Effects of thermal and hydrophysical properties of sandy Haplic Podzol on actual evapotranspiration of spring wheat

The objectives of the research were to: (1) assess the strength of relationships between the soil thermal and hydrophysical properties, (2) evaluate the strength of association of evapotranspiration of spring wheat crop with soil thermal and hydrophysical properties, and (3) estimate the ranges of the thermal and hydrophysical properties of the sandy Haplic Podzol during the growing period of spring wheat in 2022. The study included instrumental simultaneous measurements of meteorological data, soil water retention curve, soil moisture content (SMC) and thermal properties. Actual evapotranspiration was calculated according to the Allen equation. Spearman’s rank correlation coefficients showed that the increase in SMC from 0.10 cm³ cm⁻³ to 0.26 cm³ cm⁻³ resulted in a significant increase in thermal conductivity (r = 0.81, p < 0.001), volumetric heat capacity (r = 0.93, p < 0.001) and thermal diffusivity (r = 0.94, p < 0.001). Actual evapotranspiration also rose with the increasing SMC (r = 0.91, p < 0.001) and matric water potentials (r = 0.61, p < 0.05). As a consequence of the changes in SMC, the Spearman’s rank correlation coefficients supported the strong positive relationships of actual evapotranspiration with volumetric heat capacity (r = 0.97, p < 0.001), thermal conductivity (r = 0.96, p < 0.001) and thermal diffusivity (r = 0.96, p < 0.001). Pearson correlation coefficients also supported the strong input of thermal inertia to the actual evapotranspiration (r = 0.88, p < 0.01). During the whole period of observations, actual evapotranspiration varied from 0.05 to 0.59 mm hr⁻¹, soil thermal conductivity – from 0.225 to −1.056 W m⁻¹ K⁻¹, volumetric heat capacity – from 1.057 to 1.889 MJ m^–3 K⁻¹, heat diffusivity from 0.189 to 0.559 mm² s⁻¹, and thermal inertia – from 516 to 1412 J m⁻² K⁻¹ s^−0.5.