###### Abstract  
An increased planting density and decreased nitrogen (N) rate combination may obtain a stable yield and enhance N utilization. However, the effects of an increased planting density and decreased N rate combination on the yield and nutrient utilization in different ecological regions are unclear. The aim of this research was to assess the interactive impacts of the N rates and planting densities on double cropping rice yields and nutrient utilization in two ecological regions in field experiments during 2018 and 2019. The results showed that, at Shanggao, increased planting densities of 67% and 200% compensated for the biomass, nutrient uptake and yield losses from N application reductions of 20% and 27% and increased the nutrient utilization of the early and late seasons. However, at Xingguo, compared with the N\({}_{2}\)D\({}_{1}\) treatment (165 kg ha\({}^{-1}\) with 57 plants per m\({}^{2}\)), the late rice yield under the N\({}_{1}\)D\({}_{2}\) treatment (120 kg ha\({}^{-1}\) with 114 plants per m\({}^{2}\)) decreased by 6.71% and 5.02% in 2018 and 2019, respectively. The photosynthetic rate and nutrient uptake were likely related to the positive interaction on the double cropping rice yield in the two ecological regions. Our results indicate that dense planting is a feasible cultivation strategy to decrease N inputs for double cropping rice, but the low soil nutrient supplies negatively affect stable yields in different ecological regions. e 3 May 20  
water eutrophication [15] and soil microbial diversity [16]. Many cultivation technologies have been studied to reduce N loss and increase N utilization efficiency in paddy fields, such as real-time and site-specific N fertilizer management [17], controlled-release N fertilizer management [18], deep lateral N fertilizer management [19] and N fertilizer management in different growth periods [20]. To sum up the appeal, the scientific and rational N application is conducive to the high yield and N utilization for rice production. Plant density is an important factor in the formation of rice populations and affects canopy formation and yield [21]. Sparse planting promotes the development of individual rice plants but reduces the population canopy productivity and cannot give full play to the yield potential of the variety [22]. Appropriate dense planting promotes the interception of solar radiation and increases canopy productivity and dry matter accumulation [23]. Reasonably increased planting density increases the panicle number, leaf area index, biomass and yield in double cropping rice systems [24]. The high planting density of the rice population results in fierce interspecific competition, unbalanced population development and easy lodging [25]. In short, an appropriate planting density can obtain the best rice canopy productivity and yield. The N fertilizer management and plant density together play an important role in rice yield and N utilization [26; 27]. Increasing the N rate and plant density enhances the population structure, leaf area index, solar radiation interception efficiency and crop growth rate and has a consistent positive effect on aboveground biomass [28]. [PERSON] et al. [29] found that, compared with a low seedling number and high N rate treatment, an increased seedling number and a decreased basal fertilizer N application rate treatment increased rice yield and N use efficiency. [PERSON] et al. [30] showed that a reasonably increased plant density and amount of N fertilizer enhanced the photosynthetically active radiation and N utilization that could promote an increase in crop productivity. [PERSON] et al. [31] indicated that dense planting enhanced N uptake and utilization in rice, which effectively avoided the yield reduction caused by N application reduction.