Evapotranspiration (ET) is a key component of the hydrological cycle and is critical for determining crop water requirements. Accurate ET estimation is essential for improving irrigation efficiency, particularly under increasing water scarcity and climate variability. Conventional approaches such as the soil water balance, empirical formulations, the FAO Penman-Monteith method, eddy covariance flux towers, lysimeters, and scintillometers each have limitations related to spatial representativeness, accuracy, or operational cost. Unmanned aerial vehicles (UAVs) equipped with multispectral and thermal sensors offer a high spatial resolution and cost-effective alternative for field-scale assessment of surface energy balance components and ET. In this study, a field experiment was conducted on maize during rabi season of 2022-23 under two irrigation regimes based on depletion of available soil moisture (20% DASM and 40% DASM). UAV-based multispectral (0.05 m) and thermal imagery (0.33 m) were acquired at five crop growth stages and processed using the Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC) model to estimate actual evapotranspiration (ETa) and surface energy fluxes. Spatiotemporal analysis showed that the 20% DASM treatment (400 mm) resulted in a 1.7 °C lower land surface temperature, a 16.5% higher NDVI, and an 11% increase in daily ETa compared with the 40% DASM treatment (316 mm), which experienced water stress and a 20% reduction in seasonal ETa. The UAV-based METRIC estimates of daily ETa showed strong agreement with that of Penman-Monteith (PM) combination approach (R² = 0.84; RMSE = 0.22 mm day⁻¹; MAPE = 6.1%), with a slight underestimation of seasonal ETa (-7%). Agreement with the soil water balance method ranged from-3% to + 3%, demonstrating the capability of the approach to capture irrigation-induced variability in ETa and surface energy fluxes. Overall, the results highlight the potential of UAV-based METRIC for spatiotemporal assessment of crop evapotranspiration and surface energy dynamics to support precision irrigation management.

This field investigation was conducted during the rabi (winter) season (November 2022 to March 2023) at the College Farm, Professor Jayashankar Telangana Agricultural University (PJTAU), Hyderabad, Telangana, India, to evaluate the effects of sunhemp in situ green manuring at 45 days after sowing (DAS) and variable nitrogen application at the tasselling stage on microbial dynamics, nutrient cycling and physicochemical properties of the rhizosphere soil of rabi maize. At 20 days after incorporation (DAI), it was found that the green-manured treatments recorded significantly higher microbial population (cellulolytic: 83.7–92.4 × 103 CFU g-1; lignolytic: 206–244 × 104 CFU g-1 soil) and enzymatic activities (dehydrogenase: 80.5 µg triphenyl formazan (TPF) g-1 soil; fluorescein diacetate: 88.5 µg fluorescein g-1 soil) compared to sole maize because of the presence of higher amount of organic matter in those treatments which is reflecting the importance of organic manures in maintaining the soil health. Similarly, in the case of available nutrients, the green manured treatments recorded significantly higher amounts of available nitrogen (222–227 kg ha-1), phosphorus (25.5–27.8 kg ha-1) and potassium (316–324 kg ha-1) due to the release of nutrients from the decomposing green manure. The presence of higher organic matter in the green manured plots improved soil moisture (21.1–22.7 %) and soil temperature (24.2–25.1 °C) compared to sole maize (19.4 % moisture and 23.6 °C). Sunhemp produced a biomass of 1.33 to 1.42 t ha-1, with lower levels of lignin fibre (1.26–1.34 %) and higher levels of cellulose and hemicellulose, indicating rapid decomposability of the organic biomass. The study revealed that in situ green manuring benefits the rhizosphere soil nutrient status and microbial activity, thereby improving soil health and productivity of rabi maize.