Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Micheal D. K. Owen

Second Advisor

Thomas E. Loynachan


A four year field experiment was conducted from 1994 through 1997 to elucidate the effects of tillage, cropping systems, and weed management regimes on land previously under the conservation reserve program (CRP). A total of 13 weed species comprised the weed seedbank which was dominated by broadleaf weeds. The seedbank for common lambsquarters and Amaranthus species were 10,365 and 31,925 seeds M-2 in the first year out of CRP, respectively. The Amaranthus species seedbank continued to increase and climaxed at 51,670 seeds M-2 in 1996. The seedbank for Setaria species increased 19 fold between 1994 and 1997. Tillage and cropping systems did not influence weed populations or seedbanks throughout the duration of the study. Weed management had the greatest influence on weed population changes, with the no herbicide treatment having higher weed populations and weed seedbank compared to band and broadcast treatments. Band and broadcast herbicide treatments had similar effects on weeds and weed seedbanks. Continuously cropped fields in Iowa had a larger weed seedbank compared to that in adjacent CRP land. The common larnbsquarters, pigweed species, and foxtail species seedbanks differed significantly in the nine Iowa crop yield reporting districts. Soil phosphorus levels were higher in no tillage system compared to conventional tillage. The land coming out of CRP is likely to have a larger broadleaf seedbank and fewer grasses. The resident soil fungus population was dominated by Fungi Imperfecti with 38 species in 18 genera. Trichoderma and Penicillium species had the highest population densities. Generally the no herbicide treatment had higher fungal population densities per gram of oven dried soil compared to band and broadcast treatments. Three genera of Zygomycetes and two species in one genus of Ascomycetes were identified.



Digital Repository @ Iowa State University,

Copyright Owner

Joel Felix



Proquest ID


File Format


File Size

118 pages