Recognizing Localized Dry Spots:  The Possible Solution Using Wetting Agents

by Herminia Vivas

Summary

The early recognition of Localized Dry Spots could be a good tool in order to develop adequate management strategies on greens and sport field facilities. Sand based soils are more susceptible to the occurrence of this water repellency symptoms, but fortunately good result have been obtained with the utilization of wetting agents . With the possibility of future water use restrictions, continue information on surfactants use is very promising to help greenkeepers maintain a high quality turfgrass stand.

Dry spots can occur for many reasons on your greens. After checking and discarding compaction problems, excessive thatch accumulation, insects and diseases presence, poor irrigation coverage, it is time to look for other possible cause. Have you considered hydrophobic soils?

These soils are also called water repellent soils, since they restrict the entry of water on the soil profile. This type of soils seems to remain dry after irrigation as well as rainfall, and the reason is that irregular dry regions remain in the soil mass as all water passes though vertical channels formed among these dry regions .

These dry regions become visible as a logic consequence of low moisture availability, developing dead or severe wilted turf recognized as Localized Dry Spots (LDS).

Decreased germination and emergence of seeds, less availability of nutrients and increased possibilities of soil erosion are among other possible consequences.

Apparently, the cause for water repellency is because soil particles are coated with substances that repel it, much like wax .This compound is a complex organic, acidic material that appeared to be the mycelium of a fungus. (8 )

The LDS phenomenon has been reported in many parts of the world, and it is not exclusive of turfgrass, although there is a relationship with soil type. Coarse texture sandy soils with less than 5% clay are particularly susceptible to develop LDS, and since golf greens and athletic fields are sand based constructed, the symptoms are more easily developed.

The increased likelihood of the sand to undergo irrigation practices with severe wetting/drying cycles favor the severity for the development of hydrophobicity, and in most turfgrass situations affects the top 2 to 3 inches of soil (4 ) . Consequently, the best method of preventing this is frequent irrigation .

Approximately soil hydrophobicity can develop between 8 to 18 months after construction of a predominately sand based root zone. (4 )

Testing the soil could be a good tool to treat the cause of LSD saving time and money, and even when it is already developed, testing could provide a better understanding of the extent and severity in order to develop adequate management strategies.

Utilizing a Moisture sensor, could be a good indicator. If readings are below 25%, there is not enough water in the soil for the grass roots to utilize.

Researches have utilized more precise methods that require laboratory facilities to test soil hydrophobicity, and the results were consistent with the moisture sensor's water deficiency detection.

The Kaolinite clay + Rhodamine B mixture (1 ), and the water drop penetration time (WDPT) ( 5 ) are among those more precise methods used.

For the first one, a soil core of 30 cm is taken and split lengthwise to reveal the profile. The profile is sprinkled with a dust composed of finely-ground kaolinite clay containing Rhodamine B dye (1% by volume) that turns red in contact with moist soil and remains white in contact with dry soils.

This method reveals the soil moisture or dryness as well as the identification of the soil water channels developed in hydrophobic soils .

For the WDPT, a 36 ul drop of deionized water is placed on the surface at 1 cm intervals to a depth of 4 cm on soil dry cores . In presence of hydrophobic soils, the water drops tend to "ball up" on the soil core surface, and the infiltration time is more extensive.

To revert this problem and improve water infiltration into these hydrophobic soils, the use of porous -ceramic mixtures (6 ), and clay amendments (7 ) on a sand based soil have been considered with good results.

The use of nonionic surfactants, more commonly called wetting agents had also proved to be a possible solution when properly used. Wetting agents are detergent like substances that reduce the surface tension of water, allowing it to penetrate and wet the soil more easily.

Many studies have been carried out, and wetting agent products are no universally effective under all soil conditions. When applied to normal wettable soils, its results have failed to increase water infiltration, nutrient uptake or plant population. They are effective only on soils that are at least somewhat water repellent. (8 )

Here in Florida, in a 3 year study, commercially available surfactants were tested to prove their effect on reducing soil-water repellency in mature Cynodon dactylon X Cynodon transvaalensis cv. Tifdwarf sand-based greens. Cisar et al, 1999 (3 ), conclude that these surfactants significantly reduced percent dry spotting after treatment, and also improved turfgrass quality in a period of drought, when the LDS symptoms became more evident.

In other study, on bermudagrass cropped sand soils Snyder and Cisar, 1999 (7) also found that surfactants were effective to correct the LDS problem , but only for a short time when compared to the utilization of soil amendments.

In an Ohio study, applying wetting agents on turfgrass reduced the severity of the condition, but the most effective solution was to use them in combination with coring.(8).

Greenkeepers appear to have many choices to improve the quality of the turf on hydrophobic soils, that can alleviate LDS symptoms over time. Following good irrigation practices, and the availability of wetting agents and the continue research for their best application methods, combinations, etc are very promising, specially when considering the global concern about reducing water use.

References

1) Bond, R.D. 1964. The influence of microflora on the physical properties of soils II. Field studies on water repellent sands. Australian Journal of Soil Research 2: 123-31.

2) Cisar, John, 1996. Summer turf. Florida Turf Digest. Vol 13 N 5. September/October, 1996.

3) Cisar, John, L, Karen Williams, Herminia Vivas, John J. Haydu, 1999. The occurrence and alleviation by surfactants of soil-water repellency on sand-based turfgrass systems. ( In press).

4) Letey,J 1969. Measurement of contact angle, water drop penetration time and critical surface tension. Proceedings of the Symposium on water repellent Soils". University of California. Riverside, 43-47.

5) Miller, G.L., 1996. Localized Dry Spot, Water retention, and nutrient availability as influenced by a porous ceramic soil amendment. University of Florida Turfgrass Research, 1996.

6) Snyder, George and John L. Cisar, 1999 . An Evaluation of Physical and Chemical Methods for Alleviating Soil Water Repellency in Turfgrass in Florida. ( In press).

7) Sunderman, H. D. 1983. Soil Wetting Agents, North Central Regional Extension Publication 190. Colby, Kan: Kansas State University, 4pp.

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