Effects of temperature and fertilizer on activity and community structure of soil ammonia oxidizers

We investigated the effect of temperature on the activity of soil ammonia oxidizers caused by changes in the availability of ammonium and in the microbial community structure. Both short (5 days) and long (6.5, 16 and 20 weeks) incubation of an agricultural soil resulted in a decrease in ammonium concentration that was more pronounced at temperatures between 10 and 25 degrees C than at either 4 degrees C or 30-37 degrees C. Consistently, potential nitrification was higher between 10 and 25 degrees C than at either 4 degrees C or 37 degrees C. However, as long as ammonium was not limiting, release rates of N2O increased monotonously between 4 and 37 degrees C after short-term temperature adaptation, with nitrification accounting for about 35-50% of the N2O production between 4 and 25 degrees C. In order to see whether temperature may also affect the community structure of ammonia oxidizers, we studied moist soil during long incubation at low and high concentrations of commercial fertilizer. The soil was also incubated in buffered (pH 7) slurry amended with urea. Communities of ammonia oxidizers were assayed by denaturant gradient gel electrophoresis (DGGE) of the amoA gene coding for the alpha subunit of ammonia monooxygenase. We found that a polymerase chain reaction (PCR) system using a non-degenerated reverse primer (amoAR1) gave the best results. Community shifts occurred in all soil treatments after 16 weeks of incubation. The community shifts were obviously influenced by the different fertilizer treatments, indicating that ammonium was a selective factor for different ammonia oxidizer populations. Temperature was also a selective factor, in particular as community shifts were also observed in the soil slurries, in which ammonium concentrations and pH were better controlled. Cloning and sequencing of selected DGGE bands indicated that amoA sequences belonging to Nitrosospira cluster 1 were dominant at low temperatures (4-10 degrees C), but were absent after long incubation at low fertilizer treatment. Sequences of Nitrosospira cluster 9 could only be detected at low ammonium concentrations, whereas those of Nitrosospira cluster 3 were found at most ammonium concentrations and temperatures, although individual clones of this cluster exhibited trends with temperature. Obviously, ammonia oxidizers are able to adapt to soil conditions by changes in the community structure if sufficient time (several weeks) is available.     

The extraction and assay of soil trehalase

Summary Trehalase is a specific enzyme for the hydrolysis of trehalose, a storage carbohydrate of insect and microbial species. The enzyme is of rare occurrence among higher plants. In cultivated soil, trehalase activity (Ta) was linearly related to both the amount of soil and assay incubation time. Ta increased sharply in response to substrate concentration over the range of 0 to 2% (w/v); higher substrate levels, however, showed a reduced rate of increase. Soil trehalase activity increased proportionally with increased incubation temperature over the range of 20 to 50°C but declined sharply at temperatures above 50°C. Ta was maximal at pH 5.0 when 0.5M acetate or propionate buffers were used; however, activity diminished with increased ionic strength of the buffer. Based on these findings, a standard assay method for Ta was developed. The enzyme was extracted from soil and eluted from a Sephadex G 200 column as high molecular weight organic matter. Treatment of the extract with beta-glucosidase reduced the molecular weights of the elution fractions exhibiting Ta.     

Effects of paraquat on selected microbial activities in soil

Paraquat, applied as Gramoxone, to a nonamended sandy loam soil at five times the suggested field application rate (10 lb/A 115g/cm²) increased the numbers of bacteria, actinomycetes, and fungi during a 14-day incubation at 25°C. This increase was attributed to the use of compounds in the Gramoxone formulation rather than the use of paraquat. Treatment at one and five times the normal rate reduced CO₂ evolution by 44% and 67%, respectively, in soil amended with 2% glucose during a 12-day incubation. Similar treatments reduced CO₂ evolution in 1% straw-amended soil by 39% and 58%, respectively, during a 28-day incubation. Cellulose decomposition of cotton duck containing 13 and 176g of paraquat per milligram of material was inhibited for 15 and 28 days, respectively, in soil containing a large population of cellulolytic microorganisms. A concentration of 5000g/gm of paraquat was necessary to inhibit nitrification in soil by 44% druing a 28-day incubation at 20°C. Paraquat inhibited C₂H₂ reduction in artificial aggregates of soil amended with 2% glucose and incubated anaerobically at 25°C. Nitrogenase activity in aggregates was inhibited by 43% and 52% at concentrations of 580 and 720g/gm of paraquat respectively. The inhibitory effects of the herbicide were reduced when soil was amended with organic matter in the form of peat or straw. The availability of paraquat controlled the toxicity of the herbicide to soil microorganisms.     

Mineralization of the carbon and nitrogen of plant material added to soil and of the soil humus during incubation following periodic drying and rewetting of the soil

Summary The production of mineralized carbon and nitrogen by a slightly acid sandy loam soil, in the presence and absence of finely chopped fresh plant material or powdered dry plant material, was followed by determination of the amounts of carbon and nitrogen mineralized at intervals during continuous incubation over a period of twelve weeks. Mineralization of carbon and nitrogen was also followed in parallel soil samples and soil plant material mixtures which were dried at 35°C or 105°C and then rewetted every two weeks during the incubation period.The amounts of carbon and nitrogen mineralized were determined at intervals during the incubation period.Mineralization of the carbon and nitrogen of the humus of the soil was stimulated by periodic drying of the soil and particularly when the soil was dried at 105°C.It was found that more mineral nitrogen was produced from fresh plant material than from dried plant material in all the treatments. Periodic drying of the soil-plant material mixtures did not stimulate the production of mineral nitrogen from the added plant material and reduced it considerably when the drying was carried out at 105°C.Periodic drying at 35°C did not stimulate the mineralization of the carbon of fresh or dried plant material. It is clear therefore that, at temperatures occurring in nature, it is unlikely that the decomposition of plant material added to the soil will be stimulated as a consequence of drying of the soil. Periodic drying of the soil-plant material mixture at 105°C increased the mineralization of the carbon of the dried plant material. The amounts of carbon mineralized in 12 weeks from the dried plant material did not, however, exceed the amounts from fresh plant material incubated continuously in fresh soil or in soil periodically dried at 35°C.     

Biodegradation of pentachlorophenol in soil: the response to physical, chemical, and biological treatments

The effects of physical, chemical, and biological treatments on biodegradation of pentachlorophenol (PCP) were studied in a silt-loam soil contaminated with 175 mg PCP/kg and uniformly 14C-labelled PCP. Biodegradation of 14C-labelled PCP and technical-grade PCP were monitored over 210 days incubation. Mineralization of labelled PCP was significantly (p=0.05) influenced by soil treatments. Negligible biodegradation occurred in either the sterile control soil or the uninoculated control soil, with less than 1% of added 14C recovered as 14 CO2. Inoculation of unamended soil with a strain of Flavobacterium (ATCC 39723) known to degrade PCP increased biodegradation of PCP; approximately 60% of the [14C]PCP was recovered as 14CO2. Increased soil water content (60% versus 30% w/w) enhanced biodegradation (67% recovery of 14C as CO2), while increased chloride ion concentration and anoxic conditions were inhibitory (20 and 1% recoveries, respectively). Residual soil PCP concentrations were also influenced by various treatments. In the sterile control soil and noninoculated control, after 210 days incubation, concentrations of PCP were 143 and 1223 mg/kg, respectively, while the PCP concentration in the inoculated soil was 21 mg/kg. When soil organic matter was increased by adding finely ground red clover leaf and stem material, the residual PCP concentration was reduced to 6 mg/kg after 210 days. Increased soil water content resulted in a residual PCP concentration of 5 mg/kg. High-pressure liquid chromatography of soil extracts revealed no accumulation of partial PCP degradation products. The results indicated that biodegradation of PCP in soil was significantly influenced by various soil amendments.     

Effect of dithane M-45 on cellulose-decomposing fungi in Egyptian soil

The fungicide Dithane M-45 when applied to the soil was regularly and significantly toxic to the total count of fungi at all doses used (4·48, 22·4 and 44·8 mg active ingredient per kg dry soil). The toxicity was regularly increased with dose and persisted till the end of the experiment (15 weeks). When Dithane M-45 was incorporated into the agar medium all test fungi were eliminated by the high dose (24·0 ppm). The low and medium doses were tolerated by some fungi. The decay of filter paper buried in the fungicide-treated soil was significantly reduced by the high dose after 1 and 3 weeks of incubation, while the decay of filter paper treated with this fungicide and buried in untreated soil was significantly retarded by the high dose only after all experimental periods of incubation (up to 15 weeks). The growth and sporulation of nine test fungi were eliminated by the three doses of Dithane M-45 except Chaetomium globosum, Fusarium moniliforme and Trichoderma viride which could grow restrictedly at the low dose only. Production of endo-1,4β-d-glucanase and mycelial dry weight were not significantly affected by the three doses in the case of Aspergillus niger, and by the low dose in the case of Alternaria alternata, Fusarium solani and Myrothecium verrucaria. In the case of other test fungi and other doses, endo-1,4β-glucanase production and mecelial dry weight were significantly inhibited.     

好气条件下不同形态外源砷在土壤中的转化

在35%的田间持水量下,通过模拟试验研究了外源二甲基砷酸盐（DMA）、一甲基砷酸盐（MMA）、五价无机砷［As(V)］在土壤中的形态转化.结果表明: 外源砷进入土壤后,其含量均有随时间推延而逐渐下降的趋势,两种不同形态的有机砷DMA和MMA在土壤中主要发生脱甲基化过程,经150 d的恒温恒湿培养,其在土壤中主要转化为As(V),DMA处理仅在120 d时检测到少量MMA,而MMA处理则在7～60 d内均有少量的DMA生成.培养结束时土壤中DMA和MMA含量均显著降低(P<0.01),降幅分别为99.5%、94.3%,而两者的主要转化产物As(V)的含量则分别显著增加了4.61和5.15倍.表明外源有机态砷在土壤中基本上被转化为无机形态;与有机态外源砷相比,外源As(V)进入土壤后其形态基本上没有发生转化.     

秸秆预处理对土壤微生物量及呼吸活性的影响

冬小麦秸秆经8．0g·L^-1H2O2(pH11．0)溶液、12．5g·L^-1 NaOH溶液或H2SO4溶液浸泡8h并80℃烘干后,与无机N一起加入土壤,进行室内25℃恒温培养试验,在不同时间测定土壤微生物量C、N和CO2释放速率。结果表明,培养前期,秸秆预处理使土壤微生物量C数量增加了1．0～1．4倍,但降低了土壤微生物的呼吸活性;培养后期,NaOH和H2SO4处理使土壤微生物量C分别下降了28％和42％,但增加了土壤微生物的呼吸活性;H2O2处理则使土壤微生物量N增加90％;土壤微生物区系中的真菌比例在不同时刻有所增加,表明将秸秆预处理后施入土壤,将对土壤中微生物数量和呼吸活性产生一定影响。     

Azoxystrobin and soil interactions: degradation and impact on soil bacterial and fungal communities

Aims: To provide an independent assessment of azoxystrobin effects on nontarget soil bacteria and fungi and generate some baseline information on azoxystrobin’s persistence in soil. Methods and Results: Plate based assay showed that azoxystrobin exhibited differential toxicity upon cultured fungi at different application rates. While ¹⁴C labelled isotopes experiments showed that less than 1% of azoxystrobin was mineralized, degradation studies revealed over 60% azoxystrobin breakdown over 21 days. PCR DGGE analysis of 16S and 18S rRNA genes from different soil microcosms showed that azoxystrobin had some effects on fungal community after 21 days (up to 84 days) of incubation in either light or dark soil microcosms. Light incubations increased fungal diversity while dark incubations reduced fungal diversity. Bacterial diversity was unaffected. Conclusions: Significant biotic breakdown of parent azoxystrobin occurred within 21 days even in the absence of light. Azoxystrobin under certain conditions can reduce fungal soil diversity. Significance and Impact of the Study: One of the few independent assessments of azoxystrobin (a widely used strobilurins fungicide) effects on soil fungi when used at the recommended rate. Azoxystrobin and metabolites may persist after 21 days and affect soil fungi.     

Effect of soil ammonium concentration on N2O release and on the community structure of ammonia oxidizers and denitrifiers

The effect of ammonium addition (6.5, 58, and 395 microg of NH4+-N g [dry weight] of soil(-1)) on soil microbial communities was explored. For medium and high ammonium concentrations, increased N2O release rates and a shift toward a higher contribution of nitrification to N2O release occurred after incubation for 5 days at 4 degrees C. Communities of ammonia oxidizers were assayed after 4 weeks of incubation by denaturant gradient gel electrophoresis (DGGE) of the amoA gene coding for the small subunit of ammonia monooxygenase. The DGGE fingerprints were invariably the same whether the soil was untreated or incubated with low, medium, or high ammonium concentrations. Phylogenetic analysis of cloned PCR products from excised DGGE bands detected amoA sequences which probably belonged to Nitrosospira 16S rRNA clusters 3 and 4. Additional clones clustered with Nitrosospira sp. strains Ka3 and Ka4 and within an amoA cluster from unknown species. A Nitrosomonas-like amoA gene was detected in only one clone. In agreement with the amoA results, community profiles of total bacteria analyzed by terminal restriction fragment length polymorphism (T-RFLP) showed only minor differences. However, a community shift occurred for denitrifier populations based on T-RFLP analysis of nirK genes encoding copper-containing nitrite reductase with incubation at medium and high ammonia concentrations. Major terminal restriction fragments observed in environmental samples were further described by correspondence to cloned nirK genes from the same soil. Phylogenetic analysis grouped these clones into clusters of soil nirK genes. However, some clones were also closely related to genes from known denitrifiers. The shift in the denitrifier community was probably the consequence of the increased supply of oxidized nitrogen through nitrification. Nitrification activity increased upon addition of ammonium, but the community structure of ammonium oxidizers did not change.     

Labile soil carbon inputs mediate the soil microbial community composition and plant residue decomposition rates

Root carbon (C) inputs may regulate decomposition rates in soil, and in this study we ask: how do labile C inputs regulate decomposition of plant residues, and soil microbial communities? In a 14 d laboratory incubation, we added C compounds often found in root exudates in seven different concentrations (0, 0.7, 1.4, 3.6, 7.2, 14.4 and 21.7 mg C g(-1) soil) to soils amended with and without (13) C-labeled plant residue. We measured CO(2) respiration and shifts in relative fungal and bacterial rRNA gene copy numbers using quantitative polymerase chain reaction (qPCR). Increased labile C input enhanced total C respiration, but only addition of C at low concentrations (0.7 mg C g(-1)) stimulated plant residue decomposition (+2%). Intermediate concentrations (1.4, 3.6 mg C g(-1)) had no impact on plant residue decomposition, while greater concentrations of C (>7.2 mg C g(-1)) reduced decomposition (-50%). Concurrently, high exudate concentrations (>3.6 mg C g(-1)) increased fungal and bacterial gene copy numbers, whereas low exudate concentrations (<3.6 mg C g(-1)) increased metabolic activity rather than gene copy numbers. These results underscore that labile soil C inputs can regulate decomposition of more recalcitrant soil C by controlling the activity and relative abundance of fungi and bacteria.     

Growth and enzyme activities of fungi and bacteria in soil salinized with sodium chloride

In soil salinized with different concentrations of sodium chloride, the total counts of soil fungi were significantly decreased during 11 weeks of incubation. Similarly, the total count of bacteria and actinomycetes were severely depressed by increasing salinity level above 5%. Invertase and urease activities were severely decreased as NaCl concentration increase during the incubation. Also, the effect on nitrate reductase was inhibitory with most treatments.     

Selective effects of three herbicides on the fungus flora of egyptian soil

2,4-D (2,4-dichlorophenoxyacetio acid) when applied to the soil at three doses (1.9, 7.6 and 15.2 mg per kg dry soil) had a stimulating effect on the total count of soil fungi and on several fungal species especially between 5 and 20 d after treatment. When the herbicide was incorporated in the agar medium it had a stimulating effect on the counts of total fungi, Aspergillus sp., A. niger, A.fumigatus and Fusarium app. at the low dose (6.3 ppm), but wag toxic at this dose toward Humicola grisea and Myrothecium verrucaria at the medium and high doses (25.2 and 50.4 ppm), it was toxic to the total count of fungi and to the majority of fungal species. VCS-438 [2-(3,4-dichlorophenyl)-4-methyl-l,2,4-oxadiazolidine-3,5-dione] was beneficial to the total count of fungi 2 and 5 d after soil treatment with the medium dose (8.0 mg per kg dry soil). Some fungal species could benefit from the low and the high doses (2.0 and 16.0 mg per kg dry soil) after these experimental periods. In the agar medium the counts of total fungi, Aspergillus sp., A. niger and A.fumigatus were almost significantly reduced by the three doses (6.8, 27.2 and 54.8 ppm). Planavin (4-methylsulphonyl-2,6-dinitro-N,N-dipropylaniline) was stimulating for the total count of fungi, Aspergillus, A.niger and A.ochraceus 2 and 5 d after treatment with the medium dose (8.0 mg per kg dry soil), and was also stimulating to Fusarium population at the medium dose after 2 d and at the high dose (16 mg per kg dry soil) after 20 d. In the agar medium Planavin at the low dose (6.8 ppm) was stimulating to A.terreus and inhibitory to A.nidulans and A.fumigatus. The medium and high doses (27.2 and 54.8 ppm) were generally toxic to the total count of fungi.     

Microbial colonization of soil aggregates as affected by temperature

Summary Sucrose-amended soil aggregates incubated at 15, 25 and 35°C exhibited quantitative and qualitative differences in microbial ecology. Numbers of bacteria and fungi showed a faster increase to the maximum level and a faster decrease with prolonged incubation the higher the temperature. Soil yeasts developed rapidly and extensively in aggregates incubated at 15 and 25 but not at 35°C.The fungal flora that developed on the aggregates varied with temperature: (a)M. silvaticus and anAlternaria species were the predominant primary flora at 15 and 25°C; (b)Sclerotium andPseudogymnoascus species developed in abundance in the later stages of incubation at 15 but were rare at 25°C; and (c)R. rhizopodiformis andA. fumigatus were virtually the only fungi observed on aggregates incubated at 35°C.Direct microscopic examination provided an estimate of the extent and type of fungal development that occurred on the aggregates. In general, dilution plate counts reflected accurately the growth and sporulation of the primary fungal flora of high sporulating capacity. But because spores of the primary flora remained viable in the soil and dominated the dilution plates long after the mycelia of these fungi had apparently decomposed, the plate counts provided little direct information regarding the development of the secondary fungal flora on the aggregates.     

Effect of Bavistin,Cotoran and Curacron on Egyptian soil fungi

Tests were conducted to determine the effects of the fungicide Bavistin (Carbendazim), the herbicide Cotoran (Fluometuron) and the insecticide Curacron on Egyptian soil fungi when applied at the recommended field dose, and four and eightfold field doses. Bavistin when added to the soil induced a regular significant inhibition of the total count of fungi by the 3 doses after 5 and 40 days and by the higher doses after 80 days. The response ofAspergillus to this fungicide was almost similar to that of the total count. Cotoran was of no significant effect on the total count of fungi after 2 days at all doses, but after 5 days the herbicide was significantly depressive at the medium and the high doses. After 80 days the effect changed into significant promotion at the field dose only. Curacron was significantly toxic to the total count of soil fungi, after the shorter and longer periods at the 3 doses.     

Effect of Bavistin,Cotoran and Curacron on Egyptian soil fungi

Tests were conducted to determine the effects of the fungicide Bavistin (Carbendazim), the herbicide Cotoran (Fluometuron) and the insecticide Curacron on Egyptian soil fungi when applied at the recommended field dose, and four and eightfold field doses.Bavistin when added to the soil induced a regular significant inhibition of the total count of fungi by the 3 doses after 5 and 40 days and by the higher doses after 80 days. The response ofAspergillus to this fungicide was almost similar to that of the total count.Cotoran was of no significant effect on the total count of fungi after 2 days at all doses, but after 5 days the herbicide was significantly depressive at the medium and the high doses. After 80 days the effect changed into significant promotion at the field dose only.Curacron was significantly toxic to the total count of soil fungi, after the shorter and longer periods at the 3 doses.     

Isolation of keratinolytic fungi from a coal mine dump

During the study of fungal succesion in the coal mine dump in Brzezinka (Poland), soil samples were examined for keratinolytic fungi. These micro-organisms were rather poorly represented in the area studied. Out of 300 soil samples examined, only 48 (16%) were positive for keratinolytic fungi.Trichophyton ajelloi andArthroderma curreyi were the prevailing species. These species occurred practically at two locations, i.e. on the naked carbon rocks inhabited by algae crops (chiefly byCyanophyta) and in the pine litter. It can be supposed that the occurrence of keratinolytic fungi was more dependent on the favourable general conditions such as increasing organic matter content, microflora, and humidity than on the presence of keratin remains in the soil. Because of the lack of potentially pathogenic fungi, the coal mine dump examined cannot be considered as an important source of fungal infection.     

Glomalin, an arbuscular-mycorrhizal fungal soil protein, responds to land-use change

Glomalin is a soil proteinaceous substance produced by arbuscular mycorrhizal fungi. Most of the information available concerning this protein has been collected in relation to its role in soil aggregation. In this study, we explored the distribution of glomalin across soil horizons, decomposition of glomalin, and relationship with soil C and N in an agricultural field, a native forest, and an afforested system. Glomalin was present in A, B, and C horizons in decreasing concentrations. Land-use type significantly affected glomalin concentrations (mg cm^–3), with native forest soils having the highest concentrations of the three land-use types in both A and B horizons. In terms of glomalin stocks (Mg ha^–1), calculated based on corrected horizon weights, the agricultural area was significantly lower than both afforested and native forest areas. As measured after a 413 day laboratory soil incubation, glomalin was least persistent in the A horizon of the afforested area.. In agricultural soils and native soils, ca. 50% of glomalin was still remaining after this incubation, indicating that some glomalin may be in the slow or recalcitrant soil C fraction. Comparison of glomalin decomposition with CO₂-C respired during incubation indicates that glomalin makes a large contribution to active soil organic C pools. Soil C and N were highly correlated with glomalin across all soils and within each land-use type, indicating that glomalin may be under similar controls as soil C. Our results show that glomalin may be useful as an indicator of land-use change effects on deciduous forest soils.     

Differential stabilities of soil enzymes. Assay and properties of phosphatase and arylsulphatase.

Methods have been refined for the assay of phosphatase and arylsulphatase activities in soil, based on the chromogenic p-nitrophenyl ester substrates. Basic assay conditions have been defined, and pH optima and kinetic parameters have been determined. The enzymes follow Michaelis-Menten kinetics; this conclusion is based on three methods of analysis of data determined over a wide range of substrate concentrations. The enzyme activities are very stable to storage of wet soil for up to 4 weeks at soil temperatures and above. For example, phosphatase had a half-life of approximately 2 weeks at 50 degrees C; arylsulphatase was rather less stable. Both enzymes retained 80% of activity after incubation with pronase for 1 week at 25 degrees C. On the basis of this work and studies on other soil enzymes, it is concluded that remarkable stability is a general feature of soil enzymes.     

Saprophytic and pathogenic behaviour of R. solani AG2-1 (ZG-5) in a soil amended with Diplotaxis tenuifolia or Brassica nigra manures and incubated at different temperatures and soil water content

The Brassicaceae species Diplotaxis tenuifolia and Brassica nigra contain high concentrations of glucosinolates, the precursors of isothiocyanates (ITCs) that can have biofumigation effects in amended soils. In a laboratory experiment, incorporation of these plants as green manures into soil was expected to suppress Rhizoctonia solani AG2-1 (ZG5), the causal agent of damping-off in canola (Brassica napus). The manures were incorporated at 1 (1% w/w) or 5 (5% w/w) g fresh material per 100 g dry soil and incubated for 6 months at 10, 20, or 30°C and at soil water contents of 10%, 40%, or 70% of water holding capacity. R. solani survived for up to 6 months as a saprophyte in un-amended soil at all soil water contents and at 10 and 20°C. A temperature of 30°C suppressed R. solani below the level of detection in all treatments after one week. At 1% concentration, the green manures increased the colonisation of the soil by R. solani, which caused severe damping-off of canola subsequently sown in this soil treatment. Soil amendments at 1% temporarily increased soil microbial activity. The addition of B. nigra or D. tenuifolia green manure at 5% concentration suppressed the saprophytic growth of R. solani incubated at 10 or 20°C over all soil water contents and significantly increased the microbial activity at all soil temperatures and water contents. Canola sown into these pots did not succumb to damping-off. The efficiency of hydrolysis of glucosinolates in the 5% treatment in the first week of incubation ranged from 1.6% for 2-propenyl ITC, extracted from soil containing tissues of B. nigra, to 3.4% for 3-butenyl ITC extracted from soil containing tissues of D. tenuifolia. 2-propenyl ITC could not be detected after 7 d of incubation. In the longer term (weeks to months), the increase of microbial activity, caused by adding green manures at 5%, or volatiles from the green manures, most likely played a dominant role in suppressing R. solani. The impact of ITCs, if any, appears to be short-term (days). Responsible Editor: Peter A. H. Bakker