Termografia infravermelha no monitoramento do estado hídrico do meloeiro sob irrigação com déficit fixo (FDI) e regulado (RDI)

Abstract

This work aimed to evaluate, through infrared thermography, the water status of the melon crop resulting from the application of fixed (FDI) and regulated (RDI) deficit irrigation in two crop cycles. The experimental design was complete randomized blocks with 9 treatments and 4 replications. Irrigation treatments were based on crop evapotranspiration (ETc), with 4 referring to FDI (T1 - 125%, T2 - 100%, T3 - 75%, T4 - 50%) and 5 characterizing the RDI [T5 (75 % in phases I and IV and 100% in phases II and III); T6 (50% in phase I, 100% in phase II and 75% in phases III and IV); T7 (100% in phase I, 75% in phases II and III and 50% in phase IV); T8 (50% in phase II and 100% in the others); and T9 (75% in phase I, 100% in phase III and 50% in phases III and IV)]. Thermographic monitoring of water stress was performed by capturing thermal images at 08:00, 12:00 and 16:00. Subsequently, the ΔT (temperature difference between the plant and air), CWSI (crop water stress index) and IG (stomatal conductance index) indices were calculated, which were correlated with measurements of soil moisture (0.10 m ), leaf water potential and gas exchange [stomatal conductance, (gs) and transpiration (E)], performed at 8 am. In melon yield, effects were observed on productivity and water use efficiency (EUA). According to the results obtained, the gas exchanges (gs and E) were adopted inverse to the percentage of water replacement in the FDI strategy. When correlated with thermal indices, the best responses for both the FDI and RDI strategies were developed in cycle 2; the thermal indices ΔTcanopy-air, CWSI and IG correlated significantly with leaf water potential and soil moisture at all monitored times, corroborating the potential of thermography for irrigation management; Among the monitored times, it is suggested to collect thermal data around 12h. The correlations between the thermal indices suggest the ΔTcanopy-air as a practical and fast index in the thermal response of plants to water stress. The RDI strategy proved to be more effective, with average productivity and UAE higher than FDI. The T6 – RDI treatment is indicated as the best strategy for melon irrigation; Correlations between US and thermal indices disappointingly superior RDI results in cycle 1 with indices measured at 08:00 and 12:00. In cycle 2, highlight the FDI with both indices measured at the same monitored times.