A. de Varennes

Evaluation of composts and liming materials in the phytostabilization of a mine soil using perennial ryegrass

A microcosm experiment was carried out to evaluate the effects of municipal solid waste compost (MSWC) or garden waste compost (GWC), and liming materials in the rehabilitation of a soil affected by mining activities, and to study the use of perennial ryegrass (Lolium perenne L.) for phystostabilization. The performance of the amendments was assessed by soil chemical parameters, total and bioavailable metals (Cu, Pb and Zn), soil enzymatic activities, and plant relative growth and mineral composition. In general, both composts corrected soil acidity and increased the total organic matter content of the soil, although with a better performance in the case of MSWC, especially when considering total N and available P and K levels in the amended soil. The application of both composts and liming materials led to a decrease in the mobile fractions of Cu, Pb and Zn, but mobilisable fractions of Cu and Zn increased with MSWC application. Plant biomass increased more than three times in the presence of 50 Mg MSWC ha(-1) and with the combined use of 25 or 50 Mg MSWC ha(-1) and CaO, but no significant differences were observed when GWC was applied. Plant tissue analysis showed that the treatments did not significantly reduce Cu, Pb and Zn uptake by the plant. Dehydrogenase, and the enzymes related to the N-cycle, urease and protease, had increased activities with increasing MSWC application rate. Conversely, the enzymatic activities of both enzymes related to the C-cycle, cellulase and beta-glucosidase, were only positively affected by GWC application, a compost obtained from raw materials rich in C. Principal component analyses evidenced this clear separation between the effect of MSWC on soil enzymes related to the N-cycle and of GWC on soil enzymes related to the C-cycle. This study indicates that MSWC (50 Mg ha(-1), limed or unlimed) can be used successfully in the remediation of a highly acidic metal-contaminated soil, allowing the establishment of perennial ryegrass.

Assessment of chemical, biochemical and ecotoxicological aspects in a mine soil amended with sludge of either urban or industrial origin

A greenhouse pot experiment was conducted to evaluate the effect of sewage sludge (SS), of sugar beet sludge (SBS), or of a combination of both, in the remediation of a highly acidic (pH 3.6) metal-contaminated soil, affected by mining activities. The SS was applied at 100 and 200 Mg ha(-1) (dry weight basis), and the SBS at 7 Mg ha(-1). All pots were sown with Italian ryegrass (Lolium multiflorum Lam.). After 60 d of growth, shoot biomass was quantified and analysed for Cu, Pb and Zn. The pseudo-total and bioavailable contents of Cu, Pb and Zn and the enzymatic activities of beta-glucosidase, acid phosphatase, cellulase, protease and urease were determined in the soil mixtures. Two indirect acute bioassays with leachates from the soil (luminescent inhibition of Vibrio fischeri and Daphnia magna immobilization) were also used. The SS, in particular when in combination with SBS, corrected soil acidity, while increasing the total organic matter content and the cation exchange capacity. The application of SS led to a decrease in the level of effective bioavailable metals (extracted by 0.01 M CaCl(2), pH 5.7, without buffer), but caused an increase in their potential bioavailability (extracted by a solution of 0.5M NH(4)CH(3)COO, 0.5 M CH(3)COOH and 0.01 M EDTA, pH 4.7). Plant biomass increased more than 10 times in the presence of 100 Mg SS ha(-1), and more than five times with the combined use of 100 Mg SS ha(-1) and SBS, but a considerable phytotoxic effect was observed for the application rate of 200 Mg SS ha(-1). Copper, Pb and Zn concentrations in the shoots of L. multiflorum decreased significantly when using 100 Mg SS ha(-1) or SBS. The activities of beta-glucosidase, urease and protease increased with increasing SS applications rates, but cellulase had a reduced activity when using 200 Mg ha(-1)SS. Both amendments were able to suppress soil toxicity to levels that did not affect D. magna, but increased the soil leachate toxicity towards V. fischeri, especially with the application of 200 Mg SS ha(-1). This study showed that for this type of mine soils, and when using SS of similar composition, the maximum SS application rate should be 100 Mg ha(-1), and that liming the SS amended soil with SBS did not contribute to a further improvement in soil quality.

Application of an insoluble polyacrylate polymer to copper‐contaminated soil enhances plant growth and soil quality

We investigated whether an insoluble polyacrylate polymer could be used to improve the quality of a copper-contaminated soil. Growth of annual medic (Medicago polymorpha L.) was stimulated in the polymer-amended soil, such that total biomass produced was three times that of plants from unamended soil. Roots of plants cultivated in the polymer-amended soil had a concentration of copper that was 73% of that in plants from the unamended soil. Biological N 2 fixation was enhanced in the polymer-amended soil. Soil enzymatic activities at the end of the experiment were correlated with plant growth and copper concentration of plants grown in soils with different levels of copper, which were achieved by mixing the contaminated soil with varying proportions of a soil of low copper content. Shoot dry weight was positively correlated with acid phosphatase, β-glucosidase, β-galactosidase and urease, whereas copper concentration in the roots of the annual medic was negatively correlated with acid phosphatase, β-galactosidase, cellulase and urease. The results are consistent with soil remediation by the polyacrylate polymer. Soil quality as inferred from plant growth, biological N 2 fixation and soil enzymatic activities improved as a result of the remediation process.

Effects of heavy metals on the growth and mineral composition of a nickel hyperaccumulator

Abstract Alyssum pintodasilvae Dudley is a nickel (Ni) hyperaccumulator endemic to serpentine soils of north‐east Portugal. In one experiment, the effects of cadmium (Cd), chromium (Cr), copper (Cu), Ni, lead (Pb), and zinc (Zn) on the growth and mineral composition of this species were evaluated. The growth of A. pintodasilvae, measured by dry matter accumulation, was not influenced by the presence of Cr, Cu, Pb, Ni, or Zn in the soil, but Cd applications led to significant decreases in dry matter yield. The addition of heavy metals to the soil resulted in increased uptake and translocation by A. pintodasilvae but only Ni was accumulated to high levels. In a second experiment, two cuts of A. pintodasilvae, grown on a Ni‐enriched soil, were compared. Nickel concentrations were higher in the second cut, suggesting the possibility of continued growth and harvest of this plant to detoxify Ni‐contaminated soils.

The Effect of Compost Treatments and A Plant Cover with Agrostis tenuis on the Immobilization/Mobilization of Trace Elements in a Mine-Contaminated Soil

A semi-field experiment was conducted to evaluate the use of mixed municipal solid waste compost (MMSWC) and green waste-derived compost (GWC) as immobilizing agents in aided-phytostabilization of a highly acidic soil contaminated with trace elements, with and without a plant cover of Agrostis tenuis. The compost application ratio was 50 Mg ha–1, and GWC amended soil was additionally limed and supplemented with mineral fertilizers.Both treatments had an equivalent capacity to raise soil organic matter and pH, without a significant increase in soil salinity and in pseudo-total As, Cu, Pb, and Zn concentrations, allowing the establishment of a plant cover. Effective bioavailable Cu and Zn decreased as a consequence of both compost treatments, while effective bioavailable As increased by more than twice but remained as a small fraction of its pseudo-total content. Amended soil had higher soil enzymatic activities, especially in the presence of plants.Accumulation factors for As, Cu, Pb, and Zn by A. tenuis were low, and their concentrations in the plant were lower than the maximum tolerable levels for cattle. As a consequence, the use of A. tenuis can be recommended for assisted phytostabilization of this type of mine soil, in combination with one of the compost treatments evaluated.

Use of hydrophilic polymers from diapers to aid the establishment of Spergularia purpurea in a mine soil

We used hydrophilic polymers from diapers to aid the establishment of an indigenous plant (Spergularia purpurea (Persoon) G. Don fil.) in a soil from a pyrite mine. Lysimeters were filled with the mine soil with no amendment (control), with a polyacrylate polymer, with a polymer removed from diapers, and with shredded diapers. The establishment of a plant cover was faster in soil amended with polymer from diapers, and 85 days after sowing the soil was completely covered in all treatments except control. The concentrations of trace elements in plant shoots decreased in amended soil. The activities of soil acid phosphatase, beta-glucosidase, protease and cellulase were greatest in soil amended with the polyacrylate polymer or with polymer removed from diapers, while the application of shredded diapers leads to values that were in general intermediate between these treatments and unamended control. Basal- and substrate-induced respirations, and dehydrogenase were greatest in soil amended with polymers, but the presence of a plastic film and fibrous materials from shredded diapers prevented any improvement in these parameters compared with unamended soil. In the second experiment, we evaluated the risk of downward movement of polymers in columns of a sandy soil. Polymer from diapers, with or without Cu, was placed at a 10 cm-depth. Five leaching cycles with artificial rain took place and leachates were analyzed for organic matter and Cu. At the end of the experiment, the soil columns were sliced and each layer was analyzed separately. Some repacking of soil and polymer particles took place, but there was no indication that polymers moved to any great depth in soil columns.

Predicting the concentration and uptake of nitrogen, phosphorus and potassium by field-grown green beans under non-limiting conditions

As part of a program to develop a weather-driven model to predict yield and quality of green beans that also describes the accumulation and distribution of nutrients by these plants, we required information on the evolution of the N, P and K content and concentration within the crop. A field experiment with three widely grown green bean cultivars (Phaseolus vulgaris L. cv. Carlo, Cleo and Mutin) was made with eight sowing dates over 2 years. Water and nutrients were supplied to ensure that they would not limit plant growth. Weather data was collected hourly. Dry matter accumulation and the concentrations of N, P and K in the shoots were determined each week. The concentration of N was related to thermal time by a logistic equation, while P concentration was linearly related to thermal time in the early stages of development but became constant later on. A model that combined the effects of developmental stage and temperature, or saturation vapour pressure deficit, explained the concentration of K. Upper and lower boundary lines were adjusted to total uptake of nutrients, representing the maximum or minimum amount of each nutrient present in the above-ground tissues in relation to thermal time. The harvest index of nutrients depended on the partition of dry matter between pods and shoots, according to a logistic function, and the concentration of nutrients in the pods and shoots.

Sorghum detoxification mechanisms

ABSTRACT The influence of cadmium (Cd) on internal and external defense mechanisms of Sorghum bicolor (L.) Moench. x Sorghum sudanense was studied by electrochemical methods to infer the type of detoxification processes developed by the plant under environmental stress conditions. Hydroponic experiments with sorghum were conducted in nutrient solutions in the absence and presence of 0.1 mg Cd L−1. Plant exposure to Cd stimulated the release of root exudates with metal-binding affinity. However, their presence should not affect significantly the bioavailability of Cd, since the complex was dissociated within a very short period (≤ 50 milliseconds) in response to the consumption of the free metal ion at the root interface. The presence of Cd in the solution also stimulated a very significant increase of thiolic groups inside the plant, even at the very low concentration of 0.1 mg Cd L−1. These results suggest that the main defense mechanism developed by sorghum against metal toxicity is an internal process, i.e., the synthesis of phytochelatins.

Improvement in soil and sorghum health following the application of polyacrylate polymers to a Cd-contaminated soil

Contamination of soils with cadmium (Cd) is a serious global issue due to its high mobility and toxicity. We investigated the application of insoluble polyacrylate polymers to improve soil and plant health. Sorghum was grown in a Cd-contaminated sandy soil. Polyacrylate polymers at 0.2% (w/w) were added to half of the soil. Control soil without plants was also included in the experiment. Growth of sorghum was stimulated in the polymer-amended soil. The concentration of Cd in the shoots, and the activities of catalase and ascorbate peroxidase decreased in plants from polymer-amended soil compared with unamended control. The amount of CaCl(2)-extractable Cd in the polymer-amended soil was 55% of that in the unamended soil. The Cd extracted in sorghum shoots was 0.19 mg per plant grown on soil without polymer and 0.41 mg per plant grown on polymer-amended soil. The total amount of Cd removed from each pot corresponded to 1.5 and more than 6% of soil CaCl(2)-extractable Cd in unamended and polymer-amended soil, respectively. The activities of soil acid phosphatase, beta-glucosidase, urease, protease and cellulase were greatest in polymer-amended soil with sorghum. In conclusion, the application of polyacrylate polymers to reduce the bioavailable Cd pool seems a promising method to enhance productivity and health of plants grown on Cd-contaminated soils.

Soil quality indicators response to application of hydrophilic polymers to a soil from a sulfide mine

In soils impacted by mining activities a vegetal cover is required to protect the site from the erosive forces of water and wind. The success of this objective depends on plant establishment and canopy closure. Polyacryalate polymers aid the growth of crops and indigenous plants in soils from sulfide mines. Soil characteristics change as a consequence of polymer application, but indicators that pinpoint these changes have not been identified yet. Our objectives were to (1) identify the sensitive indicators of changes in soil quality following polymer application, (2) relate these with assessment based on plant growth and soil cover. A mine soil was left unamended or received a characterized polyacrylate, a polyacrylate removed from diapers, or shredded diapers. Biomass of Spergularia purpurea was measured and proportion of soil cover evaluated. Soil enzymes, microbial activity, and respiration were analyzed. Availability of potentially toxic trace elements was estimated by their concentration in shoots. Factor analysis identified three factors that accounted for 94% of the variation in parameters, and the scores separated the four treatments. The indicators with greatest communality were correlated with plant growth and soil cover. The best soil quality indicators were As and Zn in shoots, protease, β-glucosidase, and fructose-induced respiration. It seems that the most important indicators to be used to assess the restoration of sulfide mine soils are those related with bioavailability of trace elements and soil enzymatic activities.