No abstract

In order to estimate the optimum range for high stability of yield determining traits in winter rape‐seed a systematic comparison of different plant distribution patterns (3 row spaces × 4 seeding rates) was conducted during 6 growing seasons. The ecovalence originally developed for comparing genotypes was used to quantify stability. Number of vital plants after winter showed high stability at low and medium plant densities and row spaces indicating that increasing competition within rows was responsible for instability. Seed yield per plant and pod numbers per plant decreased simultaneously with increasing competition. Generally, ecovalences of both yield components proved high stability at higher plant densities whereas low densities caused high stability only in combination with lower row widths. Stability of number of seeds/pod was independent of plant densities grown in narrow row spaces. In the widest row space (41 cm), stability of n. o. seeds/pod could only be affected by an extreme plant density. 1000‐seed‐weights and their ecovalences varied little. Zusammenfassung Die Stabilität der Ertragskomponenten von Winterraps (Brasska napusL.) Zur Beurteilung des Einflusses produktions‐technischer Maßnahmen auf die Stabilität ertragsbestimmender Merkmale wurde von 1978–84 ein Feldversuch mit Winterraps durchgeführt. Durch die Aussaat in 4 Saatstär‐ken und 3 Reihenabständen wurde die Pflan‐zenverteilung auf der Fläche variiert. Zur quantitativen Erfassung der Stabilität wurde die Ökovalenz, ursprünglich zum Vergleich von Sorten entwickelt, angewandt. Die Anzahl vitaler Pflanzen nach der Über‐winterung zeigte eine hohe Stabilität bei nied‐rigen und mittleren Reihenweiten und Bestan‐desdichten (BD). Steigender Konkurrenzdruck innerhalb der Reihe führte zu Instabilität der Pflanzenzahl. Samenertrag/Pflanze und Schotenzahlen/ Pflanze stiegen mit abnehmendem Konkurrenzdruck an. In der Regel wurde durch die Ökovalenz eine hohe Stabilität beider Ertrags‐komponenten bei höheren BD nachgewiesen. Niedrige BD dagegen bewirkten nur in Ver‐bindung mit geringen Reihenweiten eine hohe Stabilität von Samenertrag und Schotenzahl je Pflanze. Hohe Flächenerträge wurden aller‐dings nur bei mittleren BD erreicht. Die Stabilität der Samenzahl/Schote war bei geringeren BD unabhängig vom Reihenab‐stand. Die extreme BD führte aber in Verbin‐dung mit dem größten Reihenabstand zur Instabilität dieses Merkmals. Die durchschnittli‐chen Samengewichte und deren Ökovalenzen wurden kaum durch die Pflanzenverteilung be‐einflußt.

Successful linseed (Linum usitatissimum L.) cropping in Central Europe depends on yielding ability and yield stability of cultivars, as well as on reliability of production systems. During 1991 and 1992, two experiments spread over 14 representative locations in Germany and one location in Switzerland were conducted to analyze the effects of cultivar, N fertilization, and seeding rate on yield and, especially, on yield stability. Experiment 1 tested the effects of seeding rate (200, 400, 600, and 800 seeds m−2) and N fertilization rate (60 and 100 kg N ha−1) at nine locations. Experiment 2 investigated yield performance and yield stability of 16 cultivars and lines at nine locations. At 60 kg N ha−1, 200 and 800 seeds m−2 resulted in the lowest yields. Additionally, 200 seeds m−2 was associated with significant yield instability. At 100 kg N ha−1, seed yields reached a plateau at seeding rates of 400 and 600 seeds m−2. At 800 seeds m−2, yield decreased significantly. Only the 400 seeds m−2 rate resulted in significant yield stability. Two cultivars (Atalante, McGregor) and two lines (DSV‐5, DSV‐6) were superior in yield to other genotypes, but only Atalante and DSV‐6 were both high yielding and stable in yield. Adjusting seeding rate in relation to soil‐available N is a useful tool to optimize linseed production in a given location. It is concluded that high‐yielding cultivars are available that respond adequately to production potential at each of the selected locations.

The effects of stand establishment and nitrogen fertilizer on yield and yield stability of winter oil‐seed rape (Brassica napus L.) were investigated in two field experiments in north eastern Germany (Mecklenburg‐Vorpommern). During six years of testing from 1984/85 to 1989/90 three sowing dates (10 Aug, 20 Aug, 5 Sept) as combined with three plant densities (60, 100, 140 plants/m2 in autumn) were compared. Although seed yield did not respond to the main effects of these treatments, the two‐way classification resulted in significant differences from the average yield. August sowing combined with lower plant densities caused comparably high yields, while delayed sowing was somewhat effective only with higher plant density. Highest yield stability was achieved at early sowing when combined with lower plant densities. From 1986/87 to 1988/89 nitrogen top‐dressings were applied during early March, at start of stem extension and shortly before start of flowering at five locations. 200 kg N/ha in one dose resulted in lowest yield performance and enhanced instability. Contrastingly, the 240 kg N/ha treatment advanced yield stability regardless of split regimes. Nevertheless, split application to 100 kg N/ha + 50 kg N/ha + 50 kg N/ha also guaranteed that high yield performance and optimum yield stability were reached simultaneously and, that the total nitrogen input could be limited to 200 kg N/ha.