Cropping Systems Effect On Weed Seed Mortality.

Weed management in arable fields involves all practices that have an effect on weeds above and below the soil surface. The soil seedbank is the main source for future weed infestations, and developing diverse strategies to deplete it is particularly important. Because weed seed mortality is related to soil management history and microbial community composition, we tested the hypothesis that the more diverse rotation corn-soybean-oat/alfalfa-alfalfa has a greater effect on giant foxtail (Setaria faberi) and velvetleaf (Abutilon theophrasti) seed decay compared to a conventional corn-soybean rotation. The study was conducted during 2008 and 2009 in a multiyear, 9-ha field experiment located at Iowa State Universtiy‘s Marsden Farm, in Boone, IA. In this site, different crop rotations were established in 2002 in a randomized complete block design where each crop phase of each rotation is present every year. We buried sets of mesh bags, containing soil and seeds of either of the two weeds, in the corn phase of the two rotations at 2 and 20 cm deep. We exhumed sets of bags at ten different times during the season and the seeds recovered were classified as germinated, dormant or decayed. In 2008, we found a higher foxtail seed decay in the 4-year rotation compared to the 2-year rotation (29% vs. 26%, respectively, p<0.0150), and higher seed mortality on the first 2 cm of the soil compared to 20 cm deep (p=0.0506). In 2009, in contrast, no seed mortality was detected. No significant differences were determined between cropping systems (p=0.6314) or burial depths (p=0.1051) on velvetleaf mortality in neither of both years. To further evaluate the effect of these crop rotations on seed mortality, this study will continue for one more year, and three different seedlots of each weed species harvested in consecutive years will be evaluated to determine possible causes of seed decay variability.