Soil Texture

• Soil texture is the term for the proportion of small (clay), medium (silt) and large (sand) particles in a soil mass. Soils with mostly small particles have a larger surface area and this can hold more water. This means soils with a high percentage of clay and silt particles have a higher water-holding capacity. Not all particles in a type of soil will be the same size, so soil texture is classified by the mixtures of particle sizes.
  
  

Organic Matter

• Wetland soils store a lot of water.Jupiterimages/Brand X Pictures/Getty Images
  
  Most water in the soil occupies the space between the particles. But in organic soils, the particles actually absorb the water. The higher the percentage of organic matter in the soil, the higher the water-holding capacity will be. The quantity of organic matter in soils varies widely. Wetlands illustrate the water storage capacity of organic matter; they have a high percentage of topsoil and organic deposits. Soil texture classes can be modified when more than 15 percent of the particles are organic.
  
  

Movement of Water in the Soil

• Water is held in the soil in two ways. It clings to the outside of the particles, or it fills the pore spaces between particles. Soil water in the pores moves either through gravity or capillary action. Capillary forces move water in any direction. Gravitational water drains quickly after the soil is saturated and is not available for plants. Capillary water is held by soil particles, and this is what plants can use. The water that remains and is stored after gravitational draining is often called "field capacity."
  
  

Improving the Water-Holding Capacity of Soil

• Soil management practices have an impact on its water-storage capacity.Jupiterimages/Photos.com/Getty Images
  
  For landscaping and agricultural purposes, it's desirable to have the largest water-holding capacity possible, as long as there is enough air in the pores soon after heavy watering or irrigation (aeration). Soil texture in the loam, clay loam and silt loam classes stores water for long periods. The capacity can be increased by improving the soil structure with the addition of organic material and effective management of tillage and planting methods.