A. K. M. Arnesen and B. R. Singh

Transcription

1 Plant uptake and DTPA-extractability of Cd, Cu, Ni and Zn in a Norwegian alum shale soil as affected by previous addition of dairy and pig manures and peat A. K. M. Arnesen and B. R. Singh Department of Soil and Water Sciences, P. O. Box. 5028, Agricultural University of Norway, N-1432 Aas. Received 18 November 1997, accepted 3 March Arnesen, A. K. M. and Singh, B. R Plant uptake and DTPA-extractability of Cd, Cu, Ni and Zn in a Norwegian alum shale soil as affected by previous addition of dairy and pig manures and peat. Can. J. Soil Sci. 78: Residual effects of cow manure, pig manure and peat soil on the DTPA-extractability and plant uptake of cadmium, copper, nickel and zinc were investigated in the second and third years after application to an alum shale soil. Wheat and barley were grown in alternate years. The effects of the organic matter applied differed among metals, sources of organic matter and time after application. The Cd concentrations in grain was reduced by the rates of peat soil, whereas the manures had no significant effect. Copper concentrations in grain and Zn concentrations in both grain and straw generally increased with rates of organic matter. Nickel concentration in grain tended to decrease with increasing rates of cow and pig manure applied, whereas it tended to increase with the addition of peat soil. The concentrations of DTPA-extractable metals in the soil were generally higher in the second and third years than in the first year after application of organic matter. Some of the metals bound by organic matter in the first year were probably released as the organic matter was decomposed. Decreases in DTPA-extractable Cd and Ni were found by the addition of pig and cow manure, whereas these manures resulted in increased DTPA-extractable Zn. The application of peat soil, on the other hand, resulted in increased amounts of DTPA-extractable Cu, Zn and Ni, probably due to decreased soil ph. Key words: Heavy metals, solubility, plant uptake, organic matter Arnesen, A. K. M. et Singh, B. R Absorption par les plantes et extractibilité au DTPA de Cd, Cu, Ni et Zn dans un sol formé sur schistes à aluns en Norvège. Effets d apports préalables de tourbe ou de fumier de vache ou de porc. Can. J. Soil Sci. 78: Nous avons examiné dans la seconde et la troisième année suivant le rapport à un sol formé sur schiste à aluns l arrière effet du d epandaaage de fumier d exploitation laitière, de fumier de porc et de tourbe sur l extractibilité au DTPA et sur l absorption par les plantes du cadmium, du cuivre, du nickel et du zinc. Le blé et l orge étaient utilisés en alternance une année sur deux comme cultures expérimentales. Les effets de l apport de m.o. différaient selon le métal, la provenance de la m.o. et le temps écoulé depuis l épandage. Les concentrations de Cd dans le grain diminuaient en fonction de l accroissement des doses d épandage de tourbe, mais les fumiers ne provoquaient pas d effets significatifs. Les concentrations de Cu dans le grain et de Zn dans le grain et la paille augmentaient en général avec la dose d apport de m.o. Les concentrations de nickel dans le grain manifestaient une tendance à la baisse en fonction de l accroissement des doses des apports de fumier, et à la hausse en fonction des apports de tourbe. Les concentrations de métaux extractibles au DTPA dans le sol étaient généralement plus élevées dans les deuxième et troisième années que dans l année d épandage de la matière organique. Certains des métaux liés par la m.o. dans la première année étaient vraisemblablement relargués à mesure que la m.o. se décomposait. Des baisses de Cd et de Ni extractibles au DTPA étaient observées après épandage de fumier de porc ou de vache, l inverse s observant pour le Zn. En revanche, l apport de tourbe se traduisait par une augmentation des concentrations extractibles des trois métaux, probablement reliée à l abaissement du ph du sol. Mots clés: Métaux lourds, solubilité, absorption par les plantes, matière organique Plant uptake of heavy metals is partly determined by the concentration and speciation of the metals in soil solution (Bingham et al. 1984, 1986). Organic matter makes strong complexes with heavy metals (Bloom 1981; Krogstad 1983). Solid organic matter may retain metals in the solid phase of the soil, whereas dissolved organic matter may increase mobility of the metals (Elliot and Denneny 1982; Japenga et al. 1992; Lo et al. 1992). The availability for uptake by plant roots may differ between metals bound in soluble complexes and free metals. As organic materials influence the binding of heavy metals in soil and speciation in soil solution (Ram and Verloo 1985; McGrath et al. 1988; Lo et al. 1992; Del Castillho et al. 1993), it may also affect 531 plant uptake (Haghiri 1974; McBride et al. 1981). Soil ph is another factor influencing the bioavailability of metals, both in terms of sorption in the soil and speciation in the soil solution. Amendment with organic matter and resulting degradation may change the soil ph and thereby indirectly influence the bioavailability of metals. Organic matter may also alter the sorption to Mn- and Fe-oxides (He and Singh 1993a; Harter and Naidu 1995). He and Singh (1993a) found that an increased rate of organic matter increased the MgCl 2 - or DTPA-extractable Cd in soils, whereas the Cd uptake in plants was decreased. The increase in extractability of Cd was assigned to the decrease in soil ph caused by organic matter application (He and Singh 1993a). The

2 532 CANADIAN JOURNAL OF SOIL SCIENCE reduced plant uptake of Cd may have been caused by a change in speciation in the soil solution. In the second and third years of cropping on the same soils, the concentrations of Cd in ryegrass was not consistently affected by rates of organic matter application (Singh et al. 1997). MacLean (1976) also reported that the higher amounts of organic matter in the soil resulted in increased DTPA-extractable Cd and Zn, but it decreased uptake of Cd by lettuce. Eriksson (1988) found a negative relationship between Cd concentration in plants and the organic matter content of soils. He and Singh (1993b) and Mellum et al. (1997) found no such relationship in field investigations. Alum shales and the soils developed on such parent material in Norway are known to contain naturally high levels of heavy metals (Jeng 1992; Jeng and Bergseth 1992). The alum shale areas of Hedmark County in South-east Norway are predominantly used for production of grain and vegetables. Plant uptake of heavy metals because of their high levels in the soil is a cause for concern. Crops grown on such alum shale soil were found to contain relatively high concentrations of Cd (Singh et al. 1995; Esser 1996; Mellum et al. 1997). Narwal and Singh (1997) investigated the effect of different sources and rates of organic materials on the solubility, speciation and plant availability of heavy metals in an alum shale soil. This was done to assess methods to reduce the heavy metal concentration in food crops. Three sources of organic material cow manure, pig manure and peat soil were used at increasing rates and their effects on the extractability of Cd, Cu, Ni and Zn in the soil and the uptake of these metals by wheat were determined. Narwal and Singh (1997) also studied the effects of organic materials on partitioning and distribution of the metals in different soil fractions. This experiment was continued in the second and third years to assess the residual effects of different organic materials on the extractability and plant uptake of heavy metals. The results presented in this paper describe the findings of the second and third years. MATERIALS AND METHODS Greenhouse Experiment A 3-yr greenhouse pot experiment was conducted. Alum shale soil (Typic Cryoboroll) was used for growing wheat in the first year, barley in the second year and wheat in the third year. The alum shale soil was collected from the cultivated field (0 20 cm) at Jønsberg (Hedmark county) in South-east Norway. The soil was air dried and passed through a 2-mm sieve. The initial soil ph was 6.1, the concentration of total organic carbon was 6.4% and the cation exchange capacity was 444 mmol(c+) kg 1 (Table 1) The soil contained 2.8 µg Cd g 1, 97 µg Cu g 1, 115 µg Ni g 1 and 217 µg Zn g 1. The types of organic material used were cow manure, pig manure and peat soil. Some chemical characteristics are presented in Table 1. The organic material was added in the moist state to the air-dried soil at rates of 0, 2, 4 and 8% on an oven-dry weight basis at the beginning of the experiment (year 1). The soil and organic materials were thoroughly mixed and filled in double-walled plastic pots (6.7 dm 3 in each pot). Each treatment was replicated three times. The basal dose of N and P in each pot was equivalent to that added through cow manure at the 8% level. The soil was also supplemented with K, Fe, Cu, Mn, Zn, B and Mo at the rates of 362, 67, 42.2, 54.3, 12.1, 1.81, and 1.74 mg pot 1, respectively. In our greenhouse experiments it is common practice to add the micronutrient mixture to minimize the risk of micronutrient deficiency caused by nutrient deficiency, management practice and growing conditions. The fertilizers used for N, P and K were NH 4 NO 3, CaH 4 (PO 4 ) 2 H 2 O and KCl. For Fe, Cu, Mn and Zn their sulphate salts were used. For B Na 2 B 4 O 7 10H 2 O and for Mo (NH 4 ) 6 Mo 7 O 24 4H 2 O were used (Narwal and Singh 1997). The results from the first year of this experiment were reported by Narwal and Singh (1997). In the second year, the soil in each pot was taken out and thoroughly mixed with the same rates of chemical salts as in the first year. Twenty seeds of barley were sown in each pot. After germination, these were thinned to 14 plants. Deionized water was used for irrigation throughout the growth period and the moisture conditions were kept at 65 to 70% of the water-holding capacity of the soil. At maturity, the crop was harvested, oven-dried at 65 C and the dry weight was determined. Soil samples were collected from each pot after harvest. In the third year, wheat was grown following the same procedure as in the second year. The total concentrations of Cd, Cu, Zn and Ni were determined in the plant samples. Soil ph and the concentrations of DTPA-extractable metals in the soil were determined. In addition, the content of organic carbon in the soil after the first and third years of cropping was determined. Soil Analysis The soil samples were dried and passed through a 2-mm stainless steel sieve. Soil ph was determined in a 1:2.5 soil:water suspension. The content of organic carbon was determined by an EC-12 LECO-carbon analyzer. The concentrations of DTPA-extractable Cd, Cu, Zn, and Ni in the soil were determined by shaking for 2 h with M DTPA M TEA M CaCl 2 (ph 7.3) at 25 C (Lindsay and Norvell 1978). The heavy metals in the soil extracts were determined either by atomic absorption spectrophotometer or by graphite furnace atomic absorption spectrophotometer (when concentration was below 25 µg L 1 ). Plant Analysis The grain and straw samples were dried and ground in a stainless steel grinder and Cd, Cu, Ni and Zn concentration were determined. The plant samples were dry ashed at 450 C, treated with 2:1 concentrated HCl:HNO 3, dissolved in 5 cm 3 1:1 HNO 3 :water and diluted to 50 cm 3 with distilled water. The heavy metals in the digested solutions were determined the same way as described for soil extracts. RESULTS AND DISCUSSION Sequential extraction of the soil samples from the first year showed that the highest amount of Cd (about 41%) was present in the exchangeable fraction (Narwal and Singh 1997).

3 ARNESEN AND SINGH PLANT UPTAKE AND EXTRACTABILITY OF METALS 533 Table 1. Chemical properties of the soil and the organic materials used ph CEC org. C Min-N Inorg.-P Zn Cu Cd Ni (mmol(+) kg 1 ) (%) (µg g 1 dry weight) Alum shale soil Cow manure Pig manure Peat soil Traces Extracted and modified from Narwal and Singh (1997). Table 2. ph in the soil after the second and third harvests at increasing rates of organic materials applied year Organic matter rate (%) a 6.27a 6.33ab 6.46b a 6.26b 6.32c 6.49d a 6.31b 6.28ab 6.29ab a 6.31b 6.25ab 6.22ab d 5.86c 5.66b 5.33a d 5.91c 5.65b 5.29a a d Means with different letters indicate significant difference (P < 0.05) within each row. The sequential extraction was based on a five step procedure; 1) 1 M MgCl 2 at ph 7 (exchangeable metals), 2) 1 M CH 3 COONa at ph 5 (carbonate bound metals), 3) 0.04 M NH 2 OH.HCl in 25% CH 3 COOH (ph2) (oxide-bound metals), 4) a mixture of 0.02 M HNO 3, 30% H 2 O 2, 3.2 M CH 3 COOH and H 2 O (organic matter bound metals) and 5) aqua regia (residual metals). Increasing rates of cow and pig manure decreased the exchangeable fraction of Cd. Cadmium extractable by 0.04 M NH 2 OH.HCl ( oxidebound ) was reduced by peat soil due to decreased ph. The exchangeable fractions of Cu, Ni and Zn were very small (<3%). More than 50% of Cu was associated with organic matter, probably due to formation of specific complexes (Bloom 1981). The concentrations of Ni and Zn were highest in the residual fraction (51 and 66%, respectively). The Ni concentration in the exchangeable fraction decreased slightly when cow and pig manure were applied, whereas it increased with peat soil addition. The rates and sources of organic matter had little effect on the partitioning of Cu and Zn in the soil (Narwal and Singh 1997). In the present study, the soil ph increased significantly with increased amounts of cow manure added (Table 2). With addition of pig manure, there was no consistent effect, but the addition of peat soil resulted in a significant decrease in soil ph. Similar ph changes were also observed in the first year (Narwal and Singh 1997). The DTPA-extractable Cd, Cu and Ni were negatively correlated with soil ph (Fig. 1), but no such relationship was seen between DTPAextractable Zn and soil ph. The content of organic matter in the soil was significantly lower after the third crop than after the first (Table 3). A significant loss of organic matter had also occured during the first growing season. Degradation of the organic matter probably influenced the interaction of heavy metals with the organic matter. During the 3 yr of experiment, the amount of organic matter and probably also its properties were altered, resulting in changes in the adsorption of the metals to the organic ligands and to the soil surfaces (Elliot and Denneny 1982; Japenga et al. 1992; Yuan and Lavkulich 1997). The concentrations of DTPA-extractable metals in the present study were generally higher in the second and third years than in the first year. After the first year, on average 20% of total Cd in the soil was DTPA-extractable. Two years later, this had increased to 44%. Of total Cu, about 4.5% was DTPA-extractable in the first year, whereas 7.7% was exrtractable after the third crop. The corresponding values for Ni were 7 and 15%, and for Zn 3.8 and 8%. Reduction in heavy metal sorption due to organic matter decomposition is also reported by others (Sadovnikova et al. 1996; Yuan and Lavkulich 1997). Yuan and Lavkulich (1997) treated two soils to partially oxidize organic matter in order to evaluate the effect of organic matter degradation on metal sorption. For a soil with ph 6.74 and organic C content of 46.9 g kg 1, loss of 11% of the total organic matter resulted in 97, 72 and 62% reduction in the original sorption capacity of Cu, Zn and Cd, respectively. For a soil with ph 4.69 and organic C content of 16.3 g kg 1, the reduction of sorption capacity was 97, 66 and 60% for Cu, Zn and Cd, respectively, following a reduction in organic C to 2.8 g kg 1. Sadovnikova et al. (1996) incubated a sandy loam (ph 6.8) with sewage sludge and farmyard manure for 6 wk. Incubating soils increased the available forms of Cu, Cd, and Pb and decreased their organically bound forms. The decrease in organically bound Cu and Pb were higher than the increase in available forms. Some of the inorganic forms arising from decomposition of metal-organic complexes may have precipitated in other forms or may have been occluded by Fe and Al oxides. The DTPA-extractable Cd decreased significantly by pig manure amendment, but there were no consistent effects of cow manure or peat soil (Table 4). This was in contrast to the experiments conducted by He and Singh (1993a), who treated a sand, a sandy loam and a clay loam with different levels of sphagnum peat and added Cd-containing NPK fertilizer. They found that the NH 4 NO 3 - and DTPAextractable Cd in the soils increased with increased addition of peat. The residual effects of the organic matter in the same soils gave results similar to those of the first year (Singh et al. 1997). This suggests that the effect of organic matter addition is different in the alum shale soil naturally high in heavy metals and containing sulphide minerals to that in soils developed on other parent materials. The con-

4 534 CANADIAN JOURNAL OF SOIL SCIENCE Fig. 1. Correlations between ph and DTPA-extractable metals in the soil.

5 ARNESEN AND SINGH PLANT UPTAKE AND EXTRACTABILITY OF METALS 535 Table 3. Contents of organic C in the soil after the first and third harvests year Organic matter rate (%) (Organic C (%)) Mean a b Mean 4.69c 5.32b 5.47b 6.28a a b Mean 4.69c 4.84bc 5.05b 6.17a a b Mean 4.69d 5.30c 5.61b 6.51a a,b Means with different letters in the same column indicate significant difference between years (P < 0.05). a d Means with different letters in the same column for each amendment indicate significant difference between rates of organic matter (P < 0.05). centration of DTPA-extractable Cd was about tenfold higher in the alum shale soil compared with the levels in the soils used by He and Singh (1993a). The ph in the soils used by He and Singh (1993a) was lower and may also have contributed to this difference, as reported by Ram and Verloo (1985). They found that farmyard manure and peat soil enhanced the mobility of heavy metals at lower ph and decreased it at higher ph. The extractable Cu in the present study increased with increasing rate of peat soil addition, but there were no consistent effects of cow or pig manures. The extractable Ni decreased with increased rates of cow and pig manure application, but it increased with rate of peat soil addition. The lowering of ph in the peat-amended soil probably decreased the sorption of metals in the soil (Ram and Verloo 1985; Yuan and Lavkulich 1997) and this effect became even more significant after degradation of organic matter. Extractable Zn increased with increased rates of all three sources of organic matter, probably due to degradation of the organic matter and release of the Zn which was complexed with organic matter in the first year. In the soils amended with cow and pig manure, the manure s relatively high content of Zn may also have contributed to this effect. Increased DTPA-Zn with higher organic matter content was also reported by MacLean (1976). Saviozzi et al. (1997) found that the addition of pig slurry significantly increased the total amount of Zn in the soil, and also resulted in a redistribution of Zn from the residual fraction to the EDTAsoluble inorganic precipitates and the 0.5 M NaOH-soluble organically bound fraction. Yield reduction as a result of organic matter amendment was reduced during the 3 yr of experiment (Tables 5 and 6). The decomposition of organic matter may have immobilized N in the first year and hence reduced crop growth. In the following years, lower organic matter decomposition may have reduced immobilization of N. Cadmium, Cu and Zn concentrations in the plants tended to increase from the first to the third year. This could be an effect of either the increased solubility of metals (seen for the DTPA-extractable metals) in the soil or the decrease in crop yield. The effect on Ni concentrations in the plants was less consistent. Hooda and Alloway (1994) studied the changes in plant availability of Cd, Cu, Pb, Ni and Zn over 1 yr after sludge application to a sand and a sandy loam. Cadmium, Pb, and Zn contents were significantly increased over the nine harvests. The Cu concentration declined over the harvests. Both decomposition of the sludge added organic material and a reduction in ph could explain the general increase in plant metal concentration. Reduction in Cu Table 4. Concentrations of DTPA-extractable Cd, Cu, Ni and Zn in the soil at increasing rates of organic matter applied (1995 and 1996) Oganic matter (%) Cd Cd Cu Cu Ni Ni Zn Zn µg g 1 dry weight 0 1.4a 1.3a 8.4b 7.3ab 18.3a 17.8a 13.5c 14.5b 2 1.3a 1.2b 8.0c 6.9c 16.8b 16.6b 14.0bc 15.3ab 4 1.3a 1.3ab 8.0c 6.9bc 16.3bc 16.0c 14.9b 15.6ab 8 1.3a 1.2ab 8.7a 7.5a 15.6c 15.1d 16.3a 17.2a LSD a 1.3a 8.4ab 7.3a 18.3a 17.8a 13.5d 14.5d 2 1.4ab 1.2b 8.1b 6.8c 17.4b 16.0b 16.9c 16.6c 4 1.3ab 1.1c 8.3ab 6.9c 16.3c 15.3c 20.2b 19.9b 8 1.2b 1.1c 8.7a 7.1b 15.4d 14.3d 26.9a 27.8a LSD a 1.3ab 8.4d 7.3d 18.3c 17.8c 13.5d 14.5c 2 1.4a 1.2b 9.3c 7.7c 19.4b 18.5bc 15.0c 15.8bc 4 1.5a 1.3ab 10.2b 8.3b 20.2a 19.1ab 16.2b 17.1b 8 1.5a 1.4a 11.4a 9.8a 20.2a 19.4a 17.2a 19.9a LSD a d Means followed by the same letter in the same columns (for each amendment) are not significantly different at P < 0.05.

6 536 CANADIAN JOURNAL OF SOIL SCIENCE Table 5. Effects of rates and sources of organic matter on the concentrations of Cd, Cu, Ni and Zn in barley (1995 experiment) Rate of org. Yield matter (%) (g pot 1 ) Cd Cu Ni Zn Grain Straw Grain Straw Grain Straw Grain Straw Grain Straw -µg g a 33a 0.207a 0.230a 2.78b 1.56a 1.01a 0.51a 29.3b 8.0b 2 31a 34a 0.177a 0.197a 3.00b 1.21a 0.76ab 0.34a 26.7b 7.9b 4 28a 31ab 0.197a 0.193a 3.41b 1.37a 0.71ab 0.44a 26.7b 8.1b 8 17b 29b 0.150a 0.180a 4.21a 1.87a 0.56b 0.33a 34.4a 10.8a LSD ab 33a 0.207a 0.230b 2.78b 1.56a 1.01ab 0.51a 29.3b 8.1b 2 33a 33a 0.207a 0.210b 3.14b 1.31a 1.17a 0.40a 30.4ab 9.8ab 4 28b 31a 0.137b 0.190b 3.25b 1.13a 0.68b 0.35a 27.4b 9.2b 8 30ab 33a 0.200a 0.290a 4.28a 0.98a 0.89ab 0.44a 33.6a 11.6a LSD a 33ab 0.207a 0.230a 2.78c 1.56a 1.01c 0.51a 29.3b 8.1c 2 29a 34a 0.167bc 0.253a 2.63c 1.09a 1.02c 0.60a 34.3a 8.9bc 4 31a 32b 0.183ab 0.243a 3.12b 1.13a 1.49b 0.72a 30.8b 9.8ab 8 32a 35a 0.140c 0.213a 3.41a 1.26a 1.85a 0.52a 33.0a 10.3a LSD a d Means followed by the same letter in the same columns (for each amendment) are not significantly different at P < Table 6. Effects of rates and sources of organic matter on the concentrations of Cd, Cu, Ni and Zn in wheat (1996 experiment) Rate of org. Yield matter (%) (g pot 1 ) Cd Cu Ni Zn Grain Straw Grain Straw Grain Straw Grain Straw Grain Straw -µg g a 29a 0.283a 0.360a 3.05ab 2.16a 1.46a 0.38a 36.7b 15.6b 2 36a 30a 0.293a 0.267b 3.65a 1.99a 1.16b 0.38a 38.3ab 18.4ab 4 35a 29a 0.290a 0.320ab 3.74a 2.31a 0.89b 0.40a 37.1ab 18.8a 8 35a 28a 0.283a 0.353a 2.08b 2.34a 0.50c 0.33a 39.0a 21.3a LSD ab 29b 0.283a 0.360bc 3.05b 2.16b 1.46a 0.38a 35.7b 15.6c 2 37a 30ab 0.260ab 0.293c 3.77ab 2.52ab 1.06b 0.36a 38.8ab 18.8bc 4 32b 28b 0.277a 0.477a 4.08a 2.34ab 0.83c 0.28b 43.7a 21.6b 8 37a 32a 0.237b 0.427ab 4.40a 2.72a 0.81c 0.32ab 42.2ab 25.8a LSD b 29b 0.283a 0.360a 3.05ab 2.16ab 1.46b 0.38b 37.1d 15.6c 2 38a 31a 0.243b 0.290a 1.42b 1.8b 0.86c 0.48ab 40.5c 20.1b 4 35b 29b 0.190c 0.350a 3.64a 1.94b 1.68ab 0.45ab 42.2b 21.1b 8 36b 30ab 0.123d 0.267a 3.82a 2.54a 2.15a 0.55a 45.1a 25.4a LSD a d Means followed by the same letter in the same columns (for each amendment) are not significantly different at P < uptake was probably due to a stronger adsorption of Cu to organic ligands or mineral surfaces. Cadmium concentration in grain decreased with increasing rates of peat soil addition, but no consistent effects of cow manure or pig manure addition on Cd concentration were observed (Table 5 and 6). The decrease in the uptake of Cd with peat soil addition was in accord with the results reported by He and Singh (1993a). They found that the Cd concentration in ryegrass decreased with increasing amounts of sphagnum peat added to a sand, a sandy loam and a clay loam.

7 ARNESEN AND SINGH PLANT UPTAKE AND EXTRACTABILITY OF METALS 537 Fig. 2. Correlations between DTPA-extractable metals in the soil and concentrations of the metals in plants.

8 538 CANADIAN JOURNAL OF SOIL SCIENCE Increased Cu concentration with increasing rates of all three organic materials was observed in the second year of cropping. In the third year, only pig manure showed a consistent effect. The increase in the Cu uptake by plants despite a non-consistent effect on the extractability of this metal in the soil suggests that a change in the speciation of Cu in the soil solution may have enhanced its plant availability. Nickel concentration in grain decreased with increased rates of cow manure in the second year and with that of cow and pig manure in the third year. Nickel concentration increased significantly in grain with peat soil addition in the second year and the same was also observed in the first year (Narwal and Singh 1997). The Zn concentration in grain and straw increased with increasing amounts of cow manure application. The Zn concentration in straw also increased in the third year in the soil treated with pig manure. Peat application generally increased the concentration of Zn in grain and straw in the second and third years, as was also observed in the first year with the application of pig manure and peat soil (Narwal and Singh 1997). Pierzynski and Schwab (1993) evaluated the influence of various amendments on the availability of Zn, Cd, and Pb to soybean grown in a metal-contaminated alluvial soil. Generally, the addition of limestone was more effective than treatment with cattle manure or poultry litter in reducing labile Zn fractions in the soil, increasing yield of soybean and reducing tissue Zn concentration. The addition of cattle manure produced similar effects, although the relative differences were not as great as for limestone. Treatment with cattle manure or poultry litter did not have any pronounced effect on Cd or Pb in soybean. The combination of both limestone and cattle manure did not produce additional reductions in metal bioavailability as compared with limestone alone. In general, the effects of increasing limestone rate were diminished as the manure rate increased. Correlation analysis indicated a positive and significant relationship between Ni and Zn in the plant material and their amounts extracted by DTPA from the soil (Fig. 2). For Cu and Cd, such relationships were not found to be significant. These results show that the different organic matter sources have about the same effect on DTPA-extractable Zn and Ni as on the concentrations of these metals in plants. For Cd and Cu, the organic matter showed opposite effects on DTPA-extractability and plant uptake. Organic matter addition may change the speciation of the metals in the soil solution (Mullins and Sommers 1986), which may be reflected differentially in the extraction procedure and plant uptake. This may explain the contradictory effect on extractability compared with plant concentrations. In a field study of plant availability of Cd, Cu, Zn, Ni and Mn in alum shale soil, Mellum et al. (1997) found that Zn was the only metal that showed a significant correlation between DTPA-extractable metal in the soil and the concentration in the plants. Correlations between plant concentrations and concentrations of metals in the soil extracted with 1 M NH 4 NO 3 were found to be significant, indicating that a weaker extraction gave better assessment of plant available metals in soils with variable properties. In a greenhouse study, Singh et al. (1995) found that Cd concentrations in wheat grain was positively correlated to DTPA-extractable Cd in the alum shale soils. CONCLUSIONS The effect of organic matter application on the solubility of heavy metals in the soil and plant uptake depended on the source of organic matter, the metals studied and the time after its application. The residual effect of the added organic matter on the extractability and plant availability differed from that of the freshly applied organic matter in the first year. Metals bound by the organic matter in the first year were probably released as the organic matter decomposed in the following years. Decreases in DTPA-extractable Cd and Ni were found by the addition of cow and pig manure, whereas these manures resulted in increased DTPAextractable Zn. The application of peat soil, on the other hand, resulted in increased amounts of DTPA-extractable Cu, Zn and Ni, probably due to decreased ph. In this soil, organic matter addition did not seem to reduce the concentrations of heavy metals in the crops as observed earlier in other type of soils. For some metals (Cu and Zn), the applied organic matter may even have resulted in an increase in their plant availability. ACKNOWLEDGEMENT The financial support for this research work by the Research Council of Norway (Project No /100) is gratefully acknowledged. The authors thank Ram Pal Narwal for initiating and Kurt Roger Johansen for looking after the experiment. Bingham, F. T., Sposito, G. and Strong, J. E The effect of chloride on the availability of cadmium. J. Environ. Qual. 13: Bingham, F. T., Sposito, G. and Strong, J. E The effect of sulfate on the availability of cadmium. Soil Sci. 141: Bloom, P. R Metal-organic matter interactions in soil. 1: Chemistry in the soil environment. ASA Spec. Publ. No.40 Madison, WI. pp Del Castillho, P., Chardon, W. J. and Salomons, W Influence of cattle-manure slurry application on the solubility of cadmium, copper, and zinc in a manured acidic, loamy sand soil. J. Environ. Qual. 22: Elliot, H. A. and Denneny, C. M Soil adsorption of cadmium from solutions containing organic ligands. J. Environ. Qual. 11: Eriksson, J. E The effect of clay, organic matter and time on adsorption and plant uptake of cadmium added to the soils. Water Air Soil Pollut. 40: Esser, K. B Reference concentrations of heavy metals in mineral soils, oat, and orchard grass (Dactylis glomerata) from three agricultural regions of Norway. Water Air Soil Pollut. 89: Haghiri, F Plant uptake of cadmium as influenced by cation exchange capacity, organic matter, zinc and soil temperature. J. Environ. Qual. 3: Harter, R. D. and Naidu, R Role of metal-organic complexation in metal sorption by soils. Adv. Agron. 55: He, Q. B. and Singh, B. R. 1993a. Effect of organic matter on the distribution, extractability and uptake of cadmium in soils. J. Soil

9 ARNESEN AND SINGH PLANT UPTAKE AND EXTRACTABILITY OF METALS 539 Sci. 44: He, Q. B and Singh, B. R. 1993b. Plant availability of cadmium in soils. II. Factors related to the extractability and plant uptake of cadmium in cultivated soils. Acta Agric. Scand. 43: Hooda, P. S. and Alloway, B. J The plant availability and DTPA extractability of trace metals in sludge-amended soils. Sci. Tot. Environ. 149: Japenga, J., Dalenberg, J. W., Wiersma, D., Scheltens, S. D., Hesterberg, D. and Salomons, W Effect of liquid animal manure applications on the solubilization of heavy metals form soil. Intern. J. Environ. Anal. Chem. 46: Jeng, A. S Weathering of some Norwegian alum shales. II. Laboratory simulations to study the influence of ageing, acidification and liming on heavy metal release. Acta Agric. Scand., Sect. B. Soil Plant Sci. 42: Jeng, A. S. and Bergseth, H Chemical and mineralogical properties of Norwegian alum shale soils with special emphasis on heavy metal content and availability. Acta Agric. Scand., Sect. B. Plant Soil Sci. 42: Krogstad, T Effect of liming and decomposition on chemical composition, ion exchange and heavy metal ion selectivity in sphagnum peat. [In Norwegian.] Scientific reports of the Agricultural University of Norway, Aas, Norway. 79 pp. Lindsay, W. L. and Norvell, W. A Development of a DTPA soil test for zinc, iron, manganese and copper. Soil Sci. Soc. Am. J. 42: Lo, K. S. L., Yang, W. F. and Lin, Y. C Effects of organic matter on the specific adsorption of heavy metals by soil. Tox. Environ. Chem. 34: MacLean, A. J Cadmium in different plant species and its availability in soils as influenced by organic matter and additions of lime, P, Cd and Zn. Can. J. Soil. Sci. 56: McBride, M. B., Tyler, L. D. and Hovde, D. A Cadmium adsorption by soils and uptake by plants as affected by soil chemical properties. Soil Sci. Soc. Am. J. 45: McGrath, S. P., Sanders, J. R. and Shalaby, M. H The effects of soil organic matter levels on soil solution concentrations and extractabilities of manganese, zinc and copper. Geoderma 42: Mellum, H. K., Arnesen, A. K. M. and Singh, B. R Extractability and plant uptake of heavy metals in alum shale soils. Commun. Soil Sci. Plant Anal. 29: Mullins, G. L. and Sommers, L. E Characterization of cadmium and zinc in four soils treated with sewage sludge. J. Environ. Qual. 15: Narwal, R. P. and Singh, B. R Effect of organic materials on partitioning, extractability and plant uptake of metals in an alum shale soil. Water Air, Soil Pollut. 103: Pierzynski, G. M. and Schwab, A. P Bioavailability of zinc, cadmium, and lead in a metal-contaminated alluvial soil. J. Environ. Qual. 22: Ram, N. and Verloo, M Effect of various organic materials on the mobility of heavy metals in soil. Environ. Pollut. 10: Sadovnikova, L., Otabbong, E., Iakimenko, O., Nilsson, I., Persson, J. and Orlov, D Dynamic transformation of sewage sludge and farmyard manure components. 2. Copper, lead and cadmium forms in incubated soils. Agric. Ecosyst. Environ. 58: Saviozzi, A., Levi-Minzi, R., Riffaldi, R. and Vanni, G Laboratory studies on the application of wheat straw and pig slurry to soil and the resulting environmental implications. Agric. Ecosyst. Environ. 6: Singh, B. R., Narwal, R. P., Jeng, A. S. and Almås, Å Crop uptake and extractability of cadmium in soils naturally high in metals at different ph levels. Commun. Soil Sci. Plant Anal. 26: Singh, B. R., Narwal, R. P. and Almås, Å Residual effects of organic matter on cadmium uptake by plants and its distribution in soils. Third International Conf. on Geochemistry of Trace Elements. Paris, May Contaminated soils CD-ROM D:/DATA/COMMUNIC/019 PDF. Yuan, G. and Lavkulich, L. M Sorption behaviour of copper, zinc, and cadmium in response to simulated changes in soil properties. Commun. Soil Sci. Plant Anal. 28: