Effects of free air temperature increase on nitrogen utilization of rice in northeastern China

Abstract

<p id="C3">Northeastern China is one of the regions where are experiencing the most significant global warming trend. Revealing the effects of anticipated warming on nitrogen absorption and utilization of rice in northeastern China can provide reference for regional sustainable production of rice and optimal management of nitrogen fertilizer. In this study, the field and pot experiments were setup based on free air temperature increase (FATI) system in Harbin, Heilongjiang province during 2019 to 2020, combined with ¹⁵N isotope tracer technique, to investigate the effects of anticipated warming (+1.5℃) on rice yield, nitrogen utilization, and the fate of fertilizer nitrogen. The results showed that warming treatment (W) promoted rice above-ground dry-matter accumulation. The mean grain yields in field and pot experiments during 2019 and 2020 under warming treatment were higher by 10.4% and 10.8% than those under control (CK), respectively. Compared with CK, the mean total nitrogen uptake of two years under W treatment significantly increased by 21.3%, however, the nitrogen utilization efficiency of rice grains showed a decreased trend. Under W treatment, the nitrogen absorbed from fertilizer decreased significantly, while the nitrogen absorbed by rice from soil increased by 31.1%, resulting in the reduction of 12.5% in fertilizer nitrogen recovery rate and the increase of 14.2% in fertilizer nitrogen loss rate. Overall, warming tended to increase rice grain yield, but decreased the proportion of fertilizer nitrogen uptake by plant, which leading to the decrease in nitrogen use efficiency and the significant increase in nitrogen loss rate. Under the background of climate warming, it was suggested to reasonably increase the transplanting density of rice to make full use of the positive effect of global warming on rice yield, as well as appropriately reduce the amount of nitrogen fertilizer application and optimize the management of nitrogen fertilizer operation to improve the nitrogen use efficiency of rice.