Abstract
In order to estimate cassava productivity in Northeast Thailand, notorious for its low and unstable agricultural production, simple yield models were developed using water use efficiency (WUE) and radiation conversion efficiency (Cs) . In the WUE model, daily dry matter production was estimated by the WUE and transpiration, whereas in the Cs model, by absorbed solar radiation, Cs and LAI. Daily transpiration was estimated by LAI and evapotranspiration, which was estimated from air temperature and solar radiation. The effect of water stress was incorporated through the calculation of actual transpiration in the WUE model, and through a water stress index, i.e. the ratio of actual against potential transpiration in the Cs model. Several experiments, conducted in an experimental farm in Khon Kaen University, located in Northeast Thailand, provided parameters necessary for the models. Validations in the experimental farm and a farmers' field indicated that the models developed were able to estimate the growth and yield of cassava to an acceptable level. Although both models were equally successful, the WUE model seems preferable for application in regional level productivity analysis, because of its simplicity.
