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In field trials in 1987\88 near Pangbourne, England, wheat (Triticum aestivum) and field beans (Vicia faba) were grown in an organic farming system as sole crops and additive intercrops. The sole crops were grown at 25, 50, 75, 100 and 150 % of the recommended density (RD) for conventionally grown crops. The intercrops consisted of all density combinations of wheat and beans from 25 to 100 % RD in a factorial experiment. The grain yield of sole cropped wheat and beans increased significantly as their density was increased. The highest yield of both was achieved at 100 % RD, indicating that the conventional recommendation was the optimum when applied to organically grown crops. Land equivalent ratio (LER) values for the intercrops were significantly greater than 1n0 when the wheat was sown at 5 % RD and beans at 50 % RD. The highest LER of 1n29 was achieved when wheat and beans were both sown at 75 % RD. There was resource complementarity, expressed as relative yield total (RYT) 1n0, in all of the density combinations. There was a significant decrease in resource complementarity with increasing wheat and bean density. The nitrogen content of the wheat grain and whole plant biomass was significantly increased when the density of beans in the intercrops was increased ; this was reflected in a significant increase in grain protein at harvest. The total amount of N accumulated by the wheat, however, decreased with increasing bean density due to a reduction in the biomass of wheat. Beans also showed a significant increase in %N as the density of the other component increased and a decrease in total N accumulation due to reduced biomass. All of the intercrops accumulated more N than the sole cropped wheat, but did not exceed that accumulated by sole-cropped beans. The biomass of weeds was greater under beans than under wheat. Weed biomass in intercrops was significantly reduced when the density of wheat and beans was increased, resulting in a lower weed biomass in the intercrops than was achieved in either the sole cropped wheat or beans. The N content of weeds was significantly reduced with increasing wheat density but was significantly increased with increasing bean density. The total amount of N accumulated by weeds per unit area was reduced significantly by increasing the density of both components. The levels of disease on the wheat were low, but mildew (Erysiphe graminis) increased significantly as bean density increased. The incidence of chocolate spot (Botrytis fabae) increased significantly with increased bean density. The experiment demonstrated that it was possible to harvest the crop with a combine harvester and the wheat and beans can be planted separately mechanically, therefore this system is suited to mechanized agricultural systems.

Summary: Résumé: Zusammenfassung Two cultivars of each of three spring cereals (wheat, barley and oats) were grown with Avena fatua in a box experiment, where the effects of root and shoot competition were separated using soil and aerial partitions. Measures of resource complementarity (RYT) and of the relative severity of competition indicated that competition for soil resources, particularly nitrogen, was more severe than competition for aerial resources, i.e. light. When both root and shoot competition occurred, oats and barley were generally more competitive than wheat, but there were significant differences in competitive ability between cultivars of all three cereals. Although competition between cereals and A. fatua occurred predominantly below‐ground, the various cultivars only differed slightly in root competitive ability against weeds. Nitrogen fertilizer did not significantly change the ranking of competitive abilities of the cultivars. Although shoot competition had less effect than root competition, the various cereals differed markedly in shoot competitive ability. The two oat cultivars, and the barley cultivar Egmont, had higher shoot competitive abilities than the two wheat cultivars or the barley cultivar Goldmarker. There was little evidence that differences in shoot competitive ability were due to differences in plant height. Une comparaison de la competition racinaire et aerienne entre les cereales de printemps et Avena fatua L. Deux cultivars de chacune des 3 céréales de printemps (blé, orge et avoine) ont été cultivés avec de l'Avena fatua dans des boites expérimentales ou les effets de la compétition aérienne et ceux de la compétition racinaire étaient séparées en utilisant des partitions de sol et d'air. Des mesures de complémentarité de ressources (RYT) et de la sévérité relative de la competition ont montré que la compétition pour les ressources du sol, en particulier l'azote, était plus forte que la compétition pour les ressources aériennes comme la lumière. Quand à fois on avait une compétition aérienne et racinaire, l'avoine et l'orge étaient généralement plus compétitives que le blé, mais il y avait des différences significatives dans l'aptitude à la compétition entre les cullivars des 3 céréales. Bien que la compétition enlre céréales et A. fatua soit apparue pour la majeure partie sous le sol, les différents cultivars ont seulement légèrement différé dans leur aptitude à la competition contre les adventices. Les engrais azotés n'ont pas changé de façon significative le niveau de la competitivité des cullivars. Bien que la compétition aérienne soit moins forte que la racinaire, les différentes céréales ont exprimé des différences nettes dans leur aptitude à la compétition aérienne. Les 2 avoines et l'orge ‘Egmont’ ont une plus grande capacité de compétition que les 2 blés et l'orge ‘Goldmaker’. II n'est pas ressorti que les différences dans la compétitivé aérienne soient liées à des différences de hauleur de plantes. Konkurrenz im Wurzel‐ und im Sproßbereich zwischen Sommergetreid...

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SUMMARY1. Reciprocal transplants were made of pairs of contrasting populations of Ant hoxant hum odoratum collected from the Park Grass Experiment at Rothamsted.2. In most cases, plants survived longer, produced more tillers and produced more dry matter when transplanted into their native plots than when transplanted into ecologically contrasting plots.3. The average half-life of plants transplanted into contrasting plots was 8 months, that of plants in their native plots was about 2 years. 4. Selection coefficients against "alien" populations based on survival after 18 months ranged from O'09 to O77 with a mean value of O36. Similar coefficients of selection were calculated for tiller number and plant weight.5. The coefficients of selection on the various plots were correlated with both the yield of herbage on the plots and the vegetation height on the plots, this is discussed in relation to the observed pattern of differentiation of A. odoratum on the plots.6. We conclude that selection pressures acting upon A. odoratum in the mosaic of environments that occur on the Park Grass Experiment are large and sufficient to account for the morphological and physiological differences that have been observed between closely adjacent populations of A. odoratum on the plots.

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