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. 芋植株的生理發育對其物質生產預測及 收穫計畫非常重要。而提高收穫指數，可期 獲有高的球莖產量，惟不同種植期會影響芋 之收穫指數的反應表現。因此，本研究利用6 個種植月份進行連續 3 週年的水田栽培試驗，發展出一個最適且簡易的動態模式，以瞭解水芋收穫指數在氣候改變下的季節性變 異。模式呈一種連續的三相分段線性函數，用以描述收穫指數在遲滯期、線性增加期及成熟期之三個直線階段的表現。無論是採用 種植後日曆天數(DAP)或生育度數(GDD)作為自變數，所有種植期下的水芋收穫指數都能與模式良好配合。根據動態模式之解析，其中以收穫指數線性增加期的反應又主栽培季節之氣象變化影響最大，尤其是溫度及日照，故造成最終收穫指數在不同種植期之間的季節性差異。GDD 模式在不同年度間最穩定，且用以解釋水芋收穫指數之變化趨勢的效能優於 DAP 模式。從 GDD 模式得知，雖然一月及三月種植期的水芋植株在其地上部快速生長階段可能遭受到颱風侵襲之傷害，旦因為其收穫指數線性增加期的持續時間較長，故有利於最終的收穫產量;七月種植期的水芋收穫指數線性增加期的增加速度較慢且持續時間較短，故造成低產。由此可知，以 GDD 所建立的水芋收穫指數動態模式，能有效地描述及預測天氣對芋作物生長的影響關係，據此所獲資訊能有利於解析水芋對季節性變異的生理反應。