Nitrogen Uptake by Rapeseed Varieties From Organic Matter and Inorganic Fertilizer Sources
Abstract Aims Improving crop utilization of N from soil organic matter (SOM) has received limited attention despite evidence that half of field crop N is often derived from SOM mineralization. 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 15N 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 While we found limited varietal differences in N uptake dynamics, SOM was an important N source across all varieties 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. High N fertilizer additions increased overall N uptake from SOM by 42% relative to low N fertilizer treatments. In contrast, microbial enzyme activity related to nutrient mineralization was suppressed by 16–58% in high N fertilizer relative to low fertilizer treatments. Conclusions Integrating plant reliance on SOM-N sources into crop breeding and system management has the potential to improve productivity and overall N use efficiency.