Anaerobic Soil Disinfestation Research Articles

Role of substrate decomposability and volatile fatty acids in anaerobic soil disinfestation activity against Sclerotinia sclerotiorum

Role of substrate decomposability and volatile fatty acids in anaerobic soil disinfestation activity against <i>Sclerotinia sclerotiorum</i>

Methods for Management of Soilborne Diseases in Crop Production

The significant problems caused by soilborne pathogens in crop production worldwide include reduced crop performance, decreased yield, and higher production costs. In many parts of the world, methyl bromide was extensively used to control these pathogens before the implementation of the Montreal Protocol—a global agreement to protect the ozone layer. The threats of soilborne disease epidemics in crop production, high cost of chemical fungicides and development of fungicide resistance, climate change, new disease outbreaks and increasing concerns regarding environmental as well as soil health are becoming increasingly evident. These necessitate the use of integrated soilborne disease management strategies for crop production. This article summarizes methods for management of soilborne diseases in crop production which includes the use of sanitation, legal methods, resistant cultivars/varieties and grafting, cropping system, soil solarization, biofumigants, soil amendments, anaerobic soil disinfestation, soil steam sterilization, soil fertility and plant nutrients, soilless culture, chemical control and biological control in a system-based approach. Different methods with their strengths and weaknesses, mode of action and interactions are discussed, concluding with a brief outline of future directions which might lead to the integration of described methods in a system-based approach for more effective management of soilborne diseases.

Temporal Responses of Microbial Communities to Anaerobic Soil Disinfestation

Anaerobic soil disinfestation (ASD) is an organic amendment-based management tool for controlling soil-borne plant diseases and is increasingly used in a variety of crops. ASD results in a marked decrease in soil redox potential and other physicochemical changes, and a turnover in the composition of the soil microbiome. Mechanisms of ASD-mediated pathogen control are not fully understood, but appear to depend on the carbon source used to initiate the process and involve a combination of biological (i.e., release of volatile organic compounds) and abiotic (i.e., lowered pH, release of metal ions) factors. In this study, we examined how the soil microbiome changes over time in response to ASD initiated with rice bran, tomato pomace, or red grape pomace as amendments using growth chamber mesocosms that replicate ASD-induced field soil redox conditions. Within 2 days, the soil microbiome rapidly shifted from a diverse assemblage of taxa to being dominated by members of the Firmicutes for all ASD treatments, whereas control mesocosms maintained diverse and more evenly distributed communities. Rice bran and tomato pomace amendments resulted in microbial communities with similar compositions and trajectories that were different from red grape pomace communities. Quantitative PCR showed nitrogenase gene abundances were higher in ASD communities and tended to increase over time, suggesting the potential for altering soil nitrogen availability. These results highlight the need for temporal and functional studies to understand how pathogen suppressive microbial communities assemble and function in ASD-treated soils.

Economic Analysis of Anaerobic Soil Disinfestation for Open-field Fresh-market Tomato Production in Southwest and North Florida

With the phase-out of methyl bromide due to its impact on ozone depletion, research has focused on developing alternative chemical and biologically based soil disinfestation methods. Anaerobic soil disinfestation (ASD) was developed to control plant-parasitic nematodes, weeds, and soilborne pathogens. However, whether farmers will adopt ASD methods on a large scale is unknown. This study evaluates the economic viability of using ASD in open-field, fresh-market tomato (Solanum lycopersicum) production, drawing on data from field experiments conducted in 2015 in Immokalee, FL, and Citra, FL. The experiment included three treatments: chemical soil fumigation (CSF), ASD1 [the standard ASD treatment with 1482 gal/acre molasses and 9 tons/acre composted poultry litter (CPL)], and ASD0.5 (the reduced rate ASD treatment with 741 gal/acre molasses and 4.5 tons/acre CPL). Results from the economic analysis show that ASD treatments require higher labor costs than CSF regarding land preparation and treatment application. However, yields from ASD treatments are higher than those resulting from CSF, and the improvement in yield was enough to offset the increased labor costs. Relative to CSF, ASD0.5, and ASD1 achieved additional net returns of $630.38/acre and $2770.13/acre, respectively, in Immokalee, FL. However, due to unexpected conditions unrelated to soil treatments, the net return of ASD1 was lower than that of CSF in Citra, FL. Breakeven analysis indicates that ASD treatments would remain favorable even with an increase in the molasses price. However, when the tomato price is low, ASD could potentially lose its advantage over CSF.

Implementation of Anaerobic Soil Disinfestation in Florida Tomato Production

Anaerobic soil disinfestation (ASD) is a relatively new technique that appears to be a promising tool for soilborne pest management and crop production improvement. This new 5-page publication of the UF/IFAS Horticultural Sciences Department is intended to introduce ASD for Florida vegetable growers. Written by Bodh R. Paudel, Francesco Di Gioia, Qiang Zhu, Xin Zhao, Monica Ozores-Hampton, Marilyn E. Swisher, Kaylene Sattanno, Jason C. Hong, and Erin N. Rosskopf. https://edis.ifas.ufl.edu/hs1345

Soil inoculation with Trichoderma asperellum, T. harzianum or Streptomyces griseoviridis prior to anaerobic soil disinfestation (ASD) does not increase ASD efficacy against Sclerotium rolfsii germination

Studies on anaerobic soil disinfestation (ASD), a non-chemical alternative to soil fumigants for controlling plant diseases caused by soilborne pathogens, have shown that ASD increases populations of beneficial microorganisms with activity against plant pathogens, including species of Trichoderma and Streptomyces, which are known to parasitize sclerotia of Sclerotium rolfsii. However, studies on ASD effectiveness paired with inoculation of Trichoderma and Streptomyces are lacking. This study compared the effects of ASD, soil incorporation of antagonists [Trichoderma asperellum, T. harzianum (RootShield®), Streptomyces griseoviridis (Mycostop®) and T. harzianum + S. griseoviridis], and ASD + soil incorporation of antagonists at the initiation of ASD treatment, on sclerotial germination and colonization. The effect of ASD and soil incorporation of antagonists on abundance of Trichoderma spp., actinomycetes, and Bacillus spp. in soil were assessed. In contrast to the negative effect of ASD on sclerotial germination, we observed positive or no effect of ASD alone on populations of beneficial microorganisms evaluated. ASD treatment that included addition of T. asperellum or T. harzianum did not increase colonization of sclerotia by Trichoderma spp. compared to ASD alone, whereas ASD treatment with inoculation of S. griseoviridis did increase sclerotia colonization by actinomycetes. Indigenous soil actinomycete populations were suppressed by incorporation of T. asperellum and T. harzianum during ASD treatment. Soil abundance of T. harzianum was increased by ASD treatment, and further increased by T. harzianum inoculation at ASD treatment initiation. Inoculation of T. asperellum, T. harzianum, or S. griseoviridis at ASD treatment did not further reduce germination of sclerotia of S. rolfsii, indicating that addition of these microorganisms to soil prior to ASD treatment is unlikely to improve ASD treatment efficacy against pathogens with resistant sclerotial survival structures.

Temporal Dynamics of the Soil Metabolome and Microbiome During Simulated Anaerobic Soil Disinfestation.

Significant interest exists in engineering the soil microbiome to attain suppression of soil-borne plant diseases. Anaerobic soil disinfestation (ASD) has potential as a biologically regulated disease control method; however, the role of specific metabolites and microbial community dynamics contributing to ASD mediated disease control is mostly uncharacterized. Understanding the trajectory of co-evolutionary processes leading to syntrophic generation of functional metabolites during ASD is a necessary prelude to the predictive utilization of this disease management approach. Consequently, metabolic and microbial community profiling were used to generate highly dimensional datasets and network analysis to identify sequential transformations through aerobic, facultatively anaerobic, and anaerobic soil phases of the ASD process and distinct groups of metabolites and microorganisms linked with those stages. Transient alterations in abundance of specific microbial groups, not consistently accounted for in previous studies of the ASD process, were documented in this time-course study. Such events initially were associated with increases and subsequent diminution in highly labile metabolites conferred by the carbon input. Proliferation and dynamic compositional changes in the Firmicutes community continued throughout the anaerobic phase and was linked to temporal changes in metabolite abundance including accumulation of small chain organic acids, methyl sulfide compounds, hydrocarbons, and p-cresol with antimicrobial properties. Novel potential modes of disease control during ASD were identified and the importance of the amendment and “community metabolism” for temporally supplying specific classes of labile compounds were revealed.

Genetic Soil Disinfestation, A Conceptual Framework to Reduce Inoculum Potential of Soilborne Plant Pathogens

Soilborne pathogens are major constraints to the production of many food and non-food crops worldwide. A wide array of strategies are employed to reduce the activities of soilborne pathogens including chemical and non-chemical methods such as solarization, fumigation, anaerobic soil disinfestation, and soil chemical treatment. This article succinctly describes these methods and proposes the concept of “genetic soil disinfestation” as an additional innovative approach for managing soilborne pathogens. Although many components of “genetic soil disinfestation” include well known and familiar tools such as crop rotation, the concept of “genetic soil disinfestation” redefines cropping systems in a unified perspective with focus on using a genetic approach to optimize the attributes of hosts and nonhosts that significantly reduce the populations of soilborne plant pathogens and the efficiency of invasiness of these pathogens.

Production of \u03b2-1,3-glucanase and chitosanase from clostridial strains isolated from the soil subjected to biological disinfestation

Biological soil disinfestation (BSD) or anaerobic (reductive) soil disinfestation (ASD/RSD) is a bioremediation method used to eliminate soil-borne plant pathogens by exploiting the activities of anaerobic bacteria in soil. In this study, two obligate anaerobic bacterial strains isolated from BSD-treated soil and identified as Clostridium beijerinckii were examined for their abilities to suppress the spinach wilt disease pathogen (Fusarium oxysporum f. sp. spinaciae) as a representative soil-borne fungal plant pathogen. Both strains degraded β-1,3-glucan and chitosan, two major polysaccharide components of ascomycetes fungal cell wall, supplemented in the medium. β-1,3-Glucanase was detected in the supernatants of cultures supplemented with different types of glucan. Similarly, chitosanase was detected in cultures supplemented with chitosan. Both the enzyme activities were also detected in cultures containing glucose as a substrate. Live cells of F. oxysporum f. sp. spinaciae that were co-incubated with each anaerobic strain under anaerobic conditions using glucose as a substrate died during incubation. Freeze-dried dead fungal biomass of the pathogen, when added to the culture, supported good growth of both anaerobes and production of both enzymes. Severe and nearly complete degradation of both live and dead fungal cells during incubation with anaerobic bacteria was observed by fluorescence microscopy. When individual anaerobic bacterial strain was co-incubated with live pathogenic fungal cells in wheat bran, a popular material for BSD-treatment, both the strains grew well and killed the fungal pathogen promptly by producing both enzymes. These results indicate that both the bacterial strains attack the fungal cells by releasing extracellular fungal cell wall-degrading enzymes, thereby eliminating the pathogen.

Effects of anaerobic soil disinfestation carbon sources on soilborne diseases and weeds of okra and eggplant in Nepal

Soilborne diseases, root-knot nematodes (Meloidogyne spp.), and weeds are the major yield-limiting factors in okra (Abelmoschus esculentus) and eggplant (Solanum melongena) production in Nepal. Anaerobic soil disinfestation (ASD) is a promising technique in developed countries to control soilborne pests, but it has not been tested in many developing countries. Experiments were conducted in the western plain region of Nepal in okra and eggplant from March to July 2016 and October 2016 to April 2017 (eggplant only) to compare locally available carbon sources for efficacy in ASD. Experiments were conducted in a randomized complete block design with three replicates of seven amendments (molasses 2 kg m−2, rice bran 2 kg m−2, rice bran 1 kg m−2 plus molasses 1 kg m−2, raw goat manure 2 kg m−2, mustard (Brassica campestris var. toria) cake 1.5 kg m−2, lentil (Lens esculenta) husks 2 kg m−2, and berseem clover (Trifolium alexandrinum) leaves 3 kg m−2), and a non-amended, uncovered (aerobic) control in the first year. Lentil husks and berseem clover were replaced by wheat bran (2 kg m−2) and wheat bran (1 kg m2) plus molasses (1 kg m−2) in the second year. Carbon sources were incorporated into soil followed by irrigation to saturation, and plots were covered with white plastic sheeting for 21 days. Significantly lower Fusarium wilt incidence, root-knot disease severity, and weed biomass were observed in ASD-treated eggplant plots compared to the control in 2016; disease, root-knot and weed pressure were low in 2017 and differences were not significant. Root knot disease severity and weed biomass were significantly reduced compared to the control in ASD-treated okra plots, depending on the carbon source used. With the exception of plots amended with molasses (eggplant, 2017) or molasses alone or combined with rice bran (okra), significantly higher fruit yields were observed in ASD-treated plots than in control plots. ASD appears to have great potential in Nepal because of its broad-spectrum impact on multiple soilborne pests and ready availability of inexpensive local inputs.

Anaerobic Soil Disinfestation to Manage Soilborne Diseases in Muck Soil Vegetable Production Systems.

Anaerobic soil disinfestation (ASD) was evaluated as a tool for managing the root-knot nematode Meloidogyne hapla in lettuce (Lactuca sativa) and clubroot disease, caused by Plasmodiophora brassicae, in mustard greens (Brassica juncea) produced on Ohio muck soils in Huron and Stark Counties. In two consecutive years of field trials, wheat bran (20.2 Mg ha-1), molasses (10.1 Mg ha-1), and wheat bran (20.2 Mg ha-1) plus molasses (10.1 Mg ha-1) were assessed as ASD carbon sources and compared with nonamended controls. Data were collected from plants grown in the field and from plants grown in field-treated soils in growth chamber-based post-ASD bioassays. Anaerobic conditions developed in ASD-treated soils in both trial years, as indicated by polyvinyl chloride pipes painted with an iron oxide paint. Soil pH did not decrease during ASD at the Huron County site of the mustard greens clubroot trials in either trial year but soil pH decreased significantly during ASD in Stark County soils treated with ASD with either wheat bran or wheat bran plus molasses compared with control soils in both trial years. Impacts of ASD on plant biomass were inconsistent in direct field measurements; however, significantly higher biomasses were observed in lettuce and mustard greens grown in bioassay soils collected from plots treated with ASD with wheat bran-based amendments compared with plants grown in soils from control plots. Based on direct field measurements and bioassays, the use of ASD with any carbon source led to significant reductions in root-knot nematode galling on lettuce compared with controls. Reductions in clubroot severity in mustard greens following ASD were less consistent; however, significant reductions in clubroot severity were observed in the field in one trial year and in both years of bioassays. The results of these studies indicate that ASD is a promising tool for managing soilborne diseases in muck soil vegetable production systems.

Assessing Anaerobic Soil Disinfestation as a Control Tactic for Delia radicum (Diptera: Anthomyiidae) in California Brussels Sprouts.

Fumigants are often the primary material used to manage plant disease agents, soil-borne arthropods, and weeds in California agriculture, particularly in the absence of crop rotation. However, some fumigants have come under increased regulatory scrutiny and are therefore no longer available for use. We tested two biologically based preplant crop-protection fumigant alternatives for their effectiveness in reducing populations of Delia radicum (L.), a soil-borne insect pest of cole crops. Laboratory and field tests compared pest survival in untreated control soil with survival under anaerobic soil disinfestation (ASD), which is induced by incorporating a carbon source (rice bran or grape pomace) and subsequently saturating the soil with water. We also measured and compared the effects of standard grower practices (fumigation), ASD and biofumigation (mustard seed meal incorporated before planting), and untreated control soils on fly abundance, pupal survival, and root damage in Brussels sprout fields. In both laboratory and field studies, D. radicum pupal survivorship was reduced in ASD-treated soils relative to control soils. Pupal survivorship of Musca domestica (L.) (Diptera: Muscidae), which was used as a proxy for D. radicum in some field experiments, was also reduced in ASD- and biofumigation-treated soils, when compared with untreated control soils. These results indicate that fumigant alternatives may provide useful insect pest management opportunities for compatible cropping systems.

Shifts in Soil Bacterial Communities as a Function of Carbon Source Used During Anaerobic Soil Disinfestation

Anaerobic soil disinfestation (ASD) is an organic amendment-based management practice for controlling soil-borne plant pathogens. Pathogen suppression appears to be carbon source-dependent and mediated by bacteria that proliferate and produce volatile organic compounds, as well as physico-chemical changes (i.e., elevated temperature, lowered redox potential and pH, release of metal ions) in soil. ASD is under study for adoption in tree crops as a replacement for chemical-fumigation, but its widespread use is limited by incomplete understanding of its suppression mechanisms and high economic costs. The carbon substrate is one component of the ASD process that can be optimized to enhance effectiveness and affordability. While rice bran is currently the standard carbon source used for ASD, we identified three alternative substrates (molasses, mustard seed meal, and tomato pomace) that are similar in efficacy to rice bran at generating and sustaining soil anoxia and reducing populations of introduced plant pathogens. Here, we used replicated ASD field trials to determine if rice bran and the alternative carbon substrates would elicit similar soil bacterial communities (characterized via amplicon sequencing of the 16S rRNA gene v4 region) and to assess if any observed community shifts were consistent across repeated trials. We found significant, but minimal differences in community composition between ASD carbon treatments (F4,30 = 2.80, P 5 log2 fold change) in all ASD treatments compared to untreated controls. A group of shared core genera belonging to the Clostridiales and Selenomonadales were identified in both trials and constituted 22.6% and 21.5% of the communities. Bacterial taxa that were most responsive to ASD treatments had the genomic potential for denitrification, nitrogen fixation, and fermentation reactions that produce organic acids (such as acetate and butyrate) known to inhibit in vitro growth of plant pathogens based on predicted metagenomes. Together, these results indicate that reproducible and effective implementation of ASD is achievable with alternative carbon substrates to rice bran.

Effects of Anaerobic Soil Disinfestation on Sclerotinia sclerotiorum in Paraguay

The effects of anaerobic soil disinfestation (ASD) on Sclerotinia sclerotiorum sclerotia viability was tested in four field trials in Paraguay. Plots were amended with wheat bran (20.2 Mg/ha), molasses (10.1 Mg/ha), or wheat bran (20.2 Mg/ha) plus molasses (10.1 Mg/ha), saturated with water, and covered with black plastic mulch for 3 weeks. Control plots were not amended but were saturated and either covered (anaerobic control) or maintained uncovered (aerobic control). Tubes painted with iron oxide paint were placed in soils to assess soil reducing conditions. Sclerotia were buried 6 cm deep in treated and control soils along with temperature data loggers. After 3 weeks, the viability of sclerotia was significantly lower in all ASD-treated soils (4 to 52%) compared with the aerobic control soil (100%), regardless of the carbon source used. Sclerotial viability was also significantly reduced compared with anaerobic controls at three sites, depending on the carbon source used. A significant negative correlation between soil reducing conditions and sclerotia viability was observed at all sites. Wheat bran and molasses are widely available and inexpensive in Paraguay, and ASD with these carbon sources provides smallholder South American vegetable farmers with a new option for sustainable management of Sclerotinia and potentially other soilborne pathogens.

The families Ruminococcaceae, Lachnospiraceae, and Clostridiaceae are the dominant bacterial groups during reductive soil disinfestation with incorporated plant residues

Reductive soil disinfestation (RSD), alternatively called biological soil disinfestation or anaerobic soil disinfestation, is an environmentally friendly method used to control soil-borne diseases. Microorganisms are regarded as the key contributors for RSD; however, there is limited information on the relative importance of these microorganisms, which is essential for understanding the mechanisms underlying RSD. In this study, RSD was performed with four soils in a pot experiment, and the bacterial communities present during the RSD process were detected using MiSeq sequencing based on bacterial 16S rDNA. The results showed that RSD significantly changed the structure of the soil bacterial communities and reduced bacterial richness and diversity. The relative abundance of Firmicutes increased significantly, and the relative abundances of Actinobacteria and Acidobacteria decreased. Ruminococcaceae, Lachnospiraceae, and Clostridiaceae, which belong to Clostridiales within Firmicutes, were the three dominant bacterial families during RSD in most soils. Ruminococcaceae and Lachnospiraceae, rather than Clostridiaceae (previously identified as the key contributor), were strongly related to the pH decrease during RSD, which is considered an indicator for the accumulation of short-chain fatty acids. In addition to these bacterial groups, the families Sphingobacteriales, Bacillales, Burkholderiales, and Bacteroidales were enriched in some RSD-treated soils. In conclusion, the RSD treatment, soil type, and their interactions jointly influenced the bacterial communities and compositions in the RSD-treated soils.

Evaluating anaerobic soil disinfestation and other biological soil management strategies for open-field tomato production in Florida

AbstractIn the search for alternative practices to chemical soil fumigation (CSF), anaerobic soil disinfestation (ASD) has proven to be a promising tool for soil-borne pest management and crop production improvement. The ASD treatment with composted poultry litter (CPL) and molasses (M, a labile carbon source) was identified as an effective approach for a biologically based soil disinfestation system in tomato (Solanum lycopersicum L.) production in Florida. However, environmental and food-safety concerns are associated with animal manure-based amendments, which led to the exploration of composted yard waste (CYW) as a potential substitute for CPL in ASD application. In this study, field trials were conducted in Citra and Immokalee, FL to examine the effects of ASD using CYW, CPL and M compared with a commercially available microbial amendment system on root-knot nematodes, weeds, fruit yield and quality of fresh-market tomato. Treatments included (1) ASD with CPL (11 Mg ha−1) and M (6.9 m3 ha−1) (ASD0.5), (2) ASD with CYW (26.9 Mg ha−1) and M (CYW1 + M), (3) ASD with CYW (13.5 Mg ha−1) and M (CYW0.5 + M), (4) Soil Symphony Amendment (SSA), (5) CYW (26.9 Mg ha−1) alone (CYW1) and (6) a combination of CYW1 + SSA, in comparison with (7) untreated control and (8) CSF (Pic-Clor 60 at 224 kg ha−1). Cumulative soil anaerobiosis was greater in ASD0.5 compared with all the other treatments. The root-knot nematode gall index ratings on the tomato crop were significantly lower in CSF, ASD0.5, CYW1 + M and CYW0.5 + M than untreated control in Citra. Although CYW1 and SSA alone had a moderately suppressive effect on weed coverage and root-knot nematodes, their positive impact on crop performance was limited when used alone. ASD0.5, CYW1 + M and CSF had significantly higher marketable and total fruit yields than untreated control in both locations, while all treatments showed promising results in the Immokalee trial in comparison with untreated control. In general, few differences in major fruit quality attributes were found. Although using CYW in ASD was not as effective as CPL in creating soil anaerobic conditions, the enhanced crop performance in CYW1 + M and CYW0.5 + M suggests the potential of using CYW as an alternative source of organic amendment in combination with M to achieve benefits similar to those obtained with CPL-based ASD.

Anaerobic soil disinfestation as an alternative to soil fumigation for management of Prunus replant disease: effects on tree growth and yield

Anaerobic soil disinfestation as an alternative to soil fumigation for management of Prunus replant disease: effects on tree growth and yield

Effect of anaerobic soil disinfestation amendment type and C:N ratio on Cyperus esculentus tuber sprouting, growth and reproduction

SummaryAnaerobic soil disinfestation (ASD) is a cultural technique primarily targeted for control of soilborne plant pathogens, but can also impact weed propagules. A repeated pot study was conducted to evaluate ASD treatment impact on sprouting and growth of introduced Cyperus esculentus (yellow nutsedge) tubers using dry molasses‐based and wheat bran‐based amendment mixtures at four carbon‐to‐nitrogen (C:N) ratios (from 10:1 to 40:1) and compared with a non‐amended control. The mean percentage of sprouted tubers recovered after ASD treatment was lower for wheat bran‐based (42%) than dry molasses‐based (65%) amendments, and tuber production was 1.6‐fold higher in dry molasses‐based than wheat bran‐based treatments. The highest percentage of sprouted tubers (79%) and the highest mean production of large tubers (threefold higher than wheat bran‐based and 1.7‐fold higher than molasses‐based amendments) were observed for the non‐amended control. Tuber sprouting was significantly lower from all ASD treatments (regardless of amendment C:N ratio) compared with the non‐amended control at a 15 cm burial depth. New tuber production was lowest at C:N ratios of 10:1 and 20:1 and more than twofold higher in the non‐amended control. Wheat bran‐based amendments reduced above‐ground C. esculentus biomass compared with the non‐amended control and ASD treatments with molasses‐based amendments, and reduced below‐ground biomass compared with molasses‐based amendments. Above‐ground biomass was highest at amendment C:N ratio of 10:1, and below‐ground biomass was highest at amendment C:N ratio of 40:1 and the non‐amended control. ASD treatment with wheat bran‐based amendments at lower C:N ratios reduced tuber sprouting and reproduction compared with the non‐amended control, but not at rates high enough to use as a primary weed management tactic.

Organic management and cover crop species steer soil microbial community structure and functionality along with soil organic matter properties

It is well recognized that organic soil management stimulates bacterial biomass and activity and that including cover crops in the rotation increases soil organic matter (SOM). Yet, to date the relative impact of different cover crop species and organic vs. non-organic soil management on soil bacteria and fungi and on SOM quantity and quality remains to be tested. We used a long-term (10 years) full-factorial field experiment to test the combined effects of organic vs. conventional soil management with different cover crop species (oat or rye) and the legacy effects of seven soil health treatments (SHTs: treatments with compost, chitin, marigold, grass–clover, biofumigation or anaerobic soil disinfestation (ASD), and fallow as control) on microbial community biomass, structure and catabolic activity and on SOM quantity and quality (dissolved organic carbon (DOC), aromaticity and water repellency).Microbial community traits were assessed using PLFA/NLFA analyses and multi-substrate induced respiration. We found that organic soil management enhanced total microbial biomass by increasing bacterial, saprotrophic and arbuscular mycorrhizal fungal biomass; and increased total microbial catabolic activity, associated with maintaining high microbial efficiency (low qCO2). Effects of organic management were amplified by oat as cover crop, which enhanced the abundance of saprotrophic fungi resulting in a higher fungal:bacterial ratio. Total SOM concentration was similar among treatments, however the most easily accessible fraction, i.e. DOC, was higher in organic compared to conventional soils. Also, the aromaticity of the DOC was lower in organic than in conventional systems, which was associated with lower water repellency. There was a legacy effect of SHTs on fungal:bacterial ratio in that chitin and marigold showed higher fungal:bacterial ratio compared to compost, biofumigation and ASD even 6 years after the last application.We conclude that organic soil management enhances the abundance of all microbial groups and their total catabolic activity, associated with a higher concentration and lower aromaticity of dissolved organic matter. These effects can be enlarged by the growth of specific cover crops and the application of certain soil health treatments.

Anaerobic disinfestation induced changes to the soil microbiome, disease incidence and strawberry fruit yields in California field trials

Soil-borne disease management in California strawberry production systems has historically relied upon pre-plant soil fumigation. Restricted efficacy of currently available fumigant chemistries towards certain pathogens and regulatory action requiring increased buffer zones has stimulated interest in development of alternative disease control strategies. Anaerobic soil disinfestation (ASD) demonstrates activity toward an array of soil-borne pathogens, however, there exist limited field-scale trials examining efficacy in strawberry systems. Multiple mechanisms, including the activity of an altered soil microbiome, are reported to function in ASD-induced disease suppression but consistency of the microbial response across soils has not been examined. The present research reports ASD-induced changes in composition of the soil microbiome which occurred in a carbon input-dependent manner and were consistent in two of the three field trials conducted. At all three field sites, ASD treatments that transformed the microbiome were consistently associated with enhanced strawberry yields, but specific compositional attributes of the microbiome in effective treatments were not uniform among all sites. Enhanced yields were associated with control of specific soil-borne pathogens at a given site, however disease control was not uniformly attained across all pathogens resident to a given soil system. Findings demonstrate that informed selection of substrate to be used in ASD and knowledge of the targeted pathogen profile resident to the strawberry field soil will be essential to successful use of ASD in commercial agricultural production settings.