PARENT SESSION
Oral Session # 14: Agro-Ecology I.
Presiding: C Salo
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 100.
Species composition of the weed seedbank with varying crop and soil management.
Sosnoskie, Lynn *,1, Herms, Catherine1, Cardina, John1, 1 The Ohio State University, Wooster, OH
ABSTRACT- We characterized weed density, species diversity, and community composition in the soil seedbank in a long-term study with three crop sequences (continuous corn, corn-soybean, corn-oat-hay) and three tillage systems (conventional-, minimum- and no-tillage). We identified and counted germinable seeds in the top 10 cm of soil in early spring (1997-1999) to calculate seed density, species diversity indices, and a synthetic relative importance index for each species. Repeated measures ANOVA showed that total seed density differed with crop sequence and tillage system, with an interaction among these factors and years. Seed density was higher in the continuous corn than the other crop sequences (two of three years), and higher in no-tillage than other tillage systems. There were more species in the corn-oat-hay sequence than in corn-soybean or continuous corn, and species diversity declined with increasing soil disturbance. Canonical discriminant analysis showed that the first axis explained 40 to 60% of the within-subjects variation for species composition and was strongly associated with crop sequence. Canonical scores for the plots planted to corn-oat-hay clustered separately from those in continuous corn and corn-soybean. These trends were statistically significant according to Mahalanobis squared distances and were confirmed with cluster analysis. Tillage systems did not show a similar degree of separation, suggesting that crop rotation was more important in influencing community composition. After one cycle of crop rotation using glyphosate-tolerant corn and soybean varieties, these patterns of community composition were no longer apparent, suggesting that the seedbank responded quickly to altered management. Weed control and other cultural practices in the corn-oat-hay system favored species with life-history characteristics that differ from species more commonly associated with corn and soybean systems.
Key words: plant community, species diversity, seedbank, canonical discriminant analysis