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Rhizobacteria have the potential to suppress plant growth. We evaluated the effect of native pseudomonads on downy brome (Bromus tectorum L.), a troublesome weed in small‐grain‐producing lands. Pseudomonas spp. were isolated from winter wheat (Triticum aestivum L.) and downy brome roots and tested to determine their potential as biological control agents for this weed. Pseudomonads were screened in agar and soil for inhibition of downy brome root growth and lack of inhibition of winter wheat root growth. Of more than 1000 isolates tested, 81 inhibited downy brome and not winter wheat in the agar seedling bioassay. Six isolates consistently inhibited downy brome growth and not winter wheat in soil contained in pots in the growth chamber. In nursery field trials in which downy brome was planted in rows and adequately fertilized, some of the bacterial isolates reduced downy brome populations up to 30% and shoot dry weight up to 42%. Field studies were also conducted at three sites in eastern Washington in which brome‐inhibitory bacteria were applied to wheat fields infested with natural populations of downy brome. Of the three isolates studied in the field, two reduced plant populations and aboveground growth of downy brome up to 31 and 53%, respectively, compared with noninoculated controls. At two of the three locations, winter wheat yields were increased 18 to 35% because of the suppression of downy brome growth. Brome‐suppressive bacteria isolated from the rhizoplane of winter wheat and downy brome can be used as biological control agents for downy brome.

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Biodynamic agriculture is a unique organic farming system that utilizes, in addition to the common tools of organic agriculture, specific fermented herbal preparations as compost additives and field sprays. The objective of this work was to determine whether biodynamic compost or field spray preparations affect the soil biological community in the short term, beyond the effects of organic management. Four fertilizer options: (i) composted dairy manure and bedding (organic fertilization), (ii) the same material composted with biodynamic compost preparations, (iii) mineral fertilizers, and (iv) no fertilizer were investigated with and without the biodynamic field spray preparations. Both biodynamic and nonbiodynamic composts increased soil microbial biomass, respiration, dehydrogenase activity, soil C mineralized in 10 d (MinC), earthworm (Lumbricus terrestris) population and biomass, and metabolic quotient of respiration per unit biomass (qCO2) by the second year of study. No significant differences were found between soils fertilized with biodynamic vs. nonbiodynamic compost. Use of biodynamic field sprays was associated with more MinC and minor differences in soil microbial fatty acid profiles in the first year of study. There were no other observed effects of the biodynamic preparations. Organically and biodynamically managed soils had similar microbial status and were more biotically active than soils that did not receive organic fertilization. Organic management enhanced soil biological activity, but additional use of the biodynamic preparations did not significantly affect the soil biotic parameters tested.