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Chemical fumigation and biofumigation are used to reduce soil-borne diseases in agricultural production systems; however, nontargeted soil microorganisms may also be affected. This study compared the effects of chemical fumigation, either used alone or combined with an organic amendment, and biofumigation on soil bacterial community diversity and composition under controlled conditions over 160 days. Treatments included: fumigation with chloropicrin (CP), fumigation with metam sodium used alone (MS) or combined with barley plant residues (MSBR), biofumigation with mustard plant residues, addition of barley plant residues and untreated control. Biofumigation had a greater impact on bacterial diversity at early time points, transiently decreasing species evenness and yielding the most dissimilar β-diversity after 3 days. MS fumigation did not affect bacterial diversity indices; however, MSBR transiently decreased species evenness after 8 days. CP-treated soil had decreased species evenness that did not recover over time and had the most dissimilar β-diversity at the end of the incubation compared with all other treatments. This study demonstrated that CP fumigation had the greatest and most persistent impact on bacterial diversity, whereas MS fumigation and biofumigation led to transient decreases in bacterial diversity. [ABSTRACT FROM AUTHOR]

Chemical fumigation is used to reduce soil-borne diseases in agricultural production systems; however, non-targeted soil microorganisms may also be affected. This study investigated the effects of chemical fumigation and substrate carbon (C) availability on the soil bacterial and fungal community diversity under controlled conditions over 128 days. This study consisted of a 3 × 3 factorial arrangement of three fumigant treatments (fumigation with chloropicrin [CP], metam sodium [MS], or no fumigation) and three soil amendment treatments (amendment with young barley, mature barley, or no amendment). MS fumigation transiently decreased bacterial species evenness when combined with young barley residues; however, it did not affect fungal diversity indices. CP fumigation, regardless of soil amendment or substrate C availability, decreased bacterial species evenness and richness that did not recover over time. However, CP fumigation only decreased fungal species evenness and richness when combined with young or mature barley residues. Although all treatments resulted in a bacterial and fungal community that was significantly dissimilar to the non-fumigated unamended soil, CP fumigated soils had the most dissimilar bacterial and fungal β-diversity after 128 days. This study demonstrated that the addition of young or mature barley residues to chemically fumigated soil did not recover microbial diversity. Instead, the addition of plant residues to chemically fumigated soil had a greater impact on microbial diversity and community composition compared to chemical fumigation used alone, subsequently promoting a less diverse and selective community for both fumigation and organic C additions. • MS only decreased bacterial species evenness when combined with young barley. • MS did not affect fungal species evenness or richness. • CP decreased bacterial and fungal species evenness and richness. • CP greatly altered the soil bacterial and fungal community composition overtime. • CP applied alone or with barley plant residues greatly impacted the soil microbiome. [ABSTRACT FROM AUTHOR]

• Soil microcosms were fumigated and amended with young or mature barley residues. • Fumigation delayed the flux of CO 2 and N 2 O in soils amended with young barley. • Fumigation decreased the percentage of apparent plant residue decomposition. • Amendment with mature barley caused net N immobilization, regardless of fumigation. • Chloropicrin had the greatest impact on soil C and N dynamics in amended soils. Chemical fumigation is used to reduce soil-borne diseases in agricultural production systems; however, soil carbon (C) and nitrogen (N) dynamics may also be affected. This study investigated the effects of chemical fumigation and substrate C availability on soil respiration, soil nitrous oxide (N 2 O) production, and soil inorganic N concentrations under controlled conditions over 128 days. This study consisted of a 3 × 3 factorial arrangement of three fumigant treatments (fumigation with chloropicrin, metam sodium, or no fumigation) and three soil amendment treatments (amendment with young barley, mature barley, or no amendment). In soils amended with young barley, chemical fumigation delayed the maximum rate of soil respiration and N 2 O production by five days compared to the amended non-fumigated soil. Additionally, chloropicrin fumigation decreased cumulative soil respiration in amended soils, regardless of substrate C availability, compared to non-fumigated soil. Chemical fumigation used alone or combined with young barley amendments significantly inhibited nitrification compared to non-fumigated soil, whereas amendment with mature barley resulted in N immobilization, regardless of chemical fumigation. This study demonstrated that chemical fumigation significantly affected soil C and N dynamics in soils amended with high and low available C substrates, indicating decreased microbial activity and significant implications for soil function. [ABSTRACT FROM AUTHOR]