Supplemental nutrient use is a critical aspect of a golf course Best Management Practice Program and embodied in the BMP Statement:
Supplement soil with appropriate rate and source of nutrients to maintain optimum availability and minimize off-site movement.
Specifically, the application of high rates (>0.5 lbs. actual Nitrogen per 1000 Square feet) soluble-Nitrogen (N) during cooler periods with less active growth conditions pose a significant risk to groundwater quality.
In the Northeast, Guillard and Kopp (2004) from the University of Connecticut collected leachate under turf plots over three years where 1 lb of N per thousand square feet as ammonium nitrate or polymer coated urea was applied annually at four different times (Figure 1).
Figure 1
First, the data demonstrate that leaching of applied N occurs primarily in late-fall to early spring in southern New England and applications of soluble N later in the season result in greater leaching. Polymer coated N had less than 2% in leachate over three years. However, there is no question that late season soluble nitrogen applications to cool season golf turf have well-established benefits:
- stimulating growth during cooler conditions
- aids in recovery from summer stress
- prepares the plants for maximum winter-hardiness
Of course, the latter benefit is critical to good spring golfing conditions, especially when spring golf traffic requires active growth as temperatures allow.
To quantify active growth use clipping volume as a measure of growth and the Growth Potential Model, as described thoroughly by Dr. Micah Woods in the 2013 article Using Temperature to Predict Turfgrass Growth Potential
(GP) and to Estimate Turfgrass Nitrogen Use. This model simply provides an overview for the amount of growth that could occur compared to maximum growth potential and can assist with moderating N applications throughout the season.
Specific turfgrass research conducted by Professor Doug Soldat in Wisconsin over a three-year period concluded that applications of soluble N made in late October and November resulted in significantly less N in the plant tissue (roots and shoots) (Figure 2). Clearly if you are applying fertilizer when growth potential is less than 20% the risk of N loss increases.
Figure 2
To conclude, the following are good, better and best practices for sand-based soils (higher risk):
A good practice is continue to spoon-feed (generally rates at or below 0.2 lbs N per thousand square feet) soluble nitrogen sources into the fall. Gradually reduce nitrogen rate as evapotranspiration rate declines. Final application should be made from early to late October depending on your location.
A better practice is to monitor growth potential and clipping volume and spoon-feed (generally rates at or below 0.2 lbs N per thousand square feet) soluble nitrogen sources into the fall. Gradually reduce nitrogen rate as evapotranspiration rate declines. Final application should be made from early to late October depending on your location.
The best practice is monitor the aforementioned parameters and evapotranspiration levels and occasionally monitor plant tissue uptake and spoon-feed (generally rates at or below 0.2 lbs N per thousand square feet) soluble nitrogen sources into the fall. Gradually reduce nitrogen rate as evapotranspiration rate declines. Final application should be made from early to late October depending on your location.
For native soils or for alternatives to spoon-feeding consider the use of slow release N sources in mid-September at 0.5 to 1.0 lbs per thousand square feet. Products should have at least 50% slow release nitrogen or less. Applications made too late will risk leaching or lingering in the soil and promoting excessive spring growth that could reduce summer stress tolerance.
