Water Use Efficiency of Coix Lacryma-Jobi L. Varieties in Response to Water Supply According to CROPWAT Analysis

It is essential to evaluate the efficiency of water supply on varieties of crop, such as Coix lacryma-jobi L. (hanjeli), particularly in water management. Coix lacryma-jobi L. (hanjeli) is one of the crops that were not listed for crop coefficient (Kc) values to estimate the crop water use by CROPWAT ver 8.0. However, this study using the Kc values of sugar cane as approach to reveal actual evapo-transpiration (ET). Hanjeli comprises two varieties, namely stenocarpa and ma-yuen, which were used in this study to observe the water requirement for irrigation when cultivating agricultural products in a loamy soil using CROPWAT. The ETa (mm day-1) generated by CROPWAT was used to calculate the sprinkler operation time (T, hour day-1) and added 0.5 hour day-1 to anticipate the less water when using Kc for sugarcane (T+0.5, hour day-1) . The results showed that the trend of T+0.5 rapidly increased from the initial to mid-stage before slowing down from the mid to the late-stage. These indicated that the fluctuated water requirement in both varieties was in accordance with the growth stages. Furthermore, the water use efficiency revealed that the yield and economic usage of hanjeli increased when irrigation was applied in accordance with T+0.5 for sprinkler operation time, which is 1.27 and 0.11 times in dry and rainy seasons for ma-yuen. This study suggested that the CROPWAT estimation efficiently supplies water supply for the evapotranspiration of hanjeli varieties.