Localized Dry Spot

As the temperatures continue to rise and soil moisture is further depleted we will become increasingly concerned with preventing and curing a soil condition known as localized dry spot (LDS). LDS is caused by the formation of an organic, wax-like coating on the soil/sand particle which makes the particle hydrophobic, or water repellant. This organic coating is a product of the natural breakdown of organic matter present in the soil.  This is a condition that is far more prevalent in the sandy soils of a greens profile, but it can be observed in almost all soil types. As the soils continue to dry down, this organic coating makes rewetting the soil very difficult. It is no longer as simple as applying water as the soils will simply repel it.

The best plan of attack to prevent or cure this problem is to apply chemicals known as wetting agents. To better understand how a wetting agent works, you first need to understand the chemical properties of water.

Water molecules are comprised of two hydrogen atoms and one oxygen atom. Water is a dipolar molecule which means it has both negatively- and positively-charged polar ends. This polarity allows water molecules to bond well with other polar molecules, but prevents it from bonding with nonpolar molecules such as the molecules that comprise the waxy, organic coatings on soils suffering from LDS.

A wetting agent is a type of surfactant. Surfactants are a class of chemicals that change the physical characteristics of the surface of a molecule. These changes occur at the interface between two substances, for example between the surface of water molecules and the waxy coating on a soil particle. All wetting agents are comprised of a water soluble (hydrophilic) end bonded to an oil soluble (lipophilic) end. When wetting agents are introduced to the soil, the lipophilic, nonpolar ends adhere to the waxy coating of the soil and the hydrophilic, polar ends adhere to the water molecule allowing the soil to hold onto the water.

This clip illustrates the effects a surfactant has on a hydrophobic soil. I know it may be boring but it is very important.