Nitrogen fertilization compensation the weak photosynthesis of Oilseed rape (Brassca napus L.) under haze weather

Abstract

Haze and cloudy weather reduce photo-synthetically active radiation (PAR), which affects the formation of crop yield and nitrogen (N) fertilizer utilization.. We conducted field trails in normal year and severe winter haze year, aiming to compare the difference of photosynthesis and N uptake in winter rapeseed under different N levels. Daily sunshine hours and averaged radiation intensity in winter haze year decreased by 54.1% and 33.3% respectively as compared with the past 30 years. Diurnal variation of net photosynthetic rate in winter haze day was 16.2% lower than that of sunny day. Leaf area and photosynthetic capacity decreased significantly during winter haze year. The shoot biomass and N uptake at the rosette stage accounted for only 9.6% and 26.6% of the total growth period in winter haze year, while 24.4% and 70.5% in normal year, respectively. However, in winter haze year, as the top dressing of N application increasing after the rosette stage, shoot biomass increased gradually. In order to achieve the target yield of 2.5 t ha^-1, after suffering winter haze, it is necessary to apply additional 73.1 kg N ha^-1. In conclusion, the haze climate reduced the radiation intensity and stability, leading to a decline in photosynthetic productivity in winter oilseed rape. Applying higher N fertilizer after winter haze can compensate the negative influence and ensure rapeseed yield.

Figure 1

Temperature variation and distribution within 69 days after transplantation.

Figure 2

Diurnal variation of average PAR in sunny (A), haze (B), and cloudy-overcast (C) days within 69 days after transplantation in the year of 2015/2016.

Figure 3

Morphological and physiological traits at the rosette stage in winter oilseed rape under N fertilizations between the years of 2013/2014 and 2015/2016. Different letters in the same year indicated significant differences among N treatments (P < 0.05). Differences between the two years in the same treatment were shown as *(P < 0.05) and ns (no significance).

Figure 4

Effects of different N application rates on photosynthetic diurnal dynamics of winter oilseed rape leaves under sunny (A), haze (B) and cloudy-overcast (C) days in the year of 2015/2016.

Figure 5

Shoot biomass and N accumulation during the growth period of oilseed rape in 2013/2014 (A,C) and 2015/2016 (B,D). Shaded area represented winter haze occurred in 2015/2016 and the same period in 2013/2014.

Figure 6

Rapeseed yield (A) and N utilization efficiency (B) in 2013/2014 and 2015/2016. B₁ and B₂ denote the relationship between N uptake and N utilization efficiency during rosette stage and after rosette stage, respectively.