February 15, 2013
By Pam Charbonneau
OMAFRA turfgrass specialist

Many of our turf agronomic practices need to be revisited to focus on minimizing the environmental impact on water quality. One common practice is an application of a nitrogen-based fertilizer in the late fall when turf is still green, but no longer growing. In southwestern Ontario, this is usually at the end of October, or the beginning of November. The benefits of this practice are to improve fall colour, early spring green-up without excessive shoot growth, more and deeper roots and increased carbohydrates in the plant for improved winter-hardiness.

The current late fall fertilizer recommendations for this application are 1.0-1.5 kg at nitrogen at 100 sq. m. The recommended nitrogen (N) sources are water soluble, or quick release N sources that do not rely on soil microbes (which are not active at that time of year because of the cool soil temperatures) for N release. These sources include urea, ammonium sulphate and IBDU. The recommendations do not take into consideration the fate of nitrogen applied to turf at this time of year with abundant rainfall and low evapotranspiration.

At the 2012 Ontario Turfgrass Symposium, Dr. Soldat from the University of Wisconsin gave a talk that surprised many in the audience. Dr. Soldat, in collaboration with Dr. Brian Horgan, University of Minnesota and some graduate students, conducted an in-depth look at all the previous research in the fall. This review cited 36 studies on late fall fertilization in North America between 1930 and 2006, as well as two international studies (Italy and Turkey).

They discovered that many of the studies were conducted in regions of North America that have a very different climate from Ontario and on different turf species than what we grow here. It is obvious that every study looked at something a little bit different, whether that was timing, rates, location, soil type, turf species and N sources.

Review reveals spring colour

Studies in Rhode Island evaluated colour, growth and cold resistance of Kentucky bluegrass under various fall N timings. Treatments of 0.98kg N/100m2 were made every two weeks from Oct. 1 to Dec. 15. Applications of N made before Nov. 1, resulted in increased fall colour. All of the fall treatments provided good spring green-up and treatments applied after Nov. 1 had greener colour and greater clipping yield by spring. Fertilizer treatments applied before Nov. 1 produced a growth response in the fall, while later applications provided a growth response in the spring. This study again was in a climate different than Ontario.

Studies in Wisconsin (Kussow, 1992) found improved spring colour, but they also found that spring growth response was observed from the late fall N applications. This study site is a bit closer to winters we experience in southern Ontario.  

More recently Mangiafico and Guillard (2006) conducted research in Connecticut that showed there were no differences in early spring green-up between N applied on Sept. 15, Oct. 15 or Nov. 15. It did show there was less N uptake when applied after Sept. 15.  

Increased root growth

In the mid-Atlantic, Hanson and Juska (1961) found that late winter root mass was significantly greater in the treatments that received 1.47 kg N/100m2 in September, or when this rate of N was split between a September and October application, compared to the unfertilized control. However, in May the greatest root mass was from turf fertilized in March. In Iowa, Moore et al. (1996) compared late fall N application with a heavy spring and a balanced N fertility program. Rooting studies conducted north of the mid-Atlantic (Kussow, 1992; Mangiafico and Guillard, 2006) did not find root mass differences from N applied in either September, October, November or December.  

Again, studies supporting the claim that late season N fertilization of turf produces more roots in temperate climates are not supported by the research.

Increased photosynthesis and carbohydrates

Work by Moon et al., 1990, brings into question the possibility of turfgrass to photosynthesize at all during the late fall. They reported an 85-90 per cent reduction on photosynthesis in perennial ryegrass with one single chilling event (8º C day and 5º C night). They also reported photosynthesis reduction lasted for five to seven days after plants were returned to more moderate temperatures (22º C day and 17º C night). Given this research and temperatures in Ontario after mid-late September, it is difficult to see much of a temperature window.  

Environmental considerations

If such a small percentage of the N is taken up by the turfgrass plant in the late fall, what happens to the other roughly 66-80 per cent?  Petrovic (1990) concluded that there is greater potential for nitrate leaching in the late fall because of reduced evapotranspiration, increased precipitation and decreased microbial mobilization of N.  Recent studies evaluating late fall N applications found elevated nitrate levels in the leachate. The amount varied with each study, depending on the rate, nitrogen source, timing and rainfall with the greatest losses from applications made after Sept. 15. In another study that looked at different sources of N, the greatest nitrate losses were from season-long fertilization with ammonium nitrate (16.8 per cent), compared to 1.7 per cent with polymer coated urea and 0.6 per cent with an organic N source.

The only benefit from late fall fertilization of turf that has been demonstrated in the literature for temperate climates like Ontario is early spring green-up. The benefit of more roots and deeper roots has not been substantiated for our climate. In addition, research has shown there is a potential for nitrate leaching. We do not have all of the answers yet, but with the information that we do have, perhaps we should follow the precautionary principle and refrain from applying nitrogen after Sept. 15.

Based on the literature review, it is also prudent to apply a slow release form of N at that time of year (which is the industry norm anyway). There is still a need to have more locally-based research to help us understand timing, rates and N sources for fall fertilization that will maximize the agronomic benefits without a negative impact on water quality.
Pam Charbonneau may be reached at pamela.charbonneau@ontario.ca.