
19.0
17.0
17.5
17.6
Total
43.1
41.6
43.3
42.0
41.5
38.2
CaCl2
0.19a
0.04b
0.04b
0.03b
0.07b
0.05b
EDTA HNO3
3.5 8.7
3.4 10.6
2.7 10.2
2.4 9.6
2.5 10.6
3.0 11.7
Total
64.9
49.7
45.8
45.0
46.8
44.2
Calculated individually by one-way ANOVA, a significant effect of treatment on the concentration of AsCa, AsE, AsN, CdCa, CrE, CrN, FeCa, FeE, FeN, MnCa, MnN, PbCa and ZnCa was recorded. The effect of treatment on concentrations of CdE, CdN, CrCa, CuCa, CuE, CuN, MnE, NiCa, NiE, NiN, PbE, PbN, ZnE and ZnN was not significant.
b
295.4ab
2539 11949
CaCl2
a
410.4b
1983 11020
1819 9169
a
233.9ab
1983 11461
HNO3 Total
a
Concentrations of AsCa, AsE and AsN were significantly correlated with the amount of As applied in the fertilisers, mainly with basic slag (Table 5). The same results were recorded for CrE, CrN, FeE, FeN, MnN, PbCa and PbE. Concentrations of FeCa, MnCa, MnE, PbE, ZnCa and ZnE were significantly correlated with the amounts of elements supplied by
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46 Table 7 Mean concentration of trace elements (mg kg-1) in 10–20 cm soil layer extracted by CaCl2 (plant available), EDTA (easily mobilisable), HNO3 (potentially mobilisable) and total concentration
Nutr Cycl Agroecosyst (2009) 83:39–50
Element
Extract
A As
CaCl2 EDTA
Cd
Cr
Cu
Fe
Mn
Ni
Pb
Zn
0.000a 0.008
a
C
0.007ab a
0.012
D
0.015bc a
0.006
F
0.025d
0.025d
b
b
0.053
0.041
1.7 26.6
1.6 22.1
CaCl2
0.03
0.04
0.02
0.03
0.03
0.03
EDTA
0.07a
0.18b
0.14b
0.16b
0.17b
0.17b
HNO3
0.15a
0.23b
0.20ab
0.23b
0.24b
0.25b
Total
0.4
0.8
0.5
0.7
0.7
0.5
CaCl2
0.021
0.041
0.053
0.027
0.029
0.015
EDTA
0.080a
0.108a
0.065a
0.258c
0.184b
0.223bc
HNO3
1.5a
2.9a
2.6a
9.3b
8.5b
8.9b
Total
54.2
56.0
54.8
65.8
64.4
64.3
CaCl2
0.3a
1.0ab
0.8ab
1.0b
0.7ab
1.1b
EDTA
2.3a
6.8b
5.9b
5.2ab
6.7b
5.0ab
HNO3
2.1
a
b
b
Total
27.5
29.4
32.9
CaCl2
0.9
1.6
1.5
EDTA
147.1a
252.0bc
HNO3 Total
1791a 10013
CaCl2
2.4a
HNO3
559.2
Total CaCl2
2.2 19.5
2.4c 23.1
2.2 20.5
b
7.6b
34.1
34.2
37.0
1.4
1.6
1.7
190.2ab
332.5cd
264.3cd
290.1cd
2898b 12050
2837b 11335
3317c 11964
3261c 13057
3287c 12561
21.2b
12.6ab
17.0b
20.4b
9.4ab
8.5
a
bc
0.056b
0.5 28.4
168.7
bc
0.023cd
HNO3 Total
a
b
E
b
6.8
bc
617.1
bc
7.3
b
494.6
8.0
cd
626.1
590.4d
d
634.8
993.4
999.7
1014.7d
1144
1128
1109
1392
1612
1550
0.43
0.25
0.21
0.11
0.27
0.17
EDTA
0.85
2.19
1.20
1.79
2.16
2.14
HNO3
2.1
a
b
5.2b
Total
21.3
22.8
20.5
23.4
26.5
27.1
CaCl2
0.23
0.17
0.31
0.36
0.27
0.20
EDTA
5.1a
9.3b
7.9b
9.2b
8.0b
8.7b
HNO3
11.3a
15.8b
14.7b
15.3b
14.5b
15.5b
Total
37.9
33.6
35.2
36.6
27.2
37.3
CaCl2
0.11
0.15
0.12
0.14
0.15
0.17
EDTA HNO3
1.4a 5.1a
2.3ab 7.2b
1.6ab 5.8ab
1.9ab 7.0b
2.0ab 7.3b
2.5b 6.8b
Total
60.7
42.7
42.9
43.2
43.9
46.2
4.3
3.6
ab
cd
d
911.8
ab
b
b
940.2
fertilisers, but the correlation was weaker than in the previous cases. Correlations were not significant in three cases: CrCa, PbN and ZnN. The average concentrations of individual elements in the 10–20 cm soil layer are given in Table 7. Significant effects of treatments on
123
B
a
EDTA
Treatments with the same letter are not significantly different. Total concentrations (bold faced) were not statistically analysed
Treatment
4.7
ab
5.2
concentrations of AsCa, AsE, AsN, CdE, CdN, CrE, CrN, CuCa, CuE, FeE, FeN, MnCa, MnE, MnN, NiN, PbE, PbN, ZnE and ZnN were recorded. The effects of treatments on concentrations of CdCa, CrCa, CuN, FeCa, NiCa, NiE, PbCa and ZnCa were not significant.
Nutr Cycl Agroecosyst (2009) 83:39–50
Discussion Tables 3 and 4 indicate that Cd concentrations in all the applied fertilisers were relatively low, including in basic slag. Cadmium concentration in basic slag was low because the high temperatures during the production process lead to its evaporation. The annual increment of Cd to the soil was substantially lower compared to elements such as As, Cr, Cu, Fe and Mn in basic slag and Fe, Mn, Pb and Zn in limestone ammonium nitrate. This observation contrasts with findings by Mortvedt (1996) and Franklin et al. (2005) indicating that fertilisers based on phosphate rocks contain Cd as the main contaminant. Following 65 years of fertiliser application in the present experiment, the total concentrations of Cr, Cu, Ni, Pb and Zn in the soil did not exceed limits permitted by Czech national legislation. These limits are 105.9, 70.6, 58.8, 70.6 and 141.2 mg kg-1 for Cr, Cu, Ni, Pb and Zn, respectively (Anonymous 2001). Paradoxically, German national norms do not cover the concentration of As in the soil, so Czech National limits have been used here. In the case of Cd, the total concentration reached the legislation threshold limit even in the control in both investigated soil layers, but there was no effect of fertilisation in the 0–10 cm layer. In the 10–20 cm layer, the effect of liming was apparent as total Cd concentrations increased in all treatments with CaO application compared to the control. Therefore, the potential effect of P fertiliser application on the increase of mobile portions of Cd in the soil was suppressed by liming, which increases soil pH and decreases Cd, Fe, Mn, and Zn mobility (He and Singh 1993; Chowdhury et al. 1997; Gavi et al. 1997; Tlustosˇ et al. 2006). Total Cd values exceeded the threshold limit in treatments B, D and E of the RGE. A strong effect of pH on the concentration of plantavailable Cd was apparent in the 0–10 cm layer with more than a fourfold increase in Cd concentrations in the control at pH(CaCl2) 4.9, whereas all limed treatments at pH(CaCl2) 6.5–6.6 exhibited significantly different values. A decrease in the mobility of Cd, Zn and Pb in limed soil and an effective decrease in the uptake of these elements by several crops has been investigated and confirmed in pot experiments and under field conditions (Lee et al. 2004; Kucharski et al. 2005; Castaldi et al. 2005). In long-term field experiments
47
(from 15 to 63 years) Gavi et al. (1997) also observed a more apparent effect of soil pH on the mobility of Cd compared to N and P fertilisation. No causality between Cd concentrations extracted by different methods is visible in the ordination diagrams (Fig. 1). Vectors for CdCa, CdE and CdN were not directed to the same treatment in both soil layers. This result is consistent with those of many other authors showing that total Cd concentrations in soils cannot be linked to the concentration of either the plant-available or easily-mobilisable Cd fraction (Mench 1998). In the 0–10 cm layer, however, total concentration of As exceeded the permitted threshold limit of 23.5 mg kg-1 in all fertilised treatments. In the 10–20 cm layer, limits were exceeded only in treatments A and B. The parent rock material might have been responsible for total Cd and As concentrations in the control. In contrast to Cd, there was a significant correlation between plant-available (AsCa), easily-mobilisable (AsE) and potentiallymobilisable (AsN) concentrations of As with all vectors exhibiting similar trends in the ordination diagrams. Furthermore, there was a significant dependence of plant-available, easily- and potentially-mobilisable soil As concentrations on the amount of applied As in basic slag. Lower concentrations in the control and increased concentrations in treatments with P application contradicted the conclusion made by Chen et al. (2007) that normal cropping practices do not have a significant effect on the total As concentration of the receiving soil. Similarly, Sisr et al. (2007) did not observe significant changes in the mobile portion of As in soil treated by phosphate solution in a laboratory experiment using artificial soil columns. According to the results from the RGE, a proportion of applied As can accumulate in the soil profile, especially in the upper 0–10 cm layer. In the RGE, the effect of As present in basic slag combined with the enhanced mobility of As caused by the addition of phosphate fertilisers was apparent. Huang et al. (2005) reported no significant changes in As mobility in limed soil, whereas in experiments published by Sza´kova´ et al. (2007) the mobile portion of As in limed soil tended to increase as in the RGE. There are many contradicting results that make it difficult to give exact explanations for these differences. Some of the discrepancies in published results may be
123
48
ascribed to the different physicochemical properties of experimental soils, the different designs of individual experiments and also to the different soil extraction procedures used for the determination of the mobile portions of elements (see Francesconi and Kuehnelt 2004). However, the effect of P on the reduction of arsenate sorption as well as on increasing mobility of arsenate due to the competitive sorption of arsenate and phosphate in soils has been highlighted by many authors (e.g. Qafoku et al. 1999; Smith et al. 2002). Tassi et al. (2004) recommended soil treatment by diammonium phosphate for enhancement of As mobility in the soil, followed by increased As uptake by plants, for chemically-assisted phytoextraction of As from contaminated soil. In the RGE, the application of basic slag introduced more than 300 g of Cr ha-1 to the soil each year. The total concentration of Cr almost doubled in the 0–10 cm layer after 65 years of fertiliser application. An increase in Cr concentrations was detected even in the 10–20 cm layer. This indicated substantial accumulation of Cr in the soil profile. Rough estimates indicate that basic slag has probably been applied for more than 100 years, in order to achieve a critical total Cr concentration in the 0–10 cm soil layer. Despite the accumulation of total Cr in the soil profile and a significant effect of basic slag application on easily-mobilisable and potentiallymobilisable Cr soil concentrations, plant-available Cr concentration was not affected by fertiliser treatment. Furthermore, no correlation was observed between the amount of Cr applied by fertilisers and plant-available Cr concentration. This indicated the relatively high ability of Cr to be fixed in the soil profile. Although treatments with basic slag application received more than 30 g ha-1 of Cu annually, no treatment effect was detected in the 0–10 cm layer. This contrasted with the 10–20 cm layer where an increase in Cu concentrations was recorded by all methods. Nevertheless, after 65 years of fertiliser application, total Cu concentrations had not increased substantially to reach a critical value. Higher concentrations of Cu in the 10–20 cm layer than in the 0–10 cm layer in all limed treatments was probably connected with enhanced Cu movement due to increased decomposition of organic matter in these treatments, which is connected with the lower content
123
Nutr Cycl Agroecosyst (2009) 83:39–50
of organic matter therein, i.e. 4.9% in the control versus 4.2–4.5% in limed treatments. On soils high in organic matter, Cu is frequently complexed to organic substances, hence decreasing Cu plant availability (Clemente et al. 2006). Nickel was applied in doses of 3.5–4.5 g ha-1 in treatments D–F, respectively. This amount was probably too small to affect Ni concentrations in the 0–10 cm layer. On the other hand, a slow increase occurred in the 10–20 cm layer, although total concentrations were far below critical values. In contrast to Cd and As, the application of phosphates can significantly decrease the mobile portions of Cr, Cu and Ni (Liu et al. 2007). The effect of KCl application on increased mobility of these three elements was not confirmed in the RGE. Lead and Zn were found at the highest concentrations in limestone ammonium nitrate. Amounts of applied Pb and Zn were comparable. In the 0–10 cm layer, an obvious effect of pH on the concentration of plant-available Zn was detected while no effect of liming was observed with Pb. These results were in accordance with other authors (Chowdhury et al. 1997; Huang et al. 2005; Sza´kova´ et al. 2007). The fact that Fe and Mn availability were increased predominantly in plots with low pH values was clear in the 0–10 cm layer (Watmough et al. 2007; Matsi et al. 2005; Wang et al. 2003). In the unfertilised control, Fe and Mn availability was substantially higher than in other treatments although treatments D–F received more than 2,500 and 740 g ha-1 of Fe and Mn per year, respectively. On the other hand, the application of basic slag resulted in an accumulation of Fe and Mn in the 0–10 cm layer. A strong effect of pH but a relatively weak effect of applied Fe and Mn in fertilisers on plantavailable soil Fe and Mn concentrations was demonstrated by regression analysis. There was a low correlation between the amounts of Fe and Mn applied by fertilisers and FeCa and MnCa soil concentrations, a higher correlation in the case of FeE and MnE, and a very high correlation in the case of FeN and MnN.
Conclusion It can be concluded that long-term application of limestone ammonium nitrate, potassium chloride and
Nutr Cycl Agroecosyst (2009) 83:39–50
potassium sulphate did not increase the mobility of excess trace elements in the RGE. On the other hand, long-term application of basic slag resulted in the accumulation of Cr and As in the soil profile. The plant availability of Cd, Cu, Fe, Mn and Zn was driven by soil pH, not by application of elements in fertilisers. Furthermore, the RGE, like any other long-term fertiliser experiment, is an excellent site at which to study the impact of trace element input on accumulation of element fractions. However, turnover and fractionation remain a matter for further research. Acknowledgements The authors gratefully acknowledge the technical support of all staff members at the Rengen Experimental Station throughout the existence of the RGE. Special thanks for managing the experiment and soil sampling go to Dieter Hoffman-Gaber and Manfred Schwickerath. The authors thank Veˇra Semelova´ for her assistance during laboratory work and anonymous reviewers for useful comments on the manuscript. Data collection and finalisation of the paper was supported by Czech projects MA 0002700601, GACˇR 521/08/1131, GACˇR 205/06/0298 and MSM 6046070901.
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