SummaryIn experiments at Sutton Bonington between 1967 and 1970, which tested 0–300 kg N/ha applied in spring, maximum oil yields of both autumn- and spring-sown oilseed rape were obtained by applying 200 kg N/ha. The seed-oil content was reduced by nitrogen application but only seriously when 300 kg/a was applied. Responses to high levels of potassium (180 rather than 60 kg K20/ha) were only obtained at 200 kg N/a. Successive increments of nitrogen from nil to 300 kg/ha improved plant growth, increasing leaf area and the dry weight of leaves and stems. The last increment from 200 to 300 kg N/ha was less effective and either reduced or did not affect pod production.In one experiment 300 kg N/ha stimulated husk growth, apparently at the expense of seed growth, with 200 kg/ha giving the highest proportion of pod dry matter as seed. More nitrogen always raised number of seeds per pod, but only increased seed weight in one autumn-sown experiment.Serial harvests of one experiment indicated that the maximum seed and oil yield was obtained by cutting plants before they were fully ripe, thus avoiding seed loss through pod shatter. The oil content of the bulk samples reached a peak about a week before maximum oil yield, probably because later-ripening seed did not reach full maturity. All nitrogen levels delayed flowering, but only the highest delayed maturity in the autumn-sown crop.

SummaryExperiments made between 1967 and 1970 tested the effects of sowing oilseed rape on different dates in autumn and spring. Much greater oil yields were obtained from autumn sowings, due to higher seed yields and oil content, but the effect varied considerably between experiments, varieties and seasons. Autumn-sown crops flowered in late April or early May, and by the time pods were developing rapidly in June the leaves had senesced almost completely. Spring-sown varieties followed a similar pattern but about a month later, and did not reach the same peak in pod growth.There was a major effect of sowing date, late-autumn sowings (after mid-September) giving lower yields than early-spring sowings. The best autumn sowings (early September) gave about 3 t/ha of seed, but late sowings less than half this; oil content also decreased with delay in sowing – from 45% to as low as 38%. Delayed sowing restricted growth, leaf area and pod production, and also had a slight effect on seed weight. Frost damage on flower buds appeared to be the cause of reduced yield from early sowing (August) in one experiment. In spring, the earliest sowing (late March) gave the best yields. Vigorous but late vegetative growth from the latest sowing (end of April) did not lead to high yields, possibly due to pest and disease effects.

Three experiments testing the effects of nitrogen on melon showed significant varietal differences. Nitrogen increased yields by increasing fruits/plant, seeds/fruit and seed weight, had no effect on fruit weight, size and husk, and increased leaf area through leaf number and leaf size. Fruit growth coincided with a rapid decline in leaf area, indicating that the mottled green fruits contributed appreciable assimilates towards their own growth. The implications of the findings, and the inefficiency of the crop in seed formation, are discussed.

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