Fall nitrogen fertilization is a widely accepted practice in the Upper Midwest. This is typically a good time to recuperate after a difficult summer, although we did not have a difficult summer this year. However, the timing of fall fertilization is critical in order to limit nutrient loss and snow mold development. My colleagues Dr. Doug Soldat and Dan Lloyd are investigating the uptake and utilization of fall-applied N to soil and sand based putting greens. The reminder of the post will focus on the research they have conducted on this topic. They conducted a survey of 42 golf courses in 2007 indicating that 55 % of the average annual N applied is applied between September and November. Why? The benefits that are often associated with fall N applications are improved fall color, earlier spring green-up, enhanced root development, an reserve carbohydrate storage. The majority of this research has been done in more temperate climates like the transition zone, which may not be applicable to the Upper Midwest.
A field study was initiated at two locations in the Midwest (Madison, WI and St. Paul, MN) on L-93 creeping bentgrass putting greens with either a sand-based rootzone or a soil based rootzone. N treatments included a unfertilized control, low N rate (0.5 lb N/1000 sq ft) and a high rate (1.0 lb N/1000 sq ft). Treatments were applied as ammonium sulfate on September 15th, October 15th or November 15th on both soil types and at both locations. Dr. Soldat and Mr. Lloyd collected clipping yields, color, and turf quality.
They found that the Sept. and Oct. applications stimulated a greening response that lasted until winter on both soil types, but no response was observed with the Nov. applications. The trends with spring green up varied with soil type. On the soil based putting green, Oct. treatments were the first to green, yet were later surpassed by the Nov. treatment. On the sand-based putting green, the high N rate applied in Sept. and Oct. were the greenest in the spring with no response from the Nov. applications.
Basically Dr. Soldat and Dan determined that Nov. N applications on sand-based putting greens did not provide a greening response. Therefore N applications should probably be completed by Oct. 15th.
There is a reason why I am writing about fall N applications. In my previous post about snow mold control, I did not mention that even the most effective fungicide can break down if the conditions are very conducive for disease development. One of the conditions that make turfgrasses more susceptible to snow molds, is over fertilization in the fall. Although we do not have data to support this yet, we consistently observe snow mold break through with late fall N applications (early to late November).
In conjunction with Dr. Soldat's research we have decided to examine the interactions of fungicide timings for snow mold and nitrogen application. We are going to initiate this study this year in collaboration with Dr. Frank Rossi.
Switching gears, this weekend was very cool with day time temperatures in the mid to low sixties and nighttime temps near 40. So Lane we are definitely in Fall! However I agree with Lane, do not let your guard down. The weather can change quickly and we could have a hot spell.