Modeling Weather-Crop Growth Relationships in Taro

Abstract

Phenological development of the crop is important for predicting biomass production and scheduling harvest in taro [Colocasia esculenta (L.) Schott]. Selecting plants with high harvest index (HI) can increase corm yield in taro. Planting time, however, affects the response of HI in taro. Data from six planting months of field-grown taro across a 3-year period were collected to develop a suitable and simple approach for modeling the seasonal variation of HI in taro under a changed climate. The calendar days after planting (DAP) and growing degree days after planting (GDD) were included as independent variables to analyze the three-phase piecewise linear function with HI. The equations describe the responses of HI during the three periods: the lag phase, linear increase phase, and maturity stage, respectively. Piecewise linear functions based on either DAP or GDD fitted well. The response during the linear increase phase of HI was most important for final HI, which depended on the temperature and solar radiation during the vigorous top-growth stage. This linear increase phase was, however, more stable across years for the GDD model. Moreover, the model based on GDD was superior to DAP for explaining the seasonal variation of HI in taro. In GDD model, taro planted in January and March had a long duration of linear increase in HI that favored yield at maturity, although their dry matter production in the aboveground vegetative organs might be damaged by typhoons during the vigorous top-growth stage. Both the low rate and short duration of linear increase in HI caused low yield for the July crop. These results indicate that the GDD model is a useful approach for determining weather-crop growth relationships in taro. Information gained in this study should help relate phenological responses to seasonal variations in taro.