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Zinc levels in vineyard soils from the Alt Penedès-Anoia region (NE Spain) after compost application
Advances in Environmental Research 8 (2004) 687–696
` Zinc levels in vineyard soils from the Alt Penedes-Anoia region (NE Spain) after compost application ´ M.C. Ramos*, M. Lopez-Acevedo ` ` Universitat de Lleida, Alcalde Rovira Roure 177, Lleida 25198, Spain Departament de Medi Ambient i Ciencies del Sol, Accepted 4 April 2003
Abstract The mechanization of fields that is taking place in some Mediterranean areas is generating soils with poor structure and lack of nutrients. The application of organic wastes for improving soil properties is becoming a frequent practice, but with the risk of producing a negative impact, because of the presence of metals. This application is carried out without any additional checks using the same rates in disturbed and in non-disturbed soils. In the present study, the influence of composted cattle manure application in vineyard soils from the NE of Spain was evaluated. The study focuses on the changes of soil total Zn content in both disturbed and undisturbed soils. The same treatments and practices were applied in both plots. The area has a Mediterranean climate and the main type of soil is Typic Calcixerept. Total levels (digestion with aqua regia) and plant available fractions (extraction with (NH4)OAc-EDTA and CaCl2-DTPA) of Zn, the main metal component of the applied organic wastes, were analysed and compared with those existing in the untreated soils. Zinc levels rose to 130 mg kgy1 , which implies increases ranging between 60 and 100% in some parts of the plots. Significant increases were observed in the treated soil samples. The available fraction represents, on average, 30% for Zn extracted with EDTA and 10.8% when it was extracted using DTPA. Significant differences were found between disturbed and undisturbed soils. The organic matter content was the soil characteristic that showed a higher influence on the Zn total levels and on the available fraction, although it was different for the two methods used. The analysis points out the importance of an analysis previous to the application of any waste at general scale. This practice, which is common in the area and repeated in each plot every 3 or 4 years implies a risk of soil pollution in a very short time period. 䊚 2003 Elsevier Ltd. All rights reserved. Keywords: Vineyards; Compost; Zinc; (NH4)OAc-EDTA, CaCl2-DTPA; Mediterranean
1. Introduction ` The dryland vineyards of the Alt Penedes-Anoia region, located in the Mediterranean area of NE Spain, have undergone important changes in production systems during the last few decades, because of mechanization. This has caused important soil movements and alterations of terrain slopes, leaving deep and poor materials on the top. The addition of different organic wastes has become common practice in the area in order *Corresponding author. Tel.: q34-973-702092; fax: q34973-702613. E-mail address: [email protected] (M.C. Ramos).
to improve soil properties. Several authors have shown the importance of organic matter to improve physical and chemical soil properties such as soil porosity, structure, organic carbon and water-holding capacity (Tisdall and Oades, 1982; Oades, 1984; Hamblin, 1991; ´ Ouedraogo et al., 2001). For this reason the application of organic wastes or compost could be beneficial for soil conservation (Pinamonti and Zorzi, 1996) especially in degraded soils and those susceptible to erosion, although the response to soil amendment is soil–sitespecific (Toogood, 1978). However, these organic wastes can also be an important source of pollution especially of heavy metals, which are potentially toxic to humans and the environment. Cu and Zn are the
1093-0191/04/$ - see front matter 䊚 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S1093-0191(03)00041-8
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Table 1 Characteristics of the composted cattle manure applied in the study Concentration (referred to dry weight) Organic matter (%) Total-N (mg gy1) Organic N (mg gy1) N-NH4 (mg gy1) N-NO3 (mg gy1) CyN ratio P (mg kgy1) K (mg gy1) K-water soluble (mg gy1) Cu (mg kgy1) Fe (mg kgy1) Zn (mg kgy1) Mn (mg kgy1) Cd (mg kgy1) Pb (mg kgy1) EC25 (1:5) (dS my1)
82.7 22.6 17.6 3.5 1.5 18.2 1411 28.9 15.0 30 67 128 61.9 0.8 9.8 16.3
A range of chemical reagents are reported in the literature as extractants to analyse the fraction available for plants, including buffered (ammonium acetate) or unbuffered (CaCl2, Ca(NO3)2, NH4NO3,«) solutions, organic complexing agents (EDTA, DTPA), diluted acids (HCl, CH3COOH) or a mixture of these reagents (Shu and Liu, 1994; Ure et al., 1993; Pinamonti et al., 1997; Vangronsveld, 1998; Schramel et al., 2000; Brun et al., 2001; Morera et al., 2001; Sun et al., 2001). The objectives of this study were to: (1) assess the influence of composted cattle manure application on Zn ` levels in vineyard soils from the Alt Penedes-Anoia areas by determining Zn concentrations in treated and untreated soils; (2) evaluate the relationship between Zn concentrations and soil properties; and (3) compare different chemical extraction methods to evaluate Zn bioavailability. The results will then be discussed in order to evaluate changes in relation to agriculture activities and to predict environmental risks and the influence on Zn availability in contaminated soils. 2. Materials and methods
main elements found in this type of organic waste. Their contaminating effect on soils depends on environmental conditions and soil characteristics, but after repeated applications of organic wastes the applied metals could have a toxic effect. Some metals such as Cu seem to be strongly absorbed. Cu is one of the less mobile elements, which remain uniformly distributed along the soil profile (Yaron et al., 1996). However, Zn contents are higher in the surface layers, and the exchange of Znq2 with Caq2 followed by Zn precipitation is the dominant reaction in alkaline soils (Weingerl and Kerin, 2000). Zn is an essential element for vineyard growth although grape varieties and rootstocks vary widely in susceptibility to Zn deficiency. Zn deficiencies are associated with soils that have low zinc levels (-0.8 ppm). Heavy applications of animal manure have been suggested when zinc deficiencies exist, which have proven most effective when carried out before planting or when incorporated into the root zone (Washington State University-Cooperative Extension (1999)). No Zn toxicity has been known up to now for vines. However, the phytotoxic effects could also affect soil micro-organisms (Filser, 1992, cited in Schramel et al., 2000). For Cu, no problems of deficiency are known. For many years fungal disease was combated by spraying copper on vines. However, in some cases the build-up of copper has become toxic. Cu toxicity is expected with a soil pH of less than 6 and more than 100 mg kgy1, extracted in N ammonium acetate of pH 7. But in the case study, total levels are below this value.
2.1. Study site ` The study area is located in the Alt Penedes-Anoia region, approximately 30 km southwest of Barcelona (NE of Spain) between the Anoia and Llobregat rivers. Vineyards are the main land use in the area (approx. 80% of the cultivated area) and they are cultivated maintaining the soil bare during most of the year. The area has a Mediterranean climate (dry subhumid) with an annual rainfall of approximately 550 mm, mainly in spring and autumn, this latter period usually with high intensity rainfalls (Ramos and Porta, 1994), which cause important erosion problems, nutrient losses and alterations of the soil surface. The soil moisture regime is xeric and the soil temperature regime is thermic. The annual average temperature is approximately 15 8C. 2.2. Sample collection and preparation Two field plots on a commercial farm with a 10 yearold vineyard (coordinate X,Y: 400 000; 4590 000) were considered for study. On this farm important soil movements took place before plantation, leaving deeper horizons on top in some parts of the farm. The plantation consists of trained vines, with a 1.3=3.1 m pattern. The vine rows are perpendicular to the maximum slope gradient. Every eight rows there is a hillside ditch or broadbase terrace (locally named ‘rasa’). Their function is to intercept surface runoff and take it out of the plot (Porta et al., 1994). Vineyards are maintained with bare soils nearly all the year by continuous tillage of the surface, and are only partially covered during the veg-
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etation period, a maximum of approximately 50%. Application of composted cattle manure has been carried out in the fields at a rate of 40 Mg hay1, in alternated rows. The two selected plots correspond to two different situations in the field. The first plot could be considered to be representative of a disturbed position. The second plot, however, could be representative of an undisturbed position in the field. The slope of the plots was approximately 6%. Soil samples from the top 0–20 cm were collected at 4 points along the slope in each plot: points Di (disturbed soils), and points Ui (undisturbed soils). At each point two samples, one at each side of the row of the vineyard were collected: one of them without added organic wastes wDi(y) and Ui(y) pointsx and the other with added organic wastes w(Di(q), Ui(q) pointsx. Soil samplings were carried out at the end of the crop cycle in 1999 and 2000. The organic waste application was made in between those samplings, according to the farmer’s criteria. The characteristics of the composted cattle manure applied are shown in Table 1. Compost was prepared in trapezoidal piles, 3–5 m wide at the bottom, 0.6–1.2 m at the top and 1.1–1.5 m high, for 4 months. During this period the compost was turned several times and the temperature was controlled at different depths. The final maturity evaluated according to the ‘rottegrade’ method was classified as level V, ¨ according to Gutezeichen Kompost (1994). For the analysis, all the samples were divided into two groups: those taken between rows of vines with added organic wastes, and those without anything added. The results obtained in treated vs. untreated soils in disturbed and undisturbed positions were compared. Rainfalls during the studied years were 490 and 550 mm, respectively, which are close to the average of the annual rainfall in the area (Ramos, 2001). However, during the two years, and especially during the last one, important erosive rainfall was recorded, which caused high soil losses in the upper part of the plots and ´ sedimentation at the bottom (Martınez-Casasnovas et al., 2002). This could have affected the results making their comparative analysis difficult. Soil samples were air dried and sieved through a stainless-steel sieve with a mesh of 2 cm in diameter to eliminate root residues and large elements. Then samples were crushed at 2 mm.
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texture, pH and Electric Conductivity (EC) were measured using the methods described in Porta et al. (1986). 2.4. Extraction procedures Two simple extraction methods, in parallel to the determination of total metal were performed in order to evaluate the plant availability of metal. (NH4)OAc – EDTA and CaCl2 –DTPA were used in the extractions, according to the methods described by Pauwels et al. (1992). All chemicals used for the preparation of extraction solutions were of analytical-reagent grade of high quality. The solutions were prepared by dissolving the compound using deionised water from Milli-Q water purification systems and adjusting the suitable pH with the acids. All measurements of the element were obtained by AA (Perkin–Elmer 5000). Two replications of each analysis were done. The average value is shown in the results. 2.4.1. Aqua regia digestion — total metal concentration Aliquots of the dry soil samples (1 g) were accurately weighed into 100 ml round bottom flasks and a few millilitres of water were added. Nitric acid (2.5 ml) and hydrochloric acid (7.5 ml) were added slowly. The flasks were shaken carefully to obtain a homogeneous mixture and stored over night at room temperature and refluxed for 2.5 h. After reaching room temperature, the condenser was rinsed with water. The solution was filtered and transferred to a 100-ml volumetric flask. The residue in the filter was washed with 0.2 N nitric to give a volume close to 100 ml and the volumetric flasks were then filled up to the 100 ml mark with water. Two extractions were carried out for each sample. 2.4.2. Single extractions: plant available metals 2.4.2.1. Extraction with (NH4)OAc-EDTA. Aliquots of 20 g of the dry soil samples were weighed into 100 ml acid-cleaned polystyrene vessels. 100 ml of extraction solution (0.5 M (NH4)OAc- 0.02 M EDTA, pH 7) were added and the vessels were shaken at room temperature on a horizontal shaker for 30 min. After extraction, the sample solution was centrifuged at 1000 rpm for 15 min (Beckman Coulter) and then filtered. The supernatant solution was used for analysis.
2.3. Soil property analysis Soils are highly calcareous. According to Soil Taxonomy (Soil Survey Staff, 1998) the soils of the experimental plots are classified as Typic Calcixerept, ´ (Martınez-Casasnovas, 1998). Some specific soil properties such as organic matter (o.m.), calcium carbonate,
2.4.2.2. Extraction with CaCl2 -DTPA. Aliquots of 10 g of the dry soil samples were weighed into 100 ml acid cleaned polystyrene vessels. 20 ml of extraction solution (0.01 M CaCl2-0.005 M DTPA-0.1 M trietanolamina) were added and the vessels were shaken at room temperature on a horizontal shaker for 30 min. After
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extraction, the sample solution was centrifuged at 1000 rpm for 15 min (Beckman Coulter) and then filtered. The supernatant solution was used for analysis. 2.5. Statistical analysis A comparative means analysis was done in order to evaluate differences between treated and untreated soils and between disturbed and undisturbed positions. Linear relations between soil properties and the total and extractable amounts were calculated. 3. Results and discussion The results shown in this study have been obtained at field scale, in the plots managed by farmers according ` to the common practices in the Alt Penedes-Anoia area (NE Spain). The results of the study are based on only one application of composted cattle manure. In both situations, disturbed and undisturbed positions, the characteristics of treated and untreated soils are compared. 3.1. Soil characteristics The analysis of the soil properties of the samples showed that all soil samples had relatively high silt and sand contents (42–49%), but low clay contents, approximately 9% in plot 1 and between 6–14% in plot 2. The pH ranged between 7.8 and 8.9. The electric conductivity (extract 1:5) showed values between 0.23 and 0.39 dSmy1 for samples without added compost and up to 0.80 dSmy1 in samples with added compost (Table 2). Significant differences were found between treated and untreated soils in the disturbed position (*P)0.05). In the undisturbed position the increase was not significant on average, but the values obtained in the upper part of the plots were higher than the critical value at which vines are affected (Carter, 1981). The vine is a crop sensitive to electric conductivity (Carter, 1981) and although the effect is not regular in all the plot, the repeated application of this compost, with high EC1:5 (16 dSmy1), will increase soil EC and could produce a decrease in the yield. Organic matter (o.m.) was generally low. In the disturbed soils (points Di), the o.m. content ranged between 1.6 and 10 g kgy1 in samples without added compost and increased up to 26.5 g kgy1 after the compost application. In the undisturbed soils 2 (points Ui) o.m. values ranged between 13.2 and 16 g kgy1, and fewer changes were produced after the compost application than in the disturbed soils. Significant differences were found in the o.m. between disturbed and undisturbed soils without compost, and between treated and untreated soils in disturbed positions (*P-0 005). The average values are shown in Table 2.
Table 2 Characteristics of the soil samples at each point: EC(q), electric conductivity of treated soils with composted cattle manure; EC (y): electric conductivity of untreated soils; o.m. (q): organic matter at each point of the soils treated with composted cattle manure; o.m. (y): organic matter at each point in untreated soils Soil sample
EC(q) dSmy1
EC(y) dSmy1
o.m.(q) (g kgy1)
o.m.(y) (g kgy1)
U1 U2 U3 U4 D1 D2 D3 D4
0.80"0.07 0.37"0.04 0.36"0.03 0.31"0.05 0.30"0.04* 0.43"0.04* 0.42"0.06* 0.39"0.04*
0.39"0.05 0.28"0.07 0.32"0.06 0.28"0.08 0.27"0.06* 0.23"0.04* 0.24"0.04* 0.24"0.05*
22.7"0.5 14.0"0.3 16.1"0.4 16.2"0.5 26.7"0.3* 12.4"0.4* 11.7"0.3* 13.8"0.4*
12.1"0.4 9.8"0.3 14.5"0.4 13.3"0.4 5.4"0.3* 2.0"0.2* 4.8"0.3* 4.9"0.2*
Ui: soil samples taken in undisturbed soils; Di: soil samples taken in disturbed soils. * (P-0.05) Significant differences between treated and untreated soils.
3.2. Soil metal content: total content Although in a preliminary analysis the effect of waste application on different element contents in the soils was evaluated, only the levels of Zn were included in this study. Cu levels did not change significantly and other elements were at very low concentrations. The Zn level in the compost used was lower than that permitted in compost for agricultural purposes (Briton, 2000). However, this practice is repeated every threeyfour years; for this reason it is necessary to evaluate the potential risk of future pollution. Fig. 1 shows the changes in the total content of Zn at each point. Zinc levels in the untreated soils ranged from 40 to 65 mg kgy1. These levels are similar to those found in the deeper layers (30–50 cm, 50–70 cm) of the undisturbed soils, which is logical taking into account that in these disturbed soil plots the deep soil layers are now on the top. There were no significant differences between disturbed and undisturbed soils without compost and they are lower than those recorded in vineyard soils in non-industrially polluted areas (Angelova et al., 1999). In the treated soils, the levels increased on average up to 120 mg kgy1, which implies Zn levels between 60 and 100% higher than the original levels (*P-0.05), however, no significant differences were found between disturbed and undisturbed soils. The Zn levels in the soil surpass the minimum levels required for a normal development of the crop. Clark et al. (1996) estimate a Zn removal due to the harvesting of 0.04 kgyha fruit for productions of 20 000 kgyha of crop, which are higher than those recorded in the area
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Fig. 1. Differences in total-Zn content in treated (q) vs. untreated (y) soils in disturbed (D) and undisturbed (U) soils.
(-15 000 kgyha). Thus, Zn inputs in the soils are much higher than outputs. Weingerl and Kerin (2000) indicate that Zn mobility is closely connected to soil reaction increasing the available fraction for plants with acidity of soil. In addition, Zn is hard to wash away and it is accumulated on the surface. 3.3. Soil metal content: plant available metals Figs. 2 and 3 show the ratio of the fraction extracted with (NH4)OAc-EDTA and CaCl2-DTPA, respectively. The results are expressed in percentages. The ratios obtained with both methods were different. Those obtained with EDTA were between 3 and 6 times higher
than those obtained with DTPA. The ratios obtained with EDTA ranged from 3 to 30% with an average value of 10.8%, while for DTPA they ranged from 2 to 7.2% with an average value of 2.9%. Although both methods are widely proposed in the literature to evaluate the available fraction of metals for plants, they did not give the same results. The use of these mixtures of (NH4)OAc ammonium acetate and CaCl2 with organic complexing agents (EDTA, DTPA) could allow evaluating the bio-available metal for plant uptake, including mobile and mobilized fractions. Different authors have pointed out that the fraction extracted using EDTA or DTPA represents the mobilized fraction while the fraction extracted using Ca-salts or NHq 4 -salts represents
Fig. 2. Differences in the available fraction for plants (extraction with NH4 OAc-EDTA) in treated (q) vs. untreated (y) soils in disturbed (D) and undisturbed (U) soils.
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Fig. 3. Differences in the available fraction for plants (extraction with CaCl2 -EDTA) in treated (q) vs. untreated (y) soils in disturbed (D) and undisturbed (U) soils.
the mobile fraction in the soil. Nevertheless, in some cases both are denoted as the ‘bio-available’ fraction for plant uptake (Wong, 1996; Devkota, 2001) and there is not a general rule for all crops. Devkota (2001), who distinguished between mobilized and mobile fractions, used Ca(NO3)2 and (NH4)NO3 to evaluate the mobile fraction and he pointed out that the use of Ca-salts gave lower values than NHq 4 -salts. Similar results were found by Homburg et al. (1995), cited by Devkota (2001). Brun et al. (2001) showed that in contaminated soils extraction with organic complexing agents (EDTA, DTPA) and extraction with ammonium acetate seem to be better adapted for estimating Cu bio-availability. On the basis that EDTA and DTPA have similar complexing effects, the result obtained with the two extractants used in the study could be interpreted, because of differences in the salt used to release the mobile fraction.
The available fraction obtained with (NH4)OAcEDTA showed significant differences between treated and untreated soils in the undisturbed positions, where the highest ratios were observed, but no significant differences were observed between disturbed and undisturbed soils (Fig. 2). With CaCl2-DTPA there were no significant differences between disturbed and undisturbed positions or between treated and untreated soils. In both extractions, the available fraction increased in treated vs. untreated soils. Both fractions correlated significantly with total Zn content, Cl2 -Ca fraction at 95% and (NH4)OAc-EDTA at 99%, with correlation coefficients of 0.58 and 0.69, respectively (Fig. 4). The result is difficult to compare with others cited in the literature because of the different extractants used. Devkota (2001) indicated that the mobile fraction extracted with Ca-salts did not increase when the total
Fig. 4. Relationship between the Zn available fraction extracted with NH4OAc-EDTA and with CaCl2-EDTA and the total-Zn content.
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Fig. 5. Relationship between total-Zn and Zn available fractions (extracted with NH4 OAc-EDTA and CaCl2 -DTPA) and the organic matter content.
Zn content increased, but the mobilizable fraction extracted with EDTA and the mobilized fraction extracted using NH4-salts increased. However, Andreu and ´ (1996) observed positive correlations Gimeno-Garcıa between the fraction extracted with EDTA and the total metal. Farmers in the study area adopted the practice of applying organic wastes after they had witnessed the experience of other farmers, but without any technical advice and further control. The results showed that the increase of Zn in the soil also increased the available fraction for plants. But taking into account the low percentage of extraction, most of the Zn applied with the organic wastes will remain in the soils increasing
the total levels which could become toxic, not only for the plants, but for the soil micro-organisms. Alternative organic wastes such as crop residues or mixtures of them with manure should be tested in order to improve organic matter levels in soil, but to reduce metal content and to avoid an excessive increase of electric conductivity. 3.4. Zn in soils vs. soil properties The observed Zn concentration in soils and the fraction available for plants obtained using the two methods were related to some soil properties. Soil variables which are supposed to affect bioavailability,
Fig. 6. Relationship between total-Zn and Zn available fractions (extracted with NH4 OAc-EDTA and CaCl2 -DTPA) and the organic matter content for disturbed soils.
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Fig. 7. Relationship between total Zn and Zn available fractions (extracted with NH4 OAc-EDTA and CaCl2 -DTPA) and the organic matter content for undisturbed (U) soils.
i.e. clay content and organic matter were taken into consideration. pH and calcium carbonate content could also affect bioavailability, but because all the samples had a similar pH and similar calcium carbonate contents their influence was not considered in the analysis. There was a significant correlation between organic matter content and the total Zn content (rs0.58, **P0.01), while for the available fraction only the DTPAZn levels were significantly correlated with organic matter (rs0.55, *P-0.05) (Fig. 5). The results were different between disturbed and undisturbed soils. In the undisturbed soils, where the original o.m contents were higher (o.m ranging from 10 to 16 g kgy1), the correlation between total Zn and o.m was significant at 95% level (rs0.57, *P-0.05) (Fig. 6). However, in the disturbed soils (o.m. approx. 5 g kgy1), the correlation coefficient was not significant. Nevertheless, the highest differences were found in the relationship between EDTA-Zn and DTPA-Zn and the o.m content in the two plots. Only in the disturbed soils there were significant correlations between the available fractions and the organic matter: for EDTA-Zn, rs0.60, *P-0.05 and for DTPA-Zn, rs0.69, ***P-0.001 (Fig. 7). No correlation was found for undisturbed soils. The results could be in agreement with that obtained by Pinamonti et al. (2000), who found that in vineyards the available fraction for the plant was positively correlated with the DTPA-extractable form of the metals in the soil, but not correlated with the total or the EDTAextractable forms. Nevertheless, it would be necessary to carry out further research on mobility of soluble fractions of metals in relation to the o.m. content. No significant correlation was found between total Zn concentration and clay content. However, the avail-
able fractions obtained with both methods show a slight trend to decrease when clay content increases. 4. Conclusions Management practices following field mechanisation, carried out in the studied Mediterranean vineyards, appears to have important effects on land degradation, increasing the risk of soil contamination. The addition of composted cattle manure increased the organic matter content significantly in treated soils, but it was associated with an increase in the electric conductivity values up to limits that could affect the vine yield. In addition, the use of this compost in the studied vineyards increased the total Zn level significantly. Although after one compost application, the Zn level is still below the maximum permitted in agricultural soils, it increased to double its original value at some points. The characteristics of the soils in each plot affected the final levels of metals accumulated in it. The Zn extracted using different reagents differs very much, being much higher when extracted with (NH4)OAc-EDTA than with CaCl2-DTPA. The available fraction had a fairly high correlation with the total increase in Zn content in treated as opposed to untreated soils. However, only the CaCl2-DTPA fraction significantly correlated with the organic matter content for all the samples. When disturbed soils were considered separately, both extractions were significantly correlated. The low available fraction indicated that most of the applied metal with the compost will remain in the soil contributing to contaminating the soil. Taking into account that this application of organic waste is a ` common practice in the vineyards in the Penedes-Anoia
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areas, and according to this preliminary result obtained after only one application, there is a potential risk of soil pollution if this practice is done without any control. Although not all composts will have the same composition, if two applications like those took place, Zn content will be 50% higher in all the vineyard. In addition, taking into account the erosion processes that take place in this area, the metal accumulated in the soil could be transported by runoff, which will give rise to a non-point pollution source for waters in the catchment area. Acknowledgments This work as part of the AMB98-0481 project, 19982001, was developed with funding from the Comision Interministerial de Ciencia y Tecnologia, (CICYT), Progama Nacional de Medio Ambiente. Financial support was also available from the CIRIT(GRC-4011L) and UdL (with the contract of technical support). References ´ E., 1996. Total content and Andreu, V., Gimeno-Garcıa, extractable fraction of cadmium, coblat, copper, nickel, lead and zinc in calcareous orchard soils. Commun Soil Sci. Plant Anal. 27, 2633–2648. Angelova, V.R., Ivanov, A.S., Braikov, D.M., 1999. Heavy metals (Pb, Cu, Zn and Cd) in the system soil-grapevinegrape. J. Sci. Food Agric. 79, 713–721. Briton, W.F., 2000. Compost Quality. Standards and Guidelines. Woods End Research Laboratoy Inc, New York. Brun, L.A., Maillet, J., Hinsiguer, P., Pepin, M., 2001. Evaluation of copper availability to plants in copper-contaminated vineyard soils. Environ. Pollut. 111, 293–302. Carter, D.L., 1981. Salinity and plant productivity. Handbook Series in Nutrition and Food. Chemical Rubber Co. Clark, C.J., Smith, G.S., Cornforth, I.S., Prasad, M., 1996. Fertilizer recommendations for horticultural crops. Hortnet䉸 The Horticultural and Food Research Institute of New Zealand Ltd. RAL, G.K., 1994. Methods for the Analysis of Compost. Federal Compost Quality Assurance Organization ¨ (FCQAO). Budesgutegemeinschaft Kompost e.V, Cologne, Germany. Hamblin, A., 1991. Sustainable agricultural systems: what are the appropriate measures for soil structure? Aust. J. Soil Res. 29, 709–715. ´ Martınez-Casasnovas, J.A., Ramos, M.C., Ribes-Dasi, M., 2002. Soil erosion caused by extreme rainfall events: mapping and quantification in agricultural plots from very detailed digital elevation models. Geoderma 105, 125–140. ´ ´ EroMartınez-Casasnovas, J.A., 1998. Suelo- Paisaje-Erosion. ´ por carcavas ´ ` sion y barrancos en el Alt Penedes-Anoia. ˜ ´ de (Cataluna). Un enfoque de estudio mediante tecnologıas ´ espacial, Bases de datos, Sistemas de inforla informacion
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´ geografica ´ ´ Ph.D Thesis. Universitat macion y Teledeteccion. de Lleida. Morera, M.T., Echeverria, J.C., Mazkiaran, C., Garrido, J.J., 2001. Isotherms and sequential extraction procedures for evaluation sorption and distribution of heavy metals in soils. Environ. Pollut. 113, 135–144. Oades, J.M., 1984. Soil organic matter and structural stability: mechanisms and implications for management. Plant Soil 76, 319–337. ´ ´ N.P., 2001. Use of Ouedraogo, E., Mando, A.M., Zombre, compost to improve soil properties and crop productivity under low input agricultural system in West Africa. Agric. Ecosystems Environ. 84, 259–266. Pauwels, J.M., Van Ranst, E., Verloo, M., Mvondo, Z.A., ´ 1992. Manuel de laboratoire de pedologie. Methodes d’analysis de sols et de plantes, equipment, gestion de stoks de vereerie et de produits chimiques, Vol. 28. Publications agricoles, pp. 265. Pinamonti, F., Zorzi, G., 1996. Experiences of compost use in agriculture and in land reclamation projects. In: De Bertoldi, M., et al. (Eds.), The Science Composting: Part 1. Blackie, Glasgow, UK, pp. 517–527. Pinamonti, F., Stringaria, G., Gasperia, F., Zorzia, G., 1997. The use of compost: its effects on heavy metal levels in soil and plants. Resour. Conserv. Recycling 21, 129–143. ´ ´ Porta, J., Lopez-Acevedo, M., Rodriguez, R., 1986. Tecnicas y experimentos en edafologia. Colegio Oficial de Ingenieros ´ ˜ Barcelona. 283 pp. Agronomos de Cataluna. Porta, J., Ramos, J.C., Boixadera, J., 1994. Mechanical measures for runoff management and erosion control in the vineyards of North East Spain. In: Rickson, R.J. (Ed.), Conserving Soil Resources: European Perspective. CAB International, Wallingford, pp. 369–378. Ramos, M.C., Porta, J., 1994. Rainfall intensity and erosive potenciality in the NE Spain Mediterranean area: first results on sustainability of vineyards. Il Nuovo Cimento 17, 291–299. Ramos, M.C., 2001. Divisive and hierarchical clustering techniques to analyse variability of rainfall distribution patterns in a Mediterranean region. Atmos. Res. 57, 123–138. Schramel, O., Michalke, B., Kettrup, A., 2000. Study of copper distribution in contaminated soils of hop fields by single and sequential extraction procedures. Sci. Total Environ. 263, 11–22. Shu, G.Y., Liu, J.C., 1994. Content and fractionation of heavy metals in soils of two contaminated sites in Taiwan. Environ Prog. 13, 89–93. Soil Survey Staff, 1998. Keys to Soil Taxonomy, 6th edition. US Department of Agriculture, Soil Conservation Service, Washington, D.C. Sun, B., Zhao, F.J., Lombi, E., McGrath, S.P., 2001. Leaching of heavy metals from contaminated soil using EDTA. Environ. Pollut. 113, 113–120. Tisdall, J.M., Oades, J.M., 1982. Organic matter and water stable aggregates in soils. J. Soil Sci. 33, 141–163. Toogood, J.A., 1978. Relation of aggregate stability to properties of Alberta soils. In: Emerson, W.W., et al. (Eds.), Modification of Soil Structure. Wiley, Chichester, UK, pp. 211–215.
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Ure, A.M., Quevauviller, P., Muntau, H., Griepink, B., 1993. Speciation of heavy metals in soils and sediments an account of the improvement and harmonization of extraction techniques undertaken the auspices of the BCR of the Commission of the European Communities. Int. J. Environ. Anal. Chem. 51, 135–151. Vangronsveld, J., 1998. Case studies in the field-Zn, Cd, Pb contaminated kitchen gardens. In: Vangronsveld, J., Cunninghan, S.D. (Eds.), Metal-Contaminated Soils. Springer, Georgetown, USA, pp. 219–226.
Weingerl, V., Kerin, D., 2000. Distribution of Zinc in vineyard areas treated with zinc containing phytopharmaceuticals. Acta Chimica Slov. 47, 453–467. WSU (Washington State University-Cooperative Extension). 1999. Pest Management Guide for Grapes in Washington. Extention Bulletin Washington. Yaron, B., Calvet, R., Prost, R., 1996. Soil Pollution-Processes and Dynamics. Springer Verlag, Heidelberg, pp. 320.
` Zinc levels in vineyard soils from the Alt Penedes-Anoia region (NE Spain) after compost application ´ M.C. Ramos*, M. Lopez-Acevedo ` ` Universitat de Lleida, Alcalde Rovira Roure 177, Lleida 25198, Spain Departament de Medi Ambient i Ciencies del Sol, Accepted 4 April 2003
Abstract The mechanization of fields that is taking place in some Mediterranean areas is generating soils with poor structure and lack of nutrients. The application of organic wastes for improving soil properties is becoming a frequent practice, but with the risk of producing a negative impact, because of the presence of metals. This application is carried out without any additional checks using the same rates in disturbed and in non-disturbed soils. In the present study, the influence of composted cattle manure application in vineyard soils from the NE of Spain was evaluated. The study focuses on the changes of soil total Zn content in both disturbed and undisturbed soils. The same treatments and practices were applied in both plots. The area has a Mediterranean climate and the main type of soil is Typic Calcixerept. Total levels (digestion with aqua regia) and plant available fractions (extraction with (NH4)OAc-EDTA and CaCl2-DTPA) of Zn, the main metal component of the applied organic wastes, were analysed and compared with those existing in the untreated soils. Zinc levels rose to 130 mg kgy1 , which implies increases ranging between 60 and 100% in some parts of the plots. Significant increases were observed in the treated soil samples. The available fraction represents, on average, 30% for Zn extracted with EDTA and 10.8% when it was extracted using DTPA. Significant differences were found between disturbed and undisturbed soils. The organic matter content was the soil characteristic that showed a higher influence on the Zn total levels and on the available fraction, although it was different for the two methods used. The analysis points out the importance of an analysis previous to the application of any waste at general scale. This practice, which is common in the area and repeated in each plot every 3 or 4 years implies a risk of soil pollution in a very short time period. 䊚 2003 Elsevier Ltd. All rights reserved. Keywords: Vineyards; Compost; Zinc; (NH4)OAc-EDTA, CaCl2-DTPA; Mediterranean
1. Introduction ` The dryland vineyards of the Alt Penedes-Anoia region, located in the Mediterranean area of NE Spain, have undergone important changes in production systems during the last few decades, because of mechanization. This has caused important soil movements and alterations of terrain slopes, leaving deep and poor materials on the top. The addition of different organic wastes has become common practice in the area in order *Corresponding author. Tel.: q34-973-702092; fax: q34973-702613. E-mail address: [email protected] (M.C. Ramos).
to improve soil properties. Several authors have shown the importance of organic matter to improve physical and chemical soil properties such as soil porosity, structure, organic carbon and water-holding capacity (Tisdall and Oades, 1982; Oades, 1984; Hamblin, 1991; ´ Ouedraogo et al., 2001). For this reason the application of organic wastes or compost could be beneficial for soil conservation (Pinamonti and Zorzi, 1996) especially in degraded soils and those susceptible to erosion, although the response to soil amendment is soil–sitespecific (Toogood, 1978). However, these organic wastes can also be an important source of pollution especially of heavy metals, which are potentially toxic to humans and the environment. Cu and Zn are the
1093-0191/04/$ - see front matter 䊚 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S1093-0191(03)00041-8
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Table 1 Characteristics of the composted cattle manure applied in the study Concentration (referred to dry weight) Organic matter (%) Total-N (mg gy1) Organic N (mg gy1) N-NH4 (mg gy1) N-NO3 (mg gy1) CyN ratio P (mg kgy1) K (mg gy1) K-water soluble (mg gy1) Cu (mg kgy1) Fe (mg kgy1) Zn (mg kgy1) Mn (mg kgy1) Cd (mg kgy1) Pb (mg kgy1) EC25 (1:5) (dS my1)
82.7 22.6 17.6 3.5 1.5 18.2 1411 28.9 15.0 30 67 128 61.9 0.8 9.8 16.3
A range of chemical reagents are reported in the literature as extractants to analyse the fraction available for plants, including buffered (ammonium acetate) or unbuffered (CaCl2, Ca(NO3)2, NH4NO3,«) solutions, organic complexing agents (EDTA, DTPA), diluted acids (HCl, CH3COOH) or a mixture of these reagents (Shu and Liu, 1994; Ure et al., 1993; Pinamonti et al., 1997; Vangronsveld, 1998; Schramel et al., 2000; Brun et al., 2001; Morera et al., 2001; Sun et al., 2001). The objectives of this study were to: (1) assess the influence of composted cattle manure application on Zn ` levels in vineyard soils from the Alt Penedes-Anoia areas by determining Zn concentrations in treated and untreated soils; (2) evaluate the relationship between Zn concentrations and soil properties; and (3) compare different chemical extraction methods to evaluate Zn bioavailability. The results will then be discussed in order to evaluate changes in relation to agriculture activities and to predict environmental risks and the influence on Zn availability in contaminated soils. 2. Materials and methods
main elements found in this type of organic waste. Their contaminating effect on soils depends on environmental conditions and soil characteristics, but after repeated applications of organic wastes the applied metals could have a toxic effect. Some metals such as Cu seem to be strongly absorbed. Cu is one of the less mobile elements, which remain uniformly distributed along the soil profile (Yaron et al., 1996). However, Zn contents are higher in the surface layers, and the exchange of Znq2 with Caq2 followed by Zn precipitation is the dominant reaction in alkaline soils (Weingerl and Kerin, 2000). Zn is an essential element for vineyard growth although grape varieties and rootstocks vary widely in susceptibility to Zn deficiency. Zn deficiencies are associated with soils that have low zinc levels (-0.8 ppm). Heavy applications of animal manure have been suggested when zinc deficiencies exist, which have proven most effective when carried out before planting or when incorporated into the root zone (Washington State University-Cooperative Extension (1999)). No Zn toxicity has been known up to now for vines. However, the phytotoxic effects could also affect soil micro-organisms (Filser, 1992, cited in Schramel et al., 2000). For Cu, no problems of deficiency are known. For many years fungal disease was combated by spraying copper on vines. However, in some cases the build-up of copper has become toxic. Cu toxicity is expected with a soil pH of less than 6 and more than 100 mg kgy1, extracted in N ammonium acetate of pH 7. But in the case study, total levels are below this value.
2.1. Study site ` The study area is located in the Alt Penedes-Anoia region, approximately 30 km southwest of Barcelona (NE of Spain) between the Anoia and Llobregat rivers. Vineyards are the main land use in the area (approx. 80% of the cultivated area) and they are cultivated maintaining the soil bare during most of the year. The area has a Mediterranean climate (dry subhumid) with an annual rainfall of approximately 550 mm, mainly in spring and autumn, this latter period usually with high intensity rainfalls (Ramos and Porta, 1994), which cause important erosion problems, nutrient losses and alterations of the soil surface. The soil moisture regime is xeric and the soil temperature regime is thermic. The annual average temperature is approximately 15 8C. 2.2. Sample collection and preparation Two field plots on a commercial farm with a 10 yearold vineyard (coordinate X,Y: 400 000; 4590 000) were considered for study. On this farm important soil movements took place before plantation, leaving deeper horizons on top in some parts of the farm. The plantation consists of trained vines, with a 1.3=3.1 m pattern. The vine rows are perpendicular to the maximum slope gradient. Every eight rows there is a hillside ditch or broadbase terrace (locally named ‘rasa’). Their function is to intercept surface runoff and take it out of the plot (Porta et al., 1994). Vineyards are maintained with bare soils nearly all the year by continuous tillage of the surface, and are only partially covered during the veg-
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etation period, a maximum of approximately 50%. Application of composted cattle manure has been carried out in the fields at a rate of 40 Mg hay1, in alternated rows. The two selected plots correspond to two different situations in the field. The first plot could be considered to be representative of a disturbed position. The second plot, however, could be representative of an undisturbed position in the field. The slope of the plots was approximately 6%. Soil samples from the top 0–20 cm were collected at 4 points along the slope in each plot: points Di (disturbed soils), and points Ui (undisturbed soils). At each point two samples, one at each side of the row of the vineyard were collected: one of them without added organic wastes wDi(y) and Ui(y) pointsx and the other with added organic wastes w(Di(q), Ui(q) pointsx. Soil samplings were carried out at the end of the crop cycle in 1999 and 2000. The organic waste application was made in between those samplings, according to the farmer’s criteria. The characteristics of the composted cattle manure applied are shown in Table 1. Compost was prepared in trapezoidal piles, 3–5 m wide at the bottom, 0.6–1.2 m at the top and 1.1–1.5 m high, for 4 months. During this period the compost was turned several times and the temperature was controlled at different depths. The final maturity evaluated according to the ‘rottegrade’ method was classified as level V, ¨ according to Gutezeichen Kompost (1994). For the analysis, all the samples were divided into two groups: those taken between rows of vines with added organic wastes, and those without anything added. The results obtained in treated vs. untreated soils in disturbed and undisturbed positions were compared. Rainfalls during the studied years were 490 and 550 mm, respectively, which are close to the average of the annual rainfall in the area (Ramos, 2001). However, during the two years, and especially during the last one, important erosive rainfall was recorded, which caused high soil losses in the upper part of the plots and ´ sedimentation at the bottom (Martınez-Casasnovas et al., 2002). This could have affected the results making their comparative analysis difficult. Soil samples were air dried and sieved through a stainless-steel sieve with a mesh of 2 cm in diameter to eliminate root residues and large elements. Then samples were crushed at 2 mm.
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texture, pH and Electric Conductivity (EC) were measured using the methods described in Porta et al. (1986). 2.4. Extraction procedures Two simple extraction methods, in parallel to the determination of total metal were performed in order to evaluate the plant availability of metal. (NH4)OAc – EDTA and CaCl2 –DTPA were used in the extractions, according to the methods described by Pauwels et al. (1992). All chemicals used for the preparation of extraction solutions were of analytical-reagent grade of high quality. The solutions were prepared by dissolving the compound using deionised water from Milli-Q water purification systems and adjusting the suitable pH with the acids. All measurements of the element were obtained by AA (Perkin–Elmer 5000). Two replications of each analysis were done. The average value is shown in the results. 2.4.1. Aqua regia digestion — total metal concentration Aliquots of the dry soil samples (1 g) were accurately weighed into 100 ml round bottom flasks and a few millilitres of water were added. Nitric acid (2.5 ml) and hydrochloric acid (7.5 ml) were added slowly. The flasks were shaken carefully to obtain a homogeneous mixture and stored over night at room temperature and refluxed for 2.5 h. After reaching room temperature, the condenser was rinsed with water. The solution was filtered and transferred to a 100-ml volumetric flask. The residue in the filter was washed with 0.2 N nitric to give a volume close to 100 ml and the volumetric flasks were then filled up to the 100 ml mark with water. Two extractions were carried out for each sample. 2.4.2. Single extractions: plant available metals 2.4.2.1. Extraction with (NH4)OAc-EDTA. Aliquots of 20 g of the dry soil samples were weighed into 100 ml acid-cleaned polystyrene vessels. 100 ml of extraction solution (0.5 M (NH4)OAc- 0.02 M EDTA, pH 7) were added and the vessels were shaken at room temperature on a horizontal shaker for 30 min. After extraction, the sample solution was centrifuged at 1000 rpm for 15 min (Beckman Coulter) and then filtered. The supernatant solution was used for analysis.
2.3. Soil property analysis Soils are highly calcareous. According to Soil Taxonomy (Soil Survey Staff, 1998) the soils of the experimental plots are classified as Typic Calcixerept, ´ (Martınez-Casasnovas, 1998). Some specific soil properties such as organic matter (o.m.), calcium carbonate,
2.4.2.2. Extraction with CaCl2 -DTPA. Aliquots of 10 g of the dry soil samples were weighed into 100 ml acid cleaned polystyrene vessels. 20 ml of extraction solution (0.01 M CaCl2-0.005 M DTPA-0.1 M trietanolamina) were added and the vessels were shaken at room temperature on a horizontal shaker for 30 min. After
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extraction, the sample solution was centrifuged at 1000 rpm for 15 min (Beckman Coulter) and then filtered. The supernatant solution was used for analysis. 2.5. Statistical analysis A comparative means analysis was done in order to evaluate differences between treated and untreated soils and between disturbed and undisturbed positions. Linear relations between soil properties and the total and extractable amounts were calculated. 3. Results and discussion The results shown in this study have been obtained at field scale, in the plots managed by farmers according ` to the common practices in the Alt Penedes-Anoia area (NE Spain). The results of the study are based on only one application of composted cattle manure. In both situations, disturbed and undisturbed positions, the characteristics of treated and untreated soils are compared. 3.1. Soil characteristics The analysis of the soil properties of the samples showed that all soil samples had relatively high silt and sand contents (42–49%), but low clay contents, approximately 9% in plot 1 and between 6–14% in plot 2. The pH ranged between 7.8 and 8.9. The electric conductivity (extract 1:5) showed values between 0.23 and 0.39 dSmy1 for samples without added compost and up to 0.80 dSmy1 in samples with added compost (Table 2). Significant differences were found between treated and untreated soils in the disturbed position (*P)0.05). In the undisturbed position the increase was not significant on average, but the values obtained in the upper part of the plots were higher than the critical value at which vines are affected (Carter, 1981). The vine is a crop sensitive to electric conductivity (Carter, 1981) and although the effect is not regular in all the plot, the repeated application of this compost, with high EC1:5 (16 dSmy1), will increase soil EC and could produce a decrease in the yield. Organic matter (o.m.) was generally low. In the disturbed soils (points Di), the o.m. content ranged between 1.6 and 10 g kgy1 in samples without added compost and increased up to 26.5 g kgy1 after the compost application. In the undisturbed soils 2 (points Ui) o.m. values ranged between 13.2 and 16 g kgy1, and fewer changes were produced after the compost application than in the disturbed soils. Significant differences were found in the o.m. between disturbed and undisturbed soils without compost, and between treated and untreated soils in disturbed positions (*P-0 005). The average values are shown in Table 2.
Table 2 Characteristics of the soil samples at each point: EC(q), electric conductivity of treated soils with composted cattle manure; EC (y): electric conductivity of untreated soils; o.m. (q): organic matter at each point of the soils treated with composted cattle manure; o.m. (y): organic matter at each point in untreated soils Soil sample
EC(q) dSmy1
EC(y) dSmy1
o.m.(q) (g kgy1)
o.m.(y) (g kgy1)
U1 U2 U3 U4 D1 D2 D3 D4
0.80"0.07 0.37"0.04 0.36"0.03 0.31"0.05 0.30"0.04* 0.43"0.04* 0.42"0.06* 0.39"0.04*
0.39"0.05 0.28"0.07 0.32"0.06 0.28"0.08 0.27"0.06* 0.23"0.04* 0.24"0.04* 0.24"0.05*
22.7"0.5 14.0"0.3 16.1"0.4 16.2"0.5 26.7"0.3* 12.4"0.4* 11.7"0.3* 13.8"0.4*
12.1"0.4 9.8"0.3 14.5"0.4 13.3"0.4 5.4"0.3* 2.0"0.2* 4.8"0.3* 4.9"0.2*
Ui: soil samples taken in undisturbed soils; Di: soil samples taken in disturbed soils. * (P-0.05) Significant differences between treated and untreated soils.
3.2. Soil metal content: total content Although in a preliminary analysis the effect of waste application on different element contents in the soils was evaluated, only the levels of Zn were included in this study. Cu levels did not change significantly and other elements were at very low concentrations. The Zn level in the compost used was lower than that permitted in compost for agricultural purposes (Briton, 2000). However, this practice is repeated every threeyfour years; for this reason it is necessary to evaluate the potential risk of future pollution. Fig. 1 shows the changes in the total content of Zn at each point. Zinc levels in the untreated soils ranged from 40 to 65 mg kgy1. These levels are similar to those found in the deeper layers (30–50 cm, 50–70 cm) of the undisturbed soils, which is logical taking into account that in these disturbed soil plots the deep soil layers are now on the top. There were no significant differences between disturbed and undisturbed soils without compost and they are lower than those recorded in vineyard soils in non-industrially polluted areas (Angelova et al., 1999). In the treated soils, the levels increased on average up to 120 mg kgy1, which implies Zn levels between 60 and 100% higher than the original levels (*P-0.05), however, no significant differences were found between disturbed and undisturbed soils. The Zn levels in the soil surpass the minimum levels required for a normal development of the crop. Clark et al. (1996) estimate a Zn removal due to the harvesting of 0.04 kgyha fruit for productions of 20 000 kgyha of crop, which are higher than those recorded in the area
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Fig. 1. Differences in total-Zn content in treated (q) vs. untreated (y) soils in disturbed (D) and undisturbed (U) soils.
(-15 000 kgyha). Thus, Zn inputs in the soils are much higher than outputs. Weingerl and Kerin (2000) indicate that Zn mobility is closely connected to soil reaction increasing the available fraction for plants with acidity of soil. In addition, Zn is hard to wash away and it is accumulated on the surface. 3.3. Soil metal content: plant available metals Figs. 2 and 3 show the ratio of the fraction extracted with (NH4)OAc-EDTA and CaCl2-DTPA, respectively. The results are expressed in percentages. The ratios obtained with both methods were different. Those obtained with EDTA were between 3 and 6 times higher
than those obtained with DTPA. The ratios obtained with EDTA ranged from 3 to 30% with an average value of 10.8%, while for DTPA they ranged from 2 to 7.2% with an average value of 2.9%. Although both methods are widely proposed in the literature to evaluate the available fraction of metals for plants, they did not give the same results. The use of these mixtures of (NH4)OAc ammonium acetate and CaCl2 with organic complexing agents (EDTA, DTPA) could allow evaluating the bio-available metal for plant uptake, including mobile and mobilized fractions. Different authors have pointed out that the fraction extracted using EDTA or DTPA represents the mobilized fraction while the fraction extracted using Ca-salts or NHq 4 -salts represents
Fig. 2. Differences in the available fraction for plants (extraction with NH4 OAc-EDTA) in treated (q) vs. untreated (y) soils in disturbed (D) and undisturbed (U) soils.
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Fig. 3. Differences in the available fraction for plants (extraction with CaCl2 -EDTA) in treated (q) vs. untreated (y) soils in disturbed (D) and undisturbed (U) soils.
the mobile fraction in the soil. Nevertheless, in some cases both are denoted as the ‘bio-available’ fraction for plant uptake (Wong, 1996; Devkota, 2001) and there is not a general rule for all crops. Devkota (2001), who distinguished between mobilized and mobile fractions, used Ca(NO3)2 and (NH4)NO3 to evaluate the mobile fraction and he pointed out that the use of Ca-salts gave lower values than NHq 4 -salts. Similar results were found by Homburg et al. (1995), cited by Devkota (2001). Brun et al. (2001) showed that in contaminated soils extraction with organic complexing agents (EDTA, DTPA) and extraction with ammonium acetate seem to be better adapted for estimating Cu bio-availability. On the basis that EDTA and DTPA have similar complexing effects, the result obtained with the two extractants used in the study could be interpreted, because of differences in the salt used to release the mobile fraction.
The available fraction obtained with (NH4)OAcEDTA showed significant differences between treated and untreated soils in the undisturbed positions, where the highest ratios were observed, but no significant differences were observed between disturbed and undisturbed soils (Fig. 2). With CaCl2-DTPA there were no significant differences between disturbed and undisturbed positions or between treated and untreated soils. In both extractions, the available fraction increased in treated vs. untreated soils. Both fractions correlated significantly with total Zn content, Cl2 -Ca fraction at 95% and (NH4)OAc-EDTA at 99%, with correlation coefficients of 0.58 and 0.69, respectively (Fig. 4). The result is difficult to compare with others cited in the literature because of the different extractants used. Devkota (2001) indicated that the mobile fraction extracted with Ca-salts did not increase when the total
Fig. 4. Relationship between the Zn available fraction extracted with NH4OAc-EDTA and with CaCl2-EDTA and the total-Zn content.
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Fig. 5. Relationship between total-Zn and Zn available fractions (extracted with NH4 OAc-EDTA and CaCl2 -DTPA) and the organic matter content.
Zn content increased, but the mobilizable fraction extracted with EDTA and the mobilized fraction extracted using NH4-salts increased. However, Andreu and ´ (1996) observed positive correlations Gimeno-Garcıa between the fraction extracted with EDTA and the total metal. Farmers in the study area adopted the practice of applying organic wastes after they had witnessed the experience of other farmers, but without any technical advice and further control. The results showed that the increase of Zn in the soil also increased the available fraction for plants. But taking into account the low percentage of extraction, most of the Zn applied with the organic wastes will remain in the soils increasing
the total levels which could become toxic, not only for the plants, but for the soil micro-organisms. Alternative organic wastes such as crop residues or mixtures of them with manure should be tested in order to improve organic matter levels in soil, but to reduce metal content and to avoid an excessive increase of electric conductivity. 3.4. Zn in soils vs. soil properties The observed Zn concentration in soils and the fraction available for plants obtained using the two methods were related to some soil properties. Soil variables which are supposed to affect bioavailability,
Fig. 6. Relationship between total-Zn and Zn available fractions (extracted with NH4 OAc-EDTA and CaCl2 -DTPA) and the organic matter content for disturbed soils.
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Fig. 7. Relationship between total Zn and Zn available fractions (extracted with NH4 OAc-EDTA and CaCl2 -DTPA) and the organic matter content for undisturbed (U) soils.
i.e. clay content and organic matter were taken into consideration. pH and calcium carbonate content could also affect bioavailability, but because all the samples had a similar pH and similar calcium carbonate contents their influence was not considered in the analysis. There was a significant correlation between organic matter content and the total Zn content (rs0.58, **P0.01), while for the available fraction only the DTPAZn levels were significantly correlated with organic matter (rs0.55, *P-0.05) (Fig. 5). The results were different between disturbed and undisturbed soils. In the undisturbed soils, where the original o.m contents were higher (o.m ranging from 10 to 16 g kgy1), the correlation between total Zn and o.m was significant at 95% level (rs0.57, *P-0.05) (Fig. 6). However, in the disturbed soils (o.m. approx. 5 g kgy1), the correlation coefficient was not significant. Nevertheless, the highest differences were found in the relationship between EDTA-Zn and DTPA-Zn and the o.m content in the two plots. Only in the disturbed soils there were significant correlations between the available fractions and the organic matter: for EDTA-Zn, rs0.60, *P-0.05 and for DTPA-Zn, rs0.69, ***P-0.001 (Fig. 7). No correlation was found for undisturbed soils. The results could be in agreement with that obtained by Pinamonti et al. (2000), who found that in vineyards the available fraction for the plant was positively correlated with the DTPA-extractable form of the metals in the soil, but not correlated with the total or the EDTAextractable forms. Nevertheless, it would be necessary to carry out further research on mobility of soluble fractions of metals in relation to the o.m. content. No significant correlation was found between total Zn concentration and clay content. However, the avail-
able fractions obtained with both methods show a slight trend to decrease when clay content increases. 4. Conclusions Management practices following field mechanisation, carried out in the studied Mediterranean vineyards, appears to have important effects on land degradation, increasing the risk of soil contamination. The addition of composted cattle manure increased the organic matter content significantly in treated soils, but it was associated with an increase in the electric conductivity values up to limits that could affect the vine yield. In addition, the use of this compost in the studied vineyards increased the total Zn level significantly. Although after one compost application, the Zn level is still below the maximum permitted in agricultural soils, it increased to double its original value at some points. The characteristics of the soils in each plot affected the final levels of metals accumulated in it. The Zn extracted using different reagents differs very much, being much higher when extracted with (NH4)OAc-EDTA than with CaCl2-DTPA. The available fraction had a fairly high correlation with the total increase in Zn content in treated as opposed to untreated soils. However, only the CaCl2-DTPA fraction significantly correlated with the organic matter content for all the samples. When disturbed soils were considered separately, both extractions were significantly correlated. The low available fraction indicated that most of the applied metal with the compost will remain in the soil contributing to contaminating the soil. Taking into account that this application of organic waste is a ` common practice in the vineyards in the Penedes-Anoia
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areas, and according to this preliminary result obtained after only one application, there is a potential risk of soil pollution if this practice is done without any control. Although not all composts will have the same composition, if two applications like those took place, Zn content will be 50% higher in all the vineyard. In addition, taking into account the erosion processes that take place in this area, the metal accumulated in the soil could be transported by runoff, which will give rise to a non-point pollution source for waters in the catchment area. Acknowledgments This work as part of the AMB98-0481 project, 19982001, was developed with funding from the Comision Interministerial de Ciencia y Tecnologia, (CICYT), Progama Nacional de Medio Ambiente. Financial support was also available from the CIRIT(GRC-4011L) and UdL (with the contract of technical support). References ´ E., 1996. Total content and Andreu, V., Gimeno-Garcıa, extractable fraction of cadmium, coblat, copper, nickel, lead and zinc in calcareous orchard soils. Commun Soil Sci. Plant Anal. 27, 2633–2648. Angelova, V.R., Ivanov, A.S., Braikov, D.M., 1999. Heavy metals (Pb, Cu, Zn and Cd) in the system soil-grapevinegrape. J. Sci. Food Agric. 79, 713–721. Briton, W.F., 2000. Compost Quality. Standards and Guidelines. Woods End Research Laboratoy Inc, New York. Brun, L.A., Maillet, J., Hinsiguer, P., Pepin, M., 2001. Evaluation of copper availability to plants in copper-contaminated vineyard soils. Environ. Pollut. 111, 293–302. Carter, D.L., 1981. Salinity and plant productivity. Handbook Series in Nutrition and Food. Chemical Rubber Co. Clark, C.J., Smith, G.S., Cornforth, I.S., Prasad, M., 1996. Fertilizer recommendations for horticultural crops. Hortnet䉸 The Horticultural and Food Research Institute of New Zealand Ltd. RAL, G.K., 1994. Methods for the Analysis of Compost. Federal Compost Quality Assurance Organization ¨ (FCQAO). Budesgutegemeinschaft Kompost e.V, Cologne, Germany. Hamblin, A., 1991. Sustainable agricultural systems: what are the appropriate measures for soil structure? Aust. J. Soil Res. 29, 709–715. ´ Martınez-Casasnovas, J.A., Ramos, M.C., Ribes-Dasi, M., 2002. Soil erosion caused by extreme rainfall events: mapping and quantification in agricultural plots from very detailed digital elevation models. Geoderma 105, 125–140. ´ ´ EroMartınez-Casasnovas, J.A., 1998. Suelo- Paisaje-Erosion. ´ por carcavas ´ ` sion y barrancos en el Alt Penedes-Anoia. ˜ ´ de (Cataluna). Un enfoque de estudio mediante tecnologıas ´ espacial, Bases de datos, Sistemas de inforla informacion
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