Growth of weeds in cereal populations

Abstract

The weeds in this study consisted mainly of Chenopodium album, Stellaria media, Viola arvensis, Polygonum convolvulus, P. aviculare and P. lapathifolium. Increasing cereal seed rates reduced the numbers, individual weights and total yields of the most abundant species, Chenopodium album. The decreases in plant weight and total yield of the weeds were very steep when the cereal seed rate was raised from 25 to 200 kg/ha. Increases in the seeding rate reduced the total yields of weeds rather than their numbers. The effect of the cereal on weeds became apparent as soon as heading of the cereal was complete and was further enhanced by prolonged competition. Added nitrogen raised the weed yields at cereal seed rates of 25—100 kg/ha but reduced them at higher seed rates. Nitrogen also raised the yield and individual plant weight of C. album. Cereal seed rate did not affect the nitrogen, phosphorus, potassium, calcium and magnesium contents of the weeds grown among the crop. Due to larger total weed yields, however, the amounts of these nutrients in the weeds were higher in sparse than in dense cereal populations.

Seeding year alfalfa population development as influenced by weed competition and density of establishment

“…When studying the importance values of the stand it was found that the same weeds which were not affected by the herbicide treatment were not controlled by the biological weed control at the high alfalfa seeding rates. Importance values show that a crop competes best with weeds at high population densities as shown by Mann and Barnes (1945, 1947, 1949, 1950, Granström (1962), Horowitz (1966), Erviö (1972). Importance values also describe adequately the requirements of seeding rates for maximum yield in herbicide controlled and noncontrolled systems as observed in this study and in alfalfa studies by Pulli (1973).…”

“…Another method widely used is the one introduced by Lampeter (1960) and applied by Hofer (1970) and Erviö (1972). The calculation method used in this study is a modification of the method introduced by de Wit (1960).…”

Weed occurrence in Finnish coastal regions: a survey of organically cropped spring cereals

“…The difference in weed dry weight between south and northwest is supported by Salonen et al (2001b) who had found higher weed dry weight in the western part of central Finland compared with the southern mainland. The significantly higher crop density in the southern coastal region probably contributed to higher competitiveness of the crop and thus to lower weed abundance (Erviö 1972, Erviö 1983. While the level of weed infestation was clearly influenced by climate, edaphic factors and management, there was only a weak positive correlation between the duration of organic farming and weed abundance in the south, and no correlation at all in the northwest.…”

Effet de la dose de semis et de l’écartement entre les rangs sur l’interférence entre le Chenopodium album et le Triticum aestivum

“…Une augmentation de la dose de semis de la céréale a donc permis de limiter l'effet négatif du chénopode. En accord avec Erviô (1972), le rendement du blé est réduit par les mauvaises herbes mais une augmentation de la dose de semis a permis d'accroître les rendements. En absence de chénopodes, une augmentation de la dose de semis de 100 à 500 grains m 2 a permis d'augmenter le rendement en grain de 45 % en moyenne, alors qu'en présence de la mauvaise herbe cette augmentation était de 100 % (Fig.…”

“…Une augmentation de la dose de semis de 100 à 500 grains m 2 a réduit la biomasse du chenopode de 58 et 52 % lorsque l'écartement entre les rangs était de 10 et 18 cm respectivement (Tableau 5). D'après Erviô (1972), une augmentation de la dose de semis du blé entraîne une réduction du nombre de mauvaises herbes ainsi que du poids individuel et du rendement du chenopode. En accord avec les travaux de Erviô (1972), l'effet d'une augmentation du taux de semis du blé permet de réduire davantage la biomasse des mauvaises herbes plutôt que leur nombre.…”