Ruth Clements* and Eric Gallandt**
*Graduate Research Assistant in Ecology and Environmental Sciences, University of Maine, Orono, ME, USA; **Professor of Weed Ecology, University of Maine, Orono, ME, USA
Interim report: February 26, 2021
Take-home points:
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Crops tended to have a higher anchorage force than weeds at 1-3 leaf stages.
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Beets and carrots measured after cultivation tended to show lower anchorage force values than those measured before cultivation.
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Non-significant correlations between anchorage force and weed control efficacy suggest anchorage force alone may not be the best explanatory factor for efficacy, but may be more useful in understanding tool selectivity and crop injury.
Problem
Physical weed control efficacy is often highly variable (Gallandt and Brainard, 2018), and effective tool combinations may provide trade-offs in crop mortality (Brown and Gallandt, 2018). Understanding the early growth characteristics of weeds and crops may help us explain part of the variation in weed control efficacy and tool selectivity. Given that weeds may be killed by uprooting during cultivation (Kurstjens and Kropff, 2001), root anchorage force (the force required to uproot a weed) is one early growth characteristic that could provide useful insights when measured across weed and crop species and growth stages.
Approach
We measured the anchorage force of select crops and ambient and surrogate weeds in field settings in order to characterize differences between species and growth stages, and identify any impacts on physical tool cultivation.
Figure 1. (a.) The force gauge displays anchorage force data in real time as each plant is pulled upward from the soil. (b.) Clips are attached to each plant at the soil surface prior to beginning data collection with the force gauge. (c.) Only plants that were uprooted, rather than those whose stems snapped in the measurement process, were included in the analysis.
Results
Figure 2. Average maximum anchorage force required to uproot select crop and weed species. At two true leaves, most crop cultivars showed a higher mean anchorage force than the surrogate weed Brassica juncea and real weeds Capsella bursa-pastoris (CAPBU), Chenopodium album (CHEAL), Galinsoga ciliata (GALCI), and Portulaca oleracea (POROL) across fields, with the exception of table beet. Carrot cultivar abbreviations: BO = Bolero, SFF = SFF, YE = Yellowstone, NB1 = inbred line.
Figure 3. Average maximum anchorage force of carrot cultivars before (left) and after (right) cultivation. Cultivation had an overall effect on carrot root anchorage force (p < 0.001), with varying impacts on each cultivar. BO = Bolero, DR = Dragon, NB1 and NB2 = inbred lines, SFF = SFF, YE = Yellowstone.
Next Steps
Anchorage force data from the field will be compared with similar data from the greenhouse to better understand differences in early weed growth characteristics between the two environments.
Future work may benefit from determining the relationship between weed control efficacy and other weed characteristics in the field that are related to, but require fewer resources to measure than, root anchorage force, such as growth stage.
Studies that compare reductions in crop root anchorage force after cultivation to longer term crop mortality and yield could provide new insights into the long-term effects of physical weed control on crops.
Literature Cited
Brown, B., & Gallandt, E. R. (2018). Evidence of synergy with ‘stacked’ intrarow cultivation tools. Weed Research , 58 (4), 284–291. https://doi.org/10.1111/wre.12309
Gallandt, E. R., et al. (2018). Developments in physical weed control. Integrated Weed Management for Sustainable Agriculture. R. Zimdahl, Burleigh Dodds Science Publishing : 261-283.
Kurstjens, D. a. G., & Kropff, M. J. (2001). The impact of uprooting and soil-covering on the effectiveness of weed harrowing. Weed Research , 41 (3), 211–228. https://doi.org/10.1046/j.1365-3180.2001.00233.x