Herbicide Performance and Weed Seedbank Dynamics as Affected by High Residue Conservation Agriculture Systems
Type of Degreethesis
Agronomy and Soils
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With the introduction of glyphosate-resistant crops in the late 1990’s, there has been widespread adoption of conservation agriculture systems throughout the southern portion of the United States, including Alabama. Beneficial aspects of conservation agriculture primarily include soil and water retention as well as reduced on-farm production costs. Weed population characteristics and management strategies under these reduced tillage practices have been shown to vary greatly in comparison to conventional agriculture systems. Understanding the extent of these variations is necessary in implementing successful weed control regimes in the future. The objectives of a greenhouse experiment was to identify the primary weed species within the weed seedbank as well as their relative densities under differing farming practices and landscape positioning; it was also conducted to determine the rate of preemergent herbicide interception by different levels of cover crop residue and subsequent weed suppression. Results showed the dominant weed species to be the winter annual, henbit (Lamium amplexicaule L.), comprising over 80% of total germinated weed seed. Both the upper and lower soil samples had statistically significant decreases in weed seed density in the no-till treatments compared to conventionally tilled plots. A two year experiment was conducted in Headland, Alabama and Dawson, GA to determine the extent of interception of pendimethalin by cover crop biomass and weed suppression within a peanut (Arachis hypogaea L.) production system. Soil sample extractions from three time intervals (7, 14, and 21 DAP) were analyzed using high performance liquid chromatography (HPLC) to determine pendimethalin present under varying residue treatments. Peanut yield was not negatively affected by cover crop residue at either site in the experiment. Pendimethalin recovery analysis revealed no significant losses of herbicide due to increased levels of cover crop residue. Weed control ratings indicated that, with increased biomass residue in comparison with winter fallow systems, cover crops offer increased and extended weed suppression capabilities. Both the Conservation Innovation Grant proposal and the Weed Science chapter included in this collection, along with the two previously mentioned experiments reveal the advantages offered to the agricultural community through the continued effort of researchers to expand the knowledge and improve upon current conservation practices in order to make conservation agriculture efficient, competitive, and profitable.