Degree Type


Date of Award


Degree Name

Master of Science




Sustainable Agriculture

First Advisor

Matt Liebman


Crop production in the Midwestern U.S. and Vietnam’s Mekong Delta requires sustainable and cost effective weed management strategies because both regions are grappling with increasing weed resistance to herbicides, and concerns over environmental damage from herbicides. Agroecological approaches that employ diverse cropping systems to subject weeds to multiple stress and mortality factors may provide reliable weed management that is cost efficient and less reliant on chemicals. Agroecological weed control is based on sound understanding of weed population dynamics, natural resources, and climate attributes, and thus is practical regardless of the level of technology to which farmers have access. We tested the effectiveness of cropping system diversification on weed control in a field experiment conducted in Boone County, Iowa, USA. We compared weed growth in three cropping systems (2-, 3- and 4-year rotation sequences) managed with two herbicide regimes (low and conventional input levels). For a given rotation system, the low herbicide regime, i.e. reduced herbicide inputs coupled with increased mechanical weed control, used 62% and 94% less herbicide active ingredient (kg a.i. ha-1) on corn and soybean, respectively, compared to the conventional regime. Averaged over herbicide regimes, the 3- and 4-year systems reduced herbicide use 33% and 50%, respectively, compared with the 2-year system. In 2014 and 2015, weed biomass was two-fold greater under the low herbicide regime compared with the conventional regime, and six- to seven-fold greater in the 3-year and 4-year rotations than the 2-year rotation. However, increases in weed biomass did not affect corn or soybean yield. We also assessed whether intensity of soil sampling used in previous research was precise enough for measuring weed seedbank density. A soil sampling intensity of ~ 87 cm2/1732 cm3 (surface area/volume), was acceptable for estimating total weed seed density, and soil material from 36 cores taken within one experimental unit could be combined for single processing. Results of our work indicate that multitactic weed management strategies within diversified cropping systems offer opportunities to reduce reliance on herbicides. Nonetheless, additional research is needed for further improvement of non-chemical weed suppression tactics, and for better understanding of the effects of cropping system diversification on weed population and community dynamics.


Copyright Owner

Huong Nguyen



File Format


File Size

107 pages