Leaf area is a valuable index in identifying taro [Colocasia esculenta (L.) Schott] growth and development. Several models for estimating the area of a taro leaf by using nondestructive measurements of length and/or width have been proposed. We evaluated these models as well as some modified versions of the models and analyzed variations in leaf area coefficients (K) across leaf developmental stages, crop seasons, and cultivars. Data were collected from experiments of two taro cultivars at three leaf developmental stages grown in two crop seasons at Taiwan Agricultural Research Institute. The models using both leaf length [maximum leaf length (LX), length from the sinus base to the apex of leaf (LSA), or length from petiole‐attaching point to the apex of leaf (LPA)] and leaf width (maximum width, leaf width passing the petiole‐attaching point and perpendicular to LPA, or leaf width passing the sinus base and perpendicular to LSA) factors (LW1–LW9) provided the most accurate estimations of taro leaf area. Using these models, the mean squared deviation (in the range 887–4862), percentage of deviation for total leaf area (<3%), and mean percentage of deviation for individual leaf area (<8%) were smaller than those from other models. However, model L1, which used only the length factor LSA, could be extended to the area estimation of nonexpanded taro leaves or leaves at initial wilting stage. Models LW1 to LW9 and L1 gave consistent K values across leaf developmental stages, crop seasons, and cultivars. With these models, estimating taro leaf area in large quantities could be done without the use of any expensive instruments.

ing those of tracing, blueprinting, photographing, or using a conventional planimeter, require the excision of Leaf area is a valuable index in identifying taro [Colocasia esculeaves from the plants. It is therefore not possible to lenta (L.) Schott] growth and development. Several models for estimake successive measurements of the same leaf. Plant mating the area of a taro leaf by using nondestructive measurements canopy is also damaged, which might cause problems of length and/or width have been proposed. We evaluated these models as well as some modified versions of the models and analyzed to other measurements or experiments. Leaf area can variations in leaf area coefficients (K ) across leaf developmental be measured quickly, accurately, and nondestructively stages, crop seasons, and cultivars. Data were collected from experiby using a portable scanning planimeter (Daughtry, ments of two taro cultivars at three leaf developmental stages grown 1990), but it is suitable only for small plants with few in two crop seasons at Taiwan Agricultural Research Institute. The leaves (Nyakwende et al., 1997). models using both leaf length [maximum leaf length (L X ), length from An alternative method to measure leaf area is to use the sinus base to the apex of leaf (L SA ), or length from petiole-attaching digital camera with image measurement and analysis point to the apex of leaf (L PA )] and leaf width (maximum width, leaf software. The capture of image by digital camera is width passing the petiole-attaching point and perpendicular to L PA , rapid, and the analysis by using proper software is accuor leaf width passing the sinus base and perpendicular to L SA ) factors rate, but the processing procedure is time consuming, (LW1-LW9) provided the most accurate estimations of taro leaf area. Using these models, the mean squared deviation (in the range 887-Abbreviations: D, percentage of deviation for total leaf area; L PA , length from petiole-attaching point to the apex of leaf; L PB(min) , length

planting and increased during the vigorous top-growth and rapid corm-bulking stages. The responses of linear Selecting plants with high harvest index (HI) can increase corm increase in HI appeared to be most important for final yield in wetland taro [Colocasia esculenta (L.) Schott]. Planting time, however, affects the response of HI during the linear increase phase,