Document: FAB-3-61-5

Weed community dynamics in response to different agricultural management practices.

MENALLED, F.D.*, K.L.GROSS and M.HAMMOND

Michigan State University, East Lansing, MI 48824, USA ¹

Abstract:
Integrated weed management programs require a clear understanding of the mechanisms influencing the establishment, growth and reproduction of non-crop plants (weeds) in agroecosystems. This study evaluates the effect of four different agricultural management practices on the aboveground and seedbank weed communities at the KBS-LTER agricultural site, Michigan. Weed species composition and biomass was assessed over two complete 3 yr crop rotation cycles (corn-soybean-wheat) in four annual cropping treatments: (1) high chemical input, moldboard plowed; (2) high chemical input, no tillage; (3) low chemical input, moldboard plowed; and (4) no chemical input, moldboard plowed. The abundance and composition of the viable weed seedbank was evaluated at the beginning and end of this study. Data were used to answer the following questions: i) Do management practices influence aboveground and seedbank weed community characteristics? ii) Do different agricultural practices favor the establishment of more predictable weed communities? iii) Is variation in the aboveground weed community and reflected in weed seedbank composition? Chemical input was the main factor conditioning aboveground and seedbank weed community characteristics. A multivariate ordination of the aboveground community showed that use of herbicides influenced the abundance, species composition and predominance of different life forms in these treatments. Perennial herbs were most prevalent in the low and no-chemical input treatments, whereas annual grasses increased in the chemical treatments. The weed species composition in the low and no-chemical treatments was more predictable across years than in the high chemical treatments. Between 1993 and 1999, there was an increase in the total number of weed seeds and species in high chemical treatments. During the same period, the species richness and number of viable seeds in the seedbank declined in the no- and low-chemical treatments. These results suggest that initial shifts in the abundance and composition of the weed community may not reflect the long-term dynamics of these communities under different types of agricultural management.

Keywords: Agroecosytems; herbicides, weed community dynamics; viable weed seedbank; weed management; temporal patterns, weed shift

This abstract is being presented at: 3:45 PM in session:
Oral Session #31: Agroecology.