The effects of seed size, autumn nitrogen and plant population density on the response to delayed sowing in winter oil-seed rape (Brassica napus)

Abstract

The aim of the experiments reported here was to investigate the possibility of minimizing yield losses due to late sowing by increasing leaf area and radiation interception during the pre-flowering period. The use of large seed did increase leaf area, radiation interception and crop weight at flowering. Normally this would be expected to lead to increased yield of late sowings, but hot, dry conditions severely affected all crops during seed growth. Applying fertilizer nitrogen in the seed bed boosted pre-flowering growth of early but not late sowings, probably because low temperatures prevented a response in the latter. Increasing plant population density did improve leaf cover and radiation interception until just before flowering, but leaf canopies in late-sown, low density crops were then able to expand more and function for longer owing to less shading by flowers and pods. Seed retention was improved and, even with as few as 8 plants/m 2 in 1973-4, a worthwhile yield was still obtained. INTRODUCTIONu 8 e l a r g e s e e d ' ^ t o a p p l y n i t r o 8 e n i n t h e s e e d b e d and thus to promote leaf expansion; and (3) to The preceding paper (Mendham, Shipway & increase the seed rate and hence number of plants, Scott, 1981) examined the response of oil-seed rape to give quicker ground cover, (cv. Victor) to delayed sowing in autumn, in seven This paper examines crop responses to these seasons from 1970 to 1977. Using standard cultural treatments in experiments conducted in three of the treatments it was shown that the wide variation in seasons covered by the preceding paper. Each yield of late sowings (after mid-September) was experiment included both early and late sowings, largely due to differences in the amount of radiation The results reported in the previous paper would intercepted and growth made by crops in the pre-not lead us to expect that early sowings would flowering period. Techniques for improving the respond greatly to such treatments. AH early sowyield of late-sown crops should therefore be ings intercept most incoming radiation during the directed mainly at increasing the leaf area, and spring period and are large by flowering time. The ability to intercept radiation, over the period up to main restriction on yield seems to occur in the postflowering, particularly in the critical spring period, flowering period when heavy pod and seed losses At this time leaf area indices are often very small, occur, apparently because the profuse flower and and yet the crop is progressing rapidly towards pod canopy creates deep shade and strong comflowering. An increase in leaf area index could be petition for assimilate. A study of the way lateachieved by increasing the speed of establishment, sown crops respond to agronomic treatments should the number of plants/m 2 , their rate of leaf pro-add to our understanding of the physiology of the duction or the size of individual leaves. Possible crop as well as indicating whether such treatments approaches to achieve these objectives are: (1) to are likely to...

Effects of seed size and seed weight on seedling establishment, vigour and tolerance of Argentine canola (Brassica napus) to flea beetles, Phyllotreta spp.

“…In cultivars of B. rapa (Ahmed and Zuberi 1973;Elliott et al 2007) and B. oleracea (Heather and Sieczka 1991), plants grown from large seeds yielded more than plants grown from small seeds. In contrast, the size of planted seed had no effect on yield of spring and winter types of B. napus (Major 1977;Mendham et al 1981). In our study, seed size had a significant effect on yield of B. napus cultivars grown without insecticides.…”

“…Under dry conditions and high flea beetle damage, establishment of summer turnip rape, B. rapa, was 5Á6% higher with large seeds than with small seeds (Elliott et al 2007). Previous investigations have shown that seed size has a significant effect on seedling vigour in wild radish, Raphanus raphanistrum L. (Choe et al 1988), wintertype B. napus (Mendham et al 1981), spring-type B. napus (Major 1977;Bodnaryk and Lamb 1991) and B. rapa (Elliott et al 2007). Seedlings from large seeds had larger cotyledons, larger true leaves and greater weight than seedlings of small seeds.…”

“…campestris), plants from large seeds had better establishment, higher shoot weights, more branches, more pods, heavier seeds and higher seed yield than plants from small seeds (Ahmed and Zuberi 1973;Elliott et al 2007). In contrast, seed size had no effect on plant densities and seed yield of spring and winter types of Argentine canola, B. napus (Major 1977;Mendham et al 1981). However, plants from large seeds had larger leaves, more leaves and higher weight than plants from small seeds.…”

Factors affecting nitrogen concentration in spring oilseed rape (Brassica napus L.)

“…Rapeseed typically gives similar yields over a wide range of sowing rate (Mendham et al 1981b, Nuttall et al 1992). However, plants at higher density are thinner and carry fewer branches, crops growth rates and net assimilation rates are smaller.…”

“…However, plants at higher density are thinner and carry fewer branches, crops growth rates and net assimilation rates are smaller. The individual leaf area per plant in the high density is 3-4 times smaller than in the low densities (Mendham et al 1981b, Morrison et al 1990. Therefore could be possible that stand population density can influence nitrogen concentration in plants and their yield.…”