Relationship between plant nitrogen and phosphorus accumulations in a canola crop as affected by nitrogen management under ample phosphorus supply conditions

Abstract

The understanding of plant nutrient uptake and dynamics is a necessary step to develop site-specific, economically viable, and environmentally responsible management practices. A field study on canola (Brassica napus L.), treated with preplant and sidedress nitrogen (N) applications under ample phosphorus (P) supply conditions, was conducted to determine seasonal plant dry matter (DM) and N and P uptake patterns. We found that periodic DM measured at 20% flowering (FL), from FL to 50% pods reaching maximum size (FL-RI), and from RI to physiological maturity (RI-PM) contributed to 30%, 57%, and 14% of total DM, respectively. Yields ranged from 111 to 447 g m−2 with a sharp decline in 2012 induced by heat and drought. The crop took up about 58%–71% of total plant N by FL, whereas up to 42% of total plant P was assembled during the RI-PM. Canola seed accounted for 60%–66% of total plant N and 59%–63% of total plant P. Accumulation of DM and N post-FL, and of P during RI-PM could explain 69%, 43%, and 55%, respectively, variations in yield, seed N, and seed P. Our data indicated that plant P uptake under adequate P supply conditions in canola was largely enhanced by N application.