Nitrogen uptake by rapeseed varieties from organic matter and inorganic fertilizer sources

Aims Half of field crop nitrogen (N) is often derived soil organic matter (SOM) mineralization, yet we do not fully understand the extent to which plant genotypic differences influence SOM mineralization dynamics across different soil N contexts. We explored the effects of rapeseed (Brassica napus) genotypic diversity on N uptake from organic and inorganic N sources. Methods In a greenhouse study, we applied dual N-15 labeled ammonium-nitrate fertilizer to examine N uptake patterns of rapeseed in different N environments. Ten varieties were grown in a full factorial experiment with four treatments, including combinations of high and low N fertilizer and SOM. Results We found limited varietal differences in total biomass or N uptake across soil environments. Across all varieties, SOM was an important, additive N source even as N fertilizer availability increased. High SOM/High Fertilizer treatment plants obtained 64% of N from SOM, while plants grown with High SOM/Low Fertilizer obtained 89% of total N from SOM. Under low SOM availability, the high fertilizer addition increased overall N uptake from SOM by 42% relative to the low N fertilizer treatment. Conclusions Integrating plant reliance on SOM-N sources into crop breeding and NUE estimates has potential to improve crop productivity and improve overall system N use efficiency.