Comparison of Methods for Quantifying Soil Water Repellency in Surfactant-Applied Soil.

Golf course superintendents often manage rootzones to avoid the development of localized dry spots caused by hydrophobic soil. Utilizing wetting agents has become a common solution for dry spot prevention. The performance of these products can be based on their abilities to reduce soil water repellency and surface tension of water. Researchers have traditionally quantified soil hydrophobicity using the water droplet penetration time test and the sessile drop method. The objective of this research is to determine if the water droplet penetration time test or a modified sessile drop method is the most time efficient and appropriate method for quantifying soil water repellency for further wetting agent research. Water droplet penetration time tests are simple and allow researchers to observe water movement as it may occur in the field. Unfortunately, this method can be time consuming when many soil samples need to be evaluated. This method is only a measurement of repellency persistence, although it has also been used as an indirect quantification of soil water repellency. The sessile drop method is more effective in assessing soil hydrophobicity because it quantifies water droplet surface tension, however the soil used has been sieved, mixed, and disrupted from its natural placement in the soil profile. Therefore, we have developed a modified sessile drop method to assess surface tension of droplets on soil profiles pulled from the field. Digital images of water droplets placed on soil profiles undergo drop analysis for contact angle estimates. We compared our modified method with the water droplet penetration time test to assess soil cores taken from a creeping bentgrass (Agrostis stolonifera L.) golf green built to United States Golf Association specifications in untreated and surfactant-applied plots. We will present results from this comparison and discuss the implications of our new assessment method on future wetting agent research.