Effects of water and nitrogen management on radiation use efficiency of different varieties of winter wheat

Radiation use efficiency (RUE) is critical for improving crop yield. It is not only related to crop canopy intercepted radiation, but also to the distribution of radiation within the canopy. The characteristics and forming processes of crop canopy are affected by genetic characteristics, management practices and other related factors. Various canopy characteristics have different end-effects on crop RUE. Winter wheat is a major crop grown in the North China Plain (NCP), accounting for about 50% of wheat production in China. Thus keeping high yields and improving resources use efficiency of winter wheat are critical in the NCP region. To explore the effects of varieties, water and nitrogen supplies on RUE of winter wheat, a field experiment was conducted at Luancheng Agro-Ecosystems Experimental Station, Chinese Academy of Sciences in the winter wheat growing season from 2012 to 2013. Three winter wheat varieties (‘Jimai585’, ‘Kenong199’ and ‘Shixin828’) were used in the experiment — the main wheat varieties grown in the study area. Three water supply levels 70 mm irrigation in jointing stage (serious deficit irrigation), total 140 mm irrigations in jointing and booting stages (moderate deficit irrigation) and total 210 mm irrigations in jointing, booting and grain-filling stages (normal irrigation) were applied, and three nitrogen supply levels 135 kg(N)·hm^-2, 180 kg(N)·hm^-2 and 225 kg(N)·hm^-2 used as fertilizer management in the study. Biomass, leaf area index and photosynthetically active radiation (PAR) were measured every 7 days. RUE was calculated using biomass and intercepted radiation during the respective growth periods of winter wheat. The results showed that RUE was significantly different for different wheat varieties. RUE was 2.10 g·MJ^-1 for ‘Jimai585’, 2.05 g·MJ^-1 for ‘Kenong199’ and 1.93 g·MJ^-1 for ‘Shixin828’. RUE under different water and nitrogen levels was also different, and ranged within 1.802.20 g·MJ^-1. RUE increased with increasing nitrogen supply. However, RUE was higher for moderate water deficit irrigation than others treatments. There was no significant difference in RUE for water and nitrogen interaction. This suggested that genetic characteristics, water and nitrogen supplies significantly influenced wheat RUE. Although increasing RUE obviously increased biomass, winter wheat yield did not significantly increase after a certain increase in biomass due to lower dry matter transfer rate. The results also showed a significantly relationship between RUE and air temperature for the period from stem-elongation to grain-filling. Given the above, it was concluded that the appropriate nitrogen and water supply for winter wheat was beneficial for dry matter accumulation and improvement of RUE, eventually resulting in high winter wheat yield.