SportsTurf

IRRIGATION & DRAINAGE 36 SportsTurf | August 2016 www.sportsturfonline.com point." The permanent wilting point occurs when soil moisture drops so low that plants wilt and cannot recover. The amount of water available to the plant between field capacity and the permanent wilting point is referred to as the "total available water holding capacity" of the soil. This can be affected by soil texture, organic matter content, the ability of the soil to accept water as well as other factors. Heavy textured soils with higher percent- ages of clay and silt will hold more water than lighter soils with high percentages of sand. Soils containing higher levels of organic matter will hold greater quantities of water than soils low in organic matter. Soils with a high level of organic non-polar coatings on soil particles will resist the acceptance of water and will hold less water than soils with less non-polar coatings. Sandy soils are more susceptible to non-polar coatings. Products that help soil retain greater quantities of water and for longer periods of time include hygroscopic humectants, polymers, and surfactants/wetting agents. TECHNOLOGIES FOR OPTIMIZING SOIL MOISTURE MANAGEMENT Hygroscopic humectants. Though they are not new to the in- dustry, hygroscopic humectants are continuing to gain notoriety with sports turf professionals as products that are very effective at reducing overall water requirements. With a history in golf, these products have been gaining greater attention due to their recent performance in drought stricken areas of California, Texas and other western states. Hygroscopic humectants manage and conserve water through two modes. As the name suggest there is a hygroscopic compontent and a humectant component. Each has a critical function in the performance of the technology. The mode of action of the hygroscopic component is to condense soil water vapor or soil humidity back into liquid droplets of water. The hygroscopic ability of these materials can be compared to condensation or "sweat" that occurs on the side of a cold drink. Rootzone humidity that cannot be absorbed by plant roots is converted into plant usable micro-droplets of water. There are other materials used in this industry that are hygroscopic in nature. These include fertilizers such as urea. The hygroscopic nature of some fertilizers may cause bridging in a spreader, or turns a bag of granular fertilizer into a "brick." The same hygroscopic materials used in hygroscopic humectants are also used in certain foods, such as breads, and in toiletry groups (e.g., toothpaste) to keep them moist and pliable. The humectant components hold the water droplets con- densed by the hygroscopic components. Do not confuse a humectant with a humate. They are completely different substances with different molecular structures. The humec- tant component holds the droplets tightly enough to prevent it from leaving the proximity of the root, but lightly enough to allow the root to absorb the water through osmosis. The humectants in hygroscopic humectants are also used in cosmetics, shampoos, and other body care products where they help hold moisture in the skin and hair. Available in both liquid and granular options, hygroscopic humectant technolo- gies must be watered-in, at which point the active ingredients will coat plant roots, soil particles and organic particles in the rootzone. The hygroscopic humectant molecules are too large to be absorbed by the roots. Once these compo- nents attach to the roots and soil particles, they remain attached and are resistant to further movement in the soil. The ingredi- ents are primarily derived from plant byproducts (some brands are rated at 93% biobased by the USDA BioPreferred Program, such as Hydretain and LESCO Moisture Manager). Therefore, they are eventually broken down by soil microbial activity. Research and users have demonstrated that the most effective hygroscopic humectants products have been able to reduce water use by up to 50% and will typically perform for up to 90 days. In addition to providing general conservation of water, hygroscopic humectants aid in seed germination, transplant establishment and in establishing sod and sprigs. Hygroscopic humectants have also been used to suppress dust on baseball infields, horse arenas, dirt race tracks, etc. Super absorbant polymer. This technology tracks its orgin to a patent by Monsanto in 1963. They described polymers as "strings of large molecules that chemists use like Tinker Toys, adding, subtracting or linking them together to create diverse uses ranging from filling for disposable diapers to dental prod- ucts. Baby diapers are a well-known use for this technology. Polymers have been adapted for use in soil to improve water availability to plants. They are used to "increase a soil's water holding capacity, increase pore sizes and numbers in the soil, increase germination rates, and decrease or mitigate the effect of soil compaction on plant growth. The five main types of soil polymers available commercially include: Cross-linked polyacrylamides (gel forming) Non-cross-linked polyacrylamides (water soluble) Polyacrylates Polyacrylontrile Starch-grafted copolymers The most commonly used polymer is the cross-linked poly- acrylamide. Soil polymers occur in a crystalline form. When exposed to water, they expand into a gelatin-like block. When used in soils, they function as mini-reservoirs of water. They absorb water and hold it until the plant removes the water. The literature indicates that cross-linked polyacrylamide polymers used in the field will absorb and hold 80 to 200 times their weight in water or more. Their ability to hold soil water is H y dra t ed vs. dry po l y m ers .

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