Agronomic application of olive mill wastewaters with phosphate rock in a semi-arid Mediterranean soil modifies the soil properties and decreases the extractable soil phosphorus

Olive mill wastewater (OMW), a by-product of the olive-mill industry, is produced in large amounts in Mediterranean countries. The presence of indigenous phosphate deposits in some countries like Tunisia provides an incentive for direct application or local chemical treatment at low cost to improve the solubility of low reactive phosphate rocks (PRs). The use of naturally occurring low-molecular weight organic acids (LMWOAs) that are present in OMW represents a new perspective in PR research and a possible solution for the recycling of the OMW. The present work was aimed at evaluating, under natural situations (field of olive trees), the effects of agronomic application of OMW (amounts applied: 30, 60 m(3) ha(-1)) with PR (amounts applied: 150 kg ha(-1)) on olive trees soil properties. We measured organic C, nitrogen (N), extractable phosphorus (P), exchangeable calcium (Ca), and exchangeable potassium (K), as well as other properties (pH and electrical conductivity). Our data provide evidence that agronomic application of OMW with PR has important effects on soil properties. Increases in organic C, total N, extractable P and exchangeable potassium (K) were found after the first agronomic application of OMW and PR. These increases were only temporary, following the second agronomic application of OMW and PR, significant reductions were detected in the extractable soil P (19.67 mg kg(-1) in the control soil vs. 8.99 mg kg(-1) in the amended soil). Changes in the extractable soil P could alter plant productivity and plant community structure because shifts in nutriment availability can affect the balance between limiting and non-limiting nutrients.     

The effect of olive mill wastewater on seed germination after various pretreatment techniques

Olive mill wastewater (OMW) management has been a major issue of environmental concern for olive oil producing countries. OMW can be a serious nuisance, when disposed of untreated, due to its significantly high organic load, its phytotoxic properties and its relatively low biodegradability. Field and plant irrigation with raw or pretreated OMW is an easy and relatively inexpensive method to treat and dispose of OMW. Typical pretreatment techniques could be comprised of phase separation through a settling basin, dilution with water, aeration to promote biological degradation and pH neutralization. A full factorial experimental design approach was used here to study the main effects and interactions of the above four pretreatment techniques on the germination of tomato and chicory seeds. Results of the study showed that the most statistically significant technique affecting OMW phytotoxicity is water dilution. The next most significant technique was aeration. In particular, phytotoxicity decreased with increased OMW dilution with water, when OMW was aerated and without pH adjustment. pH neutralization resulted in increased phytotoxicity. Settling did not significantly decrease the phytotoxicity of settled OMW and is therefore not considered necessary in an OMW management system in which plant irrigation is the goal. The interaction of aeration and pH was, marginally, the most significant two-way interaction for tomato seeds, while no interactions were significant when chicory seeds were used.     

Removal of organic pollutants and nutrients from olive mill wastewater by a sand filter

The aim of this work was to examine the performance of a sand filter in treating modern olive mill (OMW) effluents after dilution with domestic wastewater on a one-to-one basis. The experimental pilot consisted of a column of opaque PVC, and the sand filter was filled with 50 cm of sand and 10 cm of gravel in the top and the bottom of the filter. The alimentation (4 cm/day) was done sequentially following a 1 day wet/3 days dry cycle. The OMW effluent was very acidic with a pH of 4.12, and had high concentrations of phenolic compounds (7.2 g/L) and total chemical oxygen demand (65 g/L). The percolation of the diluted OMW through the sand filters caused an increase in pH from 4.84 to 8.25 and a 90% removal of total suspended solids. The sand filter treatment also led to important reductions in organic matter (90% of total COD, 83% of dissolved COD and 92% of phenolic compounds) and nutrients (91% of Kjeldahl-nitrogen, 97% of ammonia-nitrogen, 99% of nitrate-nitrogen and 99% of phosphates). The flow rate became very low indicating clogging of the sand pores after 10 weeks. HPLC analysis of the diluted OMW before and after passage through the sand filter showed an important reduction in the toxic monomeric compounds after the treatment.     

Mercury speciation in highly contaminated soils from chlor-alkali plants using chemical extractions

A four-step novel sequential extraction procedure (SEP) was developed to assess Hg fractionation and mobility in three highly contaminated soils from chlor-alkali plants (CAPs). The SEP was validated using a certified reference material (CRM) and pure Hg compounds. Total, volatile, and methyl Hg concentrations were also determined using single extractions. Mercury was separated into four fractions defined as water-soluble (F1), exchangeable (F2) (0.5 M NH4Ac-EDTA and 1 M CaCl2 were tested), organic (F3) (successive extractions with 0.2 M NaOH and CH3COOH 4% [v/v]), and residual (F4) (HNO3 + H2SO4 + HClO4). The soil characterization revealed extremely contaminated (295 +/- 18 to 11 500 +/- 500 mg Hg kg(-1)) coarse-grained sandy soils having an alkaline pH (7.9-9.1), high chloride concentrations (5-35 mg kg(-1)), and very low organic carbon content (0.00-18.2 g kg(-1)). Methyl Hg concentrations were low (0.2-19.3 microg kg(-1)) in all soils. Sequential extractions indicated that the majority of the Hg was associated with the residual fraction (F4). In Soils 1 and 3, however, high percentages (88-98%) of the total Hg were present as volatile Hg. Therefore, in these two soils, a high proportion of volatile Hg was present in the residual fraction. The nonresidual fraction (F1 + F2 + F3) was most abundant in Soil 1 (14-42%), suggesting a higher availability of Hg in this soil. The developed and validated SEP was reproducible and efficient for highly contaminated samples. Recovery ranged between 93 and 98% for the CRM and 70 and 130% for the CAP-contaminated soils.     

Chemical analysis of soil and leachate from experimental wetland mesocosms lined with coal combustion products

Small-scale (1 m2) wetland mesocosm experiments were conducted over two consecutive growing seasons to investigate the effects on soil and leachate chemistry of using a recycled coal combustion product as a liner. The coal combustion product used as a liner consisted of flue gas desulfurization (FGD) by-products and fly ash. This paper provides the chemical characteristics of mesocosm soil and leachate after 2 yr of experimentation. Arsenic, Ca, and pH were higher in FGD-lined mesocosm surface soil relative to unlined mesocosms. Aluminum was higher in the soils of unlined mesocosms relative to FGD-lined mesocosms. No significant difference of potentially phytotoxic B was observed between lined and unlined mesocosms in the soil. Higher pH, conductivity, and concentrations of Al, B, Ca, K, and S (SO4-S) were observed in leachate from lined mesocosms compared with unlined controls while Fe, Mg, and Mn were higher in leachate from unlined mesocosms. Concentrations of most elements analyzed in the leachate were below national primary and secondary drinking water standards after 2 yr of experimentation. Initially high pH and soluble salt concentrations measured in the leachate from the lined mesocosms may indicate the reason for early effects noted on the development of wetland vegetation in the mesocosms.     

Greenhouse gas emissions and soil indicators four years after manure and compost applications

Understanding how carbon, nitrogen, and key soil attributes affect gas emissions from soil is crucial for alleviating their undesirable residual effects that can linger for years after termination of manure and compost applications. This study was conducted to evaluate the emission of soil CO2, N2O, and CH4 and soil C and N indicators four years after manure and compost application had stopped. Experimental plots were treated with annual synthetic N fertilizer (FRT), annual and biennial manure (MN1 and MN2, respectively), and compost (CP1 and CP2, respectively) from 1992 to 1995 based on removal of 151 kg N ha(-1) yr(-1) by continuous corn (Zea mays L.). The control (CTL) plots received no input. After 1995, only the FRT plots received N fertilizer in the spring of 1999. In 1999, the emissions of CO2 were similar between control and other treatments. The average annual carbon input in the CTL and FRT plots were similar to soil CO2-C emission (4.4 and 5.1 Mg C ha(-1) yr(-1), respectively). Manure and compost resulted in positive C and N balances in the soil four years after application. Fluxes of CH4-C and N2O-N were nearly zero, which indicated that the residual effects of manure and compost four years after application had no negative influence on soil C and N storage and global warming. Residual effects of compost and manure resulted in 20 to 40% higher soil microbial biomass C, 42 to 74% higher potentially mineralizable N, and 0.5 unit higher pH compared with the FRT treatment. Residual effects of manure and compost on CO2, N20, and CH4 emissions were minimal and their benefits on soil C and N indicators were more favorable than that of N fertilizer.     

污染土壤修复效果评估方法研究综述简

综述了评估污染土壤修复效果的指标及方法,包括残留污染分析法、风险评估法、植物毒性法、动物毒性法、微生物毒性法、土壤酶水平法等典型的评估方法,分析了各种方法的优缺点及适用范围。其中,植物毒性法适用于再利用类型为工业、商业用地的场地;动物毒性法适用于再利用类型为居住用地的场地;土壤微生物法、土壤酶水平法适用于再利用类型为农业用地的场地;对于存在人体暴露途径的用地,应结合人体健康风险评估法进行风险评估,综合评定土壤修复的效果。最后对该领域今后的研究方向进行了展望。     

Residual soil nitrate after potato harvest

Nitrogen loss by leaching is a major problem, particularly with crops requiring large amounts of N fertilizer. We evaluated the effect of N fertilization and irrigation on residual soil nitrate following potato (Solanum tuberosum L.) harvests in the upper St-John River valley of New Brunswick, Canada. Soil nitrate contents were measured to a 0.90-m depth in three treatments of N fertilization (0, 100, and 250 kg N ha(-1)) at two on-farm sites in 1995, and in four treatments of N fertilization (0, 50, 100, and 250 kg N ha(-1)) at four sites for each of two years (1996 and 1997) with and without supplemental irrigation. Residual soil NO3-N content increased from 33 kg NO3-N ha(-1) in the unfertilized check plots to 160 kg NO3-N ha(-1) when 250 kg N ha(-1) was applied. Across N treatments, residual soil NO3-N contents ranged from 30 to 105 kg NO3-N ha(-1) with irrigation and from 30 to 202 kg NO3-N ha(-1) without irrigation. Residual soil NO3-N content within the surface 0.30 m was related (R2 = 0.94) to the NO3-N content to a 0.90-m depth. Estimates of residual soil NO3-N content at the economically optimum nitrogen fertilizer application (Nop) ranged from 46 to 99 kg NO3-N ha(-1) under irrigated conditions and from 62 to 260 kg NO3-N ha(-1) under nonirrigated conditions, and were lower than the soil NO3-N content measured with 250 kg N ha(-1). We conclude that residual soil NO3-N after harvest can be maintained at a reasonable level (<70 kg NO3-N ha(-1)) when N fertilization is based on the economically optimum N application.     

Phosphorus runoff during four years following composted manure application

Repeated manure application can lead to excessive soil test P (STP) levels and increased P concentration in runoff, but also to improved water infiltration and reduced runoff. Research was conducted to evaluate soil P tests in prediction of P concentration in runoff and to determine the residual effects of composted manure on runoff P loss and leaching of P. The research was conducted from 2001 to 2004 under natural runoff events with plots of 11-m length. Low-P and high-P compost had been applied during the previous 3 yr, resulting in total applications of 750 and 1150 kg P ha(-1). Bray-P1 in the surface 5 cm of soil was increased from 16 to 780 mg kg(-1) with application of high-P compost. Runoff and sediment losses were 69 and 120% greater with no compost than with residual compost treatments. Runoff P concentration increased as STP increased, but much P loss occurred with the no-compost treatment as well. Agronomic soil tests were predictive of mean runoff P concentration, but increases in STP resulted in relatively small increases in runoff P concentration. Downward movement of P was not detected below 0.3 m. In conclusion, agronomic soil tests are useful in predicting long-term runoff P concentration, and risk of P loss may be of concern even at moderate soil P levels. The residual effect of compost application in reducing sediment and runoff loss was evident more than 3 yr after application and should be considered in P indices.     

Influence of fly ash on soil physical properties and turfgrass establishment

A field study (1993-96) assessed the benefits of applying unusually high rates of coal fly ash as a soil amendment to enhance water retention of soils without adversely affecting growth and marketability of the turf species, centipedegrass [Eremochloa ophiuroides (Munro) Hack.]. A Latin Square plot design was employed that included 0 (control, no ash applied), 280, 560, and 1120 Mg ha-1 application rates of unweathered precipitator fly ash. The fly ash was spread evenly over each plot area, rototilled, and allowed to weather under natural conditions for 8 mo before seeding. High levels of soluble salts, indicated by the electrical conductivity (EC) of soil extracts, in tandem with an apparent phytotoxic effect from boron (B), apparently inhibited initial plant establishment as shown by substantially lower germination counts in treated soil. However, plant height and rooting depth were not adversely affected, as were the dry matter (DM) yields throughout the study period. Ash treatment did not significantly influence water infiltration rate, bulk density, or temperature of the soil, but substantially improved water-holding capacity (WHC) and plant-available water (PAW). Enhanced water retention capacity improved the cohesion and handling property of harvested sod.     

Impact of unconfined sulphur-mine waste on a semi-arid environment (Almería, SE Spain)

Thirty-five soil samples were taken from unconfined mine waste, stream sediments, and surfaces unoccupied by mining and presumably unaffected by it, in a sulphur-mining zone surrounded by carbonate material and characterized by a semi-arid climate with short torrential storms. These samples were analysed and the results compared to estimate the spread of pollution in the landscape and to assess potential environmental risk. The mean concentrations of S, Zn, Cd, Pb, and As in mine waste were between 3.5-fold (As) and 50-fold (S) greater than unaffected soils. Oxidation of S led to a sharp drop in pH, strong weathering of minerals, and solubilisation of the constituent elements, forming a toxic acidic mine drainage with highly concentrated pollutants that were discharged into the drainage channels. Successive acid mine drainage into the soil on the valley floor spreads acidification and pollution downstream. The high carbonate content in surrounding soils played an important role in the increase of the pH and precipitation of S, Pb, and Al of the affected soils. Meanwhile, high mobility of Zn, Cd and As under basic conditions and a low Fe concentration explain the broad spread of these elements, as high concentrations were detected in soil more than 2000 m from the source. Only the soil solutions from near the waste dump (first 500 m) were highly phytotoxic, and moderately phytotoxic from 500 to 1500 m away. The concentration of pollutants in the leachates was clearly higher than in soil solutions, even in the soils located over 2000 m from the source, implying that the size of the polluted area will increase with time.     

Fate of diuron and linuron in a field lysimeter experiment

The environmental fate of herbicides can be studied at different levels: in the lab with disturbed or undisturbed soil columns or in the field with suction cup lysimeters or soil enclosure lysimeters. A field lysimeter experiment with 10 soil enclosures was performed to evaluate the mass balance in different environmental compartments of the phenylurea herbicides diuron [3-(3,4-diclorophenyl)-1,1-dimethyl-urea] and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea]. After application on the agricultural soil, the herbicides were searched for in soil, pore water, and air samples. Soil and water samples were collected at different depths of the soil profile and analyzed to determine residual concentrations of both the parent compounds and of their main transformation products, to verify their persistence and their leaching capacity. Air volatilization was calculated using the theoretical profile shape method. The herbicides were detected only in the surface layer (0-10 cm) of soil. In this layer, diuron was reduced to 50% of its initial concentration at the end of the experiment, while linuron was still 70% present after 245 d. The main metabolites detected were DCPMU [3-(3,4-dichlorophenyl)-1-methylurea] and DCA (3,4-dichloroaniline). In soil pore water, diuron and linuron were detected at depths of 20 and 40 cm, although in very low concentrations. Therefore the leaching of these herbicides was quite low in this experiment. Moreover, volatilization losses were inconsequential. The calculated total mass balance showed a high persistence of linuron and diuron in the soil, a low mobility in soil pore water (less than 0.5% in leachate water), and a negligible volatilization effect. The application of the Pesticide Leaching Model (PELMO) showed similar low mobility of the chemicals in soil and water, but overestimated their volatilization and their degradation to the metabolite DCPMU. In conclusion, the use of soil enclosure lysimeters proved to be a good experimental design for studying mobility and transport processes of herbicides in field conditions.     

Simple biotoxicity tests for evaluation of carbonaceous soil additives: establishment and reproducibility of four test procedures

Biochar derived from pyrolysis has received much attention recently as a soil additive to sequester carbon and increase soil fertility. Hydrochar, a brown, coal-like substance produced via hydrothermal carbonization, has also been suggested as a beneficial soil additive. However, before soil application, both types of char need to be tested for potential toxic effects. The aim of this study was to develop simple, inexpensive, and easy-to-apply test procedures to identify negative effects of chars but not to provide false-negative results. The following tests, based partly on ISO norm biotoxicity test procedures, were chosen: (i) cress germination test for gaseous phytotoxic emissions; (ii) barley germination and growth test; (iii) salad germination test; and (iv) earthworm avoidance test for toxic substances. Test reproducibility was ensured by carrying out each test procedure three times with the same biochar. Several modifications were necessary to adapt the tests for biochars/hydrochars. The tested biochar did not induce negative effects in any of the tests. In contrast, the beet-root chip hydrochar showed negative effects in all tests. In an extension to the regular procedure, a regrowth of the harvested barley shoots without further nutrient additions yielded positive results for the hydrochar, which initially had negative effects. This implies that the harmful substance(s) must have been degraded or they were water soluble and leached. Tests with a biochar and hydrochar showed that the proposed modified quick-check test procedures provide a fast assessment of risks and effects of char application to soils within a short period of time (<2 wk).     

Experimental oxidative dissolution of sphalerite in the Aznalcollar sludge and other pyritic matrices

After the collapse on 25 Apr. 1998 of the Aznalcóllar mine tailings dike in southwestern Spain, 45 km2 of the Guadiamar valley were covered by a pyritic sludge containing up to 2% sphalerite (ZnS). Later, the sludge was mechanically removed and calcium carbonate was plowed into the soil to immobilize heavy metals. By June 2001 more than 60% of the sulfides in the residual sludge had oxidized and soil Zn contents reached locally phytotoxic levels. Therefore, the oxidative dissolution of sphalerite in the sludge and other pyritic samples was examined. Flow-through oxidation experiments showed that: (i) about 5 and 17% of the sludge Fe and Zn were in soluble form, respectively, because the sludge sample had been partly oxidized in the field; (ii) the oxidation rates of the residual pyrite and sphalerite were similar; (iii) the overall sulfide oxidation rate was relatively unaffected by the addition of calcite; and (iv) poorly crystalline Fe (hydr)oxides containing Zn in occluded form and Zn (hydroxi)carbonates were formed in the presence of calcite. The rate of oxidation of reference sphalerite greatly increased when it was incorporated in the sludge or in a reference pyrite matrix. This enhancement was due to galvanic interaction because pyrite oxidation was depressed in the presence of sphalerite. Oxidation by Fe3+ ions was less important because the oxidation rates of native sphalerite were not greater at low than at high pH. The fast oxidation rate of sphalerite in the Aznalcóllar sludge indicates a need for quick adoption of remediation measures in similar accidents elsewhere. The use of calcite amendments has little influence on the oxidation rate but does result in the accumulation of Zn in relatively insoluble forms.     

Zinc distribution in soils amended with different kinds of sewage sludge

Sewage sludge (SS) can be applied to cropland to supply and recycle nutrients and organic carbon. Potentially toxic elements in the sludge, however, are of environmental concern. This study evaluates the changes in chemical speciation of Zn in three representative pristine soils of the Pampas Region, Argentina, measured with sequential extraction over a one-year period. Pure SS or SS containing 30% (DM) of its own incineration ash (AS) was applied to the soils at an application rate of 150Mgha(-1). Zn was sequentially fractionated into exchangeable, organically bound, inorganic and residual fractions. The application of the SS and AS amendments significantly increased Zn concentration in all soil fractions at each sampling date. At day 1, Zn was mainly found in the residual fraction. A year after the application of the amendments, redistribution towards the inorganic fraction was observed (41-76% of total Zn content). Zn found in exchangeable and inorganic fractions depended on soil pH rather than on the type of soil used. A negative and significant correlation was found between exchangeable Zn concentrations and soil pH (r=0.94), and a positive and significant correlation between inorganic Zn concentrations and soil pH (r=0.92). For each amended soil and sampling date, no significant differences were observed between SS or AS treatments for the exchangeable fraction. Moreover, the use of AS did not cause significant differences in Zn concentration in the other soil fractions compared to SS. Based on these results, land spreading of AS may be similar to SS diaposal in terms of Zn mobility.     

Zinc fractionation in contaminated soils by sequential and single extractions: influence of soil properties and zinc content

We studied the fractionation of zinc (Zn) in 49 contaminated soils as influenced by Zn content and soil properties using a seven-step sequential extraction procedure (F1: NH4NO3; F2: NH4-acetate, pH 6; F3: NH3OHCl, pH 6; F4: NH4-EDTA, pH 4.6; F5: NH4-oxalate, pH 3; F6: NH4-oxalate/ascorbic acid, pH 3; F7: residual). The soils had developed from different geologic materials and covered a wide range in soil pH (4.0-7.3), organic C content (9.3-102 g kg(-1)), and clay content (38-451 g kg(-1)). Input of aqueous Zn with runoff water from electricity towers during 26 to 74 yr resulted in total soil Zn contents of 3.8 to 460 mmol kg(-1). In acidic soils (n = 24; pH <6.0), Zn was mainly found in the mobile fraction (F1) and the last two fractions (F6 and F7). In neutral soils (n = 25; pH > or =6.0), most Zn was extracted in the mobilizable fraction (F2) and the intermediate fractions (F4 and F5). The extractability of Zn increased with increasing Zn contamination of the soils. The sum of mobile (F1) and mobilizable (F2) Zn was independent of soil pH, the ratio of Zn in F1 over F1+F2 plotted against soil pH, exhibited the typical shape of a pH sorption edge and markedly increased from pH 6 to pH 5, reflecting the increasing lability of mobilizable Zn with decreasing soil pH. In conclusion, the extractability of Zn from soils contaminated with aqueous Zn after decades of aging under field conditions systematically varied with soil pH and Zn content. The same trends are expected to apply to aqueous Zn released from decomposing Zn-bearing contaminants, such as sewage sludge or smelter slag. The systematic trends in Zn fractionation with varying soil pH and Zn content indicate the paramount effect of these two factors on molecular scale Zn speciation. Further research is required to characterize the link between the fractionation and speciation of Zn and to determine how Zn loading and soil physicochemical properties affect Zn speciation in soils.     

Germination tests for assessing biochar quality

Definition, analysis, and certification of biochar quality are crucial to the agronomic acceptance of biochar. While most biochars have a positive impact on plant growth, some may have adverse effects due to the presence of phytotoxic compounds. Conversely, some biochars may have the ability to adsorb and neutralize natural phytotoxic compounds found in soil. We evaluated the effects of biochars on seedling growth and absorption of allelochemicals present in corn ( L.) residues. Corn seeds were germinated in aqueous extracts of six biochars produced from varied feedstocks, thermochemical processes, and temperatures. Percent germination and shoot and radicle lengths were evaluated at the end of the germination period. Extracts from the six biochars had no effect on percent germination; however, extracts from three biochars produced at high conversion temperatures significantly inhibited shoot growth by an average of 16% relative to deionized (DI) water. Polycyclic aromatic hydrocarbons detected in the aqueous extracts are believed to be at least partly responsible for the reduction in seedling growth. Repeated leaching of biochars before extract preparation eliminated the negative effects on seedling growth. Biochars differ significantly in their capacity to adsorb allelochemicals present in corn residues. Germination of corn seeds in extracts of corn residue showed 94% suppression of radicle growth compared to those exposed to DI water; however, incubation of corn residue extracts with leached biochar for 24 h before initiating the germination test increased radicle length 6 to 12 times compared to the corn residue extract treatments. Germination tests appear to be a reliable procedure to differentiate between effects of different types of biochar on corn seedling growth.     

Residual effects of compost and plowing on phosphorus and sediment in runoff

Manure application can lead to excessive soil test P levels in surface soil, which can contribute to increased P concentration in runoff. However, manure application often results in reduced runoff and sediment loss. Research was conducted to determine the residual effects of previously applied compost, plowing of soil with excessive soil test P, and application of additional compost after plowing on volume of runoff and loss of sediment and P in runoff. The research was conducted in 2004 and 2005 under natural rainfall events with plots of 11-m length where low-P and high-P compost had been applied during April 1998 to January 2001. During this initial application period, Bray-P1 in the surface 5-cm of depth was increased from 14 to 553 mg kg(-1) for the high-P compost. Inversion plowing in the spring of 2004 greatly decreased P levels in the surface soil and over the following year reduced runoff by 35% and total P losses by 51% compared with the unplowed compost treatments. Sediment loss was increased with plowing compared with the unplowed compost applied treatments but less than with the no-compost treatment. The application of additional compost after plowing increased surface soil P and dissolved reactive P (DRP) in runoff but did not increase particulate P in runoff. Unplowed compost-amended soil continued to reduce sediment loss but exhibited increased DRP loss even 5 yr after the last application. Plowing to invert excessively high-P surface soil was effective in reducing runoff and DRP loss.     

Degradation of N,N'-dibutylurea (DBU) in soils treated with only DBU and DBU-fortified benlate fungicides

N,N'-dibutylurea (DBU) is a breakdown product of benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazole carbamate], the active ingredient in Benlate fungicides, and has been proposed to cause crop damage after the use of Benlate 50 DF fungicide (DuPont, Wilmington, DE). Our research focused on DBU persistence after application into soil. We assessed DBU persistence on direct application of DBU (carbonyl-(14)C) at two concentrations (0.08 and 0.8 microg DBU kg(-1)) to seven soils and two potting mixes in soil microcosms incubated at various combinations of soil water potential (-0.03 or -0.1 MPa) and temperature (23, 33, 44 degrees C). For two soils at a subset of treatment variables we assessed DBU persistence in the presence of Benlate DF and SP fungicide formulations. Parent compounds, metabolites, and (14)CO(2) were tracked using chromatographic analysis with radioassay and UV detection, liquid scintillation counting, and post-extraction oxidation of the soil. DBU degradation was primarily microbial and for most soil-treatment combinations, half-lives were less than 2 wk. DBU degradation was retarded at the lower soil water potential and enhanced at 33 degrees C. In the presence of the formulation, DBU degradation was slower for one soil type. The longest half-life observed in any case was less than 7 wk; therefore, long-term persistence of DBU applied to soils through a Benlate application is very unlikely.     

Characterization of slow pyrolysis biochars: effects of feedstocks and pyrolysis temperature on biochar properties

Biochars are increasingly used as soil amendment and for C sequestration in soils. The influence of feedstock differences and pyrolysis temperature on biochar characteristics has been widely studied. However, there is a lack of knowledge about the formation of potentially toxic compounds that remain in the biochars after pyrolysis. We investigated biochars from three feedstocks (wheat straw, poplar wood, and spruce wood) that were slowly pyrolyzed at 400, 460, and 525°C for 5 h (straw) and 10 h (woodchips), respectively. We characterized the biochars' pH, electrical conductivity, elemental composition (by dry combustion and X-ray fluorescence), surface area (by N adsorption), water-extractable major elements, and cation exchange capacity (CEC). We further conducted differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffractometry to obtain information on the biochars' molecular characteristics and mineralogical composition. We investigated trace metal content, total polycyclic aromatic hydrocarbon (PAH) content, and PAH composition in the biochars. The highest salt (4.92 mS cm) and ash (12.7%) contents were found in straw-derived biochars. The H/C ratios of biochars with highest treatment temperature (HTT) 525°C were 0.46 to 0.40. Surface areas were low but increased (1.8-56 m g) with increasing HTT, whereas CEC decreased (162-52 mmol kg) with increasing HTT. The results of DSC and FTIR suggested a loss of labile, aliphatic compounds during pyrolysis and the formation of more recalcitrant, aromatic constituents. X-ray diffractometry patterns indicated a mineralogical restructuring of biochars with increasing HTT. Water-extractable major and trace elements varied considerably with feedstock composition, with trace elements also affected by HTT. Total PAH contents (sum of EPA 16 PAHs) were highly variable with values up to 33.7 mg kg; irrespective of feedstock type, the composition of PAHs showed increasing dominance of naphthalene with increasing HTT. The results demonstrate that biochars are highly heterogeneous materials that, depending on feedstock and HTT, may be suitable for soil application by contributing to the nutrient status and adding recalcitrant C to the soil but also potentially pose ecotoxicological challenges.