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Journal of Environmental Quality 30:2165-2172 (2001)
© 2001 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America

TECHNICAL REPORT
Waste Management

Evaluation of the Application of Pig Slurry to an Experimental Crop Using Agronomic and Ecotoxicological Approaches

J. A. Diez*,a, A. I. de la Torreb, M. C. Cartagenac, M. Carballob, A. Vallejoc and M. J. Muñozb

a Centro de Ciencias Medioambientales (CCMA, CSIC), C/ Serrano 115, 28006 Madrid, Spain
b CISA-INIA, Valdeolmos, 28130 Madrid, Spain
c ETS Ingenieros Agrónomos, UPM, Ciudad Universitaria, 28040 Madrid, Spain

* Corresponding author (jadiez{at}ccma.csic.es)

Received for publication May 31, 2000.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
The agronomic and ecotoxicological effects of the application of pig (Sus scrofa) slurry during a maize (Zea mays L.) crop cycle under conditions of forced irrigation were evaluated. The 0.2-ha experimental area, of typical xerofluvent soil and of known vulnerability to nitrate (NO-3) contamination, was divided into 12 plots and provided with water measurement instruments (TDR-probes, vertical tensiometers, and ceramic candles). Samples of soil, water, soil organisms, and the crop were subjected to analytical, agronomic, and biological test procedures. The following fertilizer treatments were applied to triplicate plots: urea (U;170 kg N ha-1), and an optimized (P1; 162 kg N ha-1) and triple (P3; 486 kg N ha-1) dose of pig slurry. Unfertilized plots (P0) served as controls. Calculation was made of seasonal drainage and leached NO-3 and sodium losses during the experimental period. Conductivity, heavy metal concentration, hardness, pH, and redox potential were determined in soil solutions. The ecotoxicological evaluation of the soil solution and matrix was based on ecotoxicity bioassays and the quantification of organic and inorganic compounds [phenols, indols, polychlorinated biphenyls (PCBs)]. The results suggest that the P3 treatment is highly contaminating due to the leaching of nitrates and increased soil salinity. Despite the fact that a Folsomia candida reproduction test indicated chronic ecotoxicological effects on the soil in plots treated with P1 and P3, the absence of organic compounds suggests that these effects may be attributable to contaminants not considered in this study.

Abbreviations: ET, evapotranspiration • DM, dry matter • EC, electrical conductivity • EUF, electroultrafiltration • TDR, time domain reflectometry • GC–MS, gas chromatograph–mass spectrometer (HP 5809) • DOC, dissolved organic carbon • LOEC, lowest observed effect concentration


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE RECYCLING of pig slurry in agricultural soils is an alternative and valuable practice in countries such as Spain with significant European pig production (2.529 million sows in 1998). This is particularly the case since many regions are arid and are comprised of poor soils (<1% organic matter) that support intense mineralization. Recycling supplies agricultural soils with organic matter, nutrients, and micronutrients, but also adds unwanted substances such as food additives, pesticides, pharmacological products, along with their metabolic and degradation by-products, and fecal contamination. In Spain, nearly 2.5 x 106 Mg (dry wt.) of pig manure is collected annually (Bigeriego, 1995), and it has been acknowledged (MAPA, 1997) that approximately 50% of this manure is spread on agricultural land. Current European Environmental Council Directives (CD) such as the Waste Directive (European Union, 1991a) consider the need for integrated environmental assessment to ensure "the protection of the environment and human health," through use of the best available methodologies. Thus, to evaluate the use of pig slurry, and assess its toxicity, knowledge of the fate and bioavailability of its components, and prediction of potential routes of contamination and effects on organisms are required. In our context, integrated evaluation implies the evaluation of agronomical and ecotoxicological aspects after pig slurry recycling in agricultural soils.

Nitrate contamination of ground water is now regulated by the European Council (European Union, 1991b), which establishes a limit of 50 mg NO-3/L. Nitrate pollution has been related to agricultural practices (Archer and Thompson, 1993; Keeney and Follet, 1991); thus, the amount of pig slurry applied to the land generally depends on its N content. This N is mainly found as ammonium (NH+4) (about 60%) and is quickly and easily transformed into nitrate (NO-3), which easily leaches. Further transformations can occur when the organic N present in the slurry (around 40%) is assimilated by the soil.

From an agricultural perspective, the N content of the slurry needs to be determined to adopt ways of reducing its environmental impact (CD 91/676/EEC; Diez et al., 2000). A further requisite is to establish the available soil N including potentially mineralizable N (Sanchez et al., 1998). In addition, irrigation quantity needs to be adjusted to compensate for evapotranspiration losses and thus minimize water losses through drainage (Diez et al., 1997).

The potential negative effects of heavy metals added to swine diets as micronutrients have been demonstrated in sewage sludge (Chaudri et al., 1993; McGrath et al., 1999). Thus, maximum permitted heavy metal limits have been established for agricultural soils treated with slurry (European Union, 1986). Other compounds such as the phenols and indols (Hammond et al., 1989; Lo et al., 1994) released through the bacterial decomposition of proteins in the pig intestine (Jensen et al., 1995), surfactants (Warren-Hicks and Parkhurst, 1992), PCBs (ECME, 1999), and pathogenic microorganisms (Dewi et al., 1994) have been identified, although their environmental relevance, in terms of toxicological and ecotoxicological consequences, are only just beginning to be considered (de la Torre et al., 2000). However, it is well known that for many organic compounds, toxicity can often be directly related to organic matter content (Van Gestel and Ma, 1990) and their bioavailability in the soil pore water will depend on soil properties and other factors such as their sorption capacity (Van Straalen and Van Gestel, 1998). Furthermore, some compounds such as PCBs can act as intermediates, i.e., they elicit a mixed spectrum of effects (Toppari et al., 1996).

Ecotoxicological methodologies have been proposed for assessment of the potential toxicity of different compounds (European Union, 1993) in urban (Garric et al., 1996) and industrial effluents (Sauser et al., 1997) and in receiving waters (Stewart and Konetsky, 1998). International organizations (ECB, 1996; European Union, 1997a) have established exposure pathways and tests for soils that evaluate the different trophic levels (plants, invertebrates, and microorganisms) aimed at determining the effects of chemicals and complex mixtures on the soil matrix. However, ecotoxicological test methods for soil are relatively underdeveloped. Many toxicity data still take the form of LC50s, and there has been a tendency in recent years to put more emphasis on sublethal criteria or long-term effects, especially on reproduction. This reflects the growing awareness of the general population of contaminants, and their effects on the reproduction of organisms in the lower trophic levels (Van Straalen and Van Gestel, 1998).

The complex composition of pig slurry and its associated problems dictates that its effects on agronomic and environmental factors need to be established before land application. To improve current knowledge and to provide recommendations for application dosage, a field study was performed with the aim of undertaking an integrated environmental evaluation of pig slurry. The first objective was the quantification of nutrients and contaminants present in the slurry. Following this, we conducted a 1-yr study on the agronomic and ecotoxicological effects of pig slurry. The experimental area was planted to maize cultivation (Zea mays L. cv. Juanita, Pioner) under conditions of forced irrigation and thus presented a high pollution risk. Agricultural and ecotoxicological monitoring included analytical, agronomic, and biological methodologies applied to soil, water, soil organism, and crop samples.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Production System Characterization
The experimental field was located at La Poveda Field Station (30 km southeast of Madrid) in the mid-Jarama river basin. The typical xerofluvent soil was comprised of a sandy-loam in the uppermost 0.5 m, becoming progressively sandy at greater depths. There is a dominant gravel layer at a depth of 1.5 to 2.2 m, with a varying water table located at some 4 to 4.5 m below the soil surface due to occasional periods of heavy rainfall and major river flow. Soil water measurement devices (TDR)-probes, vertical tensiometers, and ceramic candles) were placed in an experimental area of 0.2 ha containing 12 plots. The plots were 9.9 by 11.1 m.

Four of the 12 plots were selected as measuring points, taking into account the natural heterogeneity of the soil. The TDR-probes were installed at a maximum depth of 2 m and vertical tensiometers, capable of measuring water pressures of 0 to -80 kPa, at depths of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5, and 2.0 m. Soil water potential gradients served to determine water movement through the soil by relating the hydraulic head to soil depth (Roman et al., 1996).

A ceramic candle extraction system was used to obtain samples of the soil in solution (Nardeux Humisol, Les Ulis, France) by installing tubes at depths of 0.5 and 0.9 m and two tubes at 1.4 m in each plot. As the amount of water drainage at a soil depth of 1.4 m was the same as that at greater depths due the textural characteristics of the soil profile, water samples extracted using the ceramic candle were taken to represent the NO-3 concentration of the drainage water.

Determination of water storage and the hydraulic head were performed before and after each irrigation session during growing periods. Four water flow patterns were established and the appropriate water balance partitioning scheme applied. This permitted the calculation of seasonal evapotranspiration (ET) and drainage (Roman et al., 1996).

Topsoil samples (20 cm depth) were taken at the start of the experiment, before slurry and fertilizer application from the 12 plots using a blade soil core device. The soil were analyzed for pH, organic matter (Walkley and Black, 1934), and carbonate (AFNOR, 1987). Nitrogen, P, K, and Ca were estimated using the electroultrafiltration (EUF) technique (Nemeth, 1979). Total N was determined in EUF extracts (EUF-N) of soil samples by digestion with UV radiation and subsequent oxidation with potassium persulfate in alkaline medium (Diez, 1988). Nitrate determination (both in the soil water solution extracted by the ceramic candles and the EUF extracts) was performed colorimetrically using a Technicon AAII Autoanalyzer with N1 napthylethylenediamine (AOAC, 1990). Phosphorus was also determined colorimetrically using ammonium molybdate as a reagent (AOAC, 1990). Potassium and Ca were determined by flame emission photometry. Available N was estimated in the 12 plots before sowing and after harvesting the maize by determination of EUF-N fractions (Nemeth, 1979). This method takes into account the potential mineralizable N in the soil (Sanchez et al., 1998). The chemical properties of soil taken from the different plots at the beginning of the experiment experiment, before slurry and fertilizer application, are shown in Table 1.


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  		Table 1. Physicochemical properties of the soil before sowing.

 
A fattening farm comprised of 680 animals was selected to provide the pig slurry. The slurry sewage, kept in storage tanks, was collected from the discharge points. Before slurry application, N content was estimated to calculate the application doses. The pig slurry was applied using a waterspout connected to a reservoir. The characteristics of this slurry corresponded to that of a representative sample composed of portions taken at regular intervals during land application. The following variables were analyzed: NH3–N and conductivity employing ion selective electrodes (Orion Research AG, USA); pH by pH-electrode; density by proton densitometer; total N estimated by the Kjeldahl method (AOAC, 1990); and Cu, Mn, Fe, Cu, Cd, Pb, Ca, Mg, K, Na, and Zn by atomic absorption spectrophotometry (Perkin Elmer model IL 357) (Table 2). Nonvolatile residues, general organic chemicals, fatty acids, and PCBs were also quantified using a modified extraction method (de la Torre et al., 2000). An ecotoxicological evaluation of the slurry was also performed using the Daphnia magna acute toxicity test (European Union, 1984). The LC50 (% dilution for which 50% of immobility is observed) was estimated by GwBasic 3.10 (Table 3).


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  		Table 2. Physicochemical properties and heavy metal content of the pig slurry used.

 

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  		Table 3. Ecotoxicological characterization and organic compounds of the pig slurry applied to the soil (de la Torre et al., 2000).

 
Three different treatments (U, P1, and P3) were applied to triplicate plots. Three untreated plots served as controls (P0). Based on the EUF soil analysis results and according to criteria established by Sanchez et al. (1998), the optimal N dose established was 170 kg N ha-1. Thus, optimal (60 m3 ha-1, P1) and triple doses of pig slurry 180 m3 ha-1 (P3) were applied. Urea was applied at the optimal rate of 170 kg N ha-1 to compare the effects a typical N source.

Agronomic Assessment
After pig slurry application and plowing, maize was sown on 24 Apr. 1998, in rows with 75-cm spacing at a density of 75000 plants ha-1. During seedbed preparation, a fertilizer (superphosphate 18%, K2SO4 50%) was applied to the experimental field for a P and K application of 22 kg P ha-1 and 100 kg K ha-1, respectively. A combination of atrazine [6-chloro-N-ethyl-N-(1-methylethyl)-1,3,5 triazine-2,4 diamine] at 0.9 kg a.i. ha-1 and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] at 1.5 kg a.i. ha-1 was applied preemergence for weed control between pig slurry application and sowing.

An overhead mobile-line sprinkler irrigation system was used during the maize growth period. Field data provided by the instruments located at the measuring sites were used to adjust irrigation depth by increasing water storage to field capacity in 0 to 0.5 m surface layer (90% of roots in the surface 0–0.35 m during the crop). The watering frequency was once per week to avoid water stress (mean pressure measured at soil depths of 0.1, 0.2, and 0.3 m was -84.2 ± 10.5 kPa). Ten irrigation sessions were conducted ranging from 32 to 60 mm. The total amount of water applied was 428 mm. Calculation of these doses was based on the soil water balance during each session such that final drainage was around 15% of the applied water. Jarama River water was used as the irrigation water source throughout the experiment. The mean quality components of the river water were: NO-3 concentration, 5.1 ± 0.5 mg NO-3–N L-1; total solids, 650 ± 50 mg L-1; electrical conductivity (EC), 0.102 ± 0.018 S m-1; sodium adsorption ratio, 1.55; and pH, 7.6 ± 0.3.

Depending on the type of study, agronomic and ecotoxicological samples were obtained at different times that ranged from a few days before pig slurry application to harvest. Samples of soil solution were extracted monthly throughout the experiment (eight times in total). Leaching was monitored during the experiment and a crop study was performed at the time of harvesting. For the leaching study, samples were taken from each ceramic candle sampler and determination made of the conductivity and NO-3 (AOAC, 1990), sodium by flame emission photometry, and heavy metal concentration by IPC emission. Leached NO-3 and sodium were estimated by multiplying seasonal drainage by the corresponding NO-3 and sodium concentration at a soil depth of 1.4 m.

Maize was harvested on 16 Oct. 1998 when the grain was mature. Aboveground biomass was determined in plants harvested along 5 m of two adjacent rows in the middle of each plot. Ten of the harvested plants were randomly selected and their different parts (stalk, leaves, bracts, cob, and grain) separated and weighed. Whole and fraction samples were oven-dried for 24 h at 60°C and 2 h at 80°C for dry matter (DM) determination. The harvest index was calculated as the ratio of grain weight to aboveground biomass. Grain yield was calculated by multiplying aboveground biomass by the harvest index. Nitrogen concentration was determined in plant fractions previously treated with a solution of salicylic plus sulfuric acid (Bremner, 1965) according to the Kjeldhal method (AOAC, 1990). Plant N uptake was calculated by multiplying fraction yields by their respective N concentrations.

Statistical differences among the fertilizer treatments (plant yield, grain yield, and plant N uptake) and between the fertilizer treatments and soil depth (NO-3 concentration, conductivity, and sodium concentration) were established through ANOVA using sample data corresponding to the 12 plots. Statistical analysis was performed using Statgraphic-plus 4.0 software. In all the comparisons, a p < 0.05 was taken to denote significance.

Ecotoxicological Approach
Both the soil solution and matrix were subjected to ecotoxicological evaluation. Hardness (meq CaCO3 L-1) and pH were determined in the soil solutions taken from 1.4-m depth ceramic candle samplers in control (P0), P1, and P3 plots. The redox potential range was estimated by subjecting several randomly selected soil solution samples to redox potential determination using an Orion platinum redox electrode mod. 9678. Copper was only estimated in samples in which it was certain that there would be no trace copper contamination from the instruments used (cups). An ecotoxicological assay (Daphnia magna test) was also performed in these samples at 10% of dilution.

For the soil monitoring study, a homogeneous soil sample comprised of 25 subsamples taken at a depth of 20 cm per plot was used. A week before slurry application, nine randomly selected soil samples were analyzed to determine residual atrazine, metolachlor, PCBs, Floranid 32 (isobutylidendiurea), and 2,4-D (2,4-dichlorophenoxyacetic acid) in the field. Determination was made of the organic compounds (4-methylphenol, 4-ethylphenol, indole, and 3-methylindole), fatty acids, and PCBs. This was performed by extraction of a precisely weighed soil sample (30 g) with acetonitrile (2 x 50 mL) in an ultrasonic bath for 10 min. The resulting acetonitrile solution was diluted with distilled water and extracted with n-hexane (4 x 50 mL). The n-hexane solution was reduced to 1 mL, cleaned on a Florisil column (1 g), and analyzed by gas chromatography–mass spectrometry (GC-MS) procedures. Identification of these products was performed according to the method of de la Torre et al. (2000).

The potential effects of toxic compounds in the soil environment were estimated through the four ecotoxicity bioassays: Microbial Respiration Inhibition Test (de la Torre, 1997), Plant Germination Inhibition Test (USEPA, 1982), Folsomia candida Reproduction Test (European Union, 1997b), and Enchytraeus albidus Reproduction Test (European Union, 1998). Table 4 gives the general characteristics of these tests. For the F. candida and E. albidus reproduction tests, samples from the control, P1, and P3 plots were taken before (T0) and 2 mo after (T1) pig slurry application. For the inhibition of respiration and germination tests, samples were taken before (T0), and 2 mo (T1) and 5 mo (T2) after slurry application.


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  		Table 4. General characteristics of the ecotoxicity bioassays performed on soil samples after the application of pig slurry.

 
The statistical method recommended by the bioassay regulation guidelines (European Union 1997b, 1998) was applied to data derived from the soil bioassays. The optimized distribution and homocedasticity of data corresponding to each treatment was established using the Kolmogorov-Smirnov and Barlett's tests, respectively. Analysis of variance was subsequently performed on the results of each bioassay to establish statistical differences. The Dunnett test was applied to the groups showing significant differences to identify the treatment that differed (using the SPSS for Windows 8.00 package). In all the comparisons, a p < 0.05 was taken to denote significance.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Water and Solute Movement
Total rainfall of 102 mm was recorded for April to October 1998 with two main periods, May and September. The total amount of irrigation water applied was 428 mm. Together rainfall and irrigation induced drainage of 68 ± 30 mm. This was an average drainage of 0.87 mm d-1 (range 0.057–2.99 mm). Figure 1 shows the cumulative drainage curve corresponding to the experimental period. The starting point of drainage coincided with the irrigation period, with the maximum slope corresponding to August/beginning of September. Final drainage was 15.88% of the irrigation water, or 12.83% of the total (rainfall and irrigation). Evapotranspiration (375 ± 81 mm) values were in accordance with the values obtained in the irrigated crop area.



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  		Fig. 1. Cumulative drainage.

 
Table 5 shows the plant weights determined after harvesting. When the fertilizer treatment was analyzed according to plant yield, grain yield, and N uptake, no significant differences were detected (p > 0.05). Values were unaffected by the application of pig slurry at optimized (P1) (162 kg N ha-1) and triple doses (P3) (486 kg N ha-1) due to the soil's residual N content. Plant N uptake values were similar in all cases, with values ranging from 169 ± 12 to 230 ± 17 kg N ha-1 for the P0 and P3 treatments, respectively.


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  		Table 5. Plant variables at the time of harvest.

 
The effects on NO-3 concentration of the different fertilizer treatments were significant (p = 0.0001) (Table 6). Unfertilized control plots showed the lowest NO-3 concentration and lowest variation at the different depths. Plots subjected to the P3 treatment showed the highest NO-3 concentration and highest variation as a result of the high dose applied and the spatial variation produced by pig slurry distribution in the soil. The effects of urea and P1 treatment on NO-3 concentration at depths of 0.5 and 1.4 m were not significantly different, consistent with the similar doses employed (170 and 162 kg N ha-1, respectively). Significant differences between both treatments (U and P1) at 0.9 m depth were due to spatial variability. The NO-3 concentration recorded for the U and P1 treatments were moderate and a proportional relationship was shown by slurry dose applied and the NO-3 concentration of the soil solution in the 0.5 m depth sample. All three fertilized treatment were significantly higher at 1.4 m compared with the P0 treatment. However, effect of rates were obscured by the inherent spatial variation of NO-3 concentration in the soil solution (Kengni et al., 1994; Bruckler et al., 1997). The mean NO-3 concentration of the soil solution extracted at a depth of 1.4 m did not differ during drainage and nondrainage periods.


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  		Table 6. Nitrate concentration{dagger} of the soil solution at 0.5, 0.9, and 1.4 m soil depth during the experiment.

 
Nitrate concentration in the soil solution at the depth of percolation (1.4 m) indicate the possible contamination of ground water. For seasonal evaluation of NO-3 leaching, both drainage and NO-3 concentration should be determined in the field, although total leaching may depend more on drainage and less on variations in NO-3 concentration at the depth of percolation (Diez et al., 2000). Losses due to NO-3 leaching during the experimental period were calculated by multiplying seasonal drainage by the corresponding NO-3 concentration recorded at a depth of 1.4 m (Diez et al., 1997). It was estimated that NO-3 losses from this soil layer represented the potential contamination of ground water, due to the high hydraulic conductivity of the gravel layer and depth of the water table (some 4 m). Cumulative NO-3 discharge at a soil depth of 1.4 m is shown in Fig. 2 . It may be seen that these curves are similar to those of drainage. Thus, NO-3 losses are dependent on irrigation management and fertilizer treatment. The NO-3 losses from unfertilized plots (P0), urea, P1, and P3, were 11.2, 26.6, 25.7, and 39.8 kg NO-3–N ha-1, respectively, during the experimental period. The unfertilized controls showed a 50% reduction in NO-3 losses with respect to those recorded for the urea and P1 treatments. The triple dose of pig slurry induced NO-3 losses that were 1.5 times higher than those related to optimized dose treatment (P1). The P1 and urea treatments were associated with NO-3 losses of the same order of magnitude according to the optimized N doses established by Sanchez et al. (1998). Greatest NO-3 losses were noted for the P3 treatment and are attributable to the higher dose of N applied.



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  		Fig. 2. Nitrate leached according to the treatment (P0, U, P1, and P3).

 
The mean total salt content of the soil solution was seen to increase with soil depth due to enhanced mobility and vertical translocation (Table 7). Both the conductivity and Na concentration showed significant differences (p < 0.05) for both soil depth and treatment. Sodium concentration was also affected by the P3 dose, in accordance with its high concentration in the pig slurry (304 mg Na L-1). This increment was more evident 15 d after the waste application, with values of 886, 716, and 542 mg Na L-1 recorded for the P3, P1, and P0 treatments, respectively. From this time onward, the sodium concentration stabilized. No significant differences were observed between the unfertilized and urea plots. However, significant differences in sodium were recorded between both waste treatments (P1 and P3) at the depths 0.9 and 1.4 m, and between P1 and P3 and control treatments at depth of 1.4 m (Table 7). Sodium leaching losses were 310.3, 341.5, 465.3, and 523.1 kg Na ha-2 for P0, U, P1, and P3, respectively. The results shown in Table 7 are consistent with those observed by Bustos et al. (1996). Salts that accumulate throughout the soil during the growing season can leach into the ground water after the maize has been harvested, particularly during winters of high rainfall. This salt movement presents a pollution risk.


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  		Table 7. Conductivity (µS cm-1) and sodium concentration (mg L-1){dagger} determined during the experimental period.

 
Agronomic and Ecotoxicological Assessment
Heavy metal concentrations in the soil solution at the soil depth of 1.4 m were not significantly different between pig slurry treatments (Table 8). The metal analysis performed measures the soluble metal fraction plus that broken down by chemical treatment of the sample. This corresponds to all leachable metals and depends on the gradient produced by the drainage at each moment in time. The redox potential of the soil determined under very humid conditions was within the expected range (0.2–0.3 V), with pH values between 7.25 and 8.7. However, higher levels of hardness than expected were recorded, and variation was shown among plots subjected to the same treatment. In these conditions, metal bioavailability would be expected to be very low, reducing the risk of toxicity. Copper was not estimated in all samples due to some suction cups presenting small copper pieces in their structure, as was verified at the end of the study. When the samplers were built with plastic material, Cu values ranging from 0.073 to 0.12 mg L-1 were found, with the toxicity <=15% of dilution. Even though this effect of toxicity seems a residual toxicity, it should be considered that the risk of Cu from pig slurry on soil, and consequently in ground water, may be expected due to the mobility of the Cu–DOC complex (Giusquiani et al., 1998). Thus, Cu level must be evaluated. One easy method to estimate presence or absence of Cu in soil solution is to assay the soil solution samples using an ecotoxicological test as sensitive as Daphnia magna. This test detects small Cu concentrations that can be bioavailable and, in consequence, can involve a risk for water soil organisms (soil solution and ground water). In fact, Daphnia magna test presents a 48 h LC50 of 0.06 mg L-1 at 130 meq CaCO3 L-1 of hardness and pH 8.2 (Mance, 1987).


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  		Table 8. Heavy metal concentration (mg L-1), hardness (meq CaCO3 L-1) and pH of the soil solution at a soil depth of 1.4 m according to treatment.{dagger}

 
Phenols, indols, and PCBs identified in the pig slurry were absent in soil, 2 and 5 mo after field application. In contrast, Saviozzi et al. (1997) were able to observe the disappearance of phenolic substances at shorter times than ours in a laboratory experiment. None of the herbicides used were detected in the soil, although some herbicides such as atrazine and metalochlor show a persistence that, according to a report by Rouchaud et al. (1994), could have been enhanced by the presence of pig slurry.

Although four different ecotoxicity assays were employed, only Folsomia candida test showed statistical differences (Table 9). However, the use of a set of ecotoxicity tests is always recommended because it allows us to obtain information about different expression levels (related to different assay times, exposition routes, sensitivity to toxic compounds, endpoints, etc.) and in consequence, they permit us to demonstrate the different bioavailability of toxic substances on living organisms (Martikainen, 1996; Ronday and Houx, 1996). Thus, different results could be expected due to the different nature of the toxicity tests. The observed effects in Folsomia candida were not related to the presence of organic compounds, because their analytical results in soil were negative. However, other compounds like metals could be responsible for this toxicity. It has been demonstrated that Folsomia candida is sensitive to Cu with a 21 d LOEC of 200 mg Cu kg-1 dry weight (Scott-Fordsmand et al., 1997). In summary, the use of long and short assays is recommended because it allows a global estimation of compounds with both short-term and long-term toxicity effects and compounds whose biodisponibility depends on the characteristics of the soil matrix.


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  		Table 9. Results of the Folsomia candida reproduction test on soil samples.

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The fertilizer treatments and the pig slurry dose applied show clear effects on NO-3 concentration at a soil depth of 1.4 m. In general, NO-3 leaching was proportional to fertilizer dose and drainage volume. The application of pig slurry at an optimal rate gave rise to similar results to that of urea treatment. It is therefore recommended that the dose of pig slurry to be used should be calculated before application, taking into account available soil N through appropriate soil analysis. The application of high doses of pig slurry (e.g., P3 treatment) could lead to a high degree of contamination in terms of both nitrates leached into the ground water and increased soil salinity. Grain yield, total biomass, and N uptake were unaffected by urea and pig slurry application because of the residual soil N. Chronic ecotoxicological effects on the soil, determined according to the Folsomia candida reproduction test, were shown by the P1 and P3 treatments 2 mo after application. However, these effects did not appear to be related to the organic compounds provided by the slurry or to the pesticides used in crop management. At 2 and 5 mo posttreatment, no slurry phenols (4-methylphenol, 4-ethylphenol), indols (indole, 3-methylindole), or PCBs were detected in the soil.


   ACKNOWLEDGMENTS
 
This study was financed by the INIA (Spanish Ministry of Agriculture, Fisheries and Food Resources), Project SC 98-C2.2. The authors acknowledge P.J. Hernaiz of the La Poveda field station (CCMA, CSIC) for help in the field work and M.D. Atienza for technical assistance.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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M. H. Chantigny, D. A. Angers, G. Belanger, P. Rochette, N. Eriksen-Hamel, S. Bittman, K. Buckley, D. Masse, and M.-O. Gasser
Yield and Nutrient Export of Grain Corn Fertilized with Raw and Treated Liquid Swine Manure
Agron. J., August 11, 2008; 100(5): 1303 - 1309.
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P. Berenguer, S. Cela, F. Santiveri, J. Boixadera, and J. Lloveras
Copper and Zinc Soil Accumulation and Plant Concentration in Irrigated Maize Fertilized with Liquid Swine Manure
Agron. J., June 16, 2008; 100(4): 1056 - 1061.
[Abstract] [Full Text] [PDF]

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 J. Environ. Qual.Home page
A. Dauden, D. Quilez, and M. V. Vera
Pig Slurry Application and Irrigation Effects on Nitrate Leaching in Mediterranean Soil Lysimeters
J. Environ. Qual., November 1, 2004; 33(6): 2290 - 2295.
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The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Soil Science Society of America Journal Journal of Plant Registrations The Plant Genome