Summary
ALMANAC is a dynamic model for plant growth, water balance and soil nitrogen dynamics that can simulate on a daily basis two or more competing species. The simulation of competition for light is based on Beer's law, allowing a different extinction coefficient (k) for each species. Light is partitioned between species based on k‐values, leaf area index and plant heights. Total hiomass is simulated with radiation use efficiency and grain yield with a harvest index approach, sensitive to water stress. The model simulates competition for water and nutrients based on each species current rooting zone and demand by each species. The effect of crop management on the competition issue can he simulated. The model was evaluated in Dijon (France) using 4 years of experimental data on wheat:oat mixtures, differing in oat (Avena sativa L.) densities, the period of oat emergence, the date of weed suppression by herbicides and the wheat (Triticun aestivum L.) genotype. Additional data on oilseed rape (Brassica nupus L.) and vetch (Vilcia sauiva L.) competition in spring wheat were also used. The wheat grain yield was reasonably simulated with a root mean square error (RMSE) of 0.10‐0.35 t ha‐1. Corresponding values for oats were 0.10‐0.55 t ha‐1. The competitiveness of oats, oilseed rape and vetch was correctly simulated. The model appears as a reasonable tool for estimating damage thresholds in integrated weed control programmes.
Summary
Influence of 2,4‐D on toxicity of diclofop‐methyl to Avena sativa (cv. Selma) and Arena fatua at 2·5 leaf stage has been evaluated under controlled conditions. Effects of 2,4‐D on the fate of diclofop‐methyl in cultivated oat have also been studied. Mixture with 2,4‐D reduced the toxicity of diclofop‐methyl to both species. When applied immediately after diclofop‐methyl treatment, 2,4‐D still reduced herbicide toxicity to wild oat. This reduction was smaller in cultivated oat. and was only observed at higher phytotoxicity. No interaction was observed when a 10‐day period separated the two applications. In mixture, 2,4‐D enhanced diclofop‐methyl penetration and diclofop acid conjugation in cultivated oat, and it slightly increased conjugation when applied separately. None of these effects clearly explain the reduction of diclofop‐methyl toxicity by 2, 4‐D in cultivated oat. Other processes are possibly involved and could be connected with the site of action of diclofop‐methyl.
Résumé
Dans une expérience de plein champ, où tous les facteurs déographiques et génétiques de concurrence étaient déterminés, des densités différentes d'une variété d'avoine de printemps (espèce considérée comme une graminée adventice) ont étéétablies dans une culture de blé de printemps. Sur la moitié des parcelles du dispositif expérimental, l'avoine a été détruite par une application de diclofopméthyl au stade 3 talles du blé. Les mauvaises herbes dicotylédones ont été désherbées soit à la même date que celle du traitement au diclofopméthyl (traitement précoce), soit deux semaines plus tard (traitement tardif). Les poids secs de la plants cultivée el des adventices ont été mesurés plusieurs fois au cours du cycle de la culture sur des échantillons. Toutes les densités de l'avoine de printemps ont réduit le rendement et certaines composantes du rendement du blé en fonction du traitement herbicide: les rendements du blé ont été moins diminués sur les parcelles traitées que sur les parcelles témoins, les mauvaises herbes dicotylédones ont été mieux détruites par le traitement précoce que par le traitement tardif au 2,4‐D. D'après les résultats oblenus, l'existence d'interactions herbicides est susceptible de modifier les effets de compétition adventice.
Summary — Reductions in the yields of spring wheat (cv Bastion) caused by interference from spring oat (cv Selma), considered as a weed, were estimated in field studies on post-emergence weed control in Dijon (France). The
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.