GROWTH RELATIONSHIPS AND YIELD OF BRASSICA NAPUS

A detailed analysis of the growth of Brassica napus L. was carried out under field conditions during 1975 and 1976 at Saskatoon, Canada. Plant morphology was altered by the use of four planting densities and three water regimes. A comparison of broadcast and drill seeding was also made, using four seeding rates. The general growth pattern of B. napus was similar to that found in Britain and Australia. Both seeding rates and water regimes influenced the amount and distribution of dry matter. High seeding rates and non­ irrigated conditions caused a greater proportion of dry matter production to occur prior to flowering. Low seeding rates and irrigated conditions caused greater dry matter production after flowering than before flower­ing. Leaf area index (LAI) reached a maximum at about the start of flowering. The LAI values recorded were higher than those reported for Britain and Australia. Growth rates were similar to or slightly higher than those reported in Britain and Australia. There was an increase in the net assimilation rate (NAR) during ripening, which caused a concomitant increase in relative growth rate (RGR) and crop growth rate (CGR). Seed yield was highest at the high seeding rates. Yield was also markedly increased by irrigation. High seeding rates reduced number of pods per plant but had no effect on number of seeds per pod, and increased lOOO-seed weight. Irrigation increased all three yield components compared to rainfed conditions. lOOO-seed weight was the only yield component which was positively correlated with yield. Drill-seeded material out-yielded broadcast-seeded material. The difference was greatest at low seeding rates. Seeding rates had no effect on seed oil content, but irrigation increased oil content. Seeding rates and water regimes had minor effects on the fatty acid composition of the oil in 1975, but no effect in 1976. Maximum leaf area was positively correlated with seed yield, particularly in 1976. Leaf area was important during flowering, since leaves constituted the major source of assimilates at this time. The contribution of assimilates from leaves later in seed ripening depended on leaf area duration, which was strongly influenced by water regime. Measurements of the pod photosynthetic surface area in 1975 showed that maximum pod area was similar in magnitude to maximum leaf area. In 1976, maximum pod area was less than maximum leaf area. Pod area per unit land area was increased by both irrigation and high seeding rates. Correlations between pod area and yield were low, particularly in 1976. Pod photosynthesis seemed to be the most important source of assimilates during the period when number of seeds per pod was established and also during seed filling. Plant and environmental conditions which enhanced assimilate supply during seed filling resulted in greater seed yield