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FieldScience | By James Spindler, CPAg, CCA, CPSS The use of hygroscopic humectants in managing soil moisture Editor's note: The author is president of BioPro Technologies; president and owner, Spindler Enterprises; agronomist and partner, Ecologel Solutions; and agronomical and research director, OJ Noer Turfgrass Research Foundation. M OST TURFGRASS MANAGERS are familiar with the use of wetting agents, or surfactants, and super absorbent polymers in managing water movement and retention in soils. However, there is another class of chemistry that is gaining acceptance in the management of turfgrass and ornamental soil moisture. This class of chemistry is referred to as hygroscopic humectants. Before discussing hygroscopic humectants, it is important to understand how they differ from other water management technologies. First, wetting agents are chemicals that "reduce surface tension of water, allowing the water molecules to spread out." Another definition is "any compound that causes a liquid to spread more easily across or penetrate into the surface of a solid by reducing the surface tension of the liquid." Therefore, a wetting agent is a material that allows water to more 18 SportsTurf | December 2013 easily penetrate into soil and/or flow through (infiltrate) the soil. These materials are valuable when soils have become hydrophobic and will not wet easily. Super absorbent polymers, another type of water management technology, are "materials that can absorb and retain extremely large amounts of liquid relative to their own mass." These materials are utilized to absorb large amounts of rainfall or irrigation to be used by the plant at a later date. These materials are commonly used in greenhouse and nursery industries, as well as in some agricultural settings. However, the use of polymers in turfgrass is difficult for two reasons. The first is that polymers are difficult to incorporate into the soil profile. The second is that, as they absorb water, they expand, and can disrupt the soil and turfgrass surface. However, there are some new developments in polymer technology that may overcome these challenges. Hygroscopic humectants are materials that attract water vapor (the gas phase of water) from the atmosphere within the soil, condense it back into a liquid form, and retain the liquid for the plant to absorb. According to Merriam Webster's dictionary, a hygroscopic material is any material that "readily takes up and retains moisture." Most turf managers are more familiar with hygroscopic materials than they may realize. For instance, many fertilizer ingredients are hygroscopic. It is the hygroscopic nature of some fertilizers that cause them to "cake" or form chunks in the package. The definition of a humectant is "a substance that promotes retention of moisture" (Merriam-Webster). These are substances that absorb, or help another substance to retain moisture. These types of materials are commonly used in the food and cosmetic industry. For example, humectants will help keep food from drying out and becoming stale. In cosmetics they help keep different types of make-up pliable so they may be applied to the skin in an even fashion without causing dryness. The key to successfully using hygroscopic humectants to manage soil moisture is by using the right combination of raw ingredients. Some raw materials will attract moisture and condense it, but will hold it too tightly, not releasing the water to the plant. On the other hand, some raw materials may compete with the plant for soil moisture and be detrimental to plant health. Finally, some raw materials will be broken down in the soil by microbes too quickly, and have a short lived effect. The best combination of raw ingredients are those that will attract soil water vapor to itself, condense it into a droplet, and then allow the plant root to remove that droplet for use in its metabolic activities. Another vital factor in the success of a hygroscopic humectant product is to have a certain resistance to microbial degradation. Many of the raw ingredients used in a hygroscopic humectant are organic in nature, and can be used by soil microbes as a food source. We see the same types of challenges in pesticide formulations. Hygroscopic humectants have a variety of uses in the management of turf and landscapes. For example, they may be used in combination with wetting agents to relieve www.sportsturfonline.com