In this chapter, we have considered the complexity of soil pores and pore networks and how they control and complicate the processes of soil water flow. We have learned how to make a simple table to determine the gravitational, pressure, and total water potentials for soil-water systems at equilibrium and during steady, saturated flow. We have studied, compared, and contrasted three foundational laws relevant to water flow in soil: Poiseuille’s Law, Darcy’s Law, and the Buckingham-Darcy Law. And, we have learned about soil hydraulic conductivity; its role in determining soil water flow rates, the enormous variability which occurs in hydraulic conductivity, and the soil and water factors which contribute to that variability. Equipped with understanding of these fundamental concepts, we are now ready to begin studying one-by-one the processes of the soil water balance, that dynamic ebb and flow which sustains life on Earth. As we will see in the next chapter, our study must begin before the water ever reaches the soil.
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