Comparison of Lysimetric and Computational Methods for Determining Water Requirement of Juvenile Date Palm

Date palm is an important horticultural crop in Iran. In this research, after measuring the amount of plant evapotranspiration during first to third years by lysimeter, equal 274.3, 402.7 and 597.2 mm, respectively, plant evapotranspiration was estimated by five methods of FAO Penman-Monteith, FAO Blaney-Criddle, FAO pan evaporation, corrected Jensen-Heise and Hargreaves-Samani. Statistical analysis of linear regression of evapotranspiration equations compared to lysimeter showed that all equations were significant at 1% level of probability. The adjusted coefficient of determination (R2adj) was between 0.94 (FAO pan evaporation) and 0.97 (FAO Blaney-Criddle), while modeling efficiency (EF) varied from 0.93 (FAO Penman-Monteith) to 0.95 (FAO Blaney-Criddle). Minimum and maximum of maximum error (ME) were related to Hargreaves-Samani and FAO pan evaporation equations, respectively. Minimum and maximum of normalized root mean square error (nRMSE) were in FAO Blaney-Criddle and FAO Penman-Monteith equations, respectively. Also maximum and minimum of coefficient of residual mass (CRM) were in FAO Blaney-Criddle and corrected Jensen-Heise equations, respectively. The FAO Blaney-Criddle equation had the most fitting accuracy in Ahvaz region. However, the methods of FAO Penman-Monteith and FAO evaporation pan had also well accurate.