At 94 years old, Momma Fidanza still loves to bake homemade pies for her grandchildren and great-grandchildren. Their favorite is pumpkin pie, but the best part is that always-perfect, flaky pie crust. Biological crust on the surface of a golf course putting green, however, certainly is not a favorable or welcomed sight.
Biological soil crusts, also known as cryptobiotic soil crusts, are composed of living organisms of algae, cyanobacteria, fungi, lichens and mosses that typically occupy the first few millimeters of the soil surface. These crusts occur in diverse ecosystems ranging from deserts to polar regions. Wet environments favor the establishment of moss-dominated crusts, while cyanobacteria are most common with drier conditions and sandy soils. In sand dunes, these cyanobacteria are considered pioneer organisms that take advantage of the sand as an early part of succession in nature.
Cyanobacteria, also referred to as blue-green algae, are considered the primary components of most biological soil crusts, and their presence tends to impede water infiltration. Cyanobacteria grow and navigate their way between soil particles, leaving behind “sticky” tissues and substances that clump those particles together. Cyanobacteria are commonly found colonizing the surface of golf course putting greens, especially those maintained in shaded environments, and with poorly drained and compacted root zones, and where turfgrass stands are thin and not as vigorous or competitive.
Another issue with biological soil crusts is the development of water repellency upon drying. This is caused by those hydrophobic compounds and exudates produced by various microbial organisms, algae and cyanobacteria that coat sand and soil particles. On a sand-based putting green, this means a significant decrease in water infiltration, and runoff can easily occur. In other words, the putting green root zone is not receptive to irrigation water or rain. Therefore, these biological soil crusts can have a major effect on water movement and plant-available water in soil.
Research was conducted to examine the influence these organisms found in biological soil crusts have on the physical properties of sand. From a pine forest site of predominantly sandy soil, organisms of Choricystis minor (coccal green algae), Klebsormidium subtile (filamentous green algae) and Tribonema minus (stramenopile algae) were isolated from biological soil crusts at that location. These algal species were grown and maintained in laboratory petri dishes. Each species was inoculated into sterile pure sand to form crusts and evaluated over a 21-day period. Various hydrophysical parameters of those crusted sands were tested and compared to pure sand.
With all three algal species, the inoculated crust-formed sandy soil had a water repellency index of 18 times greater than pure sand. These water repellent conditions were confirmed by the much slower water infiltration rate of the sandy soil compared to pure sand. Also, the hydrophobic conditions of the sandy soil persisted 54 times longer compared to pure sand.
All three algal species formed a compact green crust on the sand. One species, K. subtile, grew primarily on the sand surface, but C. minor and T. minus penetrated a bit further into the sand. It also appeared that sand surfaces colonized primarily by K. subtile developed a denser crust or biological mat that “clogged-up” sand particle pore spaces at and near the surface. With K. subtile inoculated sand, after seven to nine days, oxygen produced by photosynthesis formed bubbles that popped, and this caused the crust to blister resulting in a patchy appearance.
Overall, this study demonstrated the ability of organisms to form biological soil crusts on sandy soil, their impact on water flow in soil, and some insight into the complex nature of those species that form these biological soil crusts.
For more information on cyanobacteria on golf course putting greens: Effect of phosphite rate, source on cyanobacteria greens colonization. Golf Course Management. March 2018. (https://gcmonline.com/course/environment/news/cyanobacteria-putting-greens).
Source: Lichner, L., P.D. Hallett, Z. Drongová, H. Czachor, L. Kovacik, J. Mataix-Solera and M. Homolák. 2013. Algae influence the hydrophysical parameters of a sandy soil. Catena 108:58-68.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 23-year member of GCSAA.