J.M. Murillo

Heavy metal pollution of soils affected by the Guadiamar toxic flood.

Total heavy metal concentrations were determined in soil samples of seven selected areas along the Guadiamar river valley affected by the toxic flood, after removal of the deposited sludge. Mean total concentrations of nine elements (As, Au, Bi, Cd, Cu, Pb, Sb, Tl and Zn) out of the 23 (As, Au, Ba, Be, Bi, Cd, Co, Cr, Cu, In, Mn, Mo, Ni, Pb, Sb, Sc, Sn, Th, Tl, U, V, Y and Zn) analysed were higher in sludge-covered soils than in unaffected soils. Mean values of total As, Au, Pb, Sb, Tl and Zn in sludge-affected soils were higher than the upper limits for normal soils world-wide. Mean concentrations of Bi, Cd and Cu were within these ranges, although some individual values exceeded the upper limits. In all sampling areas, severe heavy metal pollution was observed in the superficial layers (0-20 cm) of most of the affected soils, which decreased downward in the soil profile. Generally, in soils with more than 25% of clay, concentration of heavy metals below the 20-cm depth decreased to values close to those of the background level of the Guadiamar valley soils, while in coarser soils, heavy metal pollution penetrated below this depth, being noticeable down to a depth of at least 50-80 cm.

Bioaccumulation of As, Cd, Cu, Fe and Pb in wild grasses affected by the Aznalcóllar mine spill (SW Spain).

The collapse of the tailing dam in the Aznalcóllar pyrite mine (SW Spain) occurred in April 1998 and affected approximately 4300 ha along the Agrio and Guadiamar valleys. An urgent soil cleaning up and remediation programme was started just after the accident. Eighteen months later, mineral nutrients and trace elements concentration in soil and two wild grasses--Cynodon dactylon and Sorghum halepense--have been studied. Three types of conditions are distinguished: (a) unaffected soils (control); (b) cleaned up and remediated soils (remediated); and (c) sludge-covered soils left in a fenced plot (non-remediated). As, Cd, Cu and Pb in grasses reached toxic levels for the food web in the non-remediated plot, while on remediated soils only Cd reached a toxic level in grass tissues. However, Pb and, to a lesser extent As and Fe, reached also toxic levels in unwashed plants (as they would be ingested by animals) in remediated soils. Both native grasses seem tolerant of trace elements pollution and suitable for stabilisation of spill-affected soils.

Land treatment of olive oil mill wastewater

Experiments carried out in lysimeters filled with two calcareous clayey soils (ca 40% CaCO3; ca 40% clay), showed that a 2m layer of soil almost completely removed the organic and inorganic components of olive oil mill wastewater (OMW) when it was applied in doses of 5000–10000m3ha−1year−1. This efficiency was maintained for at least 2 years. In field experiments, the application of OMW to one of these soils during three successive years at an annual rate of up to 6000m3ha−1 caused changes in some chemical properties of the soil, especially in the upper layer (0–50cm). Concentrations of soil organic matter, Kjeldahl N, soluble NO3 and available P increased enhancing soil fertility. On the other hand, soil electrical conductivity and sodium adsorption ratio also increased but below the levels representing salinization or sodification hazard for the soil. Furthermore, leaching of Na+ and NO3− below the 1 m layer were detected.

Soil physical properties, water depletion and crop development under traditional and conservation tillage in southern Spain

Tillage methods affect soil physical properties and, thus, have a direct influence on the replenishment and depletion of soil water storage and crop performance. This study was conducted to determine the effects of traditional and conservation tillage on soil physical properties, soil water replenishment and depletion, and crop development and yield under southern Spanish conditions. The experiments were carried out from 1992 to 1995 in a sandy clay loam soil (Xerofluvent). The traditional tillage (TT) method consisted mainly of the use of mouldboard ploughing, and the conservation tillage (CT) was characterized by not using mouldboard ploughing, by reduction of the number of tillage operations and leaving the crop residues on the surface as mulch. In both tillage treatments a wheat (Triticum aestivum, L.)-sunflower (Helianthus annuus, L.) crop rotation was established. In each treatment, systematic measurements of bulk density, resistance to penetration, infiltration rate and hydraulic conductivity (using tension disc infiltrometers) in the soil top layer were carried out. Changes in water profiles through the experimental period were also followed using a neutron probe. Crop development and yield were determined. The soil bulk density in the 0 to 20 cm layer was significantly higher in the CT than in the TT treatment, mainly after tillage operations (between 10% and 24% higher in CT than in TT). After 3 years of continuous tillage treatments, the soil bulk density did not increase. The resistance to penetration at any time was higher in the CT than in the TT treatment, but not always significantly different. Infiltration rates were significantly higher in the TT than in the CT treatment (about 35% higher in TT than in CT). After 3 years of the tillage treatments the hydraulic conductivity of the soil surface layer, at a pressure head of 0 mm, was significantly higher in the CT (124 mm h−1) than in the TT (66 mm h−1). This is related to the existence of preferential paths created by an increase of the earthworm population in the CT treatment. Soil water profiles showed higher replenishment of soil water storage in the CT than in the TT treatment, particularly from October 1994 to June 1995 when the lowest precipitation of the experimental period was recorded. Plant height, leaf area index (LAI) and root length density (RLD) of the first sunflower crop were significantly higher in the TT than in the CT treatment. Nevertheless, the seed yield was slightly higher in the CT than in the TT treatment. In the second sunflower crop, plant height, LAI, RLD were significantly higher in the CT than in the TT treatment except early in the season, and yield was significantly (and extremely) higher in the CT (1521 kg ha−1) than in the TT (473 kg ha−1) treatment. During the wheat crop season, plant height and RLD were higher in the TT than in the CT treatment, but grain yield was again slightly higher in the CT than in the TT treatment. The conservation tillage applied seems to be highly effective in enhancing soil water recharge and water conservation, particularly in years with much lower than average precipitation.

Water balance and nitrate leaching in an irrigated maize crop in SW Spain

Abstract During 3 consecutive years (1991–1993) a field experiment was conducted in an intensively irrigated agricultural soil in SW Spain. The main objective of this study was to determine the water flow and nitrate (N0 3 ) leaching, below the root zone, under an irrigated maize crop and after the growing season (bare soil and rainy period). The experiment was carried out on a furrow-irrigated maize crop at two different nitrogen (N)-fertilization rates, one the highest traditionally used by farmers in the region (about 500 kg N ha −1 per year) and the other one-third of the former (170 kg N ha −1 per year). The aim was to obtain data that could be used to propose modifications in N-fertilization to maintain crop yield and to prevent the degradation of the environment. The terms for water balance (crop evapotranspiration, drainage and soil water storage) and nitrate leaching were determined by intensive field monitoring of the soil water content, soil water potential and extraction of the soil solution by a combination of neutron probe, tensiometers and ceramic suction cups. Nitrogen uptake by the plant and N0 3 -N produced by mineralization were also determined. The results showed that, in terms of water balance, crop evapotranspiration was similar at both N-fertilization rates used. During the irrigation period, drainage below the root zone was limited. Only in 1992 did the occurrence of rainfall during the early growing period, when the soil was wet from previous irrigation, cause considerable drainage. Nitrate leaching during the whole experimental period amounted to 150 and 43 kg ha −1 in the treatments with high and low N-fertilization, respectively. This occurred mainly during the bare soil and rainy periods, except in 1992 when considerable nitrate leaching was observed during the crop season due to the high drainage. Nitrate leaching was not so high during the bare soil period as might have been expected because of the brought during the experimental period. A reduction of N-fertilization thus strongly decreased nitrate leaching without decreasing yield.

Cadmium availability in soil and retention in oak roots: potential for phytostabilization

Afforestation of contaminated land by trees is considered as a feasible strategy for the extensive stabilization of contaminants. In this work, we studied the patterns of metal availability (Cd, Cu, Pb and Zn) in a contaminated and afforested area. Specifically, we observed the response of Holm oak (Quercus ilex subsp. ballota) leaves to changes in the availability of metals under field conditions, focusing on Cd. Under controlled conditions we studied the performance of oak seedlings exposed to high levels of Cd, with the aim of analyzing the patterns of translocation and tolerance of the seedlings. Cadmium was the most available metal, in relative terms; 15% of the total Cd in the soil was extracted with NH4NO3. The availabilities of Cd, Cu and Zn showed exponential relationships with soil pH (pH values ranged from 2.4 to 8.4). Cadmium accumulation in the leaves was not related to the changes in Cd availability. Greenhouse studies showed that seedlings had a high Cd retention capacity in fine roots (up to 7 gkg(-1)) and low rates of Cd translocation to the leaves (transfer coefficients below 0.03). Root biomass and thickness was altered by exposure to Cd. In spite of this, the chlorophyll fluorescence measurements (an indicator of plant stress) only differed slightly from the control treatment at a Cd dose of 200 mgL(-1). Due to the relatively high tolerance to Cd and the capacity of roots to retain this metal, Holm oak may be useful for the phytostabilization of soils contaminated by Cd.

Testing low-quality urban composts for agriculture: germination and seedling performance of plants

Abstract Two urban composts, one very coarse, low in organic matter but mature, and the other particulated, high in organic matter but not well stabilized, were tested. Germination ‘in vitro’ and in soil of cress, ryegrass and sunflower seeds, seedling performance (root, shoot and sheath lengths) and seedling composition (in soil) of ryegrass were evaluated. Other organic composts, including a vermi-compost, were used for comparison in some experiments. The less mature compost in the ‘in vitro’ assays showed a strong instant toxicity (despite a low latent toxicity), especially when using a sand-compost mixture. Pot trials showed a strong, initial shortening of the primary root of the ryegrass, and also a strong reduction of the mean seedling weight, measured 30 days after sowing. In contrast, results with the mature urban compost were excellent, being similar to those obtained using the vermi-compost. To avoid negative effects on crops, routine germination bioassays should be included in educational programs for farmers. This should enhance marketing and consumer acceptance of urban composts.

Water use and yield of maize with two levels of nitrogen fertilization in SW Spain

Abstract Maize (cv. Prisma ), managed with furrow irrigation was cropped consecutively for three years under Mediterranean management practices in the Guadalquivir river valley of SW Spain. Two N fertilization rates were used in different subplots: Subplot A had 510 kg N ha −1 yr −1 , a rate widely used in the area. Subplot B at 170 kg N ha −1 yr −1 , was one third of this. The water balance components and crop response to the irrigation regime were quantified to determine the efficiency of furrow irrigation practices in the area. Furthermore we sought to establish whether a reduced N fertilization rate would have any influence on the crop yield. No consistent differences were observed between subplots in any of the water balance components. Measured crop evapotranspiration ( ET c ) averaged 6250 m 3 ha −1 Water losses by drainage were usually below 20% of ( ET c ) Soil evaporation under the canopy ( E ) was measured by using a specially-designed microlysimeter. Root density, soil water content and soil bulk density inside the microlysimeters were similar to those measured in the surrounding soil. Average values of E between two irrigations when the crop was fully mature amounted for 18°-20% of ET c . A maximum value of 1.6 for the crop coefficient ( K c ) was calculated after using the Penman-Monteith combination equation for the calculation of the reference evapotranspiration ( ET r ). A standard formulation was used for the resistance term, which might account for the large value of ( K c ) Measurements of crop development parameters (height, leaf area index and phenological stage) showed some differences between subplots during the growing period, but no final differences were detected. No differences in yield were observed during the course of the study. Monitoring of physiological parameters (leaf water potential, leaf conductance and net photosynthesis rate) showed that water relationships of maize were not affected by the reduced N fertilization.

Response of clover Trifolium fragiferum L. cv. 'Salina' to a heavy urban compost application

The clover, T. fragiferum L. cv. ‘Salma’ was grown for two years in a greenhouse under a heavy rate of urban compost application at sowing (1001 ha−1 year−1). An inorganic fertilizer was also applied for comparison (8N-15K2O-15P2O5, 1.21 ha−1 year−1). The legumes Medicago rugosa Des. cv. ‘Paragosa’, Trifolium subterraneum L. ssp. subterraneum, T. subterraneum L. ssp. brachycalycinum were also grown for comparison. The combined N applied with the inorganic fertilizer did not impair either seedling emergence or growth of any of the legumes. Seedling emergence of legumes was in general higher under the urban compost treatment than under the inorganic and control treatments, with that of T. fragiferum being the highest. This latter species was the only one with a higher dry matter production under the urban compost treatment than under the other treatments. Urban compost application significantly increased N, P, Cu and Zn concentration and export of T. fragiferum, in relation to the inorganic and control trea...

Long-term biomonitoring of soil contamination using poplar trees: accumulation of trace elements in leaves and fruits

Phytostabilization aims to immobilize soil contaminants using higher plants. The accumulation of trace elements in Populus alba leaves was monitored for 12 years after a mine spill. Concentrations of As and Pb significantly decreased, while concentrations of Cd and Zn did not significantly over time. Soil concentrations extracted by CaCl2 were measured by ICP-OES and results of As and Pb were below the detection limit. Long-term biomonitoring of soil contamination using poplar leaves was proven to be better suited for the study of trace elements. Plants suitable for phytostabilization must also be able to survive and reproduce in contaminated soils. Concentrations of trace elements were also measured in P. alba fruiting catkins to determine the effect on its reproduction potential. Cadmium and Zn were found to accumulate in fruiting catkins, with the transfer coefficient for Cd significantly greater than Zn. It is possible for trace elements to translocate to seed, which presents a concern for seed germination, establishment and colonization. We conclude that white poplar is a suitable tree for long-term monitoring of soil contaminated with Cd and Zn, and for phytostabilization in riparian habitats, although some caution should be taken with the possible effects on the food web. Supplemental materials are available for this article. Go to the publishers online edition of International Journal of Phytoremediation to view the supplemental file.