Optimising nitrogen management strategies to minimise lodging risk while sustaining high seed yield in rapeseed

Appropriate nitrogen (N) fertiliser management is an essential strategy for improving the productivity of rape-seed (Brassica napus L.) plants. However, the increased lodging risks under higher yield potentials with enhanced N application rates have largely been overlooked. Few studies have elucidated the trade-off between lodging resistance and seed yield, and a non-destructive method for in situ evaluation of crop lodging is urgently needed. A field study with five site-year environments was conducted to elucidate the trade-off between seed yield and lodging susceptibility under various N application rates in two varieties, and to evaluate the feasibility of using root electrical capacitance (EC) and impedance (EI) as non-destructive techniques for diagnosing the risk of crop lodging. Seed yield and lodging susceptibility (quantified by safety factor, lodging angle, and visual lodging score methods) increased with increasing N application rates. The natural crop lodging occurred in 2 out of 5 site-year environments, which agreed well with lodging resistance quantified by safety factor. A strong relationship be-tween lodging susceptibility and seed yield was found (R-2 = 0.31**-0.82***, except 1 out of 5 site-year envi-ronments), and evidenced by a principal component analysis (PCA) and a structural equation model (SEM). EC was positively correlated to several root morphological parameters of taproot (R-2 = 0.18*- 0.93***), lateral root (R-2 = 0.17*-0.61***), and total root system (R-2 = 0.26**- 0.93***); whereas EI was negatively correlated to these root morphological parameters. In addition, EC and EI were found to be closely related to seed yield and root lodging susceptibility, through the Pearson correlation and partial correlation analysis. In conclusion, a moderate N application of 240 kg N ha(-1) can fully explore the yield potential and could be recommended for rapeseed production. Root electrical measurements (EC and EI) can be regarded as high-throughput techniques for pre-dicting lodging susceptibility.