Effects of Wood Amendments on the Degradation of Terbuthylazine and on Soil Microbial Community Activity in a Clay Loam Soil

The herbicide terbuthylazine is widely used within the EU; however, its frequent detection in surface and groundwater, together with its intrinsic toxicological properties, may pose a risk both for human and environmental health. Organic amendments have recently been proposed as a possible herbicide sorbent in soil, in order to limit herbicide movement from soil to water. The environmental fate of terbuthylazine depends not only in its mobility but also in its persistence. The latter is directly dependent on microbial degradation. For this reason, the effects of pine and oak residues on terbuthylazine soil microbial community functioning and on the potential of this community for terbuthylazine degradation were studied. For this purpose, degradation kinetics, soil dehydrogenase activity and the number of live bacteria were assessed in a clay loam soil treated with terbuthylazine and either amended with pine or oak wood or unamended (sterilised and non-sterilised). At day 65, 85?% of the herbicide applied still persisted in the sterile soil, 73?% in the pine-amended one and 63?% in the oak-amended and unamended ones. Pine residues increased the sorption of terbuthylazine to soil and hampered microbial degradation owing to its high terbuthylazine sorption capacity and a decrease in the bioavailability of the herbicide. On the contrary, in the presence of oak residues, the herbicide sorption did not increase significantly. The overall results confirm the active role of the soil microbial community in terbuthylazine degradation in amended and unamended soils and in a liquid enrichment culture performed using an aliquot of the same soil as the inoculum. In this clay loam soil, in the absence of amendments, the herbicide was found to be quite persistent (t _1/2?>?95?days), while in the enrichment culture, the same natural soil bacterial community was able to halve terbuthylazine in 24?days. The high terbuthylazine persistence in this soil was presumably ascribable to its texture and in particular to the mineralogy of the clay fraction.     

Fate of diuron and terbuthylazine in soils amended with two-phase olive oil mill waste

The addition of organic amendments to soil increases soil organic matter content and stimulates soil microbial activity. Thus, processes affecting herbicide fate in the soil should be affected. The objective of this work was to investigate the effect of olive oil production industry organic waste (alperujo) on soil sorption-desorption, degradation, and leaching of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and terbuthylazine [N2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine], two herbicides widely used in olive crops. The soils used in this study were a sandy soil and a silty clay soil from two different olive groves. The sandy soil was amended in the laboratory with fresh (uncomposted) alperujo at the rate of 10% w/w, and the silty clay soil was amended in the field with fresh alperujo at the rate of 256 kg per tree during 4 years and in the laboratory with fresh or composted alperujo. Sorption of both herbicides increased in laboratory-amended soils as compared to unamended or field-amended soils, and this process was less reversible in laboratory-amended soils, except for diuron in amended sandy soil. Addition of alperujo to soils increased half-lives of the herbicides in most of the soils. Diuron and terbuthylazine leached through unamended sandy soil, but no herbicide was detected in laboratory-amended soil. Diuron did not leach through amended or unamended silty clay soil, whereas small amounts of terbuthylazine were detected in leachates from unamended soil. Despite their higher sorption capacity, greater amounts of terbuthylazine were found in the leachates from amended silty clay soils. The amounts of dissolved organic matter from alperujo and the degree of humification can affect sorption, degradation, and leaching of these two classes of herbicides in soils. It appears that adding alperujo to soil would not have adverse impacts on the behavior of herbicides in olive production.     

Sorption-desorption isotherms and biodegradation of glyphosate in two tropical soils aged with eucalyptus biochar

ABSTRACT

The objective of this study was to evaluate the sorption-desorption process and biodegradation of glyphosate in two tropical soils aged with biochar derived from eucalyptus. The biochar aging period was 30 d. There was little difference between the amounts of sorbed glyphosate in Ultisol (96.8, 96.8 and 96.4%) and Alfisol (97.1, 97.5 and 97.4%) soils that were unamended or amended with biochar aged for 0 or 30 d, respectively. Similar amounts of desorbed herbicide occurred in Ultisol (3.3, 3.3 and 3.4%) and Alfisol (4.1, 4.2 and 3.9%) soils, respectively. The degradation time half-life (DT50) of glyphosate in Ultisol unamended and initial amended were higher (38 and 36 d, respectively) than DT50 in the amended soil with 30 d of biochar aging (27 d); and in the Alfisol DT50 was higher in unamended soil (38 d), and similar in soil unamended at 0 and 30 d of biochar aging (21 and 26 d, respectively). The addition of biochar to two tropical soils or its aging did not have any effect on the sorption and desorption of glyphosate and its biodegradation in relation to the unamended soils, and it can did not affect the transport and persistence of this herbicide in soil.     

Dissipation of fungicides in a vineyard soil amended with different spent mushroom substrates

The degradation kinetics and formation of metabolites for fungicides of different chemical classes (iprovalicarb, metalaxyl, penconazole, and pyrimethanil) and determination of bound residues for metalaxyl and penconazole were studied in both an unamended vineyard soil and in the same soil amended with two spent mushroom substrates (composted (C-SMS1) and fresh (F-SMS2)). The degradation kinetics was fitted to single first-order or first-order multicompartment patterns. Degradation rates decreased in C-SMS1-amended soils for all fungicides as compared to unamended soil, but in F-SMS2-amended soils, they decreased only for iprovalicarb and penconazole. The DT(50) values were higher by up to 1.8 (metalaxyl), 3.8 (pyrimethanil), 4.1 (iprovalicarb), and >1000 (penconazole) times in the soil plus C-SMS1 compared to those for soil plus F-SMS2 or unamended soil. The dissipation mechanism recorded the highest mineralization in the unamended soil for (14)C-metalaxyl and (14)C-penconazole, with the highest formation of nonextractable residues in the F-SMS2-amended soil for (14)C-metalaxyl. The results are consistent with (1) the chemical characteristics of each SMS (total and soluble organic carbon) controlling sorption and the bioavailability of fungicides and (2) the microbial activity of SMS-amended soils, which affects fungicide biodegradation. The findings of this work highlight the potential of SMS amendments with different characteristics to decrease or increase the degradation rate of a fungicide in a vineyard soil.     

Influence of organic by-products and nitrogen source on chemical and microbiological status of an agricultural soil

We assessed the influence of the addition of four municipal or agricultural by-products (cotton gin waste, ground newsprint, woodchips, or yard trimmings), combined with two sources of nitrogen (N), [ammonium nitrate (NH₄NO₃) or poultry litter] as carbon (C) sources on active bacterial, active fungal and total microbial biomass, cellulose decomposition, potential net mineralization of soil C and N and soil nutrient status in agricultural soils. Cotton gin waste as a C source promoted the highest potential net N mineralization and N turnover. Municipal or agricultural by-products as C sources had no affect on active bacterial, active fungal or total microbial biomass, C turnover, or the ratio of net C:N mineralized. Organic by-products and N additions to soil did not consistently affect C turnover rates, active bacterial, active fungal or total microbial biomass. After 3, 6 or 9 weeks of laboratory incubation, soil amended with organic by-products plus poultry litter resulted in higher cellulose degradation rates than soil amended with organic by-products plus NH₄NO₃. Cellulose degradation was highest when soil was amended with newsprint plus poultry litter. When soil was amended with organic by-products plus NH₄NO₃, cellulose degradation did not differ from soil amended with only poultry litter or unamended soil. Soil amended with organic by-products had higher concentrations of soil C than soil amended with only poultry litter or unamended soil. Soil amended with organic by-products plus N as poultry litter generally, but not always, had higher extractable P, K, Ca, and Mg concentrations than soil amended with poultry litter or unamende soil. Agricultural soil amended with organic by-products and N had higher extractable N, P, K, Ca and Mg than unamended soil. Since cotton gin waste plus poultry litter resulted in higher cellulose degradation and net N mineralization, its use may result in faster increase in soil nutrient status than the other organic by-products and N sources that were tested. Received: 15 May 1996     

Paclobutrazol effects on soil microorganisms

The side effects of paclobutrazol, a plant growth regulator, on soil microbial community and activity were assessed in soil samples from Petrolina (PE), Pernambuco State and from Lins (SP), São Paulo State, in Brazil. The first experiment was carried out with soils from mango orchards of Petrolina, subjected to frequent field applications of paclobutrazol. A second experiment was conducted with soils from Petrolina and Lins with application of paclobutrazol under greenhouse conditions. For orchard soils, plate counting of soil microorganisms was carried out, while for the greenhouse experiment the parameters evaluated were: microbial biomass C, living hyphal length, dehydrogenase activity, and paclobutrazol dissipation. The paclobutrazol addition to soils of mango orchards in Petrolina, affected negatively the soil microbial community. The average values for total number of bacteria, fungi and actinomycetes were reduced by 58, 28, and 28%, respectively, compared to the paclobutrazol unamended soil. For the greenhouse experiment, the paclobutrazol application in the soils from Petrolina influenced negatively the dehydrogenase activity and the living hyphal length, but not the microbial biomass C. The addition of this substance to the Lins soils had no effect on the microbial parameters evaluated.     

Effect of different wood pretreatments on the sorption-desorption of linuron and metalaxyl by woods

The sorption-desorption of two different pesticides, linuron and metalaxyl, by woods was studied. Sorbent/solution ratio and sorption kinetics were also determined. Untreated wood and water, NaOH, HCl, and octadecyltrimethylammonium bromide (ODTMA) treated pine (softwood) and oak (hardwood) were used as sorbents. Linuron and metalaxyl were sorbed by untreated woods up to 80 and 40%, respectively, in a short time when the sorbent/solution ratio of 1:10 was used. Sorption of pesticides was significantly higher by pine, having higher lignin content, than by oak. Freundlich sorption constants (K(f)) were 96.2 and 74.4 (linuron) and 8.28 and 4.95 (metalaxyl) for untreated pine and oak woods and increased 1.04-2.35-fold (linuron) and 1.33-2.17-fold (metalaxyl) when woods were treated. The sorption was higher by HCl- and ODTMA-treated woods. Additionally, Freundlich desorption constants also indicated greater sorption irreversibility of both pesticides for treated woods than for untreated woods. The results revealed wood residues as a promising, low-cost, and environmentally friendly material to immobilize pesticides in soils, preventing water contamination. Wood treatments aimed at removing soluble wood extracts or at modifying wood chemical structure could increase their sorption capacity.     

Comparative sorption and leaching study of the herbicides fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) in a soil amended with biochars and other sorbents

Biochar, the solid residual remaining after the thermochemical transformation of biomass for carbon sequestration, has been proposed to be used as a soil amendment, because of its agronomic benefits. The effect of amending soil with six biochars made from different feedstocks on the sorption and leaching of fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) was compared to the effect of other sorbents: an activated carbon, a Ca-rich Arizona montmorillonite modified with hexadecyltrimethylammonium organic cation (SA-HDTMA), and an agricultural organic residue from olive oil production (OOW). Soil was amended at 2% (w/w), and studies were performed following a batch equilibration procedure. Sorption of both herbicides increased in all amended soils, but decreased in soil amended with a biochar produced from macadamia nut shells made with fast pyrolysis. Lower leaching of the herbicides was observed in the soils amended with the biochars with higher surface areas BC5 and BC6 and the organoclay (OCl). Despite the increase in herbicide sorption in soils amended with two hardwood biochars (BC1 and BC3) and OOW, leaching of fluometuron and MCPA was enhanced with the addition of these amendments as compared to the unamended soil. The increased leaching is due to some amendments' soluble organic compounds, which compete or associate with herbicide molecules, enhancing their soil mobility. Thus, the results indicate that not all biochar amendments will increase sorption and decrease leaching of fluometuron and MCPA. Furthermore, the amount and composition of the organic carbon (OC) content of the amendment, especially the soluble part (DOC), can play an important role in the sorption and leaching of these herbicides.     

Microbial degradation of fomesafen by a newly isolated strain Pseudomonas zeshuii BY-1 and the biochemical degradation pathway

Fomesafen is a diphenyl ether herbicide used to control the growth of broadleaf weeds in bean fields. Although the degradation of fomesafen in soils was thought to occur primarily by microbial activity, little was known about the kinetic and metabolic behaviors of this herbicide. This paper reported the capability of the newly isolated strain Pseudomonas zeshuii BY-1 to use fomesafen as the sole source of carbon in pure culture for its growth. Up to 88.7% of 50 mg of L(-1) fomesafen was degraded by this bacterium in mineral medium within 3 days. Strain BY-1 could also degrade other diphenyl ethers, including lactofen, acifluorfen, and fluoroglycofen. During the fomesafen degradation, five metabolites were detected and identified by liquid chromatography-mass spectrometry and tandem mass spectrometry. The primary degradation pathway of fomesafen might be the reduction of the nitro group to an amino group, followed by the acetylation of the amino derivative, dechlorination, and cleavage of the S-N bond. The addition of the BY-1 stain into soils treated with fomesafen resulted in a higher degradation rate than that observed in uninoculated soils, and the bacteria community in contaminated soil recovered after inoculation of the BY-1 stain. On the basis of these results, strain P. zeshuii BY-1 has the potential to be used in the bioremediation of fomesafen-contaminated soils.     

Microbial activity and metabolic quotient of microbes in soils amended with biochar and contaminated with atrazine and paraquat

The study was conducted to determine how biochar as a soil amendment maintained the microbial community in pesticide contaminated soils. Alfisol (Adenta series – Typic Kandiustalf) and Vertisol (Akuse series – Typic Calciustert) were amended with biochar (0 t/ha biochar, 10 t/ha cocoa husk biochar (CHB), 10 t/ha rice husk biochar (RHB)) and pesticides (atrazine and paraquat at two rates each namely 0 kg/ha pesticide and 10 times the normal recommended rate of pesticide) were applied. The CHB-amended soils stimulated microbial activities such as ammonia and nitrate release more than the RHB-amended soils. Basal respiration was significantly higher in the atrazine polluted soils than in paraquat polluted soil. Significant interaction occurred between soil type and biochar and high microbial biomass carbon was recorded for vertisol amended with CHB. Metabolic quotient was lower in soils amended with biochar and polluted with atrazine than in the un-amended soil. The use of CHB in soil of high clay content (47.5%, i.e. the vertisol) was a more effective management tool in maintaining the microbial community in a pesticide-polluted environment than in soil of lower clay content (22.5%). Soils of high clay content amended with biochar can sustain the soil microbial community even in a disturbed environment.     

Microbial communities in rice rhizosphere altered by intermittent and continuous flooding in fields with long-term arsenic application

Rice cultivated on arsenic (As)-contaminated soils can, under some conditions, accumulate high concentrations of As in grain, mostly as a result of the continuous flooding practices commonly used for rice cultivation. Intermittent flooding, as opposed to continuous flooding, might reduce soluble As concentrations in the rice rhizosphere, but it might also alter soil microbial populations that may impact As chemistry. A field-scale study was conducted to analyze As concentrations and microbial populations in the rice rhizosphere, in response to intermittent and continuous flooding in plots that were historically amended with “As-containing” pesticide and unamended soil. Rhizosphere, pore-water and grain As concentrations were quantified, and microbial populations in the rhizosphere were characterized using community quantitative-PCR and 16S rRNA gene sequencing. Pore-water As concentrations decreased by 41-81% and grain As by 31-48% in the intermittently flooded plots relative to the continuously flooded plots. The relative abundance of bacteria increased over the course of the growing season, while archaeal and fungal gene abundances decreased. Bacterial community structure and composition were significantly different between As amended and unamended plots, as well as between the flooding treatments. Proteobacteria was the predominant phylum detected in most treatments with relative abundance of 24-29%. The relative abundance of iron-reducing bacteria was higher with the continuous flood compared to the intermittent-flood treatment, implying greater relative iron reduction and possibly As release from the iron oxides under the continuously flooded conditions. These differences in rhizosphere-microbial communities may have contributed to the lower pore-water arsenic concentrations in the intermittently flooded conditions.     

Short-term carbon mineralization in saline–sodic soils

Previous studies have shown that carbon (C) mineralization in saline or sodic soils is affected by various factors including organic C content, salt concentration and water content in saline soils and soil structure in sodic soils, but there is little information about which soil properties control carbon dioxide (CO₂) emission from saline-sodic soils. In this study, eight field-collected saline–sodic soils, varying in electrical conductivity (EC_e, a measure of salinity, ranging from 3 to 262 dS m⁻¹) and sodium adsorption ratio (SAR_e, a measure of sodicity, ranging from 11 to 62), were left unamended or amended with mature wheat or vetch residues (2% w/w). Carbon dioxide release was measured over 42 days at constant temperature and soil water content. Cumulative respiration expressed per gram SOC increased in the following order: unamended soil<soil amended with wheat residues (C/N ratio 122)<soil with vetch residue (C/N ratio 18). Cumulative respiration was significantly (p < 0.05) negatively correlated with EC_e but not with SAR_e. Our results show that the response to EC_e and SAR_e of the microbial community activated by addition of organic C does not differ from that of the less active microbial community in unamended soils and that salinity is the main influential factor for C mineralization in saline–sodic soils.     

Assessing biogas digestate,pot ale,wood ash and rockdust as soil amendments: effects on soil chemistry and microbial community composition

Applying by-products as soil amendments to agricultural systems is growing in popularity. We aimed to assess the efficacy of some contemporary by-products to provide nutrients to crops as well as the potential harm of adding toxic elements to the environment. Four different by-products widely available in Northern Europe were tested for their effects on two nutrient-poor agricultural soils in terms of increasing available macro- and micro-nutrients as well as toxic elements. Assessing soil microbial community as a sensitive tool for evaluating soil quality was conducted with the focus on microbial activity, carbon metabolism and on Rhizobium/Agrobacterium. Wood ash increased pH and Ca_EDTA, K_EDTA and Mg_EDTA in the soils. The only increase in EDTA-extractable micronutrients in the soils was observed by applying pot ale, increasing Cu. None of the amendments increased the availability of Pb and Cd in the soils. Soils amended with the by-products thus remained similar to the unamended control but were quite different from fully mineral fertilised soils. There were no detectable adverse effects on the physiological and genetic profiles of microbial communities. The by-products were moderately beneficial and did not change the soil microbial community as much as the fully fertilised treatment with mineral fertilisers. Changes in the microbial community profiles were probably due to direct effects on microbes limited by K, Ca and N as opposed to indirect effects on plant growth. This is potentially significant in understanding how to improve impoverished and marginal soils as microbial activity affects many other ecosystem functions.     

Taxa-specific changes in soil microbial community composition induced by pyrogenic carbon amendments

The effects of pyrogenic carbon on the microbial diversity of forest soils were examined by comparing two soil types, fire-impacted and non-impacted, that were incubated with laboratory-generated biochars. Molecular and culture-dependent analyses of the biochar-treated forest soils revealed shifts in the relative abundance and diversity of key taxa upon the addition of biochars, which were dependent on biochar and soil type. Specifically, there was an overall loss of microbial diversity in all soils treated with oak and grass-derived biochar as detected by automated ribosomal intergenic spacer analysis. Although the overall diversity decreased upon biochar amendments, there were increases in specific taxa during biochar-amended incubation. DNA sequencing of these taxa revealed an increase in the relative abundance of bacteria within the phyla Actinobacteria and Gemmatimonadetes in biochar-treated soils. Together, these results reveal a pronounced impact of pyrogenic carbon on soil microbial community composition and an enrichment of key taxa within the parent soil microbial community.     

Modifications of organic matter and enzymatic activities in response to change in soil use in semi‐arid mountain ecosystems (southern Spain)

Soil organic matter composition and biochemical properties were determined in mountain calcimorphic Mediterranean soils under different vegetation (cultivated soils, secondary bush, high mountain bush, juniper, evergreen oak and pine) to assess the impact of soil use on the size and activity of microbial communities. Our results indicated that clearing forest leads to a general decline in the performance of soil organic carbon sequestration and associated enzymatic activities. However, when soil enzymatic activities (dehydrogenase, catalase, phosphodiesterase, β‐glucosidase, urease and casein‐protease) were expressed as ratios to total organic carbon (specific activities), a conspicuous increase in their activities was observed in cleared soils as compared with forest soils, suggesting enhanced hydrolytic potential in the former. In addition, the negative correlation observed between qCO₂ (metabolic quotient) and water retention at ?1500 kPa, could be interpreted as an adaptive strategy against low soil moisture by microbial communities in cleared soils. This indicates the importance of describing soil quality in terms of long‐term soil organic C sequestration and/or resistance of the organic matter to microbial transformation. These features were reflected in the visible and infrared spectra of humic acids, which suggested humification mechanisms involving mainly an alteration of plant macromolecules with poor incorporation of characteristic microbial metabolites in the forest soils whereas the opposite effect was observed in cleared soils.     

Microbial populations involved in the suppression of Rhizoctonia solani AG1-1B by lignin incorporation in soil

Rhizoctonia solani causes worldwide losses in numerous crops. Sclerotia of R. solani remain viable for several years in soil and are an important source of primary infection. In this study the effect of soil incorporation of Kraft pine lignin, a side product of the paper industry, on viability of R. solani AG1-1B sclerotia was investigated. The efficacy of lignin was assessed in a sandy loam (Oppuurs) and a silt loam soil (Leest) collected from commercial fields in Belgium. Evaluating sclerotial viability after 4 weeks incubation in the two soils amended with 1% (w/w) Kraft pine lignin demonstrated a soil-dependent effect. In Leest soil the addition of lignin resulted in a significantly reduced sclerotial viability, together with an increased mycoparasitism by Trichoderma spp.; in Oppuurs soil, on the other hand, only a slight and insignificant reduction in sclerotial viability was observed. Based on phospholipid fatty acid analysis, different changes in microbial community structure upon lignin amendment were detected in the two soils. Both amended soils showed a significant increase in Gram negative bacteria. In Leest soil this increase was accompanied with a significantly higher increase in fungi and actinomycetes compared with Oppuurs soil. In addition, Kraft pine lignin resulted in both soils in a small but significant increase in manganese peroxidase activity and this increase tended to be higher in Leest soil. Manganese peroxidase produced by lignin-degrading basidiomycetes has previously been shown to degrade melanin, which protects the sclerotia against biotic and abiotic stress. We hypothesize that lignin-degrading fungi increased the susceptibility of the sclerotia to sclerotial antagonists such as Trichoderma, Gram negative bacteria and actinomycetes. Clearly, the effect observed here did not rely on the stimulation of one microbial group, but is the result of an interaction of different groups.     

Soil moisture and plant residue addition interact in their effect on extracellular enzyme activity

Water availability strongly affects soil microbial activity and community composition. In a laboratory incubation we investigated the combined effect of soil moisture potential (−10 kPa, −135 kPa, and <−1500 kPa) and plant residue addition on soil enzyme activities (protease, β-glucosidase, β-glucosaminidase and exocellulase) and phospholipid fatty acid (PLFA) profiles. Soil respiration was positively correlated with soil moisture potential and significantly increased with the addition of residue. In the unamended soil, enzyme activities were little affected by soil moisture potential, nor did they change much over time. The addition of residue, however, significantly increased enzyme activity at each moisture level. Furthermore, all four enzyme activities were considerably higher in the amended dry soil than in amended samples with a higher moisture potential. In contrast, in the amended dry soil, respiration and microbial biomass were reduced compared to the amended samples with a higher moisture potential. The low microbial biomass in the amended dry soil was mainly due to a decrease in Gram-negative bacteria, while the fungal biomass reached similar levels at all water potentials. Therefore, shifts in microbial community composition alone cannot explain the increased enzyme activities in the dry soil. Other factors, such as increased fungal activity, stronger interactions between enzymes and soil particles due to thinner water films, may have contributed to the observed effects. Our results suggest that under dry conditions, potential enzyme activities may be decoupled from microbial biomass and respiration in the presence of substrates.     

Microbial use of lignite compared to recent plant litter as substrates in reclaimed coal mine soils

In the Lusatian mining district, rehabilitated mine soils contain substantial amounts of lignite in addition to recent carbon derived from plant litter. The aim of this study was to examine the importance of the two organic matter types as substrates for soil microbial biomass in mine soils containing organic matter with a contrasting degree of humification. Samples were taken from the lignite-containing overburden material, from a mine soil under 14-year-old black pine (Pinus nigra) and from a mine soil under 37-year-old red oak (Quercus rubra). Overburden material was ameliorated with alkaline ash and incubated in an identical manner as the 14-year-old and 37-year-old mine soils for 16 months. Carbon mineralisation was monitored throughout. After 0, 3, 6, 12 and 16 months, samples were removed and analysed for chemical parameters and for microbial biomass. In addition, ¹⁴C activity measurements in bulk soil and microbial biomass were used to estimate their lignite content.Despite the high content of organic carbon in lignite-rich overburden material, low contents of microbial biomass were recorded. Ash-amelioration led to high pH values in the overburden material, resulting in high concentrations of dissolved organic carbon most likely derived from lignite. Development of the microbial community was subsequently stimulated by presence of an easily available carbon source. In older mine soils, larger amounts of microbial biomass are most likely related to the presence of recent organic matter. Radiocarbon analysis of the microbial biomass extracted from the 14-year-old mine soil indicated higher lignite carbon contribution than recorded for microbial biomass of the 37-year-old mine soil. The highest concentration of lignite C present in microbial biomass as indicated by the C_mic/C_org ratio was, however, observed in the ameliorated overburden material. Therefore, we conclude that the importance of lignite as a carbon source for micro-organisms decreases when recent organic matter is present in the older stages of mine soil development.     

Soil microorganisms are less susceptible than crop plants to potassium deficiency

To evaluate the relationship between the potassium (K) status in the microbial community and the exchangeable K concentration in soils, the effects of K addition on microbial activity were assessed in cultivated Andisols not having received K fertilizer. Potassium limitation was not observed in the microbial community, even in a soil amended with only nitrogen (N) and phosphorus (P) but not K since 1938, though crop plants in this soil showed severe K deficiency symptoms. Furthermore, in a soil amended with NP + compost, microbial activity was limited by K only after limitation of carbon (C) and N. These results suggest that soil microorganisms demand more C and N than K, even in soils with low K availability, and also that the soil microbial community is less susceptible to K deficiency than are crop plants.     

Availability of triazine herbicides in aged soils amended with olive oil mill waste

Amendments are frequently added to agricultural soils to increase organic matter content. In this study, we examined the influence of alperujo, an olive oil mill waste, on the availability of two triazine herbicides, terbuthylazine and atrazine, in two different sandy soils, one from Sevilla, Spain, and the other from Minnesota. The effect of aging on herbicide sorption and bioavailability was also studied. Soils were amended with alperujo at a rate of 3-5% (w:w) in laboratory studies. Apparent sorption coefficients for the triazine herbicides were calculated as the ratio of the concentrations of each herbicide sequentially extracted with water, followed by aqueous methanol, at each sampling time. These data showed greater sorption of terbuthylazine and atrazine in amended soils as compared to nonamended soils, and an increase in the amount of herbicide sorbed with increasing aging time in nonamended soils. The triazine-mineralizing bacterium Pseudomonas sp. strain ADP was used to characterize triazine bioavailability. Less mineralization of the herbicides by Pseudomonas sp. strain ADP was observed in soils amended with alperujo, as compared to the unamended soils, and, despite the increase in sorption with aging in unamended soils, herbicide mineralization also increased in this case. This has been attributed to Pseudomonas sp. strain ADP first using alperujo as a more readily available source of N as compared to the parent triazines. In summary, addition of alperujo to the soils studied was shown to increase triazine herbicides sorption and hence to reduce its availability and potential to leach.