Abstract
Nitrogen fertilization and planting density are two key factors that can interactively affect the grain yield of rice. Three different types of rice cultivars—inbred Shendao 47, inbred Shendao 505, and hybrid Jingyou 586—were applied to investigate the effects of the nitrogen (N) rate and planting density (D) on the aboveground biomass, harvest index, leaf photosynthetic features, grain yield, and yield components using a split-split-plot design at two sites over two continuous years. The main plots were assigned to four nitrogen fertilizer rates: 0 (N0), 140 (N1), 180 (N2), and 220 (N3) kg ha−1 N; the subplots were assigned to three planting densities: 25 × 104 (D1), 16.7 × 104 (D2), and 12.5 × 104 (D3) hills ha-1, and the sub-subplots were assigned to three rice cultivars. The results showed that the grain yield had a significantly positive correlation with the stomatal conductance (Gs), net photosynthesis rate (Pn), transpiration rate (Tr), chlorophyll content (SPAD value), leaf area index (LAI), panicles per unit area, and spikelets per panicle. The N rate and planting density had significant interaction effects on grain yield, and the maximum values of Shendao 47, Shendao 505, and Jingyou 586 appeared in N3D2, N2D1, and N3D3, respectively. The higher grain yield of midsized panicle Shendao 47 was mostly ascribed to both panicles per unit area and spikelets per panicle. More panicles per unit area and spikelets per panicle primarily contributed to a larger sink capacity of small-sized panicle rice Shendao 505 and large-sized panicle rice Jingyou 586. We found that the treatments N3D2, N2D1, and N3D3 could optimize the contradiction between yield formation factors for Shendao 47, Shendao 505, and Jingyou 586, respectively. Across years and sites, the regression analysis indicated that the combinations of nitrogen fertilization of 195.6 kg ha−1 with a planting density of 22 × 104 hills ha−1, 182.5 kg ha−1 with 25 × 104 hills ha−1, and 220 kg ha−1 with 13.1 × 104 hills ha−1 are recommended for medium-, small-, and large-sized panicle rice cultivars, respectively.
Highlights
Rice (Oryza sativa L.) is one of the essential staple cereal crops around the world, supplying over21% of the calorific needs of the world population and playing an important role in food security and human nutrition [1,2]
The interactive effects between cultivar and N rate, cultivar and planting density, and N rate and planting density were significant on grain yield
Our results showed that cultivars had different grain yields in response to different combinations of N rate and planting density, reaching a peak at N3D2, N2D1, and N3D3 for Shendao 47, Shendao 505, and Jingyou 586, respectively (Table 3)
Summary
Rice (Oryza sativa L.) is one of the essential staple cereal crops around the world, supplying over21% of the calorific needs of the world population and playing an important role in food security and human nutrition [1,2]. Rice is grown over an area of approximately 163 million hectares, amounting to an annual production of 758.8 million tons in 2017 [3]. China’s area under rice cultivation is 30.3 million hectares with the total yield reaching 207.7 million tons and an average yield of 6.8 t ha−1 , which is 65% higher than that of the world average [6]. In the past 10 years, increases in rice yield have been slowing down in China, and the increasing population and shortage of arable land have exerted tremendous stress on food security [7]. To ensure food security for the growing population, improving rice productivity (production per unit area) remains a priority in China
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