Experimental warming reduces fertilizer nitrogen use efficiency in a double rice cropping system

Climate warming significantly affects nitrogen (N) cycling, while its effects on the use efficiency of fertilizer N are still unclear in agroecosystems. In the present study, we examined for the first time the response of fertilizer N use efficiency to experimental warming using 15N labeling with a free-air temperature increase facility (infrared heaters) in a double rice cropping system. 15N-urea was applied in micro-plots to trace the uptake and loss of fertilizer N. Results showed that moderate warming (i.e. an increase of 1.4°C and 2.1°C in canopy temperature for early and late rice, respectively) did not significantly affect grain yield and biomass. Warming significantly reduced N uptake from fertilizer for both early and late rice, while increased N uptake from soil. The N recovery rate of fertilizer was reduced from 35.5% in the control and to 32.3% in the warming treatments for early rice and from 47.2% to 43.1% for late rice, respectively. Warming did not affect fertilizer N loss rate in the early rice season, whereas significantly increased it from 38.9% in the control and to 42.7% in the warming treatments in the late rice season, respectively. Therefore, we suggest that climate warming may reduce fertilizer N use efficiency and increase N losses to the environment in the rice paddy.