Aquatrols is committed to providing our customers with reliable and effective, proven products with distinct benefits. To achieve this we must stay on top of the science behind our technologies as well as the issues and challenges faced by turf, horticultural, agricultural and snowmaking professionals worldwide.

From the start Aquatrols has been actively involved in product testing and has become an integral part of the worldwide research community attending and contributing to conferences, lectures and seminars. We continually strive to make the information available to you as well so that you can make informed decisions about what is best for you and your business.

Properties of Water

Water is critical to your business – from the establishment and maintenance of healthy roots for uniform, vigorous crops to the distribution and effectiveness of soil-targeted chemicals and fertilizers. Water is one of our most precious natural resources, and it is becoming more expensive and less available every year. By understanding the properties of water and the factors that contribute to water-related problems - poor infiltration, percolation, excess run-off or tail water - you can institute practices that can reduce your yearly water usage, helping both the environment and your bottom line.

Chemical Properties

Many of the unique properties of water can be attributed to its molecular construction. The two hydrogen atoms and single oxygen atom of water are held together by a strong covalent bond. Although the water molecule is electronically neutral, the geometric configuration of the covalent bond of water creates a molecular structure for the entire water molecule, with oxygen having a partial negative charge and each hydrogen having a partial positive charge.

Since opposite charges attract, the hydrogen region is attracted to the oxygen region of other water molecules or negative sites on other molecules. The attraction of the hydrogen region of water molecules to negatively charged regions of other molecules is called hydrogen bonding.

Within a water droplet, water molecules are in a constant state of movement toward other water molecules. Each water molecule is subject to attractive and repulsive forces from nearby molecules that, on the average, are distributed in all directions. This strong attraction between water molecules is defined as cohesion.


Interfacial Tensions

Any time water molecules located on the boundary of the fluid come in contact with a dissimilar solid, liquid, or vapor, their properties can be different. Forces that alter or influence intermolecular attractions on the boundary of the fluid state of water are called interfacial tensions.

The inward movement of water molecules at the liquid-air interface is known as surface tension. Surface tension is what causes water to “bead” on a surface rather than spread out. Surface tension also has a great deal to do with the ability of water to infiltrate pore spaces, whether they occur at the soil surface or within the soil profile. If the size of the water droplet exceeds pore space size, penetration and infiltration of water into and through the soil profile may be restricted.

When water comes in contact with a solid surface (liquid-solid interface), the polar attractive forces between the water molecules and the solid surface (adhesion) will dictate the affinity of the water for the solid. Water molecules at the liquid solid interface will attach to surfaces containing polar sites through hydrogen bonding (hydration). Adhesive tension is associated with hydration or wetting of the soil.

Soils

Like the plants they support, there are a wide variety of soils comprising many different physical and chemical properties. These physical and chemical properties affect many parameters related to plant growth including: soil strength and stability; water infiltration, percolation, and storage; gas exchange; nutrient availability, mobility, and cycling; organic matter content and cycling; and support of other living organisms both beneficial and harmful.

Successfully managing your turf, ornamental, or agricultural crops in part depends on an understanding of the physical and chemical properties of your particular soils and how they influence the parameters mentioned above.

Soils are a dynamic environment. Physical and chemical weathering; plant, animal, and microbial organism growth and decline; and human management practices all serve to continually change the soil environment. Because soils are constantly changing, the parameters that affect plant growth are constantly changing as well.

Successfully managing your turf, ornamental, or agricultural crops in part requires regular evaluation of the parameters mentioned above and a willingness to modify management practices to account for those changes in the soil system.

One result, common to many of the dynamic soil processes is the accumulation of organic matter. Whether through surface plant turnover, root exudates or die off, or macro and micro organism life cycles, organic matter is continually added to the soil. While organic matter can be beneficial in many instances, it can also cause soils to become water repellent which can lead to water movement issues in soils.

Water Movement Issues

Water Repellency

Researchers generally agree that water repellency (hydrophobicity) in soils is caused by a range of hydrophobic organic materials that form non-polar “coatings” on soil particles. Decomposing plant materials, microbial deposits, organic acids (photo below shows Humic Acid-[organic] magnified 35,000x's), and fungal hyphae have been identified as possible sources of hydrophobic organic materials. Soil water repellency is more common than previously believed (Dekker et al) and has been identified in all soil types in a variety of climatic, geographic and vegetative conditions.

When a soil particle coated with these hydrophobic organic materials becomes dry, the normal polar characteristic of the soil is changed to a non-polar surface.  Water molecules, because of their polar nature, tend to prefer and aggregate towards other polar molecules rather than the non-polar sites of water repellent surfaces.  Therefore, since there is no polar entity to move toward, water molecules at the water boundary tend to move inward toward the bulk of other water molecules.  This is the molecular basis of water repellency.  The scientific definition of water repellency is described as a condition where the adhesive polar forces at the water solid interface are less than the cohesive force of water.

Water repellency in soils can result in a number of problems caused by poor water movement patterns.  The most obvious effect of water repellency is a reduction of infiltration rates.  (Photo shows water drops sitting on soil surface due to water repellency in the soil) Additionally,  hydration (wetting) and distribution of applied water and input chemicals can be quite irregular and incomplete.  Turf decline, localized dry spots, poor drainage and non-uniform turf quality have also been linked to water repellency in soil profiles.  Water repellency is often viewed inaccurately as a condition that:  1) occurs only in a limited number of soil profiles, 2) impacts small areas only (i.e. localized dry spots), and 3) occurs at the surface of the soil profile.

After years of investigation, soil scientists now describe water repellency in much broader terms.  Current research data generated from scientists around the world characterize water repellency as a condition that:  1) occurs to some degree in the majority of soil profiles, 2) can impact water movement to large areas of the soil profile, while visible detection is often limited to small areas, and 3) occurs from the surface to depths that would include the root zone of most turf grass varieties.

Surfactant Technology

Research has confirmed that certain surfactants (“wetting agents”) are very effective in overcoming water movement problems associated with water repellency. Surfactants are chemical compounds whose molecular structure is well suited to overcome both the water repellent (non-polar) characteristics of hydrophobic soil profiles and poor infiltration of water.

It should be noted that the construction of surfactants is very complex. Although there is similarity in the function of most surfactants, surfactant chemistries and/or their formulations may differ widely in their performance characteristics. The surfactant molecule is made up of a hydrophilic (“water loving”) polar component and a hydrophobic (“water repellent”) non-polar component.

Surfactants in Water
When surfactant molecules are applied to soils with water as the carrier (such as through irrigation systems), the hydrophilic ends of the surfactant molecules are strongly attracted to the water molecules. As a result, the surfactant molecules align themselves at the surface so that their hydrophilic ends are toward the water and their hydrophobic ends are “squeezed” away from the water. These “outward” forces at the air-water interface reduce surface tension and facilitate infiltration of water from the surface into the soil profile.

Surfactants in a Soil (Media) Profile
When a surfactant is applied to the soil profile, the hydrophobic (non-polar) end of the surfactant attaches to a non-polar water repellent site on the soil particle. This serves a very important function. As water moves into and through the soil (media) profile, individual water molecules are attracted to the polar end of the surfactant. Therefore, the polar end of the surfactant serves as an attachment site for water molecules, allowing a water repellent soil particle to hydrate (“wet”).

Efficient Water Use

The use of surfactants/wetting agents in combination with well designed and operated irrigation systems and proper cultivation has the potential to increase the efficiency of irrigation and conserve water to levels beyond what has already been achieved with equipement alone. Water does not always go where intended due to changes in soil conditions, and surfactants correct some of those changes.

Click here to read how Aquatrols soil surfactants promote Efficient Water Use

Research Industry Links For More Information

Take a look at the following articles and links for more detailed information about Water Repellency issues in soils and turf grass maintenance.

 

Alterra - The Water Repellency Project A Global Project Alterra, the Netherlands	Scottish Crop Research Institute
	Soil Water Repellency Society
University of Wales Swansea