Soil Microbial Community

1,3-Dichloropropene (1,3-D) is a likely alternative soil fumigant for methyl bromide. The objective was to determine root-knot nematode, Meloidogyne incognita, survival in microplots after exposure to 1,3-D for various periods of time in soil that have previously been amended with compost. The treatments were 1,3-D applied broadcast at 112 liters/ha and untreated controls in both compost-amended and unamended soil. Soil samples were collected from each microplot at 6, 24, 48, 72, and 96 hours after fumigation at three depths (0-15, 15-30, and 30-45 cm). One week after fumigation, six tomato seedlings were transplanted into each microplot and root galling was recorded 6 weeks later. Plants grown in fumigated compost-amended soil had more galls than plants from fumigated unamended soil at P </= 0.1. Gall indices from roots in fumigated soil amended with compost were not different from nonfumigated controls. Based on soil bioassays, the number of galls decreased with increasing time after fumigation in both compost-amended and unamended soil at 0-to-15 and 15-to-30 cm depths, but not at 30 to 45 cm deep. Higher soil water content due to the elevated levels of organic matter in the soil at these depths may have interfered with 1,3-D movement, thus reducing its efficacy.

Anaerobic soil disinfestation (ASD) has been demonstrated as an effective alternative to pre-plant chemical soil fumigation (CSF) commonly used to control soilborne pathogens. However, the ASD effects on spatial and temporal changes in soil microbial communities remain poorly understood in production systems with low soilborne disease pressure. The objective of this study was to assess the influence of ASD treatments on soil microbial community composition at different soil depths during the spring tomato production season in Florida. Soil treatments included ASD using 6.9 m3 ha−1 of molasses with 11 Mg ha−1 of composted poultry litter (CPL) (ASD0.5), ASD with 13.9 m3 ha−1 of molasses and 22 Mg ha−1 CPL (ASD1.0), and chemical soil fumigation (CSF) using a mixture of 1,3-dichloropropene and chloropicrin. Soil microbial community composition was measured at soil depths of 0–15 and 15–30 cm using phospholipid fatty acid (PLFA) analysis at 0, 36, 76, and 99 days after transplanting (DAT...

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Background and Aims Condensed tannins, a dominant class of plant secondary metabolites, play potentially important roles in plant-soil feedbacks by influencing the soil microbial community. Effects of condensed tannins on the soil microbial community and activity were examined by a short-term tannin-addition experiment under field and laboratory conditions. Methods Condensed tannins were extracted from the leaves of a dominant conifer (Dacrydium gracilis) in a tropical montane forest on Mt. Kinabalu, Borneo. The extracted tannins were added to soils beneath the conifer and a dominant broadleaf (Lithocarpus clementianus) to evaluate the dependence of the response to tannin addition on the initial composition of the soil microbial community. Results Enzyme activities in the field tannin-addition treatment were lower than in the deionized-water treatment. Carbon and nitrogen mineralization were also inhibited by tannin-addition. The fungi-to-bacteria ratio after tannin-addition was higher compared with the distilled-water treatment in the laboratory experiment. Conclusions Based on our results, we suggest that the higher concentration of condensed tannins in the leaf tissues of Dacrydium than in those of Lithocarpus is a factor influencing the microbial community and activity. This may have influences on subsequent plant performance, which induces plant-soil feedback processes that can control dynamics of the tropical montane forest ecosystem.

High value crop producers in California rely heavily on soil fumigation to control a wide array of soil borne pests including nematodes, pathogens and weeds. Fumigants with broad biocidal activity can affect soil microbial communities that contribute to nutrient cycling and plant nutrient uptake which can impact soil health. It is often thought that soil microbial communities make a relatively rapid recovery following fumigation. However, recently it has been found that repeated application of fumigants over time can have greater and longer lasting impacts on soil microorganisms than single fumigation events. Therefore, the main objective of this study was to determine the effect of long-term repeated application of fumigants on soil microbial communities and compare them with non-fumigated and organic sites. Soil samples were collected from fields in Watsonville, CA. Chronosequence sites were defined by number of years of annual fumigation (yaf) with methyl bromide (15, 26, 33, 39 yaf) at the time of sampling, and representative non-fumigated sites were also included for comparison. Phospholipid fatty acid (PLFA) analysis was used to analyze the samples. The canonical variate analysis showed that microbial communities in sites with a longer history of fumigation (33 and 39 yaf) were similar to one another; however, they differed significantly from 15 yaf site and further analysis concluded that non-fumigated sites were significantly different than fumigated sites. This study showed that the proportion of arbuscular mycorrhizal fungi (AMF) was lower in all fumigated (15, 33 and 39 yaf) sites as compared to their non-fumigated counterparts, which could be a threat to sustainability since AMF plays a major role in soil health and quality.

High value crop producers in California rely heavily on soil fumigation to control a wide array of soil borne pests including nematodes, pathogens and weeds. Fumigants with broad biocidal activity can affect soil microbial communities that contribute to nutrient cycling and plant nutrient uptake which can impact soil health. It is often thought that soil microbial communities make a relatively rapid recovery following fumigation. However, recently it has been found that repeated application of fumigants over time can have greater and longer lasting impacts on soil microorganisms than single fumigation events. Therefore, the main objective of this study was to determine the effect of long-term repeated application of fumigants on soil microbial communities and compare them with non-fumigated and organic sites. Soil samples were collected from fields in Watsonville, CA. Chronosequence sites were defined by number of years of annual fumigation (yaf) with methyl bromide (15, 26, 33, 39 yaf) at the time of sampling, and representative non-fumigated sites were also included for comparison. Phospholipid fatty acid (PLFA) analysis was used to analyze the samples. The canonical variate analysis showed that microbial communities in sites with a longer history of fumigation (33 and 39 yaf) were similar to one another; however, they differed significantly from 15 yaf site and further analysis concluded that non-fumigated sites were significantly different than fumigated sites. This study showed that the proportion of arbuscular mycorrhizal fungi (AMF) was lower in all fumigated (15, 33 and 39 yaf) sites as compared to their non-fumigated counterparts, which could be a threat to sustainability since AMF plays a major role in soil health and quality.

Soil organic carbon (SOC) mineralization was carried out on soil samples collected from two depths: 0-20 cm and 20-40 cm for all land use (LU) types (grasslands, croplands, natural forest/fallow lands, cocoa/palm plantations, and settlement/agro-forests). Microbiological analyses were carried out by measuring microbial activity in 40 g of dried soil samples wetted to 60% water holding capacity and incubated at 27˚C. Carbon dioxide (CO 2) emission was measured for 10 weeks using a CO 2 trap. Descriptive and graphical analyses of CO 2 respiration were done using CO 2 emission data. Models were developed to describe CO 2 respiration and the first order kinetic model provided best fit to C-mineralization. Potentially mineralizable carbon (C o) and C-mineralization rate were higher in grasslands than other LU types, indicating a higher rate of microbial activity and carbon cycling. Metabolic quotient was higher in forest/fallow lands and reflects greater stress of the microbial community and a high requirement of maintenance energy. Grasslands enhanced more SOC accumulation and decomposition, suggesting a better carbon sink than other land use and management systems (LUMS). Microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) varied across LU patterns with maximum values in grasslands and minimum values in natural forest/fallow lands insinuating better soil quality for grasslands. MBC and SOC positively correlated with C o and C-mineralization, which intimates that C-mineralization is influenced by availability of MBC and SOC. Metabolic quotient (qCO 2) negatively correlated with microbial quotient (MBC:SOC), depicting that higher values of qCO 2 signify difficulties in using organic substrates during microbial activity as a result of low MBC:SOC.

Despite several reports point out a rhizosphere effect shaping soil microbial communities and others an effect of altitude on plant phenotypic features, currently little is known about the impact of elevational patterns on the diversity of soil microbial communities. In this study, diversity of soil microbial communities was assessed in samples derived of bulk and rhizosphere soils associated to Californian poppy (Eschscholzia californica Cham.) populations at 1000 and 2000 m.a.s.l in Central Chile. E. californica, a native plant of North America, is considered a successful invader in Mediterranean ecosystems worldwide but its effect on diversity of soil microbial communities is yet unknown. Microbial diversity was evaluated at genetic level through T-RFLP (terminal restriction fragment length polymorphisms) using bacterial, archaeal and fungal molecular markers, and at metabolic level using CLPP (community-level physiological profiles). At genetic level, microbial diversities of bulk and rhizosphere soils at lower altitude were similar, although at higher altitude microbial diversity of both types of soils was different, suggesting a plant filtering effect more notorious at higher altitude. At metabolic level, microbial diversity of rhizosphere soils were similar independently of the altitude, suggesting a plant filtering effect that exceeds the altitude effect observed in the case of the bulk soil.

Biochar is a charcoal like substance produced from organic biomass after pyrolysis. Biochar act as a good soil conditioner by increasing microbial activities, soil nutrition and soil structure. Soil microorganisms are involved in litter decomposition and soil nutrient mineralization which is important in the sustainable development of plants and trees. The functioning of an ecosystem is controlled by biogeochemical cycles driven by microorganisms. The cell membrane of all microorganisms is composed of phospholipids that are easily metabolized after the cell death. Hence, phospholipid fatty acid (PLFA) analysis of microorganisms can be used for the characterization of living microbial communities. PLFA analysis is a lipid based, culture independent biochemical technique. Therefore, PLFAs can be used for the characterization of soil microbial community structure that are not able to cultivated by the conventional methods. This profiling act as a biological register of soil health, and as an indicator of soil response to different field management systems like biochar.

Agroecosystems in the Senegalese groundnut basin experience long periods of high temperatures and drought, which disrupt the stability of soil microbial communities. This study evaluated how that stability is affected by homefields and outfields' agricultural practices and the duration of heat stress. Specifically, we collected soils from organically farmed fields that receive continual high inputs of manure (homefields), and from fields that are rarely manured (outfields). Soil samples were submitted to artificial heat stress at 60˚C for 3, 14, and 28 days, followed by 28 days of recovery at 28˚C. We examined the functional stability of microbial communities by quantifying C mineralization, and characterized the stability of the communities' taxonomic compositions via high-throughput DNA sequencing. We found that the microbial communities have a low resistance to heat stress in soils from both types of fields. However, the manuring practice does affect how the functional stability of microbial communities responds to different durations of heat stress. Although functional stability was not recovered fully in either soil, microbial community resilience seemed to be greater in homefield soils.

Disentangling the kinetics of the soil microbial community succession, which is simultaneously driven by newly added plant materials and extant soil organic matter (SOM), can enrich our knowledge on microbial carbon (C) utilization patterns under residue amendment. This understanding might be useful to predict the rapid responses of specific microbial functional groups and develop strategies for balancing the terrestrial C budget. Therefore, our objective was to characterize and estimate the parameters of the microbial community dynamics profiled by phospholipid fatty acids (PLFA) from 13 C-labeled wheat residues and SOM. We conducted a 21-day microcosm study using two different arable systems (conventional tillage, CT; no-till, NT) amended with three types of 13 C-labeled wheat residues (grains, leaves and roots). The abundances and isotopic fractions of 13 CO 2 flux and 13 C-labeled PLFA were measured via gas trace isotope ratio mass spectrometry (IRMS) and gas chromatography-combustionisotope ratio mass spectrometry (GC-c-IRMS), respectively. A double exponential model was used to describe the synthesis-degradation kinetics of PLFA from different microbial origins. We found that the PLFA formation generally reaches its maximal abundance within 7 days (except for PLFA from actinomycetes). The SOM-and wheat residue-derived C fluxes, as well as their PLFA profiles, were inconsistently impacted by the residue quality or the tillage regime over the incubation period. Specifically, the abundances of residue-derived CO 2 and PLFAs significantly decreased in the following order: grains > leaves > roots. However, those abundances derived from SOM were the lowest with the leaf residue treatments. Residue-derived PLFA patterns were highly influenced by fungi and G À bacteria, while G + bacterial and actinomycete PLFAs were preferentially linked to extant SOM mineralization. Compared to the residue-derived counterparts, the SOM-derived microbes were characterized by higher G + /G À bacteria and cy17:0/C16:1v7c ratios, as well as lower fungi/bacteria PLFA ratios. Such distinction between residue and SOM was also evidenced by the contrasting tillage effects on C mineralization and the ratios of cy17:0/C16:1v7c and fungal/G À bacterial PLFA. Our study provides evidence with important implications for adapting the microbial-mediated processes of soil C management through residue quality control. 2015 Elsevier B.V. All rights reserved.

Anaerobic soil disinfestation (ASD) has been demonstrated as an effective alternative to pre-plant chemical soil fumigation (CSF) commonly used to control soilborne pathogens. However, the ASD effects on spatial and temporal changes in soil microbial communities remain poorly understood in production systems with low soilborne disease pressure. The objective of this study was to assess the influence of ASD treatments on soil microbial community composition at different soil depths during the spring tomato production season in Florida. Soil treatments included ASD using 6.9 m3 ha−1 of molasses with 11 Mg ha−1 of composted poultry litter (CPL) (ASD0.5), ASD with 13.9 m3 ha−1 of molasses and 22 Mg ha−1 CPL (ASD1.0), and chemical soil fumigation (CSF) using a mixture of 1,3-dichloropropene and chloropicrin. Soil microbial community composition was measured at soil depths of 0–15 and 15–30 cm using phospholipid fatty acid (PLFA) analysis at 0, 36, 76, and 99 days after transplanting (DAT...

The objectives of this study were to determine whether the invasive plant Amaranthus viridis influenced soil microbial and chemical properties and to assess the consequences of these modifications on native plant growth. The experiment was conducted in Senegal at two sites: one invaded by A. viridis and the other covered by other plant species. Soil nutrient contents as well as microbial community density, diversity and functions were measured. Additionally, five sahelian Acacia species were grown in (1) soil disinfected or not collected from both sites, (2) uninvaded soil exposed to an A. viridis plant aqueous extract and (3) soil collected from invaded and uninvaded sites and inoculated or not with the arbuscular mycorrhizal (AM) fungus Glomus intraradices. The results showed that the invasion of A. viridis increased soil nutrient availability, bacterial abundance and microbial activities. In contrast, AM fungi and rhizobial development and the growth of Acacia species were severely reduced in A. viridis-invaded soil. Amaranthus viridis aqueous extract also exhibited an inhibitory effect on rhizobial growth, indicating an antibacterial activity of this plant extract. However, the inoculation of G. intraradices was highly beneficial to the growth and nodulation of Acacia species. These results highlight the role of AM symbiosis in the processes involved in plant coexistence and in ecosystem management programs that target preservation of native plant diversity.

Deep soil stores a large amount of organic carbon (C) and nitrogen (N). However, little is known regarding the interactions between soil C and net N mineralization in deep soil, which complicates the prediction of ecosystem C and N dynamics. In this study, a 150-day laboratory soil incubation experiment was performed under 20 C and 25 C to investigate the influence of soil depth and warming on C and net N mineralization and their relationship. Soils were collected from a Hapludalfs profile in a subtropical forest with three depth intervals: 0e10 (topsoil), 10e30 (midsoil), and 30e60 cm (subsoil). Soil microbial community-level physiological profiling (CLPP) was conducted to investigate the role of the microbial community in C and N mineralization. The results demonstrated that both C and net N mineralization rates in subsoil were significantly lower than in topsoil. Compared to topsoil, subsoil had lower temperature sensitivity of C mineralization and relatively higher temperature sensitivity of net N mineralization. Cumulative soil C and net N mineralized were positively correlated in topsoil with the mineralized N per mineralized C showed as 0.19 and 0.31 at 20 C and 25 C, respectively. However, there was no significant correlation between cumulative soil C and net N mineralized in subsoil due to the low amount of net N mineralization. The lack of labile C source and degradable organic N were believed to limit the net N mineralization in subsoil. The microbial community in topsoil used relatively more easily decomposable carbohydrates and carboxylic acids, which favored C mineralization. In contrast, the microbial community in subsoil had relatively high utilization of amino acids (N-containing substrates), which indicated there was N limitation. This distinguished substrate utilization patterns of microbial communities could explain the observed C and N mineralization rates among the soil depths, and suggests that the microbial community played an important role in soil C and N mineralization. The decoupled relationships between soil C and net N mineralization in deep soil and their differentiated responses to warmer temperatures among soil depths indicated that deep soil should be considered separately from topsoil for ecosystem C and N cycling, especially for ecosystem C dynamic models.

The objectives of this study were to determine whether the invasive plant Amaranthus viridis influenced soil microbial and chemical properties and to assess the consequences of these modifications on native plant growth. The experiment was conducted in Senegal at two sites: one invaded by A. viridis and the other covered by other plant species. Soil nutrient contents as well as microbial community density, diversity and functions were measured. Additionally, five sahelian Acacia species were grown in (1) soil disinfected or not collected from both sites, (2) uninvaded soil exposed to an A. viridis plant aqueous extract and (3) soil collected from invaded and uninvaded sites and inoculated or not with the arbuscular mycorrhizal (AM) fungus Glomus intraradices. The results showed that the invasion of A. viridis increased soil nutrient availability, bacterial abundance and microbial activities. In contrast, AM fungi and rhizobial development and the growth of Acacia species were severely reduced in A. viridis-invaded soil. Amaranthus viridis aqueous extract also exhibited an inhibitory effect on rhizobial growth, indicating an antibacterial activity of this plant extract. However, the inoculation of G. intraradices was highly beneficial to the growth and nodulation of Acacia species. These results highlight the role of AM symbiosis in the processes involved in plant coexistence and in ecosystem management programs that target preservation of native plant diversity.

A B S T R A C T Phospholipid fatty acid analysis (PLFA) is used as culture-independent tool in microbial ecology studies. Classification of PLFAs into chemically distinct subgroups will assess insights into microbial community structure involved in microbial processes, and will have direct impacts on soil fertility. The PLFAs are synthesized during microbial growth, degrade rapidly during cell death, and hence provide an accurate census of living microbial community. PLFA profile of FMS dominated with monounsaturated fatty acids suggesting the abundance of gram- negative bacteria, anaerobes, actinomycetes and methanobacter. Higher poly- unsaturated fatty acids in FS suggesting abundance of arbuscular mycorrhizal fungi and fungal populations. Shannon diversity index based on the distribution of 92 PLFAs varies from 2.4735 (FMS) to 2.9401 (PTS). Besides, higher Pielou s evenness index in AS (0.8034) suggesting greater diversity as compared to FMS (0.6118). Difference in fungal-to- bac...

Atmospheric CO 2 concentration is increasing, largely due to anthropogenic activities. Previous studies of individual free-air CO 2 enrichment (FACE) experimental sites have shown significant impacts of elevated CO 2 (eCO 2) on soil microbial communities; however, no common microbial response patterns have yet emerged, challenging our ability to predict ecosystem functioning and sustainability in the future eCO 2 environment. Here we analyzed 66 soil microbial communities from five FACE sites, and showed common microbial response patterns to eCO 2 , especially for key functional genes involved in carbon and nitrogen fixation (e.g., pcc/acc for carbon fixation, nifH for nitrogen fixation), carbon decomposition (e.g., amyA and pulA for labile carbon decomposition, mnp and lcc for recalcitrant carbon decomposition), and greenhouse gas emissions (e.g., mcrA for methane production, norB for nitrous oxide production) across five FACE sites. Also, the relative abundance of those key genes was generally increased and directionally associated with increased biomass, soil carbon decomposition, and soil moisture. In addition, a further literature survey of more disparate FACE experimental sites indicated increased biomass, soil carbon decay, nitrogen fixation, methane and nitrous oxide emissions, plant and soil carbon and nitrogen under eCO 2. A conceptual framework was developed to link commonly responsive functional genes with ecosystem processes, such as pcc/acc vs. soil carbon storage, amyA/pulA/mnp/lcc vs. soil carbon decomposition, and nifH vs. nitrogen availability, suggesting that such common responses of microbial functional genes may have the potential to predict ecosystem functioning and sustainability in the future eCO 2 environment.

Forest canopy structure controls the timing, amount, and chemical character of precipitation supply to soils through interception and drainage along crown surfaces (primarily as throughfall). Yet, few studies have examined forest canopy structural connections to soil microbial communities, and none have measured how throughfall affects microbial nitrogen (N) functions. Maritime Quercus virginiana Mill. (southern live oak) forests on St Catherine's Island (GA, USA) provide an ideal venue to study this interaction as its throughfall patterns are spatially heterogeneous due to the arboreal epiphyte, Tillandsia usneoides L. (Spanish moss), and its edaphic conditions are relatively homogeneous. To test the hypothesis that throughfall patterns alter soil microbial community N-function, we examined soil microbial community N-functional (ammonia oxidizing and chitinolytic) genes, soil chemistry/texture, and throughfall amounts/chemistry for points along a canopy coverage continuum: large canopy gaps (0%), bare Q. virginiana canopy (50-60%), and Q. virginiana canopy hosting heavy T. usneoides (>=85%) over a typical growing season (Mar-Sep, 2014). Denaturing Gradient Gel Electrophoresis (DGGE) and quantitative Polymerase Chain Reaction (qPCR) analyses were used to assess changes in the diversity and abundance, respectively, of soil chitinolytic bacterial and ammonia oxidizing archaeal genes. Significant differences in throughfall water and solute delivery (Na + , Cl-, PO 4 3-, SO 4 2-, K + , Ca 2+ , NO 3-, NH 4 +) were found to alter soil sodicity and salinity. Diversity of chitinolytic bacterial and ammonia oxidizing archaeal communities significantly differed across cover classes and negatively correlated to soil salinity, soil Na + concentration, and throughfall Cl-, SO 4 2-, and PO 4 3concentrations. Results suggest throughfall can alter patterns in the soil microbial community's N-functional gene diversity.

A field study was established to assess the effects of a sewage sludge (SS), a mixed municipal solid waste compost (MMSWC) and a compost produced from agricultural wastes (AWC), in a Vertisol, using Lolium multiflorum L. The amendments were applied for two consecutive years: 6, 12 and 24 t dry matter ha À1 for SS, and the amendment doses for MMSWC and AWC were calculated to deliver the same amount of organic matter (OM) per unit area. The amendments had significant beneficial effects on some soil properties (e.g. soil OM, N Kjeldahl , extractable P and K), and on plant productivity parameters (e.g. biomass yield, chlorophyll, foliar area). For instance, soil OM increased from 0.78% to 1.71, 2.48 and 2.51%, after two consecutive years of application of 24 t dry matter ha À1 of SS, MMSWC and AWC, respectively, while the plant biomass obtained increased from 7.75 t ha À1 to 152.41, 78.14 and 29.26 t ha À1 , for the same amendments. On the plant, effects were more pronounced for SS than for both compost applications, a consequence of its higher capacity to provide N to the plant in a readily available form. However, after two years of application, the effects on soil properties were more noticeable for both composts, as their OM is more resistant to mineralization, which endures their beneficial effects on soil. Cadmium, Cr, Ni and Pb pseudo-total concentrations, were not affected significantly by the application of the organic wastes to soil, in all tested doses, neither their extractability by 0.01 M CaCl 2. On the contrary, Cu and Zn pseudo-total concentrations increased significantly in the second year of the experiment, following the application of the higher rate of MMSWC and AWC, although their extractability remained very low (<0.5% of their pseudo-total fraction). Trace elements concentrations in the aboveground plant material were lower than their maximum tolerable levels for cattle, used as an indicator of risk of their entry into the human food chain. Despite these results, it is interesting to note that the SS promoted a significant increase in the foliar concentrations of Cu, Ni and Zn that did not happen in composts application, which can be explained by the reduction of the soil pH, as a consequence of SS degradation in soil. Concluding, if this type of organic wastes were to be used in a single application, the rate could be as high as 12 or even 24 t ha À1 , however, if they are to be applied in an annual basis, the application rates should be lowered to assure their safe application (e.g. to 6 t ha À1). Moreover, it is advisable to use more stable and mature organic wastes, which have longer lasting positive effects on soil characteristics.

Previous surveys of vineyards had indicated that Mesocriconema xenoplax was present in 85% of vineyards in western Oregon, but yields were not depressed in established vines. Microplot studies were initiated in 1997 in a Willamette Valley vineyard to determine the impact of M. xenoplax on vine establishment. Plots were infested with 0.03, 0.6, and 3.0 M. xenoplax g(-1) soil and planted with self-rooted Chardonnay and Pinot Noir vines. In November 2000, four growing seasons after planting, pruning weights, fine root weights, and fruit yield of vines planted in infested soil were reduced by 58%, 75%, and 33%, respectively, relative to control vines (planted in noninfested soil). In 1998 with ca 2000 degree-day base 9 degrees C accumulation, population densities increased 32-fold and 44-fold on 1-year-old Chardonnay and Pinot Noir vines, respectively. Nematode population dynamics and pruning data suggested that the carrying capacity of vines in microplots was 5 to 8 M. xenoplax g(-1) s...

Piliostigma reticulatum is a native woody shrub found in cropped fields in the Sahel and has been shown to increase crop productivity and soil quality. Frequently occurring drying and rewetting cycles (DRW) may alter the soil quality beneath these shrubs. We investigated the effect of DRW cycles on microbial community in soil beneath and outside the P. reticulatum canopy and the roles of this shrub in the adaptation of the microbial community to abiotic stress. Soils were incubated in a climate controlled chamber for 45 days, after exposure to 10 consecutive days of DRW cycles at 75% of water holding capacity (WHC). Basal respiration, β-glucosidase activity, microbial biomass carbon (MB C), and available nitrogen (4 NH + ; 3 NO −) were measured at 2, 30, and 45 days after soil exposed to the DRW cycles. MB C increased significantly two days after the DRW cycles and was greater for soil beneath the shrub canopy compared with soil outside the shrub canopy. PCA analysis based on basal respiration, microbial biomass carbon, available nitrogen, and β-Glucosidase activity resulted in a tight clustering in the beneath shrub soil samples. Soils incubated for more than 30 days after DRW cycles had higher available nitrogen content than soils incubated for less than 30 days. Soil from beneath the shrub canopy significantly improved soil resilience based on β-glucosidase activity. Soil from beneath the shrub canopy also had higher nutrient levels and greater microbial activity even when subjected to DRW cycles, potentially improving the ability of crops to withstand in-season drought when they are adjacent to shrubs. The work should bring our scien

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Chloropicrin (CP) and metam sodium are commonly used as fumigants in agricultural soils in order to provide effective control of nematodes, soil-borne pathogens, and weeds in preparation for planting of highvalue cash crops. Repeated application of these compounds to agricultural soils for many years may result in the enrichment of microorganisms capable of degrading them. In this study, a microcosm-enrichment approach was used to investigate bacterial populations that may be components of metam-sodium-and CP-degrading microorganisms in compost-amended soils. After 6 months incubation, with repeated application of metam sodium and CP, degradation was ≥70% faster in compost-manureamended (CM) soil compared to ≤50% in the unamended soils. The accelerated fumigant degradation may have been due to the addition of compost or to the development of new microbial populations with enhanced degradation capacity. Denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified regions of 16S rRNA genes were used to identify dominant bacterial populations responsible for the accelerated fumigant degradation. The DGGE results indicated that specific bacterial types had been enriched and these were similar to strains isolated from basal minimal media. Fragments from DGGE bands and colonies were cloned, sequenced, and compared with published 16S rRNA sequences. Cloned sequences were dominated by Pseudomonas, Bacillus, Arthrobacter, Mycobacterium and uncultured bacterial species. The addition of organic amendment to soil during fumigation practices has the potential to increase the diversity of different microbial species, thereby accelerating fumigant degradation and reducing atmospheric emissions.

Piliostigma reticulatum is a native woody shrub found in cropped fields in the Sahel and has been shown to increase crop productivity and soil quality. Frequently occurring drying and rewetting cycles (DRW) may alter the soil quality beneath these shrubs. We investigated the effect of DRW cycles on microbial community in soil beneath and outside the P. reticulatum canopy and the roles of this shrub in the adaptation of the microbial community to abiotic stress. Soils were incubated in a climate controlled chamber for 45 days, after exposure to 10 consecutive days of DRW cycles at 75% of water holding capacity (WHC). Basal respiration, β-glucosidase activity, microbial biomass carbon (MB C), and available nitrogen (4 NH + ; 3 NO −) were measured at 2, 30, and 45 days after soil exposed to the DRW cycles. MB C increased significantly two days after the DRW cycles and was greater for soil beneath the shrub canopy compared with soil outside the shrub canopy. PCA analysis based on basal respiration, microbial biomass carbon, available nitrogen, and β-Glucosidase activity resulted in a tight clustering in the beneath shrub soil samples. Soils incubated for more than 30 days after DRW cycles had higher available nitrogen content than soils incubated for less than 30 days. Soil from beneath the shrub canopy significantly improved soil resilience based on β-glucosidase activity. Soil from beneath the shrub canopy also had higher nutrient levels and greater microbial activity even when subjected to DRW cycles, potentially improving the ability of crops to withstand in-season drought when they are adjacent to shrubs. The work should bring our scien

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Soil Biology & Biochemistry D imethyl disulfide (DMDS) is a relatively new compound in agriculture that has zero ozone depletion potential and is a sulfur volatile product that can be produced commercially from acid natural gas . It is common in the global sulfur cycle and is detected as a metabolite in numerous biological processes . Dimethyl disulfide is a recently registered soil fumigant approved for preplant use as an alternative to methyl bromide (MeBr). It has been shown to control soilborne pests like pathogens, plant parasitic nematodes, and weeds. Soil fumigation is a very effective method to control plant parasitic nematodes, such as root-knot (Meloidogyne spp.) and citrus (Tylenchus semipenetrans) nematodes . Root-knot nematodes are endoparasites

Producers of several high-value crops in California rely heavily on soil fumigants to control key diseases, nematodes, and weeds. Fumigants with broad biocidal activity can affect both target and nontarget soil microorganisms. The ability of nontarget soil microorganisms to recover after fumigation treatment is critical because they play an important role in sustaining the health of agricultural and natural soil systems. Fumigation trial was conducted in Parlier, CA, and the study focuses on the effects of different rates of Telone C35 and also methyl bromide fumigation with polyethylene (PE) and totally impermeable film (TIF) tarps on target and nontarget soil microorganisms using field samples. Results indicated that the populations of target organisms, such as Fusarium oxysporum and Pythium spp., were reduced at all rates of fumigants. Phospholipid fatty acid (PLFA) analysis indicated that all major nontarget soil microbial groups such as Gram positive bacteria, Gram negative bac...

Producers of several high-value crops in California rely heavily on soil fumigants to control key diseases, nematodes, and weeds. Fumigants with broad biocidal activity can affect both target and nontarget soil microorganisms. The ability of nontarget soil microorganisms to recover after fumigation treatment is critical because they play an important role in sustaining the health of agricultural and natural soil systems. Fumigation trial was conducted in Parlier, CA, and the study focuses on the effects of different rates of Telone C35 and also methyl bromide fumigation with polyethylene (PE) and totally impermeable film (TIF) tarps on target and nontarget soil microorganisms using field samples. Results indicated that the populations of target organisms, such asFusarium oxysporumandPythiumspp., were reduced at all rates of fumigants. Phospholipid fatty acid (PLFA) analysis indicated that all major nontarget soil microbial groups such as Gram positive bacteria, Gram negative bacteri...

Pre-plant fumigation of agricultural soils with a combination of methyl bromide (MeBr) and chloropicrin (CP) to control nematodes, soil-borne pathogens and weeds has been a common practice in strawberry (Fragaria X ananassa Duchesne) production since the 1960s. MeBr will be phased out by 2005, but little is known about the impacts of alternative fumigants on soil microbial processes. We investigated the response of microbial biomass and enzyme activities in soils fumigated over two years with MeBr + CP and the alternatives propargyl bromide (PrBr), InLine, Midas and CP. Results were compared to control soils, which were not fumigated for the last 4 to 5 years for Watsonville and Oxnard, respectively, but had a 10 year history of MeBr + CP fumigation (history soils). Soil samples (0-15cm) were taken from two sites in the coastal areas of California, USA, in Watsonville and Oxnard, at peak strawberry production after two years of repeated application. In addition to the soil enzymes, the activities of purified reference enzymes of β-glucosidase, acid phosphatase and arylsulfatase were assayed before and after fumigation with MeBr + CP and alternative biocides. At the Oxnard site, microbial respiration significantly decreased in soils fumigated with MeBr + CP (P = 0.036), while microbial biomass C and N showed no response to fumigation at both sites. These results may indicate that fumigation promotes the growth of resistant species or that soil microorganisms had recovered at the time of sampling. Repeated soil fumigation with MeBr + CP significantly decreased the activities of β-glucosidase and acid phosphatase at the Watsonville site, and dehydrogenase activity at the Oxnard site. Although, enzyme activities in soils fumigated with PrBr, InLine, Midas and CP were lower compared to the control soil, effects were, in general, not significant. Fumigation with MeBr + CP and alternatives reduced the activities of purified reference enzymes by 13, 76 and 28% for acid 2 phosphatase, β-glucosidase and arylsulfatase, respectively. Mean enzyme protein concentrations in fumigated agricultural soils were 2.93, 0.105, and 2.95 mg protein kg-1 soil for acid phosphatase, β-glucosidase and arylsulfatase, respectively, all lower than in control soils. Organic matter turnover and nutrient cycling, and thus, the long-term productivity of agricultural soils seem unaffected in soils repeatedly fumigated with PrBr, InLine, Midas and CP.

The effectiveness of di-nitrogen tetroxide (DNTO) as a substitute for methyl bromide in controlling soil-borne nematodes, fungi and bacteria was evaluated. Application of DNTO to soil packed into columns resulted in a reduction of the bacterial population by three orders of magnitude within 1 h, and a complete elimination after 2 h. The same treatment resulted in the destruction of all fungi and nematodes within 10 min. The most effective treatment (30 min for bacteria elimination and 10 min for nematode and fungi elimination) was achieved in soil with a low moisture level (4%), at a pumping rate of 0Á1 ml/min DNTO. In a single microplot trial, using 300 g/m 2 DNTO, a significant reduction of nematodes was observed. Lack of phytotoxicity of DNTO was demonstrated using tomato plants. In addition, at the above-mentioned soil moisture and DNTO levels, the DNTO is readily converted into nitrate. Hence, the use of DNTO can supply a considerable part of the nitrogen fertiliser requirement of the treated crops and only a small fraction of it is liberated into the atmosphere.

A sandy loam soil was fumigated in microcosms for 24 h with methyl bromide and chloropicrin (MeBr+CP), propargyl bromide (PrBr), combinations of 1,3-dichloropropene and CP (InLine), iodomethane and CP (Midas), an emulsifiable concentrate of CP (CP-EC), or methyl ...

fungal pathogens, but is not as effective against nematodes as MeBr (Wilhelm and Pavlou, 1980). Therefore, Methyl bromide (MeBr; CH 3 Br) use for soil fumigation will be a mixture of MeBr and CP is usually applied to control banned in 2005 due to its ozone depleting properties. Potential alternasoil-borne fungal pathogens such as Verticillium wilt tive chemicals to replace MeBr include chloropicrin (CP; CCl 3 NO 2), (Verticillium dahliae Kleb.) and weeds (Wilhelm et al., 1,3-dichloropropene (1,3-D; C 3 H 4 Cl 2), iodomethane (IM; CH 3 I), and propargyl bromide (PrBr; C 3 H 3 Br). The goal of this research was to 1961). Recent research found that an emulsifiable conassess changes in soil fungal populations, microbial biomass C (MB C) centrate (EC) formulation of CP applied through drip and respiration, nitrification potential, and enzyme activities after irrigation systems at rates Ͼ 200 kg ha Ϫ1 provided consisfumigation with MeBr and alternative fumigants. Four formulations tent cost-effective pest and weed control in strawberry of alternative fumigants (CP, InLine [61% 1,3-D plus 33% CP], Midas

Piliostigma reticulatum is a native woody shrub found in cropped fields in the Sahel and has been shown to increase crop productivity and soil quality. Frequently occurring drying and rewetting cycles (DRW) may alter the soil quality beneath these shrubs. We investigated the effect of DRW cycles on microbial community in soil beneath and outside the P. reticulatum canopy and the roles of this shrub in the adaptation of the microbial community to abiotic stress. Soils were incubated in a climate controlled chamber for 45 days, after exposure to 10 consecutive days of DRW cycles at 75% of water holding capacity (WHC). Basal respiration, β-glucosidase activity, microbial biomass carbon (MBC), and available nitrogen ( NH4+ ; NO3− ) were measured at 2, 30, and 45 days after soil exposed to the DRW cycles. MBC increased significantly two days after the DRW cycles and was greater for soil beneath the shrub canopy compared with soil outside the shrub canopy. PCA analysis based on basal resp...

The effectiveness of di-nitrogen tetroxide (DNTO) as a substitute for methyl bromide in controlling soil-borne nematodes, fungi and bacteria was evaluated. Application of DNTO to soil packed into columns resulted in a reduction of the bacterial population by three orders of magnitude within 1 h, and a complete elimination after 2 h. The same treatment resulted in the destruction of all fungi and nematodes within 10 min. The most effective treatment (30 min for bacteria elimination and 10 min for nematode and fungi elimination) was achieved in soil with a low moisture level (4%), at a pumping rate of 0Á1 ml/min DNTO. In a single microplot trial, using 300 g/m 2 DNTO, a significant reduction of nematodes was observed. Lack of phytotoxicity of DNTO was demonstrated using tomato plants. In addition, at the above-mentioned soil moisture and DNTO levels, the DNTO is readily converted into nitrate. Hence, the use of DNTO can supply a considerable part of the nitrogen fertiliser requirement of the treated crops and only a small fraction of it is liberated into the atmosphere.

Methyl bromide (MeBr) was identified as a stratospheric ozone depletory; therefore, the use of MeBr was phased out in the United States in 2005. Chloropicrin (CP) and allyl isothiocyanate (AITC) are MeBr replacements. A mixture of CP and AITC is commonly applied to broaden the pest control spectrum. These two fumigants have low soil mobility; however, their efficacy could be improved if their soil mobility were enhanced. This research was conducted to study the effects of surfactants applied at 5% (v/v) for CP mobility and AITC mobility in soils. Mobility of the CP/AITC mixture applied with a nonionic surfactant comprising oleic, linoleic, and palmitic acids (nonionic-1) and mobility of the CP/AITC mixture applied with a nonionic surfactant comprising C9 hydrocarbon aromatics and calcium alkylarylsuphonate (nonionic-2) were compared with mobility of the CP/AITC mixture applied without surfactants in three soils (Elder sandy loam, Chualar loam, and Blanco clay loam) during a laborato...

Recent controversy over the potential role of methyl bromide (MeBr) in damaging the ozone layer has spurred interest in increasing our understanding of the transformation and movement of this fumigant after it is applied to soil. Our research indicates MeBr is rapidly volatilized from fumigated soil (within the first 24 hours) and volatility significantly increases with temperature (35° C > 25° C = 15° C) and moisture (0.03 bar > 0.3 bar > 1 bar > 3 bar). Degradation of MeBr, measured by production of bromide ion (Br-), was also directly related to temperature and moisture. Undisturbed soil column studies indicated that MeBr rapidly volatilized (> 50% of the MeBr flux occurred in 48 h) but did not leach into subsurface soil. Residual MeBr was degraded in the soil column, evident by the high concentrations of Br-in the leachate water. In field studies, MeBr also volatilized rapidly from soil, but a significant portion of the MeBr was degraded (30% after 2 d). These studies provide pertinent information for assessing the fate of MeBr in soil, which should lead to more informed decisions regulating its use.

Piliostigma reticulatum is a native woody shrub found in cropped fields in the Sahel and has been shown to increase crop productivity and soil quality. Frequently occurring drying and rewetting cycles (DRW) may alter the soil quality beneath these shrubs. We investigated the effect of DRW cycles on microbial community in soil beneath and outside the P. reticulatum canopy and the roles of this shrub in the adaptation of the microbial community to abiotic stress. Soils were incubated in a climate controlled chamber for 45 days, after exposure to 10 consecutive days of DRW cycles at 75% of water holding capacity (WHC). Basal respiration, β-glucosidase activity, microbial biomass carbon (MBC), and available nitrogen ( NH4+ ; NO3− ) were measured at 2, 30, and 45 days after soil exposed to the DRW cycles. MBC increased significantly two days after the DRW cycles and was greater for soil beneath the shrub canopy compared with soil outside the shrub canopy. PCA analysis based on basal respiration, microbial biomass carbon, available nitrogen, and β-Glucosidase activity resulted in a tight clustering in the beneath shrub soil samples. Soils incubated for more than 30 days after DRW cycles had higher available nitrogen content than soils incubated for less than 30 days. Soil from beneath the shrub canopy significantly improved soil resilience based on β-glucosidase activity. Soil from beneath the shrub canopy also had higher nutrient levels and greater microbial activity even when subjected to DRW cycles, potentially improving the ability of crops to withstand in-season drought when they are adjacent to shrubs. The work should bring our tific community into a more comprehensive assessment of potential effects of a crop-shrub intercropping that may allow for increased crop yields in semi-arid ecosystems under drought conditions.

Soil analysis showed the increasing of TOC, TN, and amount of total DNA in correspondence with the stages of successions. In comparison to other samples, mature soil had higher amounts of C and N. The q-PCR assays showed similar trends in ribosomal and N-cycling related gene copy numbers, in which bacterial abundance was found higher than fungi, denitrification and nitrification associated genes (nirK, amoA) were the most and least abundant among others, respectively. Furthermore, statistical analysis revealed the major correlation of microbial abundance with TOC and N-cycling related gene with TN. High-throughput sequencing results revealed the predominance of Proteobacteria, Acidobacteria in all samples and the decreasing of Thaumarchaeota, Chloroflexi, Cyanobacteria as well as the increasing of Planctomycetes relative abundance during soil formation. Statistical analysis of prokaryotic diversity showed the change and increasing ofα-diversity with successional stages on site I but not on site II. Moreover, the shift in prokaryotic community composition through sand fixation process and their similar structure in the two mature soils were observed.

This study was conducted to examine the effects of three application methods of metam sodium (broadcast, single irrigation drip tape delivery, and double irrigation drip tape delivery) and two plastic covers (polyethylene film and virtually impermeable film) on volatilization and on horizontal and vertical distributions of the biologically active product of metam sodium, methyl isothiocyanate (MITC), in field plots in a Florida sandy soil. Volatilization of MITC from field beds lasted for about 20 hours after completion of metam sodium application regardless of application methods. Virtually impermeable film (VIF) was a better barrier to reduce volatilization loss than polyethylene film (PE). Since water was not applied during broadcast application, MITC was mainly retained in the shallow soil layer (0-to 20-cm depth) and downward movement of MITC was limited to about 30 cm.

Species of Prunus such as almond and peach can grow poorly when they are planted on sites with a recent history of closely related crops. Known causes of replant problems include nutrient deficiencies and toxicities, improper soil pH, limiting soil physical conditions, poor plant-soil water relations, and root or vascular system dysfunction caused by plant parasitic nematodes or fungi. Even in the absence of these non-specific replant problems, however, California almond and peach trees have often grown poorly or failed to establish at sites previously devoted to their production. Evidence suggests that this specific problem has biological cause(s), and it is referred to as Prunus replant disease (PRD). Here we report on effects of pre-plant fumigation treatments, cropping practices, and fallow periods on incidence and severity of PRD.

Producers of several high-value crops in California rely heavily on soil fumigants to control key diseases, nematodes, and weeds. Fumigants with broad biocidal activity can affect both target and nontarget soil microorganisms. The ability of nontarget soil microorganisms to recover after fumigation treatment is critical because they play an important role in sustaining the health of agricultural and natural soil systems. Fumigation trial was conducted in Parlier, CA, and the study focuses on the effects of different rates of Telone C35 and also methyl bromide fumigation with polyethylene (PE) and totally impermeable film (TIF) tarps on target and nontarget soil microorganisms using field samples. Results indicated that the populations of target organisms, such as Fusarium oxysporum and Pythium spp., were reduced at all rates of fumigants. Phospholipid fatty acid (PLFA) analysis indicated that all major nontarget soil microbial groups such as Gram positive bacteria, Gram negative bacteria, fungi, and arbuscular mycorrhizal fungi (AMF) were affected by methyl bromide (MeBr) fumigation treatment. In general, the effects of Telone C35 (299 L/ha) under PE tarp had the least impact on microbial community structure and better effect on controlling target microorganisms and, therefore, indicated the better option among fumigation treatments.

A sandy loam soil was fumigated in microcosms for 24 h with methyl bromide and chloropicrin (MeBrCCP), propargyl bromide (PrBr), combinations of 1,3-dichloropropene and CP (InLine), iodomethane and CP (Midas), an emulsifiable concentrate of CP (CP-EC), or methyl isothiocyanate (MITC). The effects of these pesticides on fatty acid methyl ester (FAME) profiles and selected enzymatic activities were evaluated in fumigated soils and a nonfumigated control at 1, 3, 7, 14, 21, 28, and 90 days post-fumigation. Bacterial (a15:0, i15:0, i16:0, cy17:0, a17:0 and i17:0) and fungal (18:2u6, 18:3u6, 18:1u9) FAMEs were initially (1 day post-fumigation) reduced by fumigation with CP-EC, InLine, and Midas. Microbial communities of soils fumigated with MeBrCCP, MITC, and PrBr resembled those of the control soil. At 14-28 days postfumigation, FAME profiles were changed in all fumigated soils relative to the control, with the exception of soils treated with MITC. At 90 days post-fumigation, FAME profiles suggested that actinomycetes (10 Me 16:0, 10 Me 17:0, 10 Me 18:0) and Gram-positive bacteria may recover preferentially after fumigation with most of the pesticides studied. Among the fumigants tested, InLine, Midas, and CP-EC had a higher potential to alter the microbial community structure in the longer term than MeBrCCP, PrBr and MITC, with MITC having the least effect. Soil enzyme activities in fumigated microcosms were significantly (P%0.037) different from the nonfumigated soil, with the exception of b-glucosidase in soils treated with PrBr and MITC, and dehydrogenase in MeBrCCP-fumigated soils. Over the 90-day study, soil fumigation (average of all fumigants and sampling dates) reduced the activities of arylsulfatase (62%), dehydrogenase (35%), acid phosphatase (22%), and b-glucosidase (6%), suggesting that S mineralization in soils and the total oxidative potential of microorganisms were more affected by fumigation than P and C mineralization. This study also indicates that soil fumigation with MeBrCCP alternative biocides has the potential to alter microbial communities and important key reactions involved in nutrient transformation. q

Pre-plant fumigation of agricultural soils with a combination of methyl bromide (MeBr) and chloropicrin (CP) to control nematodes, soil-borne pathogens and weeds has been a common practice in strawberry (Fragaria X ananassa Duchesne) production since the 1960s. MeBr will be phased out by 2005, but little is known about the impacts of alternative fumigants on soil microbial processes. We investigated the response of microbial biomass and enzyme activities in soils fumigated over two years with MeBr+CP and the alternatives propargyl bromide (PrBr), InLine, Midas and CP. Results were compared to control soils, which were not fumigated for the last 4-5 years for Watsonville and Oxnard, respectively, but had a 10 year history of MeBr+CP fumigation (history soils). Soil samples (0-15 cm) were taken from two sites in the coastal areas of California, USA, in Watsonville and Oxnard, at peak strawberry production after two years of repeated application. In addition to the soil enzymes, the activities of purified reference enzymes of beta-glucosidase, acid phosphatase and arylsulfatase were assayed before and after fumigation with MeBr+CP and alternative biocides. At the Oxnard site, microbial respiration significantly decreased in soils fumigated with MeBr+ CP (P=0.036), while microbial biomass C and N showed no response to fumigation at both sites. These results may indicate that fumigation promotes the growth of resistant species or that soil microorganisms had recovered at the time of sampling. Repeated soil fumigation with MeBr+CP significantly decreased the activities of P-glucosidase and acid phosphatase at the Watsonville site, and dehydrogenase activity at the Oxnard site. Although, enzyme activities in soils fumigated with PrBr, InLine, Midas and CP were lower compared to the control soil, effects were, in general, not significant. Fumigation with MeBr+ CP and alternatives reduced the activities of purified reference enzymes by 13, 76 and 28% for acid phosphatase, betaglucosidase and arylsulfatase, respectively. Mean enzyme protein concentrations in fumigated agricultural soils were 2.93, 0.105, and 2.95 mg protein kg(-1) soil for acid phosphatase, beta-eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. glucosidase and arylsulfatase, respectively, all lower than in control soils. Organic matter turnover and nutrient cycling, and thus, the long-term productivity of agricultural soils seem unaffected in soils repeatedly fumigated with PrBr, InLine, Midas and CP. (C)

The effectiveness of di-nitrogen tetroxide (DNTO) as a substitute for methyl bromide in controlling soil-borne nematodes, fungi and bacteria was evaluated. Application of DNTO to soil packed into columns resulted in a reduction of the bacterial population by three orders of magnitude within 1 h, and a complete elimination after 2 h. The same treatment resulted in the destruction of all fungi and nematodes within 10 min. The most effective treatment (30 min for bacteria elimination and 10 min for nematode and fungi elimination) was achieved in soil with a low moisture level (4%), at a pumping rate of 0Á1 ml/min DNTO. In a single microplot trial, using 300 g/m 2 DNTO, a significant reduction of nematodes was observed. Lack of phytotoxicity of DNTO was demonstrated using tomato plants. In addition, at the above-mentioned soil moisture and DNTO levels, the DNTO is readily converted into nitrate. Hence, the use of DNTO can supply a considerable part of the nitrogen fertiliser requirement of the treated crops and only a small fraction of it is liberated into the atmosphere.