In areas where winters are characterized by the large amount of snowfall, it is a common practice to use "de-icers" as a mean to clear pathways, sidewalks and streets. The nature and characteristics of these products vary widely. However it is a common effect among all of them the damage they cause to turf areas due to the increased salinity in the surroundings of the treated area.

Previous trials have defined a mixture of calcium chloride and urea as one of the most effective de-icers with minimum damage to turf species. Nevertheless this does not mean that areas treated with this product are exempt of injury.

It has brought to attention that varying the ratio between urea and calcium chloride could possibly decrease the negative effect on turf without decreasing considerably the melting capabilities of the de-icer.

The objective of this study is to compare the effect that different mixtures of calcium chloride and urea applied on winter can have on turf quality and appearance during spring time.

This de-icer study was conducted at the Horticulture farm of Iowa State University from December 2000 until June 2001. The site was located 6 miles north of Ames, Iowa.

Different mixtures of calcium chloride and urea were applied over Kentucky Bluegrass (Poa pratensis) plots. The study followed a complete randomized block design with 8 treatments (Table 1) including control and 3 replications. Each replication had 8 plots of 4x2 ft. separated by a 1 ft. border between them. Replications were separated by 2 ft.

Each treatment was applied weekly during 9 weeks starting on December 15. To reach a concentration of 2.5% W/V (Brine solution), 2 liters of water was used in each application. This simulated a 1/10 inch water film over the grass.

Treatments were initially applied using a backpack CO₂ sprayer, however due to the extreme cold conditions a hand sprayer was used in the last 6 applications. Control plots only received a water spray. Also it must be noted that due to the particularity of the site and weather conditions it was required to remove the snow from the treated plots in the first 3 applications. The accumulation of snow at that point reached over 12 inches, which would not allow a uniform application of treatments. A snow blower and a brush were used for this purpose.

Treatments were evaluated on 4 different dates, March 26, April 14, May 9 and June 1. The variables recorded were color, percentage coverage of turf plants coverage and % coverage of turf plants with seed heads. The index of color was based on a scale of 1 to 10 where 1 refers to total brown or white color and 10 dark even green; 6 is considered the least acceptable green. The other 2 indexes are referred on a percentage basis.

Analysis of variance and LSD were calculated for each of the recorded variables. In June 1 plant samples were collected for total nitrogen. Results of those test will be submitted at a later date of this report.

To better understand the results shown in this report, it is necessary to consider that the winter of 2000-2001 in the Ames area had over 100 days with permanent snow cover. The surrounding area where the treatments were applied maintained over 6 inches of snow since early December until late March. Temperatures were very low for a long period of time.

The readings of turf color appear in table 2. As expected after a long cold winter, the first reading indicated that most of the plants were completely brown,. At this moment plots that received a larger amount of urea were significantly different to those with very little or none urea applied. Also it can be noted that control plots had statically better appearance than the treated ones.

Near 3 weeks later in a second reading , the results have varied very little. Due to the still cold temperatures, no new growth was expected. Results are very similar to the previous date. Control plots are still statically with better color than the treated ones.

Table 2. Observed color in CaCl₂-Urea plots at 4 different dates during spring of 2001.

In May 9, during the third reading it can be appreciated that plants already started to grow and new green tissue is already present. Again there were significant differences between the treatment with the largest amount of urea and the one with 100% CaCl₂, however the relationship is inverse to the 2 previous readings. In this case the treatment with the larger amount of urea show a better color than any other treatment (excluding control). Although the increment on the 70/30 treatment is higher enough to be the best treatment in this reading, the increment in the control plots are far better. Two major points can be extracted from this observation. The first is that the availability of extra nitrogen in the high urea treatments may be already stimulating new growth. However the damage inflicted by the de-icer is still greater than the benefit obtained at this point.

In the last reading, after a considerable improvement in growing conditions, treatments with at least 20% of urea had significantly better color than the control. Treatments with 15,10 and 5 % of urea improved considerably from last reading however they were not significantly different than the control. Control plots did not show an improvement from previous readings, which may be attributed to low levels of nitrogen available in the soil. Treatments with no nitrogen added and high calcium chloride are statically with worse color than any other treatment.

It is clear at this point that supplemental nitrogen in the de-icer mix has overcome the damage inflicted previously. Due to the lack of color development in the last period of time by the control plots it is believed that the area in which the trial was applied has a very limited source of nitrogen. Other areas with higher levels of nitrogen may not have shown differences between control and de-icer applications.

Other variables recorded were percentage of coverage and percentage of area cover with seed heads (table 3). In May 9, the percent coverage followed the same pattern observed in color for the same date. The tendency (excluding control) showed a better coverage in plots with higher ratio of urea; although there were no significant differences between treatments that contained urea. The only significant difference appears between the treatment with 100% CaCl₂ and all the others.

Table 3. Percentage turf coverage and percentage of area cover with seed heads.

Control plots showed a 100% coverage at this time, indicating again that even the safest mixture of CaCl₂ and urea had a detrimental effect on the plants.

A very interesting phenomenon occurred in the treated area and surroundings. Towards the end of May the turf started to produce seed heads in a very dense fashion. Some differential effect on the treatments was observed and this variable was recorded and shown in table 3.

Before looking at the numbers it was believed that areas with low nitrogen could be the ones having the largest amount of seed heads due to a stressed condition. After looking at the analysis of variance this idea was not clear any more. Results indicate that the largest amount of seed heads appeared in control plots, however within treatments the one with higher ratio of urea showed the highest number of seed heads.

It is still possible that the low available nitrogen has triggered the higher amount of seed heads in the control plots. In the case of de-icer treatments differences may be due to the differential damage observed in previous dates and not directly to nitrogen availability. This point will be cleared when results from total nitrogen come from the laboratory.

As an extra note, during the first readings, it was appreciated that even the control plots of the study were in a worse state of color and quality that the area next to them, where no snow was removed. Its is believed that the long and cold winter affected extensively the treated area. The layer of snow that remained around the study could have protected the turf, therefore its greener color and denser condition.

There are significant differences even between small variations in the ratios of urea and CaCl₂.

Under the conditions of this study the mixture of 30% urea and 70% CaCl₂ seems to be the least damaging of the options. Also this ratio seems to be the one with higher benefits and better color development.

Benefits if there are, are not expected to be evident until late spring.