Rice is the most important crop in Lao People’s Democratic Republic (Lao PDR). The improvement of its productivity is strongly recommended, but information about its growth characteristics in farmers’ fields is limited. This study evaluated the dynamics of the leaf area index (LAI) and analyzed the relationship between the rice productivity and soil in farmers’ fields in Vientiane province, Lao PDR. Because the LAI in the farmers’ fields increased almost linearly, a straight-line regression was used for the analysis. The rice yield in the farmers’ fields ranged from 63.8 g m-2 to 411.8 g m-2 and correlated with the LAI during the later growth stage. The variability in the LAI was explained by the LAI growth rate but rarely by the effective accumulated temperatures from the estimated transplanting date. The LAI growth rate was associated with the nitrogen and carbon content in the soil. These results suggest that the rice productivity in farmers’ fields is governed by the soil fertility through LAI growth, and that LAI monitoring is an effective tool to evaluate the production.
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