|Teasdale, John - Former Ars Employee|
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2014
Publication Date: 4/1/2015
Citation: Teasdale, J.R., Mirsky, S.B. 2015. Tillage and planting date effects on weed dormancy, emergence, and early growth in organic corn. Weed Science. 63(2):477-490. DOI: 10.1614/WS-D-14-00112.1.
Interpretive Summary: Reducing tillage in organic grain production is a priority for producers as it can reduce their labor, fuel costs, and soil erosion and degradation. Weed control is a significant problem for organic producers and this challenge is magnified when they attempt to reduce tillage. It is critical to understand how management practices (e.g., cover cropping, tillage, planting date) will drive weed germination, emergence, and survivorship as well as how to increase the competitiveness of the cash crop. Therefore, we set up field experiments for three years to evaluate how cover crop management (disk-kill vs. roll-kill) and corn planting date (early, intermediate, and late) influences weed seed dormancy, emergence, and early growth patterns of three weed species with varying life history strategies (grass, early and late emerging broadleaf). The early emerging broadleaf had a narrow emergence period and was either suppressed by the cover crop in the roll-kill, or terminated by tillage in the disk-kill. Later emerging weeds dominated in both cover crop management systems; weed biomass tended to be dominated by grasses under roll-kill management whereas the tillage system selected for broadleaf weeds. This work underscores the importance of understanding how cultural management practices influence weed performance and the resulting weed community. Results from this research will provide farmers with more knowledge on weed biology in organic cropping systems and how their management will select for dominant weed species.
Technical Abstract: Weed management is a major constraint to adoption of reduced-tillage practices for organic grain production. Tillage, cover crop management, and crop planting date are all factors that influence the periodicity and growth potential of important weed species in these systems. Therefore, we assessed two hairy vetch cover crop management practices, disk-kill and roll-kill, across a range of corn planting dates from early May to late June in a three-year experiment in Beltsville, Maryland. Seed dormancy, emergence, and early weed growth patterns were determined for overseeded populations of common ragweed, giant foxtail, and smooth pigweed, three troublesome species in the mid-Atlantic states that represent early to late emergence patterns. Dormancy of common ragweed and giant foxtail seed buried 15 cm deep increased to approximately 90% from early May to late June but that of smooth pigweed decreased to 12%. In contrast, the dormancy of common ragweed and smooth pigweed seed at the soil surface increased to 98 and 76% by late June, respectively, whereas the fraction of pre-germinated giant foxtail seed at the soil surface increased to 42% by late June. Biomass of individual giant foxtail plants was higher in roll-kill than disk-kill hairy vetch in 2 of 3 years, whereas, that of smooth pigweed plants was higher in disk-kill than roll-kill in 2 of 3 years. Giant foxtail was the dominant species in roll-kill hairy vetch (averaged 79% of weed biomass at corn silking), probably because of early germination and establishment before rolling operations. Smooth pigweed was the dominant species in disk-kill hairy vetch at June planting dates (averaged 77% of weed biomass), probably because of high growth rates under warm, summer conditions in tilled soil. This research demonstrated that tillage practices and the timing of planting operations can interact with local climate to select for dominant species in organic farming systems.