The effects of plant density on the growth and yield of winter oilseed rape (Brassica napus) were examined in a series of five multifactorial experiments at Rothamsted Experimental Station between 1984 and 1989. Plant densities, manipulated by changing the seed rate and row spacing, or because of overwinter losses, ranged from 13·5 to 372 plants/m2. Normalized yields for the multifactorial plots increased with densities up to 50–60 plants/m2. In very high density plots in 1987/88, yield decreased as density increased >150 plants/m2. Plants grown at high density had fewer pod-bearing branches per plant but produced more branches/m2. Branch dry matter (DM) per plant was decreased by 42%, the number of fertile pods per plant and pod DM/plant by 37%. There was no effect of density on the number or DM of pods/m2. Over 74% of the fertile pods were carried on the terminal and uppermost branches of plants grown at high density in 1987/88 compared with only 34% in plants grown at low density in 1988/89. Seed DM/plant decreased with increase in density but seed size (1000-seed weight) increased. There was no effect of density on seed glucosinolate or oil contents.

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SUMMARYThe effects of varying the sowing date (early September-late October) and plant density (14–70 seeds/m2) on the establishment, overwinter survival, structure and yield of an autumn-sown, florallydeterminate line (CH304/70) of the white lupin (Lupinus albus) were examined in three contrasting growing seasons between 1991 and 1994. Crops established well when sown in early September and were sufficiently cold-hardy to survive prolonged and extremely severe early winter frosts, but crops sown in late October either lost many plants or were destroyed completely. There was a strong interaction between sowing date and autumn weather on crop structure and yield. Late sowing and cold autumn weather restricted the number of mainstem leaves and first-order lateral branches on the plant, and decreased plant height and yield potential.Despite considerable differences between years in the weather during the summer and autumn, all crops were harvested in early September. Grain yields ranged from 0·3 to 4·5 t/ha depending on season, sowing date and plant density. Yields were strongly correlated with the number of podbearing axes and pods per m2 and, although actual yields differed depending on growing conditions, the same number of pod-bearing axes (100/m2) was required in each year to achieve maximum yield. The effects of sowing date and autumn weather on plant structure were well predicted by a simple developmental model that related vernalization and leaf development to post-sowing temperature.

SummaryExperiments at Rothamsted in the UK and Lusignan in France examined the effect of artificially modifying plant structure on the yield and date of harvest of indeterminate autumn‐sown cultivars of Lupinus albus. Experiments in 1989/90 were done on the cv. Lugel at Rothamsted and those in 1990/91 on the cvs Lugel and Lunoble in both the UK and France.At Rothamsted in 1990, when the summer was warm and dry, the indeterminate cv. Lugel ripened at the end of August and yielded 5.2 t grain/ha. At Lusignan in 1991, where summer weather was also warm and dry, the two unpruned indeterminate cultivars ripened in late July and yielded c. 4.9 t grain/ ha. However, at Rothamsted in 1991, in a season which was predominantly cool and wet, the two indeterminate cultivars were not harvested until late October and yielded only 1.5 and 2.4 t/ha.Plants pruned to a semi‐determinate form consisting of the mainstem plus the 1st‐order branches yielded approximately the same as the unpruned inde‐terminates at Rothamsted and slightly less than the indeterminates at Lusignan. The semi‐determinates ripened 10 days earlier than the indeterminates at Rothamsted in 1990 and Lusignan in 1991, and 6 weeks earlier in the UK in 1991.Epigonal plants with only a mainstem inflorescence, ripened even earlier than the semi‐determinates but, without branch inflorescences, produced less yield and had poorer yield stability. Where disease was not a factor, as at Rothamsted in 1990 and Lusignan in 1991, epigonal plants ripened 3 weeks earlier than the indeterminates and yielded between 1.6 and 2.6 t/ha. When the pruned epigonal plants were badly infested with Pleiochaeta, as at Rothamsted in 1991, they yielded less than 0.4 t/ha.It is concluded that indeterminate genotypes of L. albus are well adapted to the climatic conditions of Lusignan but lack yield stability further north. For the cooler northern regions of Europe, an autumn‐sown, florally‐determinate genotype with one order of branching would produce adequate yield and have an acceptably early harvest date and yield stability. Such a genotype would have agricultural and economic value as a new protein break crop with a low requirement for nitrogen fertiliser.

Pod and seed growth were studied in two experiments in which the plant's source-sink relationships were modified by (a) manually pruning an autumn-sown, indeterminate white lupin variety, Lunoble, to a determinate form, and (b) by growing a determinate variety, Lucyane, at densities ranging from 7 to 35 plants/m2. The pruning experiments indicated that the faster pod growth rate of determinate genotypes was not an inherent genetic trait but an indirect physiological consequence of the plant's changed architecture. In the density experiment, crop dry matter (DM) and nitrogen (N) were maximum at the end of pod extension in late July and similar across the plant density range at c. 12 t DM and 320 kg N/ha. Therefore, the amount of dry matter per plant decreased proportionately with the increase in plant number. The DM and N contents of the pod walls were also maximum at the end of pod extension, but seeds contained only a third of their final DM and a quarter of their final N. Protein accumulation during the final stages of seed growth, therefore, depended on the remobilization of nitrogen from other plant organs, primarily the leaves and pod walls. Nitrogen withdrawn from the leaves accounted for 44% of the gain in the pods, and N withdrawn from pod walls for 50–60% of the gain in the seed.Seed number/m2 was the major yield component. Seeds and pods mainly aborted during early development, but seed number per pod was also decreased by some seed abortion after full pod extension, especially in first-order pods of plants grown at high density. The number of late-aborted seeds was negatively correlated with the amount of N remobilized from the pod wall. In determinate lupins, which have highly synchronous flowering and pod development, the large and sudden remobilization of nitrogen from leaves and pod walls for seed growth and protein accumulation triggered crop senescence.