Agronomy and Horticulture Department


First Advisor

John Lindquist

Date of this Version



A THESIS Presented to the Faculty of The Graduate College at The University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professor John Lindquist. Lincoln, Nebraska: May, 2018

Copyright 2018 Koffi Badou Jeremie Kouame


Common ragweed (Ambrosia artemisiifolia L.) and common waterhemp (Amaranthus rudis Sauer) are two problematic weeds for soybean producers in the United States. Both weeds have evolved resistance to many herbicides, including glyphosate. It is therefore essential to understand how these weeds in mixture impact soybean growth and yield and also how they deplete soil moisture in rainfed and irrigated cropping systems. The objectives of this research were to: (i) understand the influence of variable water supply on soybean yield loss in mixture with ragweed and waterhemp, (ii) quantify the influence of variable water supply on soybean growth in mixture with ragweed and waterhemp, and (iii) measure the effect of multispecies interference on soil water content. A field study was conducted over two years in order to model soybean growth and yield loss as influenced by common ragweed and common waterhemp density and irrigation level. Soybean yield loss and growth, and available soil water content were not affected by irrigation in 2016. Irrigation increased soybean weed-free yield, soybean weed-free LAI and total aboveground biomass, and soil water content in 2017. Relative leaf area at R1 and R3 soybean growth stages were the best descriptors of soybean yield loss.

Advisor: John L. Lindquist