Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2005
Publication Date: 4/6/2006
Citation: Davis, A.S., Anderson, K.I., Hallett, S.G., Renner, K.A. 2006. Weed seed mortality in soils with contrasting agricultural histories. Weed Science. 54(2):291-297. Interpretive Summary: Many weeds produce copious quantities of seeds each year. When these seeds are mixed into the soil through tillage or precipitation, they form long-lived soil seedbanks. Soil seedbanks are the most common cause of ongoing weed infestations in arable fields, yet there are currently no tools available for directly controlling weed seedbanks. Conservation biocontrol of soil microbes may offer one solution to this problem. In this approach, crop and soil management practices are chosen to enhance degradation of weed seeds by naturally occurring soil microbes. We studied the relationship between weed seed mortality and soil microbial communities in bioassays using five soils with over ten years of contrasting agricultural management histories. Seeds of both study species, giant foxtail and velvetleaf, had the highest mortality rates in conventionally managed soils and lowest mortality rates in soils receiving compost amendments. Seed mortality of both giant foxtail and velvetleaf showed a strong correlation to management-related changes in the soil fungal community. These results demonstrate that soil management history, fungal community composition and weed seed mortality are linked, and suggest that conservation biocontrol may be a viable option for reducing weed seedbanks.
Technical Abstract: Conservation biocontrol has been proposed as a means of directly reducing weed seedbanks. In this approach, cropping systems are managed to enhance degradation of weed seeds by soil microbes. We examined the relationship between long-term agricultural management practices, soil fungal and bacterial communities, soil C:N ratio, soil particle size fractions, and weed seed mortality. Soil from five fields with over 10 years of contrasting agricultural management histories was used as an incubation medium for seeds of giant foxtail and velvetleaf in controlled environment bioassays. Soil management treatments included a conventional corn-soybean-wheat rotation, an organic corn-soybean-wheat rotation, a conventional corn-corn-soybean-wheat rotation, a reduced-synthetic input corn-corn-soybean-wheat rotation receiving composted manure as a soil amendment, and an early successional system managed with burning and mowing in alternate years. Seed mortality of giant foxtail and velvetleaf were greatest in the conventionally managed systems and lowest in the compost-amended corn-corn-soybean-wheat rotation. The carbon-rich amendment appeared to inhibit microbial attack of weed seeds. There was a strong negative correlation between the first principal component of the 18S region of the fungal ribosome and both giant foxtail (-0.52, P < 0.05) and velvetleaf (-0.57, P < 0.01) seed mortality. The similar strength and direction of these correlations indicate that seeds of the two species were affected similarly by changes in the soil fungal community. None of the other measured soil properties were correlated with weed seed mortality. These results demonstrate that soil management history, fungal community composition and weed seed mortality are linked.