Soil Science Lab 3

Soil Science Lab # 3

1. Adhesive bonding is the attraction of water molecules for solid surfaces. Some water molecules are held rigidly at the surfaces of soil solids. In turn these tightly bound water molecules hold by cohesion other water molecules farther removed from the solid surfaces. Cohesion is the attraction of water molecules for eachother. Together these forces make it possible for the soil solids to retain water and control its movement and use. Make it possible for the plasticity of clays.

2. Soil water potential is the difference in energy levels between this pure water in the reference state and that of the soil water. There are several factors in the soil water potential that are due to differences in energy levels resulting from gravitational, matric, submerged hydrostatic, and osmotic forces. They all act together to influence water behavior in soils. The matric potential accounts for all other effects on soil water potential besides gravity and solute levels. The attraction of water to solid surfaces gives rise to matric potential which is always negative because the water attracted by the soil matrix has an energy state lower than that of pure water. This is operational in unsaturated soil above the water table. Osmotic potential is attributable to the presence of both inorganic and organic solutes in the soil solution. As water molecules cluster around solute ions or molecules the freedom of movement of the water is reduced. The greater the concentration of soutes the more osmotic potential is lowered. The osmotic potential has little effect of the mass movement of water in soils. Its major effect is on the uptake of water by plant root cells that are isolated from the soil solution by their semipermeable membrane.

3. Saturation percentage is the proportion of the cation exchange capacity satisfied by a particular cation for a cation. Field capacity- once the rain or irrigation has ceased water in the largest soil pores will drain...