The Effects of Soil Solarization and Compost on Soil Suppressiveness against Fusarium Oxysporum f. sp. Melonis

Soil suppressiveness against Fusarium was tested using solarized and non-solarized soils combined with composts of three maturation levels, and a non-amended control. The soils were sampled on three dates: after previous year solarization but before current year solarization (0 weeks), at the end of the solarization period of the current year (4 weeks), and 4 weeks later (recovery time). Melon seedlings were inoculated with Fusarium spores and disease severity was assessed. The study showed a reduction of soil suppressiveness capacity against Fusarium oxysporum f. sp. melonis after 1 year of solarization (0 weeks). Fusarium disease severity in artificially inoculated melon plants, expressed by area under the disease progress curve, was higher in solarized soil than in non-solarized soil. Compost addition lowered the disease severity, both in the solarized and in the non-solarized soils. However, suppression was not obtained at the end of the solarization period, whereas compost beneficial effect was found at this time.     

Effect of soil solarization on subsequent nitrification activity at elevated temperatures

Soil solarization is a nonchemical method of soil disinfection achieved by covering the soil surface with sheets of vinyl plastic to generate elevated soil temperature, generally over 45°C. Such elevated temperatures may be detrimental to some nitrifying microorganisms and favorable to others. However, little information exists to indicate how nitrification activity in soil is affected after solarization. We performed several experiments to investigate the effects of soil solarization on nitrification activity. We found that: (1) if a soil was subjected to pretreatment of 45 or 50°C for as little as 1 d, nitrification activity in a subsequent incubation at 30°C was less than that of a soil that did not receive any high-temperature pretreatment. However, if a soil received pretreatments of 45 or 50°C for more than 7 d, nitrification activity in a subsequent incubation at 45 or 50°C was greater than that of soil that did not receive high temperature pretreatment. (2) Nitrification activity in three kinds of soil taken from 0–5 cm depth after solarization treatment was greater at 45°C than 30°C. (3) Nitrification activity at 45°C in soil that had received solarization in the preceding year was greater than that in soil that had not been subjected to solarization. This was consistent with the fact that the population densities of ammonia oxidizers were greater in soils that had been subjected to solarization. These results suggest that soil solarization induces nitrifying microorganisms that are more active at 45–50°C than they are at 30°C, and that the effect of solarization on nitrification persists until the next crop season.     

Influences of organic fertilization and solarization in a greenhouse on particle-size fractions of a Mediterranean sandy soil

 The effects of a composted organic amendment and solarization on the organic matter (OM) of a sandy soil were determined by means of particle-size fractionation and analysis of carbon and nitrogen contents. After 2 years, total soil carbon increased under organic fertilization but did not significantly change with solarization. As a consequence of the climatic conditions in the greenhouse, the carbon concentrations (g kg^–1 fraction) of the particle-size fractions were lower than those found for temperate soils and closer to those for tropical soils. The carbon amounts (g kg^–1 soil) and carbon:nitrogen ratios, which were highest in fractions >200 μm, reflected the short-term influence of the industrially processed organic amendment, rich in composted coarse plant debris. In contrast, the characteristics of the OM associated with each fraction were not significantly affected by solarization. In comparison with other coarse-textured temperate or tropical soils, carbon concentrations in fine silt (2–20 μm) and clay (0–2 μm) fractions were very low. This suggests a "greenhouse effect", together with a high rate of carbon mineralization affecting fine silt and clay fractions. Received: 19 November 1999     

Evaluation of soil solar heating for control of damping-off fungi in two forest nurseries in France

Field experiments were carried out at two different forest nurseries during the summer of 1994 to examine the efficacy of soil solarization for the control of damping-off. Both soils hosted Pythium spp., Fusarium spp. and Rhizoctonia solani as damping-off agents. Soil samples from solarized, steamed, fumigated and untreated plots were periodically collected and assayed for soil infectivity. Solarization with a double layer of polyethylene film was as effective as steaming or fumigation in reducing soil infectivity in the uppermost layer. During July the temperature of covered beds rose as high as 50°C at a soil depth of 5cm. The method achieved good control of Pythium spp., the main cause of damping-off at both nurseries, whereas Fusarium spp. were more tolerant. The association of Trichoderma spp. with a reduction of soil infectivity at the last sampling date strongly suggested that biocontrol processes were induced after solarization. Soil solarization provides a suitable method for control of damping-off. Received: 29 October 1996     

Soil amidase activity in polyacrylamide-treated soils and potential activity toward common amide-containing pesticides

 Polyacrylamide (PAM) is currently used as an irrigation water additive to significantly reduce the amount of soil erosion that occurs during furrow irrigation of crops. Elevated soil amidase activity specific toward the large PAM polymer has been reported in PAM-treated field soils; the substrate specificity of the induced amidase is uncertain. PAM-treated and untreated soils were assayed for their capacity to hydrolyze the amide bond in carbaryl (Sevin), diphenamid (Dymid), and naphthalene acetamide. Based on results obtained with a soil amidase assay, there was no difference between PAM-treated and untreated soils with respect to the rate of amide bond hydrolysis of any of the agrochemicals tested. It appears that under these assay conditions the PAM-induced soil amidase is not active toward the amide bonds within these molecules. However, carbaryl was hydrolyzed by a different soil amidase. To our knowledge, this is the first soil enzyme assay-based demonstration of the hydrolysis of carbaryl by a soil amidase. Received: 23 June 1999     

Legacy effects of elevated ozone on soil biota and plant growth

Many studies have examined how human-induced atmospheric changes will influence ecosystems. The long-term consequences of human induced climate changes on terrestrial ecosystems may be determined to a large extend by how the belowground compartment will respond to these changes. In a free-air ozone enrichment experiment running for 5 years, we reciprocally transplanted soil cores from ambient and elevated ozone rings to test whether exposure to elevated ozone results in persistent changes in the soil biota when the plant and soil are no longer exposed to elevated ozone, and how these legacy effects of elevated ozone influenced plant growth as compared to current effects of elevated ozone. After one growing season, the current ozone treatment enhanced plant growth, but in soil with a historical legacy of elevated ozone the plant biomass in that soil was reduced compared to the cores originated from ambient rings. Current exposure to ozone increased the phospholipid fatty acids of actinomycetes and protozoa, however, it decreased dissolved organic carbon, bacterivorous and fungivorous nematodes. Interestingly, numbers of bacterivorous and fungivorous nematodes were enhanced when soils with a legacy of elevated ozone were placed under elevated ozone conditions. We conclude that exposure to elevated [O₃] results in a legacy effect in soil. This legacy effect most likely influenced plant growth and soil characteristics via responses of bacteria and fungi, and nematodes that feed upon these microbes. These soil legacies induced by changes in soil biotic community after long-term exposure of elevated ozone can alter the responses of ecosystems to current climatic changes.     

Effect of Flooding Lead Arsenate–Contaminated Orchard Soil on Growth and Arsenic and Lead Accumulation in Rice

Lead arsenate has been used as pesticide. Flooding soils contaminated by lead arsenate could increase plant arsenic and lead and become a human health risk. The objective was to determine the effects of flooding of lead‐arsenate soils on rice grain yield and arsenic and lead accumulation. Bagstown and Chashmont soils with high levels of arsenic and lead were planted with rice in the greenhouse under flooded and nonflooded conditions. Flooding reduced grain yield and increased grain arsenic concentration on both soils. Grain lead decreased with flooding for the Bagstown soil but increased for the Chashmont. Arsenic and lead concentrations in the straw were more than in grain. Grain arsenic and lead levels observed would not be expected to become a human health risk. However, bioavailability studies are needed. The high arsenic and lead in the straw may indirectly become a human health risk because rice straw is used for livestock feed and bedding.     

Comparison of Fenton's Reagent and Ozone Oxidation of Polycyclic Aromatic Hydrocarbons in Aged Contaminated Soils (7 pp)

Background, Aim and Scope   Polycyclic aromatic hydrocarbons (PAHs) are formed as a result of incomplete combustion and are among the most frequently occurring contaminants in soils and sediments. PAHs are of great environmental concern due to their ubiquitous nature and toxicological properties. Consequently, extensive research has been conducted into the development of methods to remediate soils contaminated with PAHs. Fenton's reagent or ozone is the most commonly studied chemical oxidation methods. However, the majority of remediation studies use soils that have been artificially contaminated with either one or a limited number of PAH compounds in the laboratory. Hence, it is essential to extend such studies to soils contaminated with multiple PAHs under field conditions. Objectives   The objective of this study is to investigate the capacity of Fenton's reagent and ozone to degrade PAHs in soils. The soils have been collected from a number of different industrial sites and, therefore, will have been exposed to different PAH compounds in varying concentrations over a range of time periods. The capacity of Fenton's reagent and ozone to degrade PAHs in industrially contaminated soils is compared to results obtained in studies using soils artificially contaminated with PAHs in the laboratory. Materials and Methods: Nine soil samples, contaminated with PAHs, were collected from five different industrial sites in Sweden. For the Fenton's reagent procedure, the pH of the soil slurry samples was adjusted to pH 3 and they were kept at a constant temperature of 70oC whilst H2O2 was added. For the ozone procedure, soil samples were mixed with 50% water and 50% ethanol and kept at a constant temperature of 45 oC. Ozone was then continually introduced to each soil sample over a period of four hours. Following the Fenton's reagent and ozone oxidation procedures, the samples were filtered to isolate the solid phase, which was then extracted using pressurized liquid extraction (PLE). The sample extracts were cleaned up using open columns and then analysed by gas chromatography-mass spectrometry (GC-MS). Results: The relative abundance of the detected PAHs varied between soils, associated with different industries. For example, low molecular weight (LMW) PAHs were more abundant in soil samples collected from wood impregnation sites and high overall PAH degradation efficiencies were observed in soils originating from these sites. In the contaminated soils studied, PAHs were more effectively degraded using Fenton's reagent (PAH degradation efficiency of 40-86%) as opposed to ozone (PAH degradation efficiency of 10-70%). LMW PAHs were more efficiently degraded, using ozone as the oxidizing agent, whereas the use of Fenton's reagent resulted in a more even degradation pattern for PAHs with two through six fused aromatic rings. Discussion: The degradation efficiency for both methods was largely dependent on the initial PAH concentration in the soil sample, with higher degradation observed in highly polluted soils. LMW PAHs are more susceptible to degradation than high molecular weight (HMW) PAHs. As a result of this the relative abundance of large (often carcinogenic) PAHs increased after chemical oxidation treatment, particularly after ozone treatment. Repeated Fenton's reagent treatment did not result in any further degradation of soil PAHs, indicating that residual soil PAHs are strongly sorbed. The effectiveness of the two oxidation treatment approaches differed between industrial sites, thus highlighting the importance of further research into the influence of soil properties on the sorption capacity of PAHs. Conclusions: This study demonstrates that the degree to which chemical oxidation techniques can degrade soil bound PAHs chemical degradation is highly dependent on both the concentration of PAHs in the soils and the compounds present, i.e. the various PAH profiles. Therefore, similarities in the PAH degradation efficiencies in the nine soil samples studied were observed with the two chemical oxidation methods used. However, the degradation performance of Fenton's reagent and ozone differed between the two methods. Overall, Fenton's reagent achieved the highest total PAH degradation due to stronger oxidation conditions. LMW PAHs showed higher susceptibility to oxidation, whereas high molecular weight (HMW) PAHs appear to be strongly sorbed to the soils and therefore less chemically available for oxidation. This study highlights the importance of including soils collected from a range of contaminated sites in remediation studies. Such soil samples will contain PAH contaminants of varying concentrations, chemical and physical properties, and have been aged under field conditions. In addition to the chemical and physical properties of the soils, these factors will all influence the chemical availability of PAHs to oxidation. Recommendations and Perspectives: We recommend including aged contaminated soils in chemical degradation studies. In future chemical remediation work, we intend to investigate the potential influence of the chemical and physical properties of PAHs and soil parameters potential influence on the chemical oxidation efficiency in aged contaminated soils. Due to the vast number of contaminated sites there is a great need of efficient remediation methods throughout the world. This study shows the difficulties which may be experienced when applying remediation methods to a variation of contaminated sites.     

Soil solarization: Effects on soil properties,crop fertilization and plant growth

Summer solarization of six wet field soils of four different textures raised soil temperatures by 10–12°C at 15cm depth. Soil solarization increased concentrations of NO^?₃N and NH⁺₄N up to six times those in nontreated soils. Concentrations of P, Ca²⁺, Mg²⁺ and electrical conductivity (EC) increased in some of the solarized soils. Solarization did not consistently affect available K⁺, Fe³⁺, Mn²⁺, Zn²⁺, Cu²⁺, Cl^? concentrations, soil pH or total organic matter. Concentrations of mineral nutrients in wet soil covered by transparent polyethylene film, but insulated against solar heating, were the same as those in nontreated soil. Increases in NO^?₃N plus NH⁺₄N were no longer detected in fallowed soils 9 months after solarization. No significant correlation between mineral-nutrient concentration in plant tissue and plant growth was found. Fresh and dry weights of radish, pepper and Chinese cabbage plants usually were greater when grown in solarized soils than in nontreated soils. Fertilization of solarized soils sometimes resulted in greater plant growth responses than observed in solarized but nonfertilized soils.     

Abbau und biozide Wirkung von Pflanzenschutz-und Schädlingsbekämpfungsmitteln im Boden am Beispiel von Kelevan

Degradation and biocide effect of chemical plant protecting agents and pesticides in soils by the example of the insecticide Kelevan By the example of the insecticide Kelevan it is proved that by means of a combined test plan degradation and biocide effect of chemical plant protecting agents and pesticides in soils can be tested simultaneously. For this test two different test soils as described in leaflet No. 36 of the Biologische Bundesanstalt (BBA), Braunschweig, are each divided in test samples of about 200 g dry matter. To answer the question whether besides the biotic an abiotic degradation of Kelevan and its primary subsequent products takes place in top soil, too, one part of the soil samples was sterilized by overheated steam. Afterwards these and the non-sterilized soil samples were treated with known amounts of Kelevan[cage-U-¹⁴C] and in accordance to leaflet No. 36 of the BBA stored in the dark at 22°U65% r. h. or under field conditions for different periods. To investigate the effect of Kelevan and its metabolites on microorganisms in top soil, further soil samples were treated with increasing amounts of Kelevan and also stored for different periods. At the end of storage periods on an average W,2 % of applicated radioactivities were recovered in the soil samples with Kelevan[cage-U-¹⁴C]. Whereas readioactivities of sterilized soil samples were nearly quantitatively extractable, increasing radioactivity amounts were held back under the same extraction conditions by the native soil samples, which were present as organic residue components of Kelevan(cagc-U-¹⁴C) and not as ¹⁴C-containing carbonate. During degradation, in both test soils as well under laboratory conditions as under field conditions, about one third of Kelevan[cage-U-¹⁴C] was transferred within 30 months via Kelevan acid[cage-U-¹⁴C] to Chlordecon[cage-U-¹⁴C] and about two thirds were transferred into various unknown ¹⁴C-labelled degradation products. The results of microbiological investigation prove that microorganisms were evidently neither selected nor decimated in both test soils by Kelevan and its degradation products.     

Effects of fertilizer and soil components on pesticide photolysis

An environmental fate study was performed analyzing the effects of soil composition on the soil photolysis of a chemical. The study was conducted in two phases in which both moist and air-dried soils were fortified with either the common fertilizer sodium nitrate or the natural soil components iron or humic acid and dosed with niclosamide. The soils were photolyzed under a xenon lamp for 7 days. Increasing concentration of sodium nitrate did not affect the degradation pattern but did produce a lower concentration of aminoniclosamide. Soils fortified with iron displayed an unknown, which was not observed in other experiments, and the degradation of niclosamide from these soils was slower than from the sodium nitrate-fortified soils. There were no extractable degradates from any of the soils fortified with humic acid. In irradiated moist soils, the half-life of niclosamide increased when sodium nitrate was present at 20 ppm, and the half-lives of niclosamide in iron- and humic acid-fortified soil were increased slightly over that in unfortified soil. The effect of the nitrate and iron on the half-lives in dark control moist soils was minimal, but humic acid increased the dark control half-life from 420 to 611 h. No transformation of niclosamide was observed in the dark control air-dried soils. Soils with higher organic or iron contents or exposed to fertilizers do not affect as dramatically the half-life of pesticides as does the presence of moisture in the soil. Soil photolysis samples that were not maintained with moisture exhibited differences in half-life and degradation pattern. The maintenance of moisture was found to be more crucial to the reliability of soil photolysis studies than soil composition.     

Emission of Pesticides into the Air

During and after the application of a pesticide in agriculture, a substantial fraction of the dosage may enter the atmosphere and be transported over varying distances downwind of the target. The rate and extent of the emission during application, predominantly as spray particle drift, depends primarily on the application method (equipment and technique), the formulation and environmental conditions, whereas the emission after application depends primarily on the properties of the pesticide, soils, crops and environmental conditions. The fraction of the dosage that misses the target area may be high in some cases and more experimental data on this loss term are needed for various application types and weather conditions. Such data are necessary to test spray drift models, and for further model development and verification as well. Following application, the emission of soil fumigants and soil incorporated pesticides into the air can be measured and computed with reasonable accuracy, but further model development is needed to improve the reliability of the model predictions. For soil surface applied pesticides reliable measurement methods are available, but there is not yet a reliable model. Further model development is required which must be verified by field experiments. Few data are available on pesticide volatilization from plants and more field experiments are also needed to study the fate processes on the plants. Once this information is available, a model needs to be developed to predict the volatilization of pesticides from plants, which, again, should be verified with field measurements. For regional emission estimates, a link between data on the temporal and spatial pesticide use and a geographical information system for crops and soils with their characteristics is needed.

     

Ecotoxicological assessment of the effects of glyphosate and chlorpyrifos in an Argentine soya field

Background, Aim and Scope

Continuous application of pesticides may pollute soils and affect non-target organisms. Soil is a complex ecosystem; its components can modulate the effects of pesticides. Therefore, it is recommended to evaluate the potential environmental risk of these compounds in local conditions. We performed an integrated field-laboratory study on an Argentine soya field sprayed with glyphosate and chlorpyrifos under controlled conditions. Our aim was to compare the sensitivity of a series of endpoints for the assessment of adverse effects of the extensive use of these agrochemicals.

Materials and Methods

A RR soya field in a traditional farming area of Argentina was sprayed with glyphosate (GLY) or chlorpyrifos (CPF) formulations at the commercially recommended rates, according to a randomized complete block design with 3 replicates. In laboratory assays, Eisenia fetida andrei were exposed to soil samples (0–10 cm depth) collected between the rows of soya. Endpoints linked to behavior and biological activity (reproduction, avoidance behavior and bait-lamina tests) and cellular/subcellular assays (Neutral Red Retention Time — NRRT; DNA damage — Comet assay) were tested. Field assays included litterbag and bait-lamina tests. Physico/chemical analyses were performed on soil samples.

Results

GLY reduced cocoon viability, decreasing the number of juveniles. Moreover, earthworms avoided soils treated with GLY. No effects on either reproduction or on avoidance were observed at the very low CPF concentration measured in the soils sampled 10 days after treatment. Both pesticides caused a reduction in the feeding activity under laboratory and field conditions. NRRT was responsive to formulations of CPF and GLY. Comet assay showed significantly increased DNA damage in earthworms exposed to CPF treated soils. No significant differences in DNA migration were observed with GLY treated soils. Litterbag field assay showed no differences between treated and control plots.

Discussion

The ecotoxicological effects of pesticides can be assessed by monitoring the status of communities in real ecosystems or through the use of laboratory toxicity tests. Litterbag field test showed no influence of the treatments on the organic matter breakdown, suggesting a scarce contribution of soil macrofauna. The bait-lamina test, however, seemed to be useful for detecting the effects of GLY and CPF treatments on the activity of the soil fauna. CPF failed to give significant differences with the controls in the reproduction test and the results were not conclusive in the avoidance test. Although the field population density of earthworms could be affected by multiple factors, the effects observed on the reproduction and avoidance tests caused by GLY could contribute to its decrease, with the subsequent loss of their beneficial functions. Biomarkers measuring effects on suborganism level could be useful to predict adverse effects on soil organisms and populations. Among them, NRRT, a lysosomal destabilization biomarker, resulted in demonstrating more sensitivity than the reproduction and avoidance tests. The Comet assay was responsive only to CPF. Since DNA damage can have severe consequences on populations, it could be regarded as an important indicator to be used in the assessment of soil health.

Conclusions

Reproduction and avoidance tests were sensitive indicators of GLY exposure, with the former being more labor intensive. Bait-lamina test was sensitive to both CPF and GLY. NRRT and Comet assays revealed alterations at a subcellular level, and could be considered complementary to the biological activity tests. Because of their simplicity, some of these bioassays seemed to be appropriate pre-screening tests, prior to more extensive and invasive testing.

Recommendations and Perspectives

This study showed deleterious effects of GLY and CPF formulations when applied at the nominal concentrations recommended for soya crops. Further validation is needed before these endpoints could be used as field monitoring tools in Argentine soya soils (ecotoxicological risk assessment — ERA tools).

     

Effect of pesticide application on soil microorganisms

Modern agriculture largely relies on the extensive application of agrochemicals, including inorganic fertilizers and pesticides. Indiscriminate, long-term and over-application of pesticides have severe effects on soil ecology that may lead to alterations in or the erosion of beneficial or plant probiotic soil microflora. Weathered soils lose their ability to sustain enhanced production of crops/grains on the same land. However, burgeoning concern about environmental pollution and the sustainable use of cropping land have emphasized inculcation of awareness and the wider application of tools, techniques and products that do not pollute the environment at all or have only meager ecological concerns. This review covers the types of, concerns about and current issues regarding the extensive application of agrochemicals, in particular pesticides, on a variety of microorganisms integrated in successive food chains in the soil food web.     

3种烟碱类杀虫剂在土壤中的降解吸附特性及对地下水的影响

采用室内模拟实验方法,以太湖水稻土、江西红壤和东北黑土为代表性土壤,研究了噻虫啉等3种烟碱类杀虫剂在土壤中的降解、吸附特性,并利用GUS（Ground Ubiquity Score）指数分析了其对地下水污染的影响。结果表明,3种烟碱类杀虫剂在3种土壤中均较易降解,降解半衰期在5～31d之间,属于易降解农药,降解特性与土壤理化性质及农药本身性质有关。3种烟碱类杀虫剂在江西红壤、太湖水稻土与东北黑土中的吸附较好地符合Freundlich方程,Kd值在0.30～14.70之间,KOC在42.8～1750.9之间,属难吸附农药。吸附性强弱与农药本身溶解性和土壤有机质含量有关,水溶性越强吸附越弱,有机质含量越高,吸附性越强。3种烟碱类杀虫剂在太湖水稻土中的GUS值均小于1.8,而在江西红壤中,其GUS值均大于1.8,这3种杀虫剂在江西红壤中均有一定的淋溶性,对地下水均有一定的污染风险。     

Impact of ecological and conventional arable management systems on chemical and biological soil quality indices in Nicaragua

We measured the activity and soil microbial biomass in volcanic ash soils from 10 sites under ecological farming (no pesticides, shallow ploughing, mulching, organic fertilizers, crop rotation) and 15 sites under conventional farming (pesticides, mineral fertilizers, deep ploughing). Our aim was to determine the effects of management system on soil quality and soil fertility in tropical Nicaragua in relation to soil type. None of these sites were irrigated. Conventional management led to significantly increased amounts of total soil P and a significantly larger biomass C-to-P ratio compared to ecological management. Almost all of the other microbial properties, i.e. soil basal respiration, ergosterol and biomass C were significantly improved by ecological management. Also the biomass C-to-soil C ratio was significantly increased, but not the metabolic quotient qCO₂ or the ergosterol-to-biomass C ratios, indicating that the positive effects of ecological management were mainly due to increased C input rates. Biomass C, ergosterol, and basal respiration rate were significantly larger at the loamy sites than at the sandy sites. The same was true for the biomass C-to-soil C ratio, but the ergosterol-to-biomass C ratio and the metabolic quotient qCO₂ were larger at the sandy sites. Our results demonstrate that ecological management is an important tool for soil conservation and sustainable management of arable land in Nicaragua. However, the decline in total P and the low P availability to soil microorganisms need attention as a precaution against P deficiency. The improvement was greatest at the loamy sites, although the effects of management system were in most cases independent of the soil type. For this reason, ecological management should be preferably promoted on loamy soils.     

生物炭对黄土高原不同质地土壤中NO3-N运移特征的影响

为了解生物炭在抑制黄土高原农田土壤可溶态养分淋失方面的功效,通过人工模拟实验,研究土壤中添加生物炭后对硝态氮运移的影响,为黄土高原地区农田非点源污染防治及氮循环研究等提供科学依据。选择黄土高原地区三种不同质地土壤类型（风砂土、黄绵土、塿土）,通过室内土柱模拟研究方法,用连续流动分析仪（SKALAR-SAN⁺⁺）测定出流液的硝态氮浓度,通过硝态氮的穿透曲线分析在稳态条件下,生物炭添加及不同添加量对土壤中硝态氮运移的影响。结果表明:对于质地较粗黄绵土和风沙土,生物炭输入能够降低硝态氮的淋失,随添加量增加,其阻滞作用越强。对于质地较为粘细的土,添加生物炭反而促进了硝态氮淋失,随添加量增加,其促进作用越强。稳态条件下,三种土壤的硝态氮穿透过程均符合对流弥散方程。研究表明加入生物炭对不同质地土壤中可溶态养分的影响不同,可以促进质地较粗土壤的保肥能力,却不利于质地较为粘细土壤硝态氮养分的保持。     

Involvement of soluble organic matter in increased plant growth in solarized soils

 Although soil solarization is used to control soil-borne pests, it also results in increased growth response (IGR) of plants, beyond the effect of pest control. IGR is attributed to various abiotic factors (e.g. increased mineral nutrient concentrations) and biotic factors. In this work, we studied the role played by dissolved organic matter (DOM) in soil extracts in the IGR. DOM concentrations were about twice as high in solarized soil than in untreated soil. In two out of three soils, solarization appeared to increase amino acid synthesis, indicating that it had a favorable effect on microbial activity. Elemental composition, carbohydrate levels, E₄ : E₆ ratios and FTIR spectra did not differentiate between DOM extracted from solarized soils and DOM extracted from untreated soils. Growth of corn plants increased with increasing concentrations of DOM. Addition to the soil of DOM extracted from leonardite increased populations of fluorescent pseudomonads, known as beneficial bacteria, and reduced fungal populations. We conclude that the increase in DOM concentration following soil solarization is a potentially positive plant-growth-enhancement factor. Received: 21 June 1999     

施用土壤改良剂对磷素流失的影响研究

以滇池设施农业土壤和坡耕地土壤为研究对象,采用外源施用土壤改良剂（硫酸亚铁FES,硫酸铝ALS,聚丙烯酰胺PAM）和土壤消毒剂（五氯硝基苯PCNB）的办法,在不同解吸时间和解吸类型的条件下,研究了土壤改良剂对土壤解吸过滤液中总磷（TP）和可溶性总磷（TDP）的浓度变化影响。研究显示：无论是在连续解吸（2 ~ 10 h）的长时间情况下,还是在两种解吸类型（2 h强度解吸和6 h连续解吸）的情况下,除PCNB外,FES,ALS和PAM都可以显著降低两种土壤过滤液中TP浓度（p＜0.05）。并且发现FES和PAM在连续解吸情况下,对设施农业土壤过滤液中TDP浓度变化具有显著影响,且在两种解吸类型下,还可以均显著降低两种类型土壤中的TDP浓度。野外田间试验表明：施加改良剂后,径流雨水中TP和TDP值也得到明显降低,FES,ALS和PAM的施用对降低P素流失具有明显的效果。可见,无论从解吸持续时间、解吸类型还是土壤类型方面看,FES和PAM都具有显著的防控P素流失的效果,适宜在滇池流域设施农业和坡耕地等土壤中应用。     

Effect of soil pH on the sorption capacity of soil organic matter for polycyclic aromatic hydrocarbons in unsaturated soils

Sorption by soil organic matter (SOM) is considered the most important process affecting the bioavailability of hydrophobic organic chemicals (HOCs)in soil.The sorption capacity of SOM for HOCs is affected by many environmental factors.In this study,we investigated the effects of soil pH and water saturation level on HOC sorption capacity of SOM using batch sorption experiments.Values of soil organic carbon-water partition coefficient (K_OC) of six selected polycyclic aromatic hydrocar...