Over the past decade, Global Positioning System (GPS) has been promoted for variable rate application (VRA) of fertilizers on turf. Based on a large number of soil test data to develop fertility maps, computer-controlled rates of application of N, P and K are applied using GPS to locate the applicator machine relative to the fertility map. This complex technology is reported to reduce fertilizer use, avoid pollution and provide very uniform growth.
The technology for VRA based on GPS is expensive, resulting in the application being conducted primarily by commercial applicators. Continued monitoring of the fertility of the turf area is required to upgrade the fertility maps. The most critical disadvantage, however, is the nitrogen rate. There is no generally accepted nitrogen soil test for turf on which to base the rate. Rather, the turf manager has been advised to adjust the fertilizer applications for nitrogen to provide the color and density that he desires. In general, if the color is satisfactory, density will be OK. Therefore, if a method of rating the color is available, VRA systems can be developed for precise application of nitrogen according to the appearance of the growing turf.
There is a recent development of a VRA system based on light reflection or color of the plant. From the light sensor readings, the amount of nitrogen the applicator should apply is determined as is passes over the plants at speeds up to 25 kph. The equipment, developed by Oklahoma State University, in conjunction with NTech Industries, is now available.
Sensors monitor the color on a space about 2-feet-by-2-feet. At this stage of the development of the unit, nitrogen is applied as a liquid. Using a three-nozzle system, one of seven different rates of nitrogen can be delivered precisely to the plant leaf.
The author is secretary of the Sports Turf Association of Ontario, Guelph, Ontario. This article was originally published in the association’s publication. For more information, visit, www.gti.uoguelph.ca/sta.