4. Soil Water Flow

In the second chapter we considered the complex and hierarchical spatial organization of the soil solid phase across scales ranging from kilometers to micrometers. We briefly discussed the relevance of these patterns to issues ranging from climate change to agricultural management to pesticide transport. In the third chapter, we focused on two of the most important and dynamic descriptors of the soil’s condition, soil water content and soil water potential, and the relationship between those two variables, the soil water retention curve.  Now the main aim of this chapter is to build a foundation for accurately understanding soil water flow. But before we can do that, we first need to focus on some of the most fascinating, intricate, and life-giving physical features of soil, the soil pore spaces. We will begin this chapter by focusing on understanding soil pores and pore networks and their significance, and then we will spend the rest of the chapter learning the fundamental physical properties and processes that govern the flow of water in those pores spaces.