Water droplet penetration test
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Localized dry spot can be caused by a number of factors including water repellent thatch and mat layers. The water droplet penetration test provides a simple method for evaluating water repellency of the thatch, mat and soils. For an example of the use of this technique, refer to this video of symptoms and this video of the droplet test. For a general guideline, if the drop does not penetrate the soil within 10 seconds, water repellency is a likely problem and application of wetting agents should be considered. The longer it takes for the droplet to penetrate the soil, the more serious the water repellency is and the more difficult it will be to correct.
