Nitrogen-saving effect of nitrogen fertilizer residue in hybrid middle rice stored for regeneration on the following year’s first season rice in winter paddy area

To improve the nitrogen (N) fertilization efficiency of hybrid middle rice -retained regeneration paddies, the N-saving effect of N residue in the previous year on the next year’s first season rice was investigated with the aim of laying a theoretical foundation and a practical basis for a reasonable N fertilizer management strategy in regeneration paddies. In 2021–2023, a three-year positioning experiment was performed in the winter paddy area of South Sichuan, using the high-quality hybrid medium rice variety ‘Jing 3 you 6150’ as the test material. Treatments were set up with 0, 25%, 50%, 75%, 100% thinning of regeneration rice and reserving N fertilization for the following year’s first season rice, to shape the N-saving relationship between N savings and N conservation of the previous year’s first season rice through thinning of regeneration rice at the peak of seedling stage and the different N sinking balance of the paddy caused by the difference of regeneration rice yield. Furthermore, this study aimed to explore the relationship between N residue in the previous year and N savings in the following year’s first-season rice through the regeneration of rice seedling season sparse hole shaping to regeneration rice yield difference to different N residue in the rice field. The results indicate that N residue was significantly negatively correlated with the yield of regenerated rice. The N dry matter production efficiency of first-season rice was 15.48% higher than that of regenerated rice, whereas the N rice production efficiency and N harvest index were 5.56% and 16.51% lower, respectively, than those of regenerated rice. Most of the regenerated rice grain sprout fertilizer (¹⁵N) was absorbed by the first season rice of the current year, indirectly promoting the regeneration of buds and seedlings, and was directly absorbed and utilized by the regenerated rice to a lesser extent, and residues in the soil for the use of the first season rice in the following year. N saving in the following year’s first season rice was significantly and positively correlated with the previous year’s N sinking residue (r=0.955^**), and both paddy sinking residue and N saving in the following year’s first season rice increased with an increase in the previous year’s regeneration rice thinning rate. The N content of the first-season rice in the following year was significantly negatively correlated with the yield of regenerated rice in the previous year. The yield of regenerated rice in the previous year was within the range of 0−4 125 kg∙hm⁻², and the N application rate for the first season of rice in the following year could be reduced by 99.11−0.11 kg∙hm⁻² according to the local high-yield N application level. Compared with the first-season rice, the N dry matter production efficiency of regenerated rice decreased, whereas the N rice production efficiency and N harvest index increased. This indicated that the N content of the first-season rice in the following year had a synergistic effect with the N sink balance of the previous year. Therefore, increasing the yield of regenerated rice is the key to reducing the N sink balance in rice fields.