Ecotoxicological assessment of organic wastes using the soil collembolan Folsomia candida

The reproduction test with the collembolan Folsomia candida is used as a tool to evaluate the ecotoxicological potential of organic wastes currently applied to soil. Seven organic wastes (dewatered sewage sludges, thermally dried sewage sludges, composted sewage sludges, and a thermally dried pig slurry) were tested. These wastes had different origins, treatments, and pollutant burdens, and were selected as a representative sample of the wide variety of wastes currently generated. F. candida showed varied sensitivity depending on the waste, but also depending on the endpoint assessed. Reproduction was more sensitive than survival, although no correlations between reproduction and physico-chemical parameters and pollutant burden could be found. On the other hand, mortality was directly related to the lack of stability of wastes, probably reflecting the toxicity of end-products such as ammonium. Body length was not shown to be a sensitive endpoint for waste testing, as it was neither affected nor even stimulated by waste concentrations.Organic matter, pH, and electrical conductivity varied with waste concentration in soil-waste mixtures, although their effect on collembolan performance was expected to be low and part of the complex effect exerted by wastes when applied to real soils. Selection of the water content is the most problematic aspect in waste testing, as it may affect the performance of test organisms. In this study, a qualitative approach for water content selection in waste testing was considered to be the most suitable.Treatment of wastes affected composition and toxicity. Composting of sewage sludge increased its stability, compared to the initial sludge, but decreased its non-persistent organic pollutant burden and toxicity. On the other hand, thermally dried wastes from sludge and pig slurry displayed high toxicity, mainly attributable to their low stability. The results from the study indicate the inability of chemical methods to predict the effects of complex mixtures on living organisms with respect to ecotoxicity bioassays, but also the need for stabilization treatments of organic wastes prior to their reuse in soils.     

Toxicity of phenmedipham and carbendazim to Enchytraeus crypticus and Eisenia andrei (Oligochaeta) in Mediterranean soils

Purpose

The main objective of the present study was to evaluate the toxicity of two reference chemicals, Carbendazim and Phenmedipham, for the compostworm Eisenia andrei (effects of Carbendazim) and the potworm Enchytraeus crypticus (effects of Phenmedipham) in 12 Mediterranean soils with contrasting soil properties. The observed toxicity was also compared to that obtained for OECD standard soil, used as a control.

Materials and methods

The soils were selected to be representative for the Mediterranean region and to cover a broad range of soil properties. The evaluated endpoints were avoidance behavior and reproduction. Soils were also assembled in two groups according to their pedological properties.

Results and discussion

Toxicity benchmarks (AC50s) obtained for E. andrei avoidance behavior in carbendazim-contaminated soils were generally higher for sandy soils with low pH. The toxic effects on the reproduction of the compostworms were similar in the six tested soils, indicating a low influence of soil properties. The avoidance response of E. crypticus towards Phenmedipham was generally highly variable in all tested soils. Even though, a higher toxicity was observed for more acidic soils. The EC50s for reproduction of the latter species varied by a factor of 9 and Phenmedipham toxicity also tended to be increasing in soils with lower pH, except for the soils with extreme organic matter content (0.6 and 5.8%).

Conclusions

A soil effect on chemical toxicity was clearly confirmed, highlighting the influence that test soils can have in site-specific ecological risk assessment. Despite some relationships between soil properties and toxicity were outlined, a clear and statistically significant prediction of chemical toxicity could not be established. The range of soil properties was probably narrow to give clearer and more consistent insights on their influence. For the four groups of tests, the toxicity observed for OECD soil was either similar, lower, or generally higher if compared with Mediterranean soils. Moreover, it did represent neither the organic matter content found in Mediterranean soils nor their textural classes.     

Ecotoxicity of mercury to Eisenia fetida, Enchytraeus albidus and Folsomia candida

Despite growing concerns about the potential adverse effects of elevated mercury concentrations in the environment, only a few toxicity data are available for soil invertebrates. The chronic toxicity of mercury (II) was therefore assessed for Eisenia fetida, Enchytraeus albidus and Folsomia candida using standard test protocols. The 21-day EC₅₀ (the concentration causing 50% effect) for the cocoon production of E. fetida was 9.16 mg Hg kg^-1 dry wt. Based on the reproduction, a 42-day EC₅₀ of 22.0 mg Hg kg^-1 dry wt was observed for E. albidus while for F. candida the 28-day EC₅₀ was 3.26 (2.45-4.05) mg Hg kg^-1 dry wt. Although these data can be considered as a step forward in the assessment of the potential risks of mercury in terrestrial environments, further research is needed to evaluate the influence of soil parameters on the toxicity of mercury and to quantify the effect of ageing on the bioavailability.     

Toxicity of metals to the earthworm Eisenia fetida

Summary Development of methods to measure the effect of man's residuals on soil ecosystems is desirable. Earthworms, as one of the largest and most easily obtained components of the soil biota, are suitable for evaluating perturbations to soil ecosystems.The impact of five metals (Cd, Cu, Ni, Pb, and Zn) on the survival of the earthworm Eisenia fetida (Savigny) was evaluated using the contact and artificial soil tests. There was no difference in toxicity between the different metal salts (acetate, chloride, nitrate, and sulfate) of each of the five metals using the contact test. In the contact test, the order of toxicity, from most toxic to least toxic, was Cu > Zn > Ni Cd > Pb. The nitrate salt of the five metals was tested using the artificial soil test and the order of toxicity, from most toxic to least toxic, was Cu Zn Ni > Cd > Pb. Stress on earthworm populations, as shown by weight loss, was shown to increase with increasing concentrations of metal salts.These studies indicate that: (a) earthworms can be a suitable biomonitoring tool to assist in measuring the effect of metals in wastes added to soils and (b) the contact and artificial soil tests can measure the biological impacts.Research Associate, Research Technician, and Research Support Specialist, respectivelyAt the time of this research, Dr. Loehr was a Professor of Agricultural Engineering and of Environmental Engineering, Cornell University. He currently is the H.M. Alharthy Centennial Chair Professor, Civil Engineering Department, University of Texas, Austin, Texas 78712     

Short-term exposure to carbaryl and UV radiation increases the reproduction output of the collembolan Folsomia candida

Purpose

Ecotoxicological risk assessment of chemical compounds is considered more accurate when mixtures of chemicals and/or interactions between chemicals and natural stressors are considered. To further simulate natural conditions, under which organisms are often exposed to combinations of natural and anthropogenic stressors, the combined exposure of a widely used insecticide, carbaryl, under UV radiation was evaluated. It is more than likely that soil organisms are confronted with a combination of chemical exposure and increasing UV irradiance on the terrestrial habitat. Considering the heterogeneity of contamination in field soils and the probability of collembolan to avoid contaminated soil (less time under exposure), combined effects of carbaryl and ultraviolet radiation were evaluated, by using a short exposure to Folsomia candida.

Materials and methods

Single exposures to carbaryl and UV radiation were performed, and adult mortality and number of laid and hatched eggs were reported. Following the results, a combined exposure was carried out, using the same conditions performed previously in the single tests. Organisms were exposed simultaneously to carbaryl (from 1 to 7 mg kg^?1) and UV doses (from 1,121.29 to 3,795.26 J m^?2), the last corresponds to 1 to 4 h of exposure. Mortality was reported, and organisms were left to lay eggs in culture boxes.

Results and discussion

Both ultraviolet radiation and high concentrations of carbaryl as single stressors increased the number of produced eggs of F. candida, with significant differences at higher concentrations (4, 5.5, and 7 mg kg^?1) of carbaryl and an EC50 of 5.93 mg kg^?1. In the case of UV radiation, statistical differences were found at all concentrations compared with control, with an EC50 of 1,248.24 J m^?2. In both cases, no significant mortality was observed. When combined, both stressors acted independently on egg production, showing additivity of effects (independent action (IA) model to data on laid eggs; SS?=?0.00056; r2?=?0.75; p?Conclusions This study highlights the importance of taking UV exposure conditions into account when assessing the impact of pesticides to soil biota and looking for more realistic scenarios while showing that soil sheltering occurs only up to a certain extent and that indirect effects can be observed. The opposite trends on responses obtained under standardized tests and short exposures to carbaryl provided some insight on the possible effects of carbaryl during collembolan life cycle.     

Toxicity of chemical-warfare agent HD to Folsomia candida in different soil types

We investigated the ecotoxicity of the chemical-warfare agent (CWA) HD (Mustard) using Collembola reproduction test with numbers of adults and juveniles as measurement endpoints. Toxicity tests were conducted using soils with contrasting parameters to investigate the effects of soil properties on chemical toxicity. These included standard artificial soil (SAS; 10% OM; 6 pH), O’Neill-Hall sandy loam (OHSL; natural soil with 4.3% OM; 5.1 pH), and Sassafras sandy loam (SSL; natural soil with 2% OM; 4.9 pH). Soils were individually spiked with HD concentrations ranging from 1 to 125 mg kg^–1. Lowest observed effect concentrations (LOECs) for adult mortality were 25, 50, and 6.97 mg kg^–1 for SAS, OHSL, and SSL, respectively. The LOECs for reproduction were 6.97, 6.25, and 1.9 mg kg^–1 for SAS, OHSL, and SSL, respectively. HD toxicity to both adults and juveniles was greater in SSL. These results show that soil toxicity testing should not rely solely on the adult acute endpoints using artificial soils, but should include assays with reproductive endpoints using natural soils with varying physical and chemical parameters to adequately assess toxicity to test species.     

Colonization of nonmycorrhizal plants by mycorrhizal neighbours as influenced by the collembolan, Folsomia candida

 Soil microarthropods have been shown to stimulate or be detrimental to arbuscular mycorrhizal function by their grazing actions, but their role as dispersal agents has not been assessed. The ability of three species of arbuscular mycorrhizal (AM) fungi (Glomus etunicatum, Acaulospora denticulata, Scutellospora calospora) infecting Plantago lanceolata roots to further colonize neighbouring plants was measured in response to the distance between root systems and the presence of the collembolan, Folsomia candida. In the absence of collembola, all three fungal species infected neighbouring plants in two weeks or less (at short distances), but were not successful when neighbouring plants were placed 45 cm away or further. Colonization by G. etunicatum was the quickest at short distances, but S. calospora showed greatest ability to colonize at increasing distance,whereas A. denticulata was intermediate. In the presence of the collembolan, G. etunicatum took longer to colonize neighbouring plants, but was able to infect at least 30 cm further, illustrating the arthropod's ability to disperse the AM inoculum. A. denticulata increased its range by 10 cm in the presence of F. candida, but unlike G. etunicatum, there was no delay in the colonization. In contrast, colonization of neighbouring plants by S. calospora was negatively affected both in terms of overall distance and time. These data support the hypothesis that soil arthropods can act as dispersal agents for AM inoculum, but the extent of this is fungal species-specific. Received: 1 July 1998     

聚丙烯酰胺对蚯蚓的毒性效应

聚丙烯酰胺作为全球应用最广泛,用量最大的水处理剂,而其排放到环境中可能会对生态环境形成潜在的威胁。该研究在人工土壤条件下,通过急性和亚急性暴露试验研究了聚丙烯酰胺和丙烯酰胺对赤子爱胜蚓存活、生长和繁殖的影响,旨在评价聚丙烯酰胺和丙烯酰胺对蚯蚓的毒性效应。结果表明,聚丙烯酰胺和丙烯酰胺对蚯蚓的半致死剂量分别为大于2000和164.01?mg/kg,聚丙烯酰胺比丙烯酰胺毒性低;在急性和亚急性毒性暴露期内,聚丙烯酰胺对蚯蚓的存活和生长无显著影响;而当丙烯酰胺浓度大于100?mg/kg时即对蚯蚓的存活和生长产生显著的影响（P＜0.05）。聚丙烯酰胺和丙烯酰胺均对蚯蚓的繁殖能力有非常显著的影响（P＜0.05）。因此残留于污泥中的聚丙烯酰胺对环境有一定的潜在风险。     

Biochemical responses of the earthworm Eisenia fetida andrei exposed to contaminated artificial soil,effects of carbaryl

The aim of this study was to investigate the effects of carbaryl, at different concentrations and exposure times, on the biochemical responses of the earthworm, Eisenia fetida andrei (E. andrei) to: (1) elucidate the mechanisms of action of carbamate compounds; and (2) explore the potential for using these responses as biomarkers to monitor carbamate-contaminated soils or for use in sublethal assays to test chemicals in the laboratory. Thus, earthworms were exposed to increasing concentrations of carbaryl (CA) (12, 25 and 50 mg kg⁻¹ artificial soil) for different periods of time (2, 7 and 14 days) using the standard soil test method. The activities of the following enzymes were measured: catalase (CAT), acetylcholinesterase (AChE), glutathione reductase (GR), glutathione-S-transferase (GST), methoxyresorufin-O-deethylase (MROD) and NADH (NADH Red) and NADPH (NADPH Red) cytochrome reductases activities. Levels of lipid peroxides (LP), peroxidizable lipids (LPI), total glutathione (total GSH) and the percentage of oxidized glutathione (%GSSG) were also determined. Our results showed that cholinesterases are the main target of carbaryl in E. andrei. Carbaryl also inhibited biotransformation enzyme activities but did not induce oxidative stress. Changes were detected in phase I and acetylcholinesterase activities upon exposure to the lowest dose of carbaryl (12 mg kg⁻¹). This demonstrated the sensitivity of these parameters in E. andrei. In addition, discrimination between doses and exposure times was clearer when all the responses were considered rather than a selective choice of biomarkers. This confirms our previous finding that a suite of biochemical responses could be used as a sublethal assay for testing chemicals in the laboratory or for soil contamination surveys.     

Comparison of the effects of zinc nitrate-tetrahydrate and tributyltin-oxide on the reproduction and avoidance behavior of the earthworm Eisenia andrei in laboratory tests using nine soils

The aim of this contribution was to evaluate whether the sensitivity of the earthworm avoidance test is comparable to that of the earthworm reproduction test (standard test guidelines for both are available). The objective was to determine if relatively simple short-term tests are useful as an initial screening step for the environmental risk assessment (ERA) of potentially contaminated soils prior to performing long-term, elaborate tests. Therefore, the effects of two model substances, zinc nitrate-tetrahydrate and tributyltin-oxide (TBT-O) on the reproduction and the avoidance behavior of the earthworm Eisenia andrei were compared using Organization for Economic Co-operation and Development (OECD) artificial soil as well as eight natural soils, including LUFA St. 2.2 soil, covering a wide range of pH-values, organic matter content and texture. Almost all tests fulfilled the validity criteria defined in the two standard guidelines published by the International Organization for Standardization (ISO), despite the fact that the properties of natural soils differed clearly from those of OECD artificial soil. The median effective concentration (EC50) values estimated for zinc nitrate-tetrahydrate in 48-h avoidance tests and in 56-day reproduction tests were often similar when using the same soil (seven out of nine soils). However, in the case of TBT-O, the outcome was more complex: in two test soils the avoidance EC50 values were by a factor >3 higher than the reproduction EC50 values. In one of the test soils it was the other way around and the remaining soils showed comparable EC50 values in both tests. Summarizing the results obtained here and according to experiences reported in the available literature, the earthworm avoidance test may be recommended as an initial screening tool in the ERA of potentially contaminated soils. However, further research is needed to understand the factors that contribute to the difference in sensitivity between reproduction and avoidance tests.     

The influence of soil characteristics on the toxicity of four chemicals to the earthworm Eisenia fetida andrei (Oligochaeta)

Summary The acute toxicity of Cd (chloride), chloroacetamide, 3,4-dichloroaniline and pentachlorophenol to the earthworm Eisenia fetida andrei was determined using the OECD (1984) artificial soil and contact testing procedures. To investigate the influence of two soil characteristics (pH and organic-matter content), the toxicity of the chemicals was also determined in two natural sandy soils. It is concluded that the filter-paper contact test cannot be recommended to predict earthworm toxicity of these chemicals in soil. Toxicity in soil was influenced by both pH and organic-matter content. Differences between LC₅₀ values in the high-organic-matter artificial soil and in an acid, low-organic-matter sandy soil were, however, not greater than a factor of 3–4. The results of this study therefore support the use of a well-defined artificial soil substrate for standardized earthworm toxicity tests.     

A comparison of the biology of Eisenia fetida and Eisenia andrei (Oligochaeta)

Summary Specimens of locally occurring Eisenia fetida were compared with specimens of E. fetida and E. andrei obtained from France. All specimens were cultured in the laboratory under controlled conditions and growth, maturation, cocoon production, hatching success, and the number of hatchlings were compared. The results showed some differences between the two forms. The eventual worm biomass was the same for both, although the growth reats and the rate at which maturity was attained differed. E. andrei had a higher cumulative cocoon production. Although the local worms resembled E. andrei in appearance their cocoon production rate resembled that of E. fetida from France. E. andrei produced higher numbers of hatchlings per cocoon. The results show that the biology of the two species/forms is similar. The study did not provide convincing proof to substantiate a taxonomic distinction between the two forms of Eisenia.     

Density-dependent grazing on the extraradical hyphal network of the arbuscular mycorrhizal fungus, Glomus intraradices, by the collembolan, Folsomia candida

The effect of microarthropod density on the relative palatibility of selected microfungi and on the integrity of extraradical arbuscular-mycorrhizal (AM) hyphal networks was examined. A series of microcosm experiments were conducted using two conidial fungi (Alternaria alternata and Trichoderma harzianum), one AM fungus (Glomus intraradices) and the microarthropod Folsomia candida (Collembola). We did not detect a significant effect of athropod density on food preference. Food preferences for conidial over mycorrhizal hyphae were consistent across a wide range of collembolan densities. Collembolan density did, however, have a significant effect on the numbers of extraradical AM hyphae which were severed from the plant root in vitro. Even in the presence of a preferred food source, numbers of severed AM hyphal networks increased with increasing collembolan density. Also, the fecundity of Folsomia candida increased in the presence of preferred food sources. We conclude that microarthropod population densities are influenced by the fungal species available and that the potential of microarthropods to impair the efficacy of AM symbioses is density-dependent. Received: 16 May 1997     

Terbuthylazine and carbofuran effects on growth and reproduction within three generations of Eisenia andrei (Oligochaeta)

Sublethal effects of terbuthylazine and carbofuran on the growth and reproduction of Eisenia andrei were investigated over a period of three generations. Reproduction was assessed by measuring the coccon production of worms treated chronically with pesticides. Inhibition of cocoon production was found in the parental generation. Hatchlings were raised from cocoons to provide the F₁ generation. During raising a more rapid growth of juveniles treated with terbuthylazine was observed, compared with the growth of untreated worms. The increase in vitality was also found in cocoon production. Groups treated with terbuthylazine produced more cocoons than controls. The F₂ generation was raised from hatchlings of the F₁ generation, and here, also the terbuthylazine treatments increased earthworm growth, but not cocoon production. Exposure to carbofuran decreased cocoon production in all generations. Growth of the F₁ generation was not influenced by low concentrations of carbofuran.     

Toxicity of chlorpyrifos,carbofuran, mancozeb and their formulations to the tropical earthworm Perionyx excavatus

Effects of chlorpyrifos, carbofuran, mancozeb and their formulated products on survival, growth and reproduction of the tropical earthworm Perionyx excavatus were investigated in standard artificial soil. The toxicity of the three chemicals decreased in the order carbofuran > chlorpyrifos > mancozeb. In general, formulations were more toxic than the active ingredients, but differences in LC₅₀ and EC_x values were significant only in two cases and not more than a factor of 2.0. This could mainly be due to masking of the effects of additives in the soil. Comparison with available survival data revealed that P. excavatus is more sensitive than the standard test species Eisenia andrei or E. fetida. The use of tropical species in the risk assessment of pesticides in tropical regions should therefore be encouraged.     

Factors affecting the structural stability of three contrasting soils of China

The structural stability of eight samples representing three soil profiles from tropical and subtropical regions of China (Latosol, Red Earth and Yellow Brown Earth) was studied by dispersion treatments. The samples were treated with the following solutions in order without previous mechanical disruption: (I) H₂O, (II) 0.1 N NaCl, (III) 0.002% Na₂CO₃, (IV) 0.1 N NaOH, (V) acid oxalate, (VI) 0.1N NaOH. These procedures were designed to disperse soil samples by removal of potentially aggregating substances and by anion adsorption. After each treatment the clay dispersed was separated by sedimentation and its mineralogical composition was studied by XRD, Mössbauer spectroscopy and magnetic susceptibility measurements to assess the role of mineralogy in the maintenance of soil structure. The amounts of iron extracted by Na-dithionite–citrate–bicarbonate were 9.6–10.8% in the Latosol, 3.1–3.4% in the Red Earth and 0.9–2.1% in the Yellow Brown Earth. It was concentrated in clay fractions and existed mainly as superdispersed particles. The hematite/goethite ratio varied from 1.7 for the Latosol to 0.2 for the Yellow Brown Earth. The clay fraction of the Yellow Brown Earth is vermiculitic and has a permanent negative charge. This soil's structural stability is mainly influenced by exchangeable Ca²⁺. In the Latosol and the Red Earth, surfaces with variable (pH-dependent) charges prevail because of the large free Fe-oxides contents. Alkaline treatment (IV) promoted most dispersion of these soils, indicating the mainly electrostatic nature of interactions between mineral particles. Thus, the role of the Fe oxide minerals in these soils is one of aggregation rather than cementation. The aggregation properties of the Latosol and Red Earth are relict paleosol features inherited from an earlier period of cooler and wetter climate than the present.     

Transformation of 15N-labelled leguminous plant material in three contrasting soils

Summary Two soils from Pakistan (Hafizabad silt loam and Khurrarianwala silt loam) and one from Illinois, USA (Drummer silty clay loam) were incubated with ¹⁵N-labelled soybean tops for up to 20 weeks at 30°C. Mineralization of soybean ¹⁵N was slightly more rapid in the Pakistani soils, and after 20 weeks of incubation, 50%, 53%, and 56% of the applied ¹⁵N was accounted for as (NH₄ ⁺+NO₃ ^–)-N in Drummer, Hafizabad, and Khurrarianwala soils, respectively. Potentially mineralizable N (determined by anaerobic incubation) varied between 1.5% and 10% of the applied ¹⁵N in the three soils at different stages of incubation; somewhat higher percentages were mineralizable in the Pakistani soils than in the Drummer soil. From 3.7% to 9% of the applied ¹⁵N was accounted for in the microbial biomass. From 10% to 32% of the applied N was recovered in the humic acid and fulvic acid fractions of the organic matter by sequential extraction with Na₄P₂O₇ and NaOH; from 12% to 49% was recovered in the humin fraction. Of the three soils, Drummer soil contained more ¹⁵N as humic and fulvic acids. In all cases, the ¹⁵N was approximately equally distributed between the humic and fulvic acid fractions. A significant percentage of the humin ¹⁵N (52%–78%, equivalent to 8%–34% of the applied ¹⁵N) occurred in non-hydrolyzable (6 N HCl) forms. Of the hydrolyzable ¹⁵N, 42%–51% was accounted for as amino acid-N followed in order by NH₃ (17%–30%), hydrolyzable unknown forms (20%–22%), and amino sugars (6%–2%). The recovery of applied ¹⁵N for the different incubation stages was 87±22%. Recovery was lowest with the Khurrarianwala soil, presumably because of NH₃ volatilization losses caused by the high pH of this soil.     

Differences in ionic properties of salts affect saline toxicity to the earthworm Eisenia fetida

Most studies on the effect of salinity on soil organisms are conducted with NaCl but this might not be representative of effect when other salt ions are predominant. To assess the impact of different salt cations and anions on saline toxicity to earthworms, two experiments were conducted with specimens of Eisenia fetida exposed in the laboratory for 28 days using OECD artificial soil. In both experiments, series of concentrations (0–125 mM) of different salts were used. In experiment 1, which focused on cations, soil salinity was adjusted using NaCl, KCl, CaCl₂ or MgCl₂ while in the second experiment, which focused on anions: NaCl, NaNO₃, NaHCO₃, Na₂HPO₄ or Na₂SO₄ were used to allow partial comparison of the toxic effects of the cations and anions. The changes in electrical conductivity (EC) of substrates under the different salts were assessed at the beginning of the experiments. Mortality and weight change of worms were assessed at days 14 and 28. In experiment 1, the chlorides of the divalent cations (Mg²⁺ and Ca²⁺) had similar EC values which were higher than those of the monovalent cations (Na⁺ and K⁺) and this could explain their higher effects on all worm parameters than those of the monovalent cations. In experiment 2, among the anions, SO₄²⁻ had the highest EC value while HCO₃²⁻ had the lowest. The toxicity of the ions did not correlate perfectly with the EC values; therefore the use of EC in the assessment of saline toxicity to soil organisms should be used with caution. These results suggest that the ionic constitution of salts could define the severity of saline toxicity to earthworms, therefore a site specific assessment of soil salinization in affected areas with respect to type of predominant ions should be considered.     

The response of a high-yielding canola hybrid to sulfur fertilization in three contrasting Saskatchewan soils

Abstract

Canola (Brassica napus) is the primary oilseed crop in western Canada; however, it is often grown on sulfur (S)-deficient soils. Moreover, canola has a high S demand compared to cereals and, therefore, is particularly sensitive to S deficiency. This study examined the growth and nutrient uptake responses of a high-yielding canola hybrid cultivar to S fertilization when grown on three contrasting soils differing in S fertility, with and without the addition of fertilizer S. The soils were collected from three soil-climatic zones within Saskatchewan (Brown, Black, and Gray) and three different fertilizer S forms were used: ammonium sulfate (AS); ammonium thiosulfate (ATS); and a composite fertilizer containing nitrogen (N), phosphorus (P), and S (NPS; 50-50 blend of sulfate (SO₄) salt and elemental S). Sulfur fertilization increased the canola biomass, along with plant uptake of N, P, and S on all three soils. Fertilizer S use efficiency (i.e. recovery) ranged from 11-75%. For all three soils, the general trend among fertilizer S forms for biomass, nutrient uptake, and fertilizer use efficiency was AS?>?ATS?>?NPS. The greatest differences were observed with the Gray soil, which had the poorest S fertility. Residual soil SO₄ after harvest was greater for ATS and NPS; reflecting continued oxidation of thiosulfate and elemental S to SO₄. Principal component analysis demonstrated the importance of tissue N:S ratio as a key diagnostic measurement related to canola growth and nutrient uptake in S-deficient soils.