Effects of nitrogen application rates on nitrogen use efficiency and grain yield of indica hybrid rice F You498 under controlled intermittent irrigation

Objectives Effects of different nitrogen (N) rates on grain yield and nitrogen absorption and utilization of indica hybrid rice under the controlled intermittent irrigation were studied with expectations for providing theoretical basis for rational use of irrigation water and nitrogen fertilizer in indica hybrid rice.

Methods A single-factor random block experiment based on 5 nitrogen rates (0, 90, 135, 180 and 225 kg/hm²) with the combination of the controlled intermittent irrigation and super indica hybrid rice F You498 as material was conducted in 2015 and 2016. The nitrogen absorption and translocation amounts and growing indices of rice were measured at the main growing stages.

Results 1) Nitrogen application had significant effects on grain yield and nitrogen use efficiency of rice, and the grain yield and irrigation water use efficiency were increased with the increase of N application level from 0 to 180 kg/hm², and then decreased when the N application level was further increased. The highest grain yields in 2015 and 2016 were obtained at the N application rates of 180 kg/hm² and 135 kg/hm², respectively, which were closely related to the soil fertility and temperature-light condition. 2) With the increase of N application rate, the N accumulation at the mature stage was increased gradually, and the N recovery efficiency (NRE), N agronomic efficiency (NAE) as well as the N harvest index (NHI) were first increased and then decreased. However, the N partial factor productivity (NPP), N production efficiency (NPE), N dry matter production efficiency (NMPE) and soil N dependent rate (SDNR) were decreased gradually. There was a significant positive correlation between NRE and grain yield (r = 0.92**), and the highest NRE could be obtained at the N application rate of 135 kg/hm². 3) Correlation analysis indicated that the grain yield was significantly and positively correlated with leaf area index (LAI), high valid LAI, total root length (TRL), total root surface area (TRSA) and total root volume (TRV). The appropriate N application rate under controlled intermittent irrigation could facilitate the cooperative growth of aboveground and underground part, which was beneficial to construct the high-yielding population.

Conclusions With the consideration of high grain yield and nitrogen utilization efficiency, based on the soil fertility and temperature-light condition, the optimal N application rate of indica hybrid rice F You498 under the controlled intermittent irrigation condition should be about 135–180 kg/hm².