Ratios of controlled-release nitrogen fertilizer effects on yield and nitrogen use efficiency of double-cropping direct seeding rice in red soil area

In this study, an appropriate proportion of controlled-release nitrogen fertilizer for double-cropping direct seeding rice in red soil area was examined in order to provide theoretical guidance for scientific and efficient fertilization of direct seeding rice. The experiment was carried out in the direct seeding rice area in Jiangxi Province in 2021, and five treatments were designed as following: no nitrogen fertilizer (N₀), 80% compound fertilizer plus 20% urea (N₁), 50% controlled-release fertilizer plus 50% urea (N₂), 60% controlled-release fertilizer plus 40% urea (N₃), and 70% controlled-release fertilizer plus 30% urea (N₄). The early and late rice yields, nitrogen uptake, nitrogen use efficiency and nitrogen apparent surplus were measured; and the correlation between nitrogen surplus and nitrogen use efficiency were analyzed. The results showed that compared with conventional fertilization, N₂ and N₃ treatment had the best effect in increasing nitrogen uptake and nitrogen utilization rate of early and late rice, which increased the yield and nitrogen uptake by 5.7% ~ 6.5% and 7.5% ~ 7.7% in early rice, while the yield and nitrogen uptake by 9.0% ~ 10.0% and 8.6% ~ 9.7% in the late rice. The yield, nitrogen uptake and nitrogen utilization efficiency of late rice were lower than those of early rice. The nitrogen apparent surplus was the highest in N₄ followed by N₂ and N₃. The nitrogen apparent surplus of late rice was higher than that of early rice. There was a significant negative correlation between nitrogen apparent surplus and nitrogen use efficiency. When nitrogen apparent surplus increased by 10 kg·hm⁻², nitrogen use efficiency decreased by 6.3% and 6.2% in early rice and late rice, respectively. Therefore, at the same nitrogen level, 50% ~ 60% of controlled-release nitrogen fertilizer is more conducive to the improvement of double cropping direct seeding rice yield, nitrogen absorption and nitrogen use efficiency, which is the best application proportion of controlled-release nitrogen fertilizer for double cropping direct seeding rice in red soil area.