Abstract
Temperature gradients exist in the field under brackish water irrigation conditions, especially in northern semi–arid areas of China. Although there are many investigators dedicated to studying the mechanism of brackish water irrigation and the effect of brackish water irrigation on crops, there are fewer investigations of the effects of temperature gradient on the water–salt transport. Based on the combination of a physical experiment and a mathematical model, this study was conducted to: (a) build a physical model and observe the redistribution of soil water–heat–salt transfer; (b) develop a mathematical model focused on the influence of a temperature gradient on soil water and salt redistribution based on the physical model and validate the proposed model using the measured data; and (c) analyze the effects of the temperature gradient on the soil water–salt transport by comparing the proposed model with the traditional water–salt model in which the effects of temperature gradient on the soil water–salt transfer are neglected. Results show that the soil temperature gradient has a definite influence on the soil water–salt migration. Moreover, the effect of temperature gradient on salt migration was greater than that of water movement.
Highlights
Freshwater resources are relatively limited [1], but groundwater resources are abundant in many countries or regions [2]
The aims of this study were to (a) build a physical model of the non-isothermal vertical soil column in the laboratory; (b) observe the redistribution of the water–heat–salt transfer; (c) develop a mathematical model focused on the influence of temperature gradient on soil water and salt redistribution based on the physical model; (d) validate the proposed model by the measured data and analyze the accuracy of the model; and (e) analyze the effects of temperature gradient on soil water–salt transport by comparing the proposed model with the traditional water–salt model where the effects of temperature gradient on soil water–salt transfer was neglected
In Phase 3, the mean absolute error of the soil salt content under Condition 2 was 1.805 times, 1.197 times, and 1.562 times, respectively, all of which were greater than that of Condition 1; and the maximum root mean square error under Condition 2 was 3.030 times, 1.567 times, and 2.106 times, respectively, all of which were greater than that of Condition 1. These results indicated that simulated accuracy for the soil salt content under Condition 1 was higher than that of Condition 2 given that the soil water was the carrier of soil salt, so the effect of temperature gradient on soil salt migration was mainly reflected in the effect of temperature gradient on soil water movement and solute diffusivity
Summary
Freshwater resources are relatively limited [1], but groundwater (or seawater) resources are abundant in many countries or regions [2]. The rational use of groundwater resources is an important approach to solve water resource crises [3,4]. Research shows that brackish water irrigation is propitious to crop quality in a certain range of salinity [5,6]. In an agricultural system that involves brackish water irrigation, an interaction occurs between salt and water in the soil [7]. Soil moisture is a medium of heat and mass transfer, and can induce heat and salt migration. Soil water movement can lead to a new salt concentration and temperature gradient [11]; the effects of temperature gradient on soil water and salt transport cannot be disregarded [12]
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