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Improving nutrient management is critical to increase nutrient use efficiency, promote translocation of photoassimilates to sinks, and increase crop yield. In this study, we determined the effects of phosphorus (P) fertilization on dry matter (DM) and P accumulation, partitioning and remobilization from vegetative tissues to the grains in oilseed flax (Linum usitatissimum L.). We hypothesized that P accumulation and remobilization depended on the level of P supply and varied with vegetative tissues. The cultivar Baxuan 3 was sown under low P (LP, 15 kg P ha−1), moderate P (MP, 30 kg P ha−1), and high P (HP, 45 kg P ha−1) conditions along with a zero P control in a randomized complete block design, with three replicates, in 2011 and 2012. At mid‐anthesis, leaf DM (average 1970 kg ha−1) and stem DM (average 1826 kg ha−1) were more than 20 times that of the nongrain reproductive DM (77 kg ha−1); as plants grew to maturity, the DM in the stem and nongrain reproductive parts increased but leaf DM decreased. Compared with the control, oilseed flax grown under the LP, MP, and HP conditions increased leaf DM by 76%, stem DM by 46%, nongrain reproductive DM by 39%, and improved grain yield by an average of 45%. The fertilized oilseed flax increased the P translocation from vegetative tissues to the grains by 150% in 2011 and 201% in 2012. The P content in leaves reached the peak at anthesis and then decreased rapidly to maturity, whereas P contents in the stem and nongrain reproductive parts increased gradually and reached the peak at maturity, showing that leaves are the major contributor to the grain P, whereas the stem and nongrain reproductive parts are stronger P‐demanding organs in oilseed flax. We suggest that advanced techniques, such as 32P labeling, may be used to further quantify the amount of P remobilized from the stems and nongrain reproductive parts to the grain.

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Oilseed flax (Linum usitatissimum L.) yields are primarily fertilizer‐limited, especially by N supply in the semiarid regions of North China. This study was conducted to determine whether N accumulation, translocation and N use efficiency (NUE) could be manipulated through N. The effects of N on N translocation, oilseed flax yield, oil content and NUE were studied at Zhangjiakou, China. Plants were grown at 0, 45, 90, and 135 kg N ha−1 (designated as the control, low N, moderate N, and high N, respectively), in 2011 and 2012. We found that N accumulation in leaves and capsule pericarps reached the maximum at anthesis and kernel developmental stage, respectively, then decreased rapidly before maturity. Averaged over 2 yr, N translocation from leaves to the seeds increased by 43, 150, and 150% under low N, moderate N, and high N, respectively, compared to the control; similarly, N translocation in capsule pericarps increased by 43, 243, and 190%, respectively. We discovered that leaves contributed the largest proportion of the seed N (averaging 80% in both years), and secondarily by the capsule pericarp N, which contributed 12% (in 2011) and 9% (in 2012) of the seed N. The highest seed yields were 2270 kg ha−1 (in 2011) and 1903 kg ha−1 (in 2012) which were obtained with the moderate N. Oil content was not affected by N. Nitrogen use efficiency decreased with progressively higher rates of N. The results suggest the moderate‐N supply was adequate for promoting N translocation, and increasing N harvest index, NUE, and the productivity of oilseed flax.