*3.2. Hydrological Conditions and Water Level Changes*

Groundwater table depths were shallow during wet seasons, especially from July to September. Similar trends of groundwater level fluctuations were observed for both years. As shown in Figure 2, groundwater depth below the ground surface fluctuated between 21 and 33 cm in July, between 18 and 57 cm in August, and between 20 and 63 cm in September, gradually declining after the second week of September.

;ďͿ 'ƌŽƵŶĚǁĂƚĞƌ ůĞǀĞů ďĞůŽǁ ƚŚĞ ŐƌŽƵŶĚ ƐƵƌĨĂĐĞ

**Figure 2.** Average field water (**a**) and groundwater (**b**) level fluctuations in the study site during 2014 and 2015. Field water level fluctuations presented were the average of SA15 × SD1 × V1 plots, while average groundwater level was from the three groundwater observation wells installed in the site.

In October, groundwater table depths ranged from 51 to 84 cm during 2014 and 60 to 163 cm in 2015. In terms of field water depths, (using average water level data for SA15 × SD1 × V1 plots as example), it fluctuated between 5 cm (above the surface) and −15 cm (below the ground surface) during the crop growth stage in both years. Water levels were slightly above the ground surface (0–2 cm) during the first week after transplanting; after the plants fully recovered from transplanting shock, water levels fluctuated between 6 cm and –15 cm. While rice plants received ample rains in 2014 and 2015, the rains were not evenly distributed during the crop growth period. As a result, the paddy soil surface experienced five drying cycles in 2014 and about six drying cycles in 2015. This means that there was some form of AWD condition of the soil surface in the field experiment. Field water level fluctuations in September and October (Figure 2) were due to the application of supplemental irrigation as the rains became limited.
