Effects of dazomet on soil organisms and recolonisation of fumigated soil

Fumigation is a common practice to control soil pathogens, but little is known about the impacts of fumigation on other soil biota groups. The purpose of this study was to investigate the effects of fumigation on soil biota, including microorganisms, nematodes, and microarthropods. Bacteria were the most resistant group and some survived following treatment with 2000 mg kg⁻¹ dazomet. Some soil fungi survived 100 mg kg⁻¹ dazomet, although they were mainly Trichoderma. The fungi pathogenic to ginseng were all killed at 100 mg kg⁻¹, and showed both inter- and intra-species variation with respect to dazomet susceptibility. Among the nematodes, Aphelenchus was relatively resistant. The results suggested that susceptibility of soil organisms to dazomet differs between species, and that tolerant organisms may engage in recolonisation. In microcosm experiments, the microbial biomass and community were assessed using phospholipid fatty acid (PLFA) analysis while recolonisation of soil organisms was controlled by mesh size. The bacterial PLFA levels were changed little after fumigation, whereas the fungal PLFA levels gradually increased after fumigation. Principal analysis of the PLFA levels and the ratio of gram-negative to gram-positive bacteria showed that fumigation altered the microbial community. The number of nematodes did not recover even at 12 weeks after fumigation. The increased Collembolan numbers suggest that fumigated soil could be recolonised by specific organisms that have adapted to the conditions. In field experiments, we tested the ability of organic materials to enhance the recolonisation of fumigated soil by soil organisms. Bean powder and rice bran increased the microbial PLFA levels and nematode numbers at 6 weeks and 12 weeks after treatment, and the abundance of nematodes continued to increase 42 weeks after fumigation. The abundance of microarthropods was only slightly affected by the presence of the organic materials. We suggest that treating fumigated soils with organic materials is an effective technique to promote soil organism numbers. In addition, Trichoderma was observed to be relatively resistant to fumigation, and therefore, we propose that the fumigation effect can be improved by using a combination of resistant Trichoderma and dazomet.     

Bacterial community structure in fumigated soil

Soil microbial biomass has been determined since the mid 1970's by the chloroform fumigation incubation technique as proposed by Jenkinson and Powlson (1976). The microbial biomass C can be determined by subtracting the CO₂ emitted from an unfumigated soil (mineralization of soil organic matter) from that emitted from a chloroform fumigated inoculated soil (mineralization of soil organic matter and killed soil microorganisms) and dividing the difference by a proportionality factor (k_C = 0.45). The question remained which microorganisms recolonized a fumigated soil. An arable soil was fumigated for one day with ethanol-free chloroform or left unfumigated and incubated aerobically after removal of the chloroform for 10 days. The bacterial population structures were determined in the fumigated and unfumigated soil after 0, 1, 5 and 10 days by means of 454 pyrosequencing of the 16S rRNA gene. Fumigating the arable soil reduced significantly the relative abundance of phylotypes belonging to different groups, but increased the relative abundance of only four genera belonging to two phyla (Actinobacteria and Firmicutes) and two orders (Actinomycetales and Bacillales). The relative abundance of phylotypes belonging to the Micromonospora (Micromonosporaceae) increased significantly from 0.2% in the unfumigated soil to 6.7% in the fumigated soil and that of Bacillus (Bacillaceae) from 3.6% to 40.8%, Cohnella (Paenibacillaceae) from undetectable amounts to 0.6% and Paenibacillus (Paenibacillaceae) from 0.3% to 4.2%. The relative percentage of phylotypes belonging to the Acidobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes and Proteobacteria (α- β-, δ- and γ-Proteobacteria) were significantly lower in the fumigated than in the unfumigated soil and in most of them the relative abundance of different bacterial orders (i.e. Gp3, Gp4, Gp6, Sphingobacteriales, Gemmatimonadales, Rhodospirillales, Burkholderiales, Xanthomonadales) was reduced strongly (P < 0.001). It was found that the relative abundance of a wide range of bacteria was reduced shortly after fumigating an arable soil, but only a limited group of bacteria increased in a fumigated arable soil indicating a capacity to metabolize the killed soil microorganisms or recolonize a fumigated soil.     

Organic matter dynamics in a compost-amended anthropogenic landfill capping-soil

The application of municipal waste compost and other organic materials may serve to improve fertility and organic carbon (C) stocks of soils used in land reclamation activities, particularly in the recovery of degraded areas at exhausted quarries, mines and landfill sites amongst others. We investigated long-term organic matter dynamics in such anthropogenic soils by collecting samples at different depths over a 10-year chronosequence subsequent to compost application to the top layer of a landfill capping-soil. Variations in the stable isotope composition (¹³C and ¹⁵N) of the soil samples showed that, even after 10 years, amended topsoils were enriched in compost-derived organic matter. The addition of compost to the superficial layer also resulted in an input of soluble organic compounds that was subject to leaching along the soil profile. Sorption isotherms for compost-derived water-extractable organic matter onto mineral materials used for landfill covering suggest that sorptive preservation was primarily responsible for the increase in C content and the shift in the C isotopic signature to values similar to that of the applied compost, in the deeper soil horizons over the 10-year period. This was also confirmed by the accumulation of lignin-derived phenolic compounds in the deeper horizons. Nevertheless, analysis for non-cellulosic carbohydrates in soil samples and their respective water-extractable fractions suggest that a proportion of the compost-derived, labile organic matter fraction is leached through the profile and potentially lost from the soil system.     

Molecular changes in organic matter of a compost-amended soil

The molecular changes of organic matter in a cultivated soil after compost amendments was followed by off-line-pyrolysis-TMAH GC-MS. Thermochemolysis of soil and compost provided a detailed molecular characterization of soil organic matter (SOM) by releasing a large amount of different molecules mainly derived from plant biopolymers such as lignin, waxes and bio-polyesters. No significant differences were found before and after 1 year of cultivation in the pyrolytic products released by control soil, which were mainly fatty acids, oxidized forms of lignins, and minor amounts of microbial bio-products and biopolyesters derivatives. Conversely, significant qualitative and quantitative variations were found in the molecular characteristics of SOM between control and compost-amended soils after 1 year of cultivation. Increasing amounts and diversified components of fatty acids, n -alkanes and various biopolyesters derivatives such as hydroxy-alkanoic and alkandioic acids were found in the compost-amended soil. These results indicate that a significant amount of exogenous compost-derived organic molecules were incorporated into SOM after 1 year of cultivation. The organic structural indexes derived from these results indicated direct inputs of undecomposed lignin residues and hydrocarbon waxes from compost material. When compared with the control soil, small but significant amounts of plant biomarkers, such as cyclic di- and triterpenes derivatives, were found only in the compost-amended soil. These findings suggest that the molecular changes of SOM brought about by amendment with biomass residues can be followed by using thermochemolysis of bulk soil samples.     

Bromine in wheat grown on soil fumigated with methyl bromide

Abstract

Patches of discoloured ("scorched") plants developed on winter wheat growing in a field that had been fumigated with methyl bromide. Scorching was most marked round the methyl bromide injection sites and was associated with bromine uptake by the plants: the above‐ground parts of the scorched plants contained up to 0.61% bromine. In one scorched area, the first, second and third wheat crops after fumigation contained 0.42, 0.25 and 0.09% bromine respectively, so that three years was not sufficient to leach all the residual bromine from the soil.

The greater the organic content of a soil, the more bromine remained after fumigation with methyl bromide. Thus a soil containing 2.81% organic carbon contained 63 ppm bromine after fumigation in the laboratory, whereas an otherwise similar soil with 0.93 organic carbon contained only 25 ppm. The residual bromine from methyl bromide fumigation could be extracted with N potassium sulphate, whereas the native soil bromine could not.     

The dynamics of dissolved organic N in the fumigated soils

The aim of this study was to investigate the dynamics of dissolved organic N in soils fumigated separately with chloropicrin (CP), 1,3-dichloropropene, and metam sodium (MS) for 7 days and then incubated at 25°C for 84 days. The dissolved organic N (DON) at 14 days after fumigation was mainly dissolved amino acids (DAA) which were then rapidly mineralized to ammonium. However, the DON pool at later incubation times was mainly high molecular weight organic N which was resistant to microbial decomposition. Three soil fumigants all increased the proportions of DON in total dissolved N and DAA in DON. Dissolved organic N became much more important mobile N source in CP- and MS-fumigated soils, and this may increase the risks of DON leaching in agricultural ecosystems.     

Effects of fungivorous nematodes on corky root disease of tomato grown in compost-amended soil

Abstract

The effect of fungivorous nematodes, Aphelenchus avenae and Aphelenchoides spp., against corky root disease of tomato caused by Pyrenochaeta lycopersici was investigated. Three different greenhouse trials were conducted using soil naturally infested with P. lycopersici, alone or mixed with four different types of compost consisting of green manure, garden waste and horse manure (20% compost by volume). The fungivorous nematodes were propagated in cultures of the fungus Pochonia bulbillosa and inoculated (3 or 23 nematodes ml^?1 substrate) into the soil and soil-compost mixtures one day after transplanting of tomato seedlings. Greenhouse experiments were terminated after ten weeks and disease was measured from infected roots after harvesting. Aphelenchus avenae significantly reduced the disease severity when added to infested soil without compost in all experiments. Aphelenchoides spp. did not suppress the disease either in the presence or absence of compost. Among the composts tested, only a garden waste compost was found to be suppressive to the disease. Neither A. avenae nor Aphelenchoides spp. improved the suppressive effect of the compost.     

Population dynamics of soil microorganisms associated with fungicide-dusted caladium seedpieces

The effects of three fungicidal dusts (captan ; a mixture of benomyl, thiram and streptomycin sulfate; and a mixture of chloroneb, thiram and streptomycin sulfate) on the short-term populations dynamics of fungi and bacteria associated with caladium seedpieces planted in raw muck soil were investigated. Both germinating seedpieces and seedpieces which were decomposing after the removal of eyes were used. To determine microbial populations, dilutions of a comminuted suspension of a seed-piece and surrounding soil were plated on selective media at 0,2,4, 8 and 12 weeks after seedpieces were planted. Addition of seedpieces to soil resulted in increases in populations in the following approximate chronological order: fluorescent Pseudomonas spp, Pythium spp, total bacteria, Fusarium spp and other genera of fungi. Most organisms assayed reached higher populations on decomposing than on germinating seedpieces. The effects of the fungicidal dusts on populations of microorganisms associated with seedpieces were not related to changes in populations that followed incorporation of the dusts into soil without seedpieces. The fungicidal dusts reduced total fungal population increases on germinating, but not on decomposing, seedpieces. Bacterial population increases were similar for all treatments of germinating seedpieces, but were prolonged on decomposing, fungicide-dusted seedpieces, as compared to controls.     

Mineralization and immobilization of nitrogen in fumigated soil and the measurement of microbial biomass nitrogen

Immobilization of N was measured in a fumigated and in an unfumigated soil by adding (¹⁵NH₄)₂SO₄ and following the disappearance of inorganic label from the soil solution and its simultaneous conversion to soil organic N. Calculations based on the measurement of organically-bound ¹⁵N gave more consistent values for immobilization than did calculations based on the measurement of the disappearance of label from solution. The fumigated soil immobilized 6.6 μg N g^?1 N g^?1 soil in 10 days at 25°C, the unfumigated control 4.8 μg. The corresponding gross mineralization rates were 34.9 and 5.6 μg N g^?1 soil in 10 days.Addition of 58 μg N as (¹⁵NH₄)₂SO₄ to the fumigated soil increased the quantity of the ynlabelled NH₄-N extracted at the end of 10 days from 33.8 to 37.8 μg Ng^?1 soil, i.e. there was a positive Added Nitrogen Interaction (ANI). The added labelled N produced this ANI, not by increasing the rate of mineralization of organic N, but by standing proxy for unlabelled N that otherwise would have been immobilized.A procedure for calculating biomass N from the size of the flush of mineral N caused by fumigation is proposed. Biomass N (B_N) is calculated from the relationship B_N = F'_N/0.68 where F'_N is [(N in fumigated soil incubated for 10 days — (N in unfumigated soil incubated for 10 days)].     

几种土壤调理剂改良大棚种植草莓土壤的效果

随着草莓产业的稳定高效发展,设施草莓大棚土壤连作障碍问题日益突出.采用硅钙钾镁、钙镁磷、月桂醇乙氧基硫酸铵、天然海洋萃取物碳酸钙与椰子提取物混合物和聚丙烯酰胺5种土壤调理剂进行了小区试验,分析了不同处理下草莓种植大棚的土壤养分、酶活、盐分以及草莓的产量和品质.结果表明,硅钙钾镁是改良大棚草莓连作障碍土壤中比较理想的土壤...     

Effect of plant roots on soil strength

Roots of plants have been shown, under some circumstances, to increase soil strength. To test whether this applies to rice-growing soils, a pot experiment was conducted using a soil from East Java, Indonesia, to which a series of puddling-irrigation treatments was applied consistent with rice-growing soils and preparation techniques in the East Java region. Plants were grown in half of the pots. Measurements included the bearing capacity and shear vane resistance of soil 45 and 70 days after emergence, and root weight and plant height at Day 70.

The results showed that in most cases rice roots increased both the bearing capacity and shearing resistance. A linear relationship between bearing capacity and shearing resistance was found, and agreed with published data for dry soils. The implication of the results for traffic in wet soils is discussed.     

Temporal changes of soil physical and hydraulic properties in strawberry fields

Even over short time intervals, soil properties are subject to variation, especially in managed soils. The objective of this study was to assess the temporal changes of soil physical and hydraulic properties in strawberry fields cultivated under surface drip fertigation in Turuçu, Brazil. Intact core samples were collected from the near surface soil layer of seedbeds to determine the total porosity (TP), macroporosity (MA), matrix porosity, bulk density (BD), available water capacity (AWC), field capacity, wilting point and Dexter’s S index. Aggregate samples were collected from the arable layer to determine the aggregate size distribution and aggregate mean weight diameter. All samples were collected from 15 strawberry fields and at four different times during the 2007–2008 strawberry growing cycle. Although soil pore‐solid relations are expected to adjust soon after seedbed construction, their variation was only evident after >13 weeks. Even though values of TP and MA decreased with time, and those of BD increased near the end of the growing cycle, all the soils maintained their capacity to support root activity as indicated by critical values of Dexter’s index (S > 0.03). The amount of relatively large aggregates (9.51–2.00 mm) and AWC increased towards the end of the strawberry cultivation cycle. With changes in soil structure improving soil physical quality, strawberry development benefitted. We showed that if farmers gradually increase the amount of water through fertigation to a maximum value occurring at the end of crop cycle instead of applying water at a constant rate, water and energy use efficiency in agriculture would improve.     

Effect of chemical fumigation on soil fungal communities in Spanish strawberry nurseries

Strawberry runners are a high-value cash crop in Spain that requires vigorous transplants free of pathogens. Pre-plant soil fumigation with methyl bromide (MB), or with mixtures of MB and chloropicrin (Pic), are standard practices for controlling soil-borne diseases. However, use of MB will be forbidden in European Union countries by the year 2005; for this reason several soil fumigants have been tested as chemical alternatives to MB in Spanish strawberry nurseries. Because of the known broad activity of these compounds, their effects on strawberry soil fungal communities were studied. Experiments were conducted over a 5-year period, with pre-plant applications at two different locations each year. Soil fungal populations were estimated in each plot before and after treatments on potato-dextrose agar amended with 0.5 g l⁻¹ streptomycin sulphate and selective media for Fusarium spp., Pythium spp., Verticillium spp., Phytophthora spp., and Rhizoctonia spp. Soil fungal populations in Spanish strawberry nurseries were clearly reduced in number and composition after pre-plant soil fumigation. Differences in the level of reduction was obtained with some treatments. Penicillium sp., following by Alternaria sp., Fusarium sp., Morteriella sp., Cladosporium sp., Pythium sp., and Verticillium spp. were usually presented in Spanish nursery soils from March to April, whereas Phytophthora spp. and Rhizoctonia spp. were only sporadically isolated. All the fumigants reduced the soil fungal population quantitatively, but only MB:Pic and dazomet caused a clear change in their fungal genera composition. A total reduction was observed on Pythium and Morteriella populations after application of all the fumigants, except for DMDS. Populations of Verticillium spp. were also reduced by the applied fumigants in the strawberry nursery soils tested; the lowest reductions were obtained with 1,3-D:Pic + Virtually Impermeable Film, metam sodium, metam potassium and DMDS.     

Use of 13C and 15N natural abundance techniques to characterize carbon and nitrogen dynamics in composting and in compost-amended soils

Isotope fractionation during composting may produce organic materials with a more homogenous δ¹³C and δ¹⁵N signature allowing study of their fate in soil. To verify this, C, N, δ¹³C and δ¹⁵N content were monitored during nine months covered (thermophilic; >40 °C) composting of corn silage (CSC). The C concentration reduced from 10.34 to 1.73 g C (g ash)⁻¹, or 83.3%, during composting. Nitrogen losses comprised 28.4% of initial N content. Compost δ¹³C values became slightly depleted and increasingly uniform (from −12.8±0.6‰ to −14.1±0.0‰) with composting. Compost δ¹⁵N values (0.3±1.3 to 8.2±0.4‰) increased with a similar reduced isotope variability.The fate of C and N of diverse composts in soil was subsequently examined. C, N, δ¹³C, δ¹⁵N content of whole soil (0-5 cm), light (<1.7 g cm⁻³) and heavy (>1.7 g cm⁻³) fraction, and (250-2000 μm; 53-250 μm and <53 μm) size separates, were characterized. Measurements took place one and two years following surface application of CSC, dairy manure compost (DMC), sewage sludge compost (SSLC), and liquid dairy manure (DM) to a temperate (C₃) grassland soil. The δ¹³C values and total C applied (Mg C ha⁻¹) were DM (−27.3‰; 2.9); DMC (−26.6‰; 10.0); SSLC (−25.9‰; 10.9) and CSC (−14.0‰; 4.6 and 9.2). The δ¹³C of un-amended soil exhibited low spatial (−28.0‰±0.2; n=96) and temporal (±0.1‰) variability. All C₄ (CSC) and C₃ (DMC; SSLC) composts, except C₃ manure (DM), significantly modified bulk soil δ¹³C and δ¹⁵N. Estimates of retention of compost C in soil by carbon balance were less sensitive than those calculated by C isotope techniques. One and two years after application, 95 and 89% (CSC), 75 and 63% (SSLC) and 88 and 42% (DMC) of applied compost C remained in the soil, with the majority (80-90%) found in particulate (>53 μm) and light fractions. However, C₄ compost (CSC) was readily detectable (12% of compost C remaining) in mineral (<53 μm) fractions. The δ¹⁵N-enriched N of compost supported interpretation of δ¹³C data. We can conclude that composts are highly recalcitrant with prolonged C storage in non-mineral soil fractions. The sensitivity of the natural abundance tracer technique to characterize their fate in soil improves during composting, as a more homogeneous C isotope signature develops, in addition to the relatively large amounts of stable C applied in composts.     

Effect of soil application of cadmium contaminated lime on soil cadmium distribution and cadmium concentration in strawberry leaves and fruit

Heavy metal environmental pollution which occurs as a result of lime contaminated with cadmium (Cd) poses a potential health hazard. This investigation was undertaken to study uptake of Cd by strawberry plants grown in soil amended with three different sources and two different rates of industry waste lime containing 3.4, 14.3, and 60.0 mg Cd/kg, respectively. The effects of Cd applied to the soil were investigated, including its distribution in the soil and effect on Cd concentration in strawberry cv. Senga Sengana (Fragaria anassa) leaves and fruit in response to soil organic matter content and lime rates. Cadmium accumulated mainly in the plough layer, increasing from 0.170 mg Cd/kg (background level) to a maximum of 1.2 mg Cd/kg. Fruit had very high, hazardous Cd concentrations regardless of its content in the soil. This indicates that Cd was easily taken up by strawberry plants and accumulated in upper plant parts, including the fruit. Soil Cd content had no effect on concentration of this element in strawberry fruit. However, plant Cd uptake and fruit concentration was increased in acid soils even when soil Cd concentration was low.     

Population dynamics and ecology of ciliates (Protozoa,Ciliophora) in an anoxic rice field soil

Wetland rice fields cover 1.46 million km² globally; the flooded soil of these fields is largely anoxic. While biogeochemistry and microbiology have been studied in detail, the microbial loop and especially the dynamics and function of ciliates are largely unknown. We used anoxic microcosms prepared with soil from an Italian rice field and recorded species composition, abundance and volume of ciliates together with numbers, volume and size distribution of bacteria. Ciliates were the dominating protists observed in the microcosms, but could be outnumbered by flagellates if the soil was amended with rice straw. The number of ciliate taxa was 23. Metopus species were dominant, but 16 of the species recorded in the anoxic soil were facultative anaerobes. Another 29 species were found in accompanying experiments that included the oxic soil surface. Total abundance in the anoxic soil was on average 110 cells g^–1 dry weight and comparable to that of other soils. The population of ciliates declined around 30 days after flooding, but recovered later. The period before the population declined was characterized by a rapid species turnover, many facultative anaerobes and large species. After recovery, the average cell size was much smaller, but even then a facultative anaerobe, Plagiacampa pentadactyla , was common. About 90% of all species were bacteriovores while the others—mainly Gymnostomatidae—were predators. Grazing ciliates may have controlled bacteria during the first 5 days after flooding, as could be shown by a negative correlation between the respective volumes and by the size spectra of the bacteria.     

Screening of fungal strains responsible for strong fungistasis against Fusarium oxysporum f. sp. radicis-lycopersici in a coffee compost-amended soil

(pp. 817–824)
Disease incidence of crown and root rot of tomato, caused by Fusarium oxysporum f. sp. radicis-lycopersici J3 (FOL J3) was significantly lower in a soil (CC-soil) amended with coffee compost and chemical fertilizers (CF) than in a soil (CF-soil) amended with only CF. Germination of microconidia of various plant-pathogenic Fusarium oxysporum strains was consistently lower in the CC-soil than in the CF-soil, suggesting that the CC-soil possessed a higher degree of fungistasis. When the CC-soil was supplemented with rifampicin and kanamycin, germination of FOL J3 didn't increase, suggesting that the higher degree of fungistasis in the CC-soil may not be of bacterial origin. The substrate-induced respiration inhibition method demonstrated that the CC-soil possessed higher microbial activity and was dominated by fungi. PCR-DGGE analysis showed that the microbial community structure of the two soils was different. Fungal mycelia were isolated from the soils and the effect of the isolates on soil fungistasis was examined. Three isolates, all belonging to F. oxysporum out of 49 showed strongest suppressive effect on the germination of FOL J3 and two isolates suppressed Fusarium crown and root rot disease when they were inoculated into autoclaved CC-soil. These results might suggest that the isolates close to F. oxysporum were responsible for highly fungistatic capability in the CC-soil and were a possible source for disease suppression.     

施肥模式对连作草莓枯萎病控制效果及土壤微生物群落特征的影响

通过营养调控防治连作病害是近年来的发展方向之一。本研究通过不同施肥处理的田间小区试验,采用微生物培养方法和Biolog微生物自动分析系统分析了不同施肥模式下草莓抗病能力、连作土壤微生物群落特征。研究结果表明:与当地习惯施肥相比,优化施肥模式I和II可以促进草莓生长,并有效地控制草莓枯萎病;优化施肥模式I提高了草莓连作土壤细菌/真菌和放线菌/真菌比例;Biolog结果显示在短期内不同施肥模式对土壤微生物群落碳源利用能力和Shannon指数、Simpson指数、Mcintosh指数的影响有限;PCA分析表明,优化施肥模式I的土壤微生物群落碳源利用特征与当地习惯施肥模式明显不同。综合考虑控病效果及施肥量,优化施肥模式I是更为经济有效的施肥模式。     

Effect of superphosphate applications on soil phosphorus and on crop phosphorus removal by the strawberry

Abstract

Rate of superphosphate application significantly increased the Bray #2 (easily acid soluble plus adsorbed P) and “AlPO₄”; fractions for 3 successive years. A single dolomitic limestone application increased “FePO₄”; by an average of 36% one year after application. Crop P removal by the strawberry cv. ‘Acadia’ was approximately 2–3 ppm each year and it was not possible to relate this small amount to any of the soil P fractions determined.