These elements include iron, manganese, copper, zinc, boron, chlorine, cobalt, and molybdenum. The availability of micronutrients is determined by how acidic or alkaline the soil is. 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.