Introduction

• The retention, movement, and loss of water in soil, plants, and the atmosphere are governed by energy dynamics.
• Soil water possesses kinetic energy (negligible due to slow movement) and potential energy (the primary driver of water movement).
• Potential energy depends on position and determines water flow direction, as water moves from higher to lower potential energy until equilibrium is reached.
• Free energy (energy available to do work) defines soil water’s energy status, decreasing due to soil matrix, solutes, and gravity. Water flows from high free energy (wet soil) to low free energy (dry soil).
• Location also affects potential energy—higher elevation means greater potential energy, creating flow within the soil profile.