Nitrogen accumulation, partition, and nitrogen-use efficiency in canola under different nitrogen availabilities

Nitrogen (N) accumulation and its partition in a canola (Brassica napus L. ssp. oleifera var. annua) crop growing under different N availabilities were evaluated. Spring canola (cultivar Printol) plants were grown with 0, 30, 60, 90, 120, or 150 kg N ha(-1) applied at sowing. They were harvested at D I (flower buds covered by leaves), G1 (first flowers fall), and G5 (maturity) phenological stages and separated into stems, leaves, inflorescences, reproductive structures, and seeds according to its development stage. Dry matter and N concentration of each fraction were evaluated. At maturity, seed yield, harvest index and N use efficiencies were evaluated. Nitrogen concentration in the whole plant and its different organs increased with the increase of N applied in the three stages analyzed. The greatest N accumulation (14.44 gm(-2) for 150kg Nha(-1)) was registered at G I and then it decreased 11% toward maturity. Nitrogen accumulated in seed increased from 2.83 gm(-2) to 7.66 gm(-2) (170% over the control) with application of 150 kg Nha(-1). The highest N harvest index was observed with 30kg Nha(-1) applying. The apparent N recovery in plant averaged 57% at G1 and it was not modified by N applications. In contrast, N utilization efficiency declined with the N rate increase. The results show that N application at sowing time increases total N accumulated by canola but has little effect on N partition among plant parts even at high rates. Also, it is confirmed the important response of this crop to fertilization but the decrease in its N use efficiency with the increase of N rate. The low average values of apparent N recovery found in this experiment point out the need of adjust fertilizer-applying practices in order to improve N recovery possibilities of the crop.