The effect of sowing date and season on growth and yield of oilseed rape (Brassica napus)

Abstract

Experiments 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.