Chapter 7

Soil Water

(book excerpts)

Soil water is important because water is essential for plant life processes on the Earth. Soil water may come from sources such as precipitation and upward movement of groundwater, or by human interventions with inputs such as irrigation. A consistent soil water supply to support plant root adsorption and transpiration is necessary to sustain crop productivity. In both cropped and natural systems, soil water is transferred back to the atmosphere through a combination of evaporation and transpiration. These processes tightly connect the terrestrial hydrologic cycle (mass transfer) to the land-surface energy balance (heat transfer). Soil water is in a cycle of continuous exchange with its surroundings according to gradients in water potential and temperature. Through these exchanges, soil water storage can vary between extremely dry and saturation. Soil–water interactions determine the rates of water loss by leaching, surface runoff, evapotranspiration, the balance between air and water in soil pores, the rate of change in soil temperature, the kind of soil organisms, nutrient transport, and the capacity of soil to store and provide water for plant growth. Effective management of water, a natural resource, requires the producer to understand relationships between soil, water, and plants.

Click on the following topics for more information on soil water.

Topics Within This Chapter:

  • Hydrologic Cycle
  • Fluxes
  • Soil Water Thresholds
  • Saturation
  • Field Capacity
  • Permanent Wilting Point
  • Plant Available Water
  • Management Allowable Depletion
  • Soil Water Potential
  • Gravitational Potential
  • Matric Potential
  • Osmotic Potential
  • Water Uptake from Soils by Roots
  • Soil Water Movement
  • Saturated Flow
  • Factors Influencing Saturated Flow
  • Unsaturated Flow
  • Water Vapor Movement
  • Measuring Soil Water Status
  • Gravimetric Method in Measuring Soil Water Status
  • Indirect Methods in Measuring Soil Water Status
  • Volumetric Soil Water Content (% vol)
  • Soil Matric Potential (kPa)