Seed Yield and Nitrogen Efficiency in Oilseed Rape After Ammonium Nitrate or Urea Fertilization.

Diana Heuermann,Nicolaus Von Wirén,Heike Hahn

doi:10.3389/fpls.2020.608785

Abstract

In agricultural plant production, nitrate, ammonium, and urea are the major fertilized nitrogen forms, which differ in root uptake and downstream signaling processes in plants. Nitrate is known to stimulate cytokinin synthesis in roots, while for urea no hormonal effect has been described yet. Elevated cytokinin levels can delay plant senescence favoring prolonged nitrogen uptake. As the cultivation of winter oilseed rape provokes high nitrogen-balance surpluses, we tested the hypotheses whether nitrogen use efficiency increases under ammonium nitrate- relative to urea-based nutrition and whether this is subject to genotypic variation. In a 2-year field study, 15 oilseed rape lines were fertilized either with ammonium nitrate or with urease inhibitor-stabilized urea and analyzed for seed yield and nitrogen-related yield parameters. Despite a significant environmental impact on the performance of the individual lines, which did not allow revealing consistent impact of the genotype, ammonium nitrate-based nutrition tended to increase seed yield in average over all lines. To resolve whether the fertilizer N forms act on grain yield via phytohormones, we collected xylem exudates at three developmental stages and determined the translocation rates of cytokinins and N forms. Relative to urea, ammonium nitrate-based nutrition enhanced the translocation of nitrate or total nitrogen together with cytokinins, whereas in the urea treatment translocation rates were lower as long as urea remained stable in the soil solution. At later developmental stages, i.e., when urea became hydrolyzed, nitrogen and cytokinin translocation increased. In consequence, urea tended to increase nitrogen partitioning in the shoot toward generative organs. However, differences in overall nitrogen accumulation in shoots were not present at the end of the vegetation period, and neither nitrogen uptake nor utilization efficiency was consistently different between the two applied nitrogen forms.

Highlights

In Northern Europe, winter oilseed rape is nowadays grown as the most important oil crop (Rathke et al, 2006)
Several studies on N use efficiency (NUE) in oilseed rape focused on genotypic differences in NupE and N utilization efficiency (NutE) at different N levels (e.g., Schulte auf ’m Erley et al, 2011; Kessel et al, 2012; Nyikako et al, 2014; Stahl et al, 2015), while the impact of N forms on NUE has been poorly studied, N forms may affect N uptake and N partitioning in winter oilseed rape as well
Compared to the unfertilized variants of this genotype, ammonium nitrate application led to a significant yield gain of ∼60% or even 170% in 2012/13 or 2013/14, respectively, while urea significantly increased the seed yield by ∼40% or 160% in the respective years according to Tukey’s test at p < 0.05

Summary

Introduction

In Northern Europe, winter oilseed rape is nowadays grown as the most important oil crop (Rathke et al, 2006). Agricultural production of rape causes high surpluses in the nitrogen (N) balance (Schulte auf ’m Erley et al, 2011), which is a major source for N losses to the environment and represents an important problem in sustainable crop production It is of increasing importance in oilseed rape production to reduce the amount of applied N fertilizer. In order to improve NUE of oilseed rape, it has been suggested to focus breeding efforts on N uptake during generative plant development and on N retranslocation from vegetative organs to seeds (Wiesler et al, 2001a). Regarding these two traits, the N supply level plays an important role (Bouchet et al, 2016). This research question has so far been rarely addressed, and if so with inconsistent results (Fismes et al, 2000; Arkoun et al, 2012)

Methods

Results

Conclusion