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Radiation-Use Efficiency in Summer Rape

Agric. Canada, Plant Res. Ctr., Bldg. 75
Ctr. for Land and Biological Resources Res, Bldg 74. Central Exp. Farm, Ottawa, ON K1A 0C6

^* Corresponding author (Email:. Morrisonm{at}em.agr.ca).

The radiation-use efficiency (RUE) is a parameter that represents a crop canopy's ability to convert intercepted solar energy to dry matter. The RUE is used in simulation models and can vary with crop type and environment. The objective was to examine the effects of varying row width and seeding rate on the amount of intercepted photosynthetically active radiation (IPAR) and the RUE in summer rape (Brassica napus L.). ‘Westar’ summer rape was seeded at rates of 1.5, 3.0, 6.0, and 12.0 kg ha^–1 in rows spaced 15 or 30 cm apart. Plant sampling was done at key growth stages, and the leaf and pod areas and total plant dry weights were determined. After flowering, plants intercepted more PAR when grown in 15-cm-wide rows than 30-cm-wide rows. For both row widths, as seeding rate increased from 1.5 to 12.0 kg ha^–1, IPAR increased. The RUE was greater for plants grown in 15-cm-wide rows than for those grown in 30-cm rows; however, RUE decreased with increasing seeding rate. The mean RUE value was 2.83 g MJ^–1 PAR. When the pod area was added to the leaf area, the IPAR increased and the RUE decreased.

Received for publication September 30, 1994.