Impact of sowing density and nitrogen fertilization on Rumex obtusifolius L. development in organic winter cereal crops

The control of Rumex obtusifolius L. (broad-leafed dock) is very important in organic farming systems. Indeed, concerns about managing this weed without the use of herbicides is one of the major factors limiting the uptake of these systems by conventional farmers. Against this background, we analyzed the impact of two management practices on the development of R. obtusifolius populations in two winter cereal trials: spelt (Triticum spelta [L.] Thell.) and triticale (×Triticosecale [A.Camus] Wittm.). The management factors were sowing density (SD) and nitrogen fertilization (NF) at the tillering stage. The results showed that an increase in SD and NF led to stronger crop growth and better soil coverage by the end of spring, demonstrated by a significant decrease in photosynthetic active radiation (PAR) at soil level. However, although there was an SD effect, it was too weak in April to restrict an increase in R. obtusifolius populations through the recruitment of new R. obtusifolius plants. An increase in R. obtusifolius population density was also linked to an increase in the NF level, illustrating the nitrophilic character of this weed. Although an increase in SD and NF at the tillering stage led to a higher canopy density, these two practices failed to reduce R. obtusifolius density in the cereal crops. Nevertheless, cereal yields were shown to be maintained or improved. Our results indicate that, even when combining weed harrowing and some cultural weed control methods, this perennial weed is difficult to control.