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Improvement of water management and water use efficiency at field scale is highly important under simultaneous salinity and water stress. The models that can translate the effects of different quantity and quality of water to crop yield, are useful tools for water management and improving water productivity (WP). AquaCrop (v4.0) simulates yield, water requirement, WP, soil water content and salinity under different conditions in the field, including water‐limiting and different quality of irrigation water. This study was carried out as split plot design (factorial form) in Birjand, in the east of Iran, in order to evaluate the AquaCrop model. Treatments consisted of three levels of irrigation water salinity (S1, S2, S3 corresponding to 1.4, 4.5, 9.6 dS m‐1) as the main plot, two wheat varieties (Ghods and Roshan), and four levels of irrigation water amount (I1, I2, I3, I4 corresponding to 125, 100, 75, 50% water requirement) as subplot. The model was nested, calibrated and validated separately for each salinity treatment, and also simultaneously for all three salinity treatments. The overall model accuracy was higher for estimating soil moisture profile, as compared to soil salinity profile. For simulation of soil water content, the average values of RMSE, d, CRM and R2 in both calibration and validation were 11.8%, 0.79, 0.05 and 0.61 respectively, while for simulation of soil salinity they were 24.4%, 0.72, 0.19 and 0.57 respectively. The AquaCrop successfully simulated yield, biomass and WP for two wheat varieties under salinity and water‐limiting treatments with high accuracy. Average values of NRMSE, d, CRM, and R2 for both calibration and validation of simulated grain yield were 7.1%, 0.97, 0.001 and 0.9 respectively, for the Roshan variety, while these measures were 8.2%, 0.98, −0.004 and 0.87 respectively, for the Ghods variety. Crop transpiration coefficient (KcTr), normalized crop water productivity (WP*), reference harvest index (HIO), volumetric water content at field capacity (θFC), soil water content at saturation (θsat), and temperature were the most sensitive parameters. Copyright © 2016 John Wiley & Sons, Ltd.

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Dynamical analysis of an impacting liquid drop on superhydrophobic surfaces is mostly carried out by evaluating the droplet contact time and maximum spreading diameter. In this study, we present a general transient model of the droplet spreading diameter developed from the previously defined mass-spring model for bouncing drops. The effect of viscosity was also considered in the model by definition of a dash-pot term extracted from experiments on various viscous liquid droplets on a superhydrophobic surface. Furthermore, the resultant shear force of the stagnation air flow was also considered with the help of the classical Homann flow approach. It was clearly shown that the proposed model predicts the maximum spreading diameter and droplet contact time very well. On the other hand, where stagnation air flow is present in contradiction to the theoretical model, the droplet contact time was reduced as a function of both droplet Weber numbers and incoming air velocities. Indeed, the reduction in the droplet contact time (e.g., 35% at a droplet Weber number of up to 140) was justified by the presence of a formed thin air layer underneath the impacting drop on the superhydrophobic surface (i.e., full slip condition). Finally, the droplet wetting model was also further developed to account for low temperature through the incorporation of classical nucleation theory. Homogeneous ice nucleation was integrated into the model through the concept of the reduction of the supercooled water drop surface tension as a function of the gas-liquid interface temperature, which was directly correlated with the Nusselt number of incoming air flow. It was shown that the experimental results was qualitatively predicted by the proposed model under all supercooling conditions (i.e., from -10 to -30 °C).

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