Thermal Behavior and Yield of Yellow Melon Subjected to Different Irrigation Strategies in a Semiarid Region

This study aimed to evaluate the performance of melon, during the third phase (flowering and fruiting), under strategies of sustained irrigation (SI) and regulated deficit irrigation (RDI), in a semiarid region. Nine irrigation treatments based on crop evapotranspiration (ETc) (%) were applied, including four SI treatments (T1–125%; T2–100%; T3–75%; and T4–50% throughout the cycle) and five RDI treatments (T5–75% in phases I and IV; T6–50% in phase I and 75% in phases III and IV; T7–75% in phases II and III and 50% in phase IV; T8–50% in phase II; and T9–75% in phase I and 50% in phases III and IV), with replacement by 100% of ETc in stages without water deficit. The variables obtained included plant (Tc) and air (Ta) temperatures were at 8, 12, and 16h00 for calculating the thermal indices (ΔT_canopy-air, crop water stress index (CWSI) and conductance index (IG)); leaf water potential (Ψ_Leaf); gas exchange (gs and E); and soil moisture (SMO). After harvest, yield and water use efficiency (WUE) were determined. ΔT_canopy-air, CWSI, and IG indices correlated significantly with Ψ_Leaf and SMO at the monitored times; however, 12h00 was demonstrated to be the most suitable for monitoring via infrared thermography in the melon crop. Productivity and WUE were higher in the RDI treatments. Correlations between WUE and thermal indices showed better results for RDI in cycle I, with both indices at 8h00 and 12h00. In cycle II, better correlations were presented by SI at both monitored times.