SportsTurf

www.stma.org August 2016 | SportsTurf 35 thanks to gravity. The most common solution to this situation is the use of a penetrant, such as a surfactant or wetting agent. Water channeling through soils. Beyond the influence of salts, bicarbonates or hydrophobic conditions, there may be other times when water will not disperse evenly through the soil. This may occur as a result of varying soil structure, compaction, inconsistent composition, layering, etc. Water will always following the path of least resistance and may drain through channels in the profile, leaving adjacent areas void of adequate water to supply plants. As a result, these areas become much more susceptible to drought or wilt, even under ideal irrigation coverage. These conditions are a primary cause of localized dry spots (LDS). The use of wetting agents or surfactants combined with cultural practices including aeration is often used to alleviate water loss to channeling. Total water holding capacity of soil. Soil has the ability to hold a certain amount of water. The maximum amount of water soil is able to hold is generally referred to as "field capacity." Field capacity is the condition that occurs after soil is completely saturated and excess water is allowed to drain away. The remaining water is either used by plants or lost to evaporation until the soil reaches the "permanent wilting of gravity and evaporation are constantly working to move water away from plant roots. Gravity plays a role in water lost to runoff, channeling and percolation. When it comes to evaporation, most people consider the evaporative loss that occurs immediately, before water has entered the soil; however, as soils dry between watering, the bonds that hold water molecules together break, causing liquid water to dissipate into its gaseous form. The resulting water vapor is not usable by plant roots and is continually lost to the atmosphere above. Additional irrigation to compensate for water lost to gravity or evaporation may be ineffective based on a number of factors, including soil chemical and physical properties, which affect infiltration and soil holding capacity. Failure for water to move into or infiltrate the soil. Wa- ter may sit on top of a turf or soil surface or flow across that surface away from the intended target. It may find a site to drain through soil, but not disperse evenly into and throughout the rootzone. There are a number of causes for this, but let's consider three possibilities. The first would occur with soils or irrigation water containing high levels of sodium salts. Sodium breaks down soil structure by removing the ability of soil particles to be "glued" together to construct various formations. Soil structure allows for the rapid movement of water into and throughout the soil. Salts may also physically "seal" the soil, preventing water penetration. The solutions for this are either calcium or acid. Calcium containing products, such as gypsum, liquid calcium chloride or calcium nitrate, etc., displace sodium ions and allow for the restoration of soil structure. Sulfuric acid, reacted with urea for safety, will convert lime that occurs naturally or is applied to soil, into gypsum, which supplies the calcium needed to make high salt conditions more permeable. The second cause may be bicarbonates. Bicarbonates are common in regions where irrigation water comes from limestone aquifers. The bicarbonates will build up in a similar manner as salts and cause a "sealing" of the soil. A simple test for this condition is to drip some vinegar (an acid) solution on the questionable area. If the drop causes a fizz, then high bicarbonates are most likely present. These conditions may be treated with acids or acid forming materials that break down the bicarbonates into CO2 and water. These treatments would include acid materials injected through an irrigation system or applications of acid forming fertilizers, such as ammonium sulfate or ammonium thiosulfate liquid. A third possibility may be caused by a waxy, organic coating on soil particles. The waxy coating comes from the decay of organic materials and certain species of fungi that exude waxy substances. These waxy coatings form non-polar hydrophobic surfaces that have no charge to attract water molecules. The water does not enter and disburse through the soil. The only polar surfaces are the surfaces of other water molecules. The water will find the path of least resistance and may either flow across the surface and/or find a channel through the soil profile to drain,

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