Biomass accumulation and nutrient uptake of oilseeds at different growth stages in the parkland region of Saskatchewan
Field experiments were conducted with canola (Brassica napus and B. rapa, cv. Quantum and Tobin), mustard (cv. AC Vulcan) and flax (cv. Norlin) in 1998 and 1999 at Melfort, Saskatchewan, Canada, to determine biomass and nutrient accumulation in oilseeds at different growth stages and their relationship to seed yield. In general, all oilseed crops followed a similar pattern in biomass accumulation and nutrient uptake, which increased at early growth stages, reached maximum and then decreased at late growth stages. Oilseed crops usually reached their maximum biomass at medium to end of pod forming growth stages (74-80 days after emergence), although Quest canola cultivar had a several day delay at early ripening stage (84 days after emergence) in 1998. Maximum biomass accumulation rate was 146-190 kg ha-1d-1 for canola, 158-182 kg ha-1d-1 for mustard and 174-189 kg ha-1d-1 for flax. Maximum nutrient uptake usually occurred at flowering to seed filling stage (59-85 days after emergence. Maximum nutrient uptake rate for N, P, K, S and B, respectively, was 2.3-4.5, 0.3-0.5, 2.5-5.7, 0.7-1.1 and 0.005-0.008 kg ha-1d-1 for canola, 2.3-3.9, 0.4-0.5, 2.6-4.9, 1.2-1.4 and 0.006-0.008 kg ha-1d-1 for mustard and 3.2-4.0, 0.3-0.4, 2.9-4.1, 0.3-0.5 and 0.004-0.009 kg ha-1d-1 for flax. Both seed yield and nutrient uptake in seed were lower in 1999 than in 1998, due to differences in weather conditions in the growing season in the two years. In summary, maximum nutrient accumulation rate occurred earlier than maximum biomass accumulation rate, and maximum nutrient uptake was earlier than maximum biomass. This indicates that in order to get high seed yields, there should be sufficient supply of nutrients to plants to ensure higher nutrient uptake rate at side shooting to bud forming stage, and then a greater biomass accumulation rate at early to late bud forming stage. This further suggests that adequate supply of nutrients from soil/fertilizers at early growth stages is of great importance for high-yield crop production systems.
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