*2.1. Site Description*

A field experiment was conducted at the Agricultural Research Center (ARC) of the National Agriculture and Forestry Research Institute (NAFRI) in Vientiane, Lao PDR to investigate the effect of seedling age (SA) and seedling density (SD) on post-transplanting performance of selected waxy Lao rice varieties in terms of crop growth, grain yield, water input, and water productivity. The experimental area (16◦29' N, 104◦49' E) in the research center was characterized by loam soil (21% clay and 39% silt), which is typical for lowland rice. The soil properties are shown in Table 1. The area was previously used as a production plot and was cropped with lowland rice in both wet and dry seasons. Vientiane province has a monsoonal climate, with the southwest monsoons being associated with distinct wet (May–October) and dry (November–April) seasons. Mean annual rainfall at the experimental area (taken at a nearby agrometeorological station 200 m away) is about 1790 mm, of which 1500 mm (89% of total rainfall) falls during the wet season, and only about 197 mm (or 11%) falls during

the dry season. Annual mean solar radiation in the area is about 20 MJ m−<sup>2</sup> d−1, with a range of 18–24 MJ m−<sup>2</sup> d<sup>−</sup>1. Temperatures increase gradually from around 28–30 ◦C in January to about 35 ◦C in April. Peak monthly maximum temperature is recorded in April, immediately before the start of the wet-season rains. The temperature remains above 30 ◦C between April and October and starts to decline from late October. Minimum temperatures also follow a similar pattern, with 18−20 ◦C in January to about 26−27 ◦C in April, then gradually declining from late October [5].

**Table 1.** Soil properties of the top soil layer (0–20 cm) in the experimental site.

