Speaker
Description
Introduction. Promoting biological weed regulation by shifting resource availability and use from weed to crop may provide an option for a more sustainable weed management. Light is generally the main resource for which crops and weeds compete in conventional cropping systems. But, with the need to reduce mineral nitrogen fertilizer use, better management of crop-weed competition for nitrogen may become crucial. Especially, applying nitrogen fertilisers locally on the crop sowing row (rather than broadcasted across the whole field) could make more nitrogen available to the crop to the detriment of weed plants (mainly located in the inter-row) (Ditomaso 1995). This option could be valuable for crops with wide-spaced rows and early nitrogen requirements (as nitrogen fertilisers could be applied at sowing time), such as sugar beet. Studies on the placement of nitrogen fertilisers on the sowing row focussed on the environmental and economic advantages of this technique. However, the consequences on crop-weed competition have been less studied, and no references are available on sugar beet. In this context, the present study was conducted with a two-fold objective in order to determine:
(O1) To which extent placing nitrogen fertilisers on the sowing row affects the dynamics in space and time of nitrogen in soil,
(O2) The consequences of on-row nitrogen application on crop-weed competitive relationships.
Material and Methods. O1 was addressed in a field experiment (2021 and 2022), while O2 was addressed by combining the results from a field experiment (2022) and a systematic review of the literature.
The field experiment was conducted on sugar beet in the Somme region (North-Western France). Two nitrogen application techniques were compared: a field-wide broadcast vs. an on-row application. The dynamics of soil mineral nitrogen were monitored with measurements at two depths, four distances from the sowing row, and two or three dates after sowing (from 7 to 45 days). In addition, in 2022-2023, sugar beet and weed biomass was measured about four months after sowing. In parallel to our field experiment, the literature was reviewed following the method of Mahé et al. (2022) without restriction on crop species and geographical region.
Results and discussion. Results from our field experiment showed that the amount of nitrogen in the soil was greater around the point of application when nitrogen fertiliser was applied on the sowing row (vs. broadcasted). This effect persisted over time but faded away. It was visible in the superficial soil layer in both years, but was visible in the deeper layer only the rainy year.
Despite significant effects on soil nitrogen dynamics, applying nitrogen fertilizers on the sowing row (vs. broadcasted) did not significantly affect sugar beet and weed biomass in our field experiment. This finding contrasted with that of our systematic review of the literature showing that, in most cases (10 out of 12 articles in total), crop growth was increased and/or weed growth decreased when nitrogen fertiliser was applied on the sowing row. This discrepancy between results from our field experiment and those of the literature may be due to differences in the studied crop species, their spatial arrangement (interrow distance) and geographical area.
Conclusion. Placing nitrogen fertiliser on the sowing row (vs. broadcasted) does modify soil nitrogen dynamics, but the consequences on crop-weed competition vary. Therefore, this technique can help to promote crop vs. weed growth, but not systematically, and further studies are needed to better understand the conditions of success.
Funding. INRAE, Agrotransfert Ressources et Territoires, and COPRAA project funded by the Office Français de la Biodiversité (OFB)
Cited references. Ditomaso JM (1995) Weed Science 43: 491-497. Mahé I et al. (2022) Agronomy for Sustainable Development 42: 50.
| Keywords | Weed; nitrogen; competition |
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