Impact of Transplanting Date Shifts on Rice Production in Rain-fed Northeast Thailand

抄録

Northeast Thailand, home to 60% of the nation's rice paddies, is a crucial rice-producing area. Over 90% of its fields are rain-fed, making them highly vulnerable to climate variability. Therefore, studying the impact of climate change on rice cultivation and proposing adaptation strategies is essential. One such strategy is shifting the transplanting date (TPD), which can help avoid extreme summer temperatures and increase water availability. Many studies have shown that shifting the TPD can improve rice yields, but in rain-fed systems, the harvest area is equally vital because of water limitations. Thus, this study examined the differences in the effects of TPD adjustments when evaluated using unit yield versus total rice production. A model was developed to estimate both crop growth and harvest area, with TPD determined by the condition that free water levels remained above a threshold for three consecutive weeks. The threshold was set at 12.9 mm based on a previous study. The model was calibrated using data from 2007 to 2016 and validated using data from 1997 to 2006. The model accuracy during both periods, evaluated using RMSE, demonstrated good agreement with the observed data for all provinces except Loei. To identify the optimal TPD for maximizing unit yield and total production, the threshold was adjusted in 5 mm increments, ranging from 12.8mm to 32.8mm. In 1991, the results showed that 10 out of 16 provinces had different optimal TPDs depending on whether the objective was to maximize unit yield or total production. Specifically, in seven provinces, the optimal TPD for total production occurred later than that for unit yield, likely due to heterogeneous rainfall patterns. These findings suggest that climate change adaptation strategies should prioritize total rice production over unit yield when assessing their impacts.