Estimation of Solar Radiation Use Efficiency in Paddy and Cassava Fields

Abstract

               The estimation of solar radiation use efficiency in rice and cassava fields was studied in Sukhothai and Nakhon Ratchasima provinces, during November 2004 to January 2006. Crop growth was divided into three periods of cultivation: early vegetative, actively growing and before harvesting. The objectives of the study were to: 1) compare the radiation use efficiency (RUE) between rice and cassava; and 2) study the relationship between biomass and absorbed photosynthetically active radiation (PARa). The results of the experiment may be used as basic data for studying the energy balance of other watershed areas with different land uses.

               The comparison of photosynthetically active radiation (PAR) between cassava and rice revealed that PARa in cassava was higher than in rice. In a cassava crop, the greatest value (10.99 MJm^-2) of daily PARa was obtained during the actively growing period, with an average PARa of 8.98 MJ m^-2 and a radiation use efficiency (RUE) of 1.09–4.42 g MJ^-1. Similarly, in a rice crop, the greatest value (9.53 MJ m^-2) of daily PARa was observed during the actively growing period, with an average PARa of 6.41 MJ m^-2 and an RUE of 0.58–0.66 g MJ^-1. PARa in the cassava crop, however, was higher than in the paddy field. The relationships between total biomass and PARa in the paddy and cassava crops were linear with R2 values of 0.97 and 0.89, respectively.