**5. Conclusions**

Grain yield was significantly influenced by the interaction of seedling age and variety and their interactions subjected to AWD conditions during the study. Grain yields of V1 (IRUBN0300-63-5-4) and V2 (TDK10239-SSD4-303-1) increased with increasing seedling age, while grain yield of V3 (TDK-8) decreased with increasing seedling age, especially in 2014. The effect of seedling age on grain yields largely depended on the variety used particularly during the wet season in Lao PDR. Regardless of the variety, the seedling density treatments (one, three, and five seedlings per hill) had significant effects on tillering dynamics but not on grain yield. Moreover, the use of varieties with a stronger tillering propensity ameliorated the effects of delayed transplanting on crop performance. Late transplanting of seedlings improved total water productivity, but it might decrease irrigation water productivity due to the delay in harvesting. Total crop growth duration was extended with late transplanting, which required one or two supplemental irrigations until harvest when rainfall is not available. However, the total duration of stay of the rice plants in the main field was only reduced by 3–5 d for every 10 d delay in transplanting. Proper selection of varieties to use under delayed transplanting coupled with appropriate seedling density can improve crop performance, yield, and water productivity. More so, safe AWD can be implemented in rainfed areas, thus a high potential for methane emissions reduction during wet seasons.

**Author Contributions:** R.L. designed and supervised the research, analyzed the data and wrote the paper. P.X. co-supervised the research and advised on the varietal treatments. C.B. advised on the methodologies and commented to improve the manuscript.

**Funding:** The research was supported by funding provided to the International Rice Research Institute by the Swiss Agency for Development and Cooperation for the CORIGAP project (Grant no. 81016734).

**Acknowledgments:** We thank Duangsavang Lovanxay (ARC, NAFRI) and Sonephom Xayachack (ERRDC, NAFRI) for their assistance in facilitating the field experiment establishment and management, data collection, soil analysis and initial data processing. We also sincerely thank the anonymous reviewers for their helpful comments that improved the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
