Runoff and leaching of atrazine and alachlor on a sandy soil as affected by application in sprinkler irrigation

Abstract

Rainfall simulation was used with small packed boxes of soil to compare runoff of herbicides applied by conventional spray and injection into sprinkler‐irrigation (chemigation), under severe rainfall conditions. It was hypothesized that the larger water volumes used in chemigation would leach some of the chemicals out of the soil surface rainfall interaction zone, and thus reduce the amounts of herbicides available for runoff. A 47‐mm rain falling in a 2‐hour event 24 hours after application of alachlor (2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)‐acetamide) and atrazine (6‐chloro‐N‐ethyl‐N‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine) was simulated. The design of the boxes allowed a measurement of pesticide concentrations in splash water throughout the rainfall event. Initial atrazine concentrations exceeding its’ solubility were observed. When the herbicides were applied in 64000 L/ha of water (simulating chemigation in 6.4 mm irrigation water) to the surface of a Tifton loamy sand, subsequent herbicide losses in runoff water were decreased by 90% for atrazine and 91% for alachlor, as compared to losses from applications in typical carrier water volumes of 187 L/ha. However, this difference was not due to an herbicide leaching effect but to a 96% decrease in the amount of runoff from the chemigated plots. Only 0.3 mm of runoff occurred from the chemigated boxes while 7.4 mm runoff occurred from the conventionally‐treated boxes, even though antecedent moisture was higher in the former. Two possible explanations for this unexpected result are (a) increased aggregate stability in the more moist condition, leading to less surface sealing during subsequent rainfall, or (b) a hydrophobic effect in the drier boxes. In the majority of these pans herbicide loss was much less in runoff than in leachate water. Thus, in this soil, application of these herbicides by chemigation would decrease their potential for pollution only in situations where runoff is a greater potential threat than leaching.     

Phytotoxicity of atrazine and alachlor in soil amended with sludge,manure and activated carbon

Abstract

Greenhouse studies were conducted to determine the influence of waste‐activated carbon (WAC), digested municipal sewage sludge (DMS), and animal manure on herbicidal activity of atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐trazine] and alachlor [2‐chloro‐2’,6'‐diethyl‐N‐(methoxymethyl)acetanilide] in a Plainfield sandy soil. Amendments generally reduced bioactivity against oat (Avena sativa L.) and Japanese millet (E. crus‐galli frumentacea). The extent to which herbicide phytotoxicity was inhibited depended upon the application rate and the kind of soil amendment. WAC, applied at the loading rate of 2.1 mt C/ha, showed a significant inhibitory effect on both herbicides. In DMS‐ and manure‐amended soil, the reduction of atrazine activity was not significant at the rate of 8.4 mt C/ha, but reduction of alachlor activity was significant at the rate of 4.2 mt C/ha. Despite inhibition of herbicidal activity, the ED₅₀ of atrazine and alachlor was below 2 ppm in most of the amendment treatments. Before adopting carbon‐rich waste amendments as management practices for controlling pesticide leaching in coarse‐textured soils, further studies are needed to characterize how alterations in sorption, leaching and degradation may affect herbicidal activity.     

Ultrasonic decomposition of atrazine and alachlor in water.

Abstract

The collapse of ultrasonically‐generated cavitation bubbles can result in sonochemical reactions. The kinetics of sonochemical decomposition of alachlor and atrazine in water were determined using a sonicator operating in the continuous mode at maximum output. Alachlor and atrazine solutions, 3.1 nmol L^‐1, were kept at constant temperature during the sonication. Decomposition at 30°C followed first‐order kinetics: k = 8.01 × 10^‐3 min^‐1 and 2.10 × 10^‐3 min^‐1 for alachlor and atrazine, respectively. It is not clear from the product analysis whether the decomposition was due to a thermal or free radical reaction. However, regardless of the decomposition mechanisms, the extrapolated half‐lives (86 and 330 min for alachlor and atrazine, respectively) support the potential development of ultrasonic waves to decompose herbicides in contaminated water.     

Enhanced retention of linuron, alachlor and metalaxyl in sandy soil columns intercalated with wood barriers

A study has been made of the effect a reactive barrier made of pine (softwood) or oak (hardwood) wood intercalated in a sandy soil column has on the retention of linuron, alachlor and metalaxyl (pesticides with contrasting physicochemical characteristics). The leaching of pesticides has been carried out under a saturated flow regime and breakthrough curves (BTCs) have been obtained at flow rates of 1 mL min⁻¹ (all pesticides) and 3 mL min⁻¹ (linuron). The cumulative curves in the unmodified soil indicate a leaching of pesticides >80% of the total amount of compound added. After barrier intercalation, linuron leaching decreases significantly and a modification of the leaching kinetics of alachlor and metalaxyl has been observed. The theoretical R factors increased ∼2.6-3.3, 1.2-1.6-fold, and 1.4-1.7-fold and the concentration of the maximum peak decreased ∼6-12-fold, 2-4-fold and 1.2-2-fold for linuron, alachlor and metalaxyl, respectively. When considering the three pesticides, significant correlations have been found between the theoretical retardation factor (R) and the pore volume corresponding to the maximum peaks of the BTCs (r = 0.77; p < 0.05) or the total volume leached (r = −0.78; p < 0.05). The results reveal the efficacy of reactive wood barriers to decrease the leaching of pesticides from point sources of pollution depends on the type of wood, the hydrophobicity of the pesticide and the adopted water flow rate. Pine was more effective than oak in decreasing the leaching of hydrophobic pesticide linuron or in decreasing the maximum peak concentration of the less hydrophobic pesticides in soils. Efficacy of these wood barriers was limited for the least hydrophobic pesticide metalaxyl.     

Phosphorus and copper leaching from dredged sediment applied on a sandy loam soil: column study

In this paper, downward movement of phosphorus and copper as dredged sediment applied on sandy loam soil was studied by column leaching experiments. Three sediment application rate, (i.e., 1, 2 and 5-cm depth of sediments) were applied to the top of the soil columns. Two and a half months leaching experiments were conducted, which include a 15-day un-watered period. Concentrations of phosphorus and copper in the leachate and the vertical distribution of Olsen-P and diethylenetriaminepentaacetic acid (DTPA) extractable Cu in the soil columns were determined. The results showed that, un-watered period could increase the downward movements of phosphorus and copper. Sediment application significantly increased Olsen-P concentration in the top 15 cm of the soil columns, but has not significantly affected that in the deeper soil layer. The 1-cm depth sediment treatment did not increase the DTPA extractable Cu concentration in the whole soil column. The 5-cm depth sediment treatment, however, significant increased the DTPA extractable Cu in the deeper soil layers. This study suggested that the application of dredged sediment laden with P and Cu on sandy loam soil might cause the significant downward movement of phosphorus and copper.     

Effect of biochar amendment on sorption and leaching of nitrate, ammonium, and phosphate in a sandy soil

When applied to soils, it is unclear whether and how biochar can affect soil nutrients. This has implications both to the availability of nutrients to plants or microbes, as well as to the question of whether biochar soil amendment may enhance or reduce the leaching of nutrients. In this work, a range of laboratory experiments were conducted to determine the effect of biochar amendment on sorption and leaching of nitrate, ammonium, and phosphate in a sandy soil. A total of thirteen biochars were tested in laboratory sorption experiments and most of them showed little/no ability to sorb nitrate or phosphate. However, nine biochars could remove ammonium from aqueous solution. Biochars made from Brazilian pepperwood and peanut hull at 600 °C (PH600 and BP600, respectively) were used in a column leaching experiment to assess their ability to hold nutrients in a sandy soil. The BP600 biochar effectively reduced the total amount of nitrate, ammonium, and phosphate in the leachates by 34.0%, 34.7%, and 20.6%, respectively, relative to the soil alone. The PH600 biochar also reduced the leaching of nitrate and ammonium by 34% and 14%, respectively, but caused additional phosphate release from the soil columns. These results indicate that the effect of biochar on the leaching of agricultural nutrients in soils is not uniform and varies by biochar and nutrient type. Therefore, the nutrient sorption characteristics of a biochar should be studied prior to its use in a particular soil amendment project.     

Effect of biochar amendment on sorption and leaching of nitrate,ammonium, and phosphate in a sandy soil

When applied to soils, it is unclear whether and how biochar can affect soil nutrients. This has implications both to the availability of nutrients to plants or microbes, as well as to the question of whether biochar soil amendment may enhance or reduce the leaching of nutrients. In this work, a range of laboratory experiments were conducted to determine the effect of biochar amendment on sorption and leaching of nitrate, ammonium, and phosphate in a sandy soil. A total of thirteen biochars were tested in laboratory sorption experiments and most of them showed little/no ability to sorb nitrate or phosphate. However, nine biochars could remove ammonium from aqueous solution. Biochars made from Brazilian pepperwood and peanut hull at 600 °C (PH600 and BP600, respectively) were used in a column leaching experiment to assess their ability to hold nutrients in a sandy soil. The BP600 biochar effectively reduced the total amount of nitrate, ammonium, and phosphate in the leachates by 34.0%, 34.7%, and 20.6%, respectively, relative to the soil alone. The PH600 biochar also reduced the leaching of nitrate and ammonium by 34% and 14%, respectively, but caused additional phosphate release from the soil columns. These results indicate that the effect of biochar on the leaching of agricultural nutrients in soils is not uniform and varies by biochar and nutrient type. Therefore, the nutrient sorption characteristics of a biochar should be studied prior to its use in a particular soil amendment project.     

Use of amendments to reduce leaching loss of phosphorus and other nutrients from a sandy soil in Florida

Goal, Scope and Background Transport of P from agricultural land contributes to the eutrophication of surface waters. Soil amendment is considered one of the best management practices (BMPs) to reduce P loss from sandy soils. Laboratory column leaching experiments were conducted to evaluate the effectiveness of different soil amendments in reducing P leaching from a typical sandy soil in Florida. Methods The tested amendments were CaCl₂, CaCO₃, Al(OH)₃, cellulose, and mill mud, and applied at the rate of 15 g/kg for a single amendment and each 7.5 g/kg if two amendments were combined. Leaching was conducted every four days for 32 days, 250 mL of deionized water being leached for each column per leaching event. Leachates were collected from each leaching event and analyzed for reactive P, PO₄-P, and macro and micro-elements. Results and Discussion Except for the soils amended with CaCl₂, or CaCl₂+CaCO₃, reactive P and PO₄-P leaching losses mainly occurred in the first three leaching events. Phosphorus leaching from the soils amended with CaCl₂ or CaCl₂+CaCO₃ was less but more persistent than that of other amendments. Reactive Pleaching loss was reduced by 36.0% and 40.4% for the amendments of CaCl₂, and CaCl₂+CaCO₃, respectively, as compared with chemical fertilizer alone, and the corresponding values for PO₄-P were 70.8% and 71.9%. The concentrations of K, Mg, Cu, and Fe in leachate were also decreased by CaCl₂ or CaCl₂+CaCO₃ amendment. Among the seven amendments, CaCl₂, CaCO₃, or their combination were most effective in reducing P leaching from the sandy soil, followed by cellulose and Al(OH)₃, the effects of mill mud and mill mud + Al(OH)₃ were marginal. Conclusions These results indicate that the use of CaCl₂, CaCO₃, or their combination can significantly reduce P leaching from sandy soil, and should be considered in the development of BMPs for the sandy soil regions. Recommendations and Outlook Most agricultural soils in south Florida are very sandy with minimal holding capacities for moisture and nutrients. Repeated application of fertilizer is necessary to sustain desired yield of crops on these soils. However, eutrophication of fresh water systems in this area has been increasingly concerned by the public. Losses of P from agricultural fields by means of leaching and surface runoff are suspected as one of the important non-point contamination sources. The benefits and effectiveness of soil amendment in reducing P losses from cropping production systems while sustaining desired crop yield need to be demonstrated. Calcium chloride, CaCO₃, or their combination significantly reduce Pleaching from sandy soil, and should be considered in the development of BMPs for the sandy soil regions.     

Mango performance as affected by the soil application of zeolite and biochar under water salinity stresses

This study was carried out during two consecutive seasons, 2020 and 2021, on 12-year-old mango (Mangifera indica L.). cv. Ewaise grown in region Idku, El Beheira Governorate, Egypt. The trees were planted at 5?×?4 m apart and grafted on “Sokary” root stock to study the influence of zeolite and biochar on growth, yield, and fruit quality of “Ewaise” mango cultivar irrigated by agricultural drainage water. The trees were treated by the following treatments: zeolite or biochar solely at 1, 2, and 3 kg for tree and their different combinations such as 1 kg zeolite?+?1 kg biochar; 1 kg zeolite?+?2 kg biochar; 1 kg zeolite?+?3 kg biochar; 2 kg zeolite?+?1 kg biochar; 2 kg zeolite?+?2 kg biochar; 2 kg zeolite?+?3 kg biochar; 3 kg zeolite?+?1 kg biochar; 3 kg zeolite?+?2 kg biochar; and 3 kg zeolite?+?3 kg biochar as well as control zero soil application. The obtained results showed that the soil application of zeolite or biochar gave a positive effect on improving the soil characteristics which reflects on the tree trunk thickness, shoot length and thickness, number of inflorescences, yield in kg per tree, and fruit quality. The greatest positive effect on the previous mentioned parameters was obtained by the combined application of the soil application of 2 kg zeolite?+?3 kg biochar; 2 kg zeolite?+?2 kg biochar; 3 kg zeolite?+?2 kg biochar; and 3 kg zeolite?+?3 kg biochar over the rest-applied treatments or control in the two seasons.

     

NLEAP model simulation of climate and management effects on N leaching for corn grown on sandy soil

The Nitrate Leaching and Economic Analysis Package (NLEAP) model was used to evaluate effects of climate and N fertility on nitrate leaching from a 3-yr field experiment of continuous corn (Zea mays L.). Half of the plots were randomly chosen to be either nonirrigated or irrigated (based upon calculated potential evapotranspiration). Three replications of nitrogen (N) fertility (56, 112 and 224 kg ha⁻¹) were used. Soil was a Hecla sandy loam to loamy sand (Pachic Udic Haploboroll). Soil and climate data were from the upper Midwest U.S.A. database for NLEAP. On-site data were used in the model when available.This study shows that NLEAP is capable of integrating data collected for nonirrigated and irrigated conditions on sandy soil for a wide range of N treatments and predicting the nitrate available for leaching (NAL). Precipitation distribution and amount were different in each year. Calculated NAL provided an excellent indicator of potential nitrate leaching hazard. NLEAP output showed that leaching of residual N on this sandy soil is very sensitive to early-spring precipitation. The NLEAP model provided valuable insights concerning effects of climate and N and irrigation management on N leaching. To obtain optimum yields while minimizing nitrate leaching, this study indicates the need to use soil and plant-tissue testing, post-emergence N-fertilizer application, and modem irrigation-scheduling technology. Also, use of the NLEAP model along with field-plot experiments provide additional important information concerning timing of N-leaching events relative to climate and an additional assessment of the effectiveness of fertilizer-N management decisions.     

Leaching and reduction of chromium in soil as affected by soil organic content and plants

The oxidation state of chromium in contaminated soils is an important indicator of toxicity and potential mobility. Chromium in the hexavalent state is highly toxic and soluble, whereas the trivalent state is much less toxic and relatively insoluble. A laboratory study investigated the impact of growing plants and supplemental organic matter on chromium transport in soil. Plants alone had no appreciable effect on the chromium oxidation state in soil. Soil columns with higher organic content were associated with lower ratios of chromate:total chromium than the columns with lower organic matter. Analyses of column leachate, plant biomass, and soil indicate that more chromium leaching occurred in the vegetated, low organic columns. Retention of Cr in the soils was correlated to the Cr(III) content. Plant uptake of chromium accounted for less than 1% of the chromium removed from the soil. Overall, the addition of organic matter had the strongest influence on chromium mobility.     

Transport of simazine in unsaturated sandy soil and predictions of its leaching under hypothetical field conditions

The potential contamination of groundwater by herbicides is often controlled by processes in the vadose zone, through which herbicides travel before entering groundwater. In the vadose zone, both physical and chemical processes affect the fate and transport of herbicides, therefore it is important to represent these processes by mathematical models to predict contaminant movement. To simulate the movement of simazine, a herbicide commonly used in Chilean vineyards, batch and miscible displacement column experiments were performed on a disturbed sandy soil to quantify the primary parameters and processes of simazine transport. Chloride (Cl(-)) was used as a non-reactive tracer, and simazine as the reactive tracer. The Hydrus-1D model was used to estimate the parameters by inversion from the breakthrough curves of the columns and to evaluate the potential groundwater contamination in a sandy soil from the Casablanca Valley, Chile. The two-site, chemical non-equilibrium model was observed to best represent the experimental results of the miscible displacement experiments in laboratory soil columns. Predictions of transport under hypothetical field conditions using the same soil from the column experiments were made for 40 years by applying herbicide during the first 20 years, and then halting the application and considering different rates of groundwater recharge. For recharge rates smaller than 84 mm year(-1), the predicted concentration of simazine at a depth of 1 m is below the U.S. EPA's maximum contaminant levels (4 microg L(-1)). After eight years of application at a groundwater recharge rate of 180 mm year(-1) (approximately 50% of the annual rainfall), simazine was found to reach the groundwater (located at 1 m depth) at a higher concentration (more than 40 microg L(-1)) than the existing guidelines in the USA and Europe.     

Phytostabilization of a metal contaminated sandy soil. II: Influence of compost and/or inorganic metal immobilizing soil amendments on metal leaching

A lysimeter approach (under natural climatologic conditions) was used to evaluate the effect of four metal immobilizing soil treatments [compost (C), compost+cyclonic ashes (C+CA), compost+cyclonic ashes+steel shots (C+CA+SS)) and cyclonic ashes+steel shots (CA+SS)] on metal leaching through an industrially contaminated soil. All treatments decreased Zn and Cd leaching. Strongest reductions occurred after CA+SS and C+CA+SS treatments (Zn: -99.0% and -99.2% respectively; Cd: -97.2% and -98.3% respectively). Copper and Pb leaching increased after C (17 and >30 times for Cu and Pb respectively) and C+CA treatment (4.4 and >3.7 times for Cu and Pb respectively). C+CA+SS or CA+SS addition did not increase Cu leaching; the effect on Pb leaching was not completely clear. Our results demonstrate that attention should be paid to Cu and Pb leaching when organic matter additions are considered for phytostabilization of metal contaminated soils.     

Transport of copper as affected by titania nanoparticles in soil columns

The effects of TiO₂ nanoparticles on the transport of Cu through four different soil columns were studied. For two soils (HB and DX), TiO₂ nanoparticles acted as a Cu carrier and facilitated the transport of Cu. For a third soil (BJ) TiO₂ nanoparticles also facilitated Cu transport but to a much lesser degree, but for a fourth soil (HLJ) TiO₂ nanoparticles retarded the transport of Cu. Linear correlation analysis indicated that soil properties rather than sorption capacities for Cu primary governed whether TiO₂ nanoparticles-facilitated Cu transport. The TiO₂-associated Cu of outflow in the Cu-contaminated soil columns was significantly positively correlated with soil pH and negatively correlated with CEC and DOC. During passage through the soil columns 46.6-99.9% of Cu initially adsorbed onto TiO₂ could be “stripped” from nanoparticles depending on soil, where Cu desorption from TiO₂ nanoparticles increased with decreasing flow velocity and soil pH.     

Volatilisation of triallate as affected by soil texture and air velocity

The rate of volatilisation of the formulated herbicide triallate was investigated in a wind tunnel under controlled wind-speed conditions. An experimental set-up is described which allows the monitoring of wind speed (w.s.), soil-water content, and the temperature of air and soil. A system controlling soil-water content is also described. The influence of air velocity and soil texture was investigated measuring the cumulative volatilisation losses of triallate from soil. The herbicide volatilisation losses after application ranged from 40% at 3 m/s to 53% at 9 m/s for loam soil and from 60% at 3 m/s to 73% at 9 m/s for sandy soil.     

Long-term dynamics of the atrazine mineralization potential in surface and subsurface soil in an agricultural field as a response to atrazine applications

The dynamics of the atrazine mineralization potential in agricultural soil was studied in two soil layers (topsoil and at 35-45 cm depth) in a 3 years field trial to examine the long term response of atrazine mineralizing soil populations to atrazine application and intermittent periods without atrazine and the effect of manure treatment on those processes. In topsoil samples, ¹⁴C-atrazine mineralization lag times decreased after atrazine application and increased with increasing time after atrazine application, suggesting that atrazine application resulted into the proliferation of atrazine mineralizing microbial populations which decayed when atrazine application stopped. Decay rates appeared however much slower than growth rates. Atrazine application also resulted into the increase of the atrazine mineralization potential in deeper layers which was explained by the growth on leached atrazine as measured in soil leachates recovered from that depth. However, no decay was observed during intermittent periods without atrazine application in the deeper soil layer. atzA and trzN gene quantification confirmed partly the growth and decay of the atrazine degrading populations in the soil and suggested that especially trzN bearing populations are the dominant atrazine degrading populations in both topsoil and deeper soil. Manure treatment only improved the atrazine mineralization rate in deeper soil layers. Our results point to the importance of the atrazine application history on a field and suggests that the long term survival of atrazine degrading populations after atrazine application enables them to rapidly proliferate once atrazine is again applied.     

Macro-porosity and leaching of atrazine in tilled and orchard loamy soils

Atrazine is the most commonly detected herbicide in the groundwater. Leaching of atrazine largely depends on soil management practices. The aim of this study was to examine leaching of atrazine in tilled and orchard silty loam soils. The experimental objects included: conventionally tilled field (CT) with main tillage operations including pre-plow (10 cm) + harrowing, mouldboard ploughing (20 cm), and a 35 year-old apple orchard (OR) with a permanent sward. To determine leaching of atrazine soil columns of undisturbed structure were taken with steel cylinders of 21.5 cm diameter and 20 cm high from the depth of 0–20 cm. All columns were equilibrated at water content corresponding to field capacity (0.21 kg kg⁻¹). Atrazine suspended in distilled water was dripped uniformly onto the surface of each column. Then water was infiltrated and breakthrough times of leachates were recorded. Atrazine concentration in the leachates was determined by means of HPLC Waters. Macro-porosity and percolation rate were higher in OR than CT soil. Cumulative recovery % of the atrazine applied was 1.267% for OR and approximately one third more from the CT soil but the rate of leaching (per unit of time) was greater from the OR soil. The lower leaching under OR than CT can be due to a greater SOM and the presence of earthworm burrows with organic burrow linings that could adsorb atrazine and contribute to preferential flow allowing solutes to bypass parts whereas the greater rate of leaching due to a greater infiltration rate.The results indicate potential of management practices for minimizing atrazine leaching.     

Persistence, distribution, and emission of Telone C35 injected into a Florida sandy soil as affected by moisture, organic matter, and plastic film cover

With the phase-out of methyl bromide scheduled for 2005, alternative fumigants are being sought. This study of Telone C35, a mixture of (Z)- and (E)-1,3-dichloropropene (1,3-D) with chloropicirin (CP), focuses on its emissions, distribution, and persistence in Florida sandy soil in microplots with different soil-water and organic matter carbon (C) content with and without two different plastic film mulches. The addition of CP did not affect the physical behavior of the isomers of 1,3-D. Slower subsurface dispersion and longer residence time of the mixed fumigant occurred at higher water content. An increase in the percent organic carbon in the soil led to a more rapid decrease for chloropicirin than for 1,3-dichloropene isomers. The use of a virtually impermeable film (VIF) for soil cover provided a more even distribution and longer persistence under all the conditions studied in comparison to polyethylene (PE) film cover or no cover. The conditions of near field capacity water content, low organic matter, and a virtually impermeable film cover yielded optimum conditions for the distribution, emission control, and persistence of Telone C35 in a Florida sandy soil.     

Hydrocarbon deposition and soil microflora as affected by highway traffic.

The proximity of a busy highway (90,000 vehicles/day) increased the amount of polycyclic aromatic hydrocarbons (PAHs) in soil at the depth of 5-15 cm from 106 ng/g as a grassland background to 3095 ng/g dry soil at the highway verge (a sum of 10 PAH species). The PAH concentration was related to the distance from the source and exhibited a biphasic character, which is interpreted in terms of bimodal distribution of the exhaust microparticles with different rates of deposition. Similarly, the tendency of benz(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, and indeno(1,2,3-cd)pyrene to decrease their proportion with distance from the highway, in contrast to phenanthrene, fluoranthene, pyrene, benzo(a)pyrene, and benzo(g,h,i)perylene, was attributed to their prevalent localisation on the heavier particle fraction. The abundance of bacteria (8.33 x background) and fungi (3.17 x background) close to the highway is thought to be a consequence of hydrocarbon deposition from the traffic that serves as a significant energetic input into the soil. The elevated concentrations of hydrocarbon substrates, as indicated by PAHs, increased both the absolute and relative numbers of the microbial degraders of diesel fuel, biphenyl, naphthalene, and pyrene. Their maximum numbers at 0.5-1.5 m from the pavement reached 1.3 x 10(4), 1.2 x 10(5), 1.1 x 10(4), and 6.6 x 10(3) colony-forming units (CFU) or infection units per gramme dry soil, respectively. On the other hand, the number of anthracene degraders (1.1 x 10(3) CFU per g dry soil) remained close to the detection limit of the enumeration technique used (0.1-0.2 x 10(3) per g dry soil), consistently with the absence of anthracene and higher linear PAHs in the investigated soil samples. The amounts of persisting PAHs justify artificial inoculation with effective degrader strains in the vicinity of motorways.     

Extractable soil lipids and microbial activity as affected by Bt and non Bt maize grown on a silty clay loam soil

Pyrolysis-gas (Py-GC) chromatography was used to characterize extractable lipids from Bt and non-Bt maize shoots and soils collected at time of harvesting. Py-GC-MS (mass spectrometry) showed that the concentrations of total alkenes identified in non-Bt shoots and soils were 47.9 and 21.3% higher than in Bt maize shoots and soils, respectively. N-alkanes identified were of similar orders of magnitude in Bt and non-Bt maize shoots, but were 28.6% higher in Bt than in non-Bt soils. Bt maize shoots contained 29.7% more n-fatty acids than non-Bt maize shoots, whereas the concentrations of n-fatty acids in Bt soils were twice as high as those in non-Bt soils. Concentrations of unsaturated fatty acids in Bt maize shoots were 22.1% higher than those in non-Bt maize shoots, while concentrations of unsaturated fatty acids were 22.5% higher in non-Bt than in Bt soils. The cumulative CO2-C evolved from soils under Bt and non-Bt crops was 30.5% lower under Bt as compared to non-Bt crops, whereas when maize shoots were added to Bt and non-Bt soils, the decrease in CO2-C evolved were 16.5 and 23.6%, respectively. Our data showed that the cultivation of Bt maize significantly increased the saturated to unsaturated lipid ratios in soils which appeared to negatively affect microbial activity.