Anaerobic soil disinfestation (ASD) is a proven but relatively new strategy to control soil borne pests of horticultural crops through anaerobic decomposition of organic soil amendments. The ASD technique has primarily been used to control soil borne pathogens; however, this technique has also shown potential to control plant parasitic nematodes and weeds. ASD can utilize a broad range of carbon (C) amendments and optimization may improve efficacy across environments. In this context, a meta-analysis using a random-effects model was conducted to determine effect sizes of the ASD effect on soil borne pathogens (533 studies), plant parasitic nematodes (91 studies), and weeds (88 studies) compared with unamended controls. Yield response to ASD was evaluated (123 studies) compared to unamended and fumigated controls. We also examined moderator variables for environmental conditions and amendments to explore the impact of these moderators on ASD effectiveness on pests and yield. Across all pathogen types with the exception of Sclerotinia spp., ASD studies show suppression of bacterial, oomycete and fungal pathogens (59 to 94%). Pathogen suppression was effective under all environmental conditions (50 to 94%) and amendment types (53 to 97%), except when amendments were applied at rates less than 0.3 kg m-2. The ASD effect ranged from 15 to 56% for nematode suppression and 32 to 81% for weed suppression, but these differences were not significant. Significant nematode moderators included study type, soil type, sampling depth, incubation period, and use of mixed amendments. Weed suppression due to ASD showed significant heterogeneity for all environmental conditions, confirming that these studies do not share a common effect size. Total crop yield was not reduced by ASD when compared to a fumigant control and yield was significantly higher (30%) compared to an unamended control, suggesting ASD as a feasible option to maintain yield without chemical soil fumigants. We conclude ASD is effective against soil borne pathogens and while not conclusive due to a limited number of studies, we expect the same for nematodes and weeds given observed effect sizes. Findings should assist researchers in exploring ASD efficacy in particular environmental conditions and allow for development of standard treatment protocols.

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Growth chamber and field studies were conducted with organic amendment mixtures of carbon (C) and nitrogen (N) at C:N ratios 10:1, 20:1, 30:1, and 40:1 and amendment rates of C at 2, 4, 6, and 8 mg/g of soil (C:N ratio 30:1) to evaluate anaerobic soil disinfestation (ASD) effects on germination and colonization of Sclerotium rolfsii. In the growth chamber, sclerotial germination was reduced in all ASD treatments regardless of C:N ratio (0.6 to 8.5% germination) or amendment rate (7.5 to 46%) as compared with nonamended controls (21 to 36% and 61 to 96%, respectively). ASD treatment increased Trichoderma spp. colonization of sclerotia, with consistently higher colonization in ASD treatments with amendment rates of C at 2 or 4 mg/g of soil (>87% colonization) compared with nonamended controls (<50% colonization). In the 2014 field study, sclerotial germination was reduced by 24 to 30% in ASD treatments when compared with the nonamended control. Sclerotial colonization by Trichoderma spp. was predominant; however, other potential mycoparasites (i.e., Aspergillus spp., Fusarium spp., zygomycetes, and other fungi) were present in the field study. Amendment C:N ratios in the range of 10:1 to 40:1 were equally effective in reducing sclerotial germination and enhancing colonization by potentially beneficial mycoparasites of sclerotia.

Anaerobic 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 nonamended 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 belowground 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.

A meta-analysis of anaerobic soil disinfestation (ASD) efficacy against Fusarium oxysporum (Fo) and Fo f. sp. lycopersici (Fol) was conducted emphasizing effects of environment and organic amendment characteristics, and pot and field studies conducted on ASD amendment C:N ratio and soil temperature effects on Fol inoculum survival. In a pot study, two organic amendments, dry molasses-based or wheat bran-based applied at 4 mg C/g soil, with 40:1, 30:1, 20:1, and 10:1 C:N ratios, were evaluated against Fol at 15-25°C. This was followed by a pot study at temperature regimes of 15-25°C and 25-35°C, and two C:N ratios (20:1 and 40:1), and a field study at 40:1, 30:1, 20:1, and 10:1 C:N ratios, 30:1 C:N ratio at lower C rate (2 mg C/g soil), and an anaerobic control. Soil temperature above 25°C, and more labile amendments, increased ASD suppression of Fo/Fol in the meta-analysis. In pot studies, Fol survival was reduced for molasses-based mixtures at 20:1 and 30:1 C:N ratios, compared to wheat bran-based, but not compared to the anaerobic control. At 25-35°C, all ASD treatments suppressed Fol relative to controls. In the field, all ASD treatments reduced Fol survival compared to the anaerobic control, and 4 mg C/g soil amendment rates induced increased anaerobic conditions and higher Fol mortality compared to the 2 mg C/g soil rate. While amendment C:N ratios from 10 to 40:1 were similarly suppressive of Fo, lower temperatures reduced ASD effectiveness against Fo/Fol and further work is warranted to enhance suppression at soil temperatures below 25°C.

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