DataSheet_1_Simplified panicle fertilization is applicable to japonica cultivars, but splits are preferred in indica rice for a higher paddy yield under wheat straw return.docx

IntroductionThe panicle fertilization strategy for japonica and indica rice under wheat straw return (SR) has not been updated, especially on the elaboration of their impacts on spikelet differentiation and degeneration. This study aimed to verify the hypothesis that SR increases spikelet number by reducing spikelet degeneration and to explore the possibility of simplifying panicle fertilization.MethodsIn three consecutive years, four varieties of japonica and indica rice were field-grown in Yangzhou, Jiangsu Province, China. Six panicle fertilization rates and split treatments were applied to SR and no straw return (NR) conditions.ResultsThe results showed that SR promoted rice yield significantly by 3.77%, and the highest yields were obtained under the T2 (split panicle fertilization at the panicle initiation (PI) and spikelet primordium differentiation (SPD) stages) and T1 (panicle fertilization only at the PI stage) treatments, for indica and japonica rice, respectively. Correlation and path analysis revealed that the number of spikelets per panicle was the most attributable to yield variation. SR significantly increased the concentration of alkali hydrolyzable N in the soil 40 days after rice transplantation, significantly increased the nitrogen accumulation per stem (NA) during the SPD-pollen mother cell meiosis (PMC) stage, and increased the brassinosteroids level in the young panicles at the PMC stage. SR also reduced the degeneration rate of spikelets (DRS) and increased the number of surviving spikelets (NSS). The dry matter accumulation per stem was more important to increasing the NA in japonica rice at the PMC stage, whereas NA was more affected by the N content than the dry matter accumulation in indica rice. In japonica rice, panicle N application once only at the PI stage combined with the N released from SR was enough to improve the plant N content, reduce the DRS, and increase the NSS. For indica rice, split application of N panicle fertilization at both the PI and SPD stages was still necessary to achieve a maximum NSS.DiscussionIn conclusion, under wheat SR practice, panicle fertilization could be simplified to once in japonica rice with a significant yield increase, whereas equal splits might still be optimal for indica rice.

引言：在小麦秸秆还田（SR）条件下，关于籼稻和粳稻的穗粒 fertilization 策略尚未得到更新，特别是在其对于穗粒分化与退化影响的阐述方面。本研究旨在验证SR通过降低穗粒退化来增加穗粒数的假设，并探讨简化穗粒 fertilization 的可能性。

方法：在江苏省扬州市连续三年田间种植了四种籼稻和粳稻品种。针对SR和未还田（NR）条件，应用了六种穗粒 fertilization 速率和分蘖处理。

结果：结果显示，SR显著提高了稻谷产量，增幅达3.77%，在籼稻和粳稻中，最高产量分别出现在T2（在分蘖起始期（PI）和穗粒原基分化期（SPD）进行分蘖 fertilization）和T1（仅在PI阶段进行分蘖 fertilization）处理下。相关性分析和路径分析揭示了每穗穗粒数是导致产量变化的最主要因素。SR在水稻移植后40天显著提高了土壤中碱性水解氮的浓度，在SPD-花粉母细胞减数分裂（PMC）阶段显著增加了每株氮积累量（NA），并在PMC阶段的幼穗中提高了 brassinosteroids 的水平。SR还降低了穗粒退化率（DRS）并增加了存活穗粒数（NSS）。在粳稻中，PMC阶段的干物质积累对增加NA更为重要，而在籼稻中，NA受氮含量影响大于干物质积累。在粳稻中，仅在PI阶段进行一次分蘖 N fertilization，并结合SR释放的氮，足以提高植物氮含量，降低DRS并增加NSS。对于籼稻，仍需在PI和SPD阶段进行分蘖 N fertilization 的等量分施，以达到最大的NSS。

讨论：综上所述，在小麦秸秆还田实践中，粳稻的穗粒 fertilization 可简化为一次，可显著提高产量，而对于籼稻，等量分施可能仍是最优选择。