Plant nutrients such as nitrogen and sulfur exist mostly as negatively charged ions in the soil and therefore are not held by soil colloids. As a result, these elements are subject to leaching by water moving through the soil, especially in sandy soils. Leaching of nitrogen into the groundwater is a serious environmental problem in sandy irrigated regions. Water is held in the soil by cohesion to other water molecules and by adhesion to colloid surfaces. Soils with smaller pores are more effective at holding water against the forces of gravity.
Large pores are best at conducting water through the soil when water content is high.
When the ground is saturated, all the pores in a soil are filled with water. After about two days, water drains from the large pores, and the soil is in a condition known as field capacity. This is the maximum amount of water a soil can hold against the forces of gravity. Some water is held so tightly by adhesion that plants cannot pull it away. When plants cannot remove any more water from the soil, the field has reached what is called the wilting point.