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Nitrogen accounts for the largest energy input in oilseed production. Understanding N use characteristics of oilseed crops will help improve N use efficiency and minimize production costs. This study determined nitrogen use efficiency (NUE, defined as seed yield produced per unit of N supply), nitrogen fertilizer use efficiency (NFUE, defined as seed yield produced per unit of fertilizer N), and crop N uptake for oilseed crops under diverse environments. Five oilseed crops, namely Brassica juncea, B. napus,and B. rapacanolas, and B. junceaand Sinapis albamustards, were grown at seven rates of N fertilizer (0, 25, 50, 100, 150, 200, and 250 kg N ha−1), at 11 sites (year × location combinations) in Saskatchewan from 2003 to 2005. At sites with low soil N supply or low rainfall, albamustard, junceacanola, and rapacanola had lower NUE and NFUE than junceamustard and napuscanola. At sites with high soil N supply or rainfall, napuscanola had the greatest NUE and was the most sensitive to the gradient of productivity among the five oilseeds. All oilseed species responded to N fertilizer rates in a similar manner; both NUE and NFUE decreased as N fertilizer rate increased. The minimum NUE and NFUE were obtained with N fertilizer rate greater than 150 kg N ha−1. At sites with low soil N supply or rainfall, albamustard had the least NUE or NFUE response to increasing N fertilizer rates and napuscanola the greatest. At sites with high soil N supply or rainfall, junceamustard had the least NUE and NFUE response to increasing N fertilizer rates and rapacanola the greatest. On average, seed N uptake was greatest for junceacanola and junceamustard and least for albaand rapacanola. The five oilseed species had similar response patterns of seed N uptake to N fertilizer rates, while the magnitude of response varied among species. Improving NUE in oilseed production systems requires optimizing rates of N fertilizer which vary depending on environmental conditions, and soil N supply and rainfall during the critical growth period of the oilseed crops play an important role in affecting NUE.

Brassica junceavar. junceacanola is a new oilseed species that is developed from B juncea(L.) Czern. mustard with its oil and meal quality equivalent to conventional canola species. Understanding of the phenological characteristics and yield responses to diverse environments will allow the crop to be better adapted to target production areas. This study determined the responses of the junceacanola to various soil‐climatic conditions and was compared with B napusL. canola, B rapaL. canola, junceamustard, and Sinapis albaL. mustard. The five oilseed species/cultivars were grown under various N fertilizer rates (0, 25, 50, 100, 150, 200, and 250 kg N ha−1), at four Saskatchewan locations from 2003 to 2005. On average, flowering began 40 d after seeding (DAS) for albamustard and rapacanola (earliest), 49 DAS for napuscanola (latest), and 44 DAS for junceacanola (intermediate). Flowering duration was longest for junceacanola (30 d) and shortest for napuscanola (22 d). The napuscanola and junceamustard produced higher (1684 kg ha−1) seed yields than the three other oilseeds (1303 kg ha−1on average). For all oilseed species, the seed yield was highly responsive to N fertilizer rates from zero to about 100 kg N ha−1, and thereafter, the rate of yield responses declined. The amount of N fertilizer required to achieve the maximum seed yield was 106 kg N ha−1for rapacanola, 135 kg N ha−1for albamustard and napuscanola, and 162 kg N ha−1for the two junceaspp. Overall, junceacanola had lower seed yield than more popular hybrid napuscanola, and the yield stability of junceacanola was lowest among the five oilseed species when examined across diverse environments. Earlier flowering, longer flowering duration, and greater tolerance to drought stress exhibited by junceacanola make the crop best adapted to the drier areas of the northern Great Plains. The improvement of seed yield and yield stability is the key to potentially adapt this new oilseed species to a wider range of environmental conditions.