To measure turfgrass performance, professionals have traditionally relied on trained human evaluators who provide visual assessments of turf quality. But human evaluators require training and may be distracted by many factors that can affect accuracy and consistency of the assessments. New optical sensing technology has recently been introduced to measure the reflectance from turf canopies to determine turfgrass growth, wear tolerance, herbicide tolerance, and fertility.
A new study published in HortTechnology assessed a handheld optical sensor (GreenSeeker) for evaluating overall turfgrass quality in three turf species over two growing seasons. The research team of Gregory E. Bell, Dennis L. Martin, Kyungjoon Koh, and Holly R. Han from Oklahoma State University compared the combined time required for visual evaluation and data entry with the time required for the same functions using the handheld optical sensor.
The study was conducted at the Oklahoma State University Turfgrass Research Center in Stillwater. Visual quality ratings and sensor ratings were collected on schedules prescribed by the National Turfgrass Evaluation Program for the 2002 bermudagrass (Cynodon spp.), 2002 buffalograss (Buchloe dactyloides), and 2002 zoysiagrass (Zoysia spp.) studies in 2003 and 2004.
The GreenSeeker handheld sensor used in the study incorporated a sensor head, a telescoping tube, a PDA, and a control box. A single sensor was mounted to a telescoping pole that comprised the primary structure of the handheld. A rechargeable battery rested on the opposite end of the pole to provide power and counterbalance the weight of the sensor. The entire unit weighed approximately 11 pounds and was suspended from an adjustable shoulder strap.
The researchers concluded that use of the sensor reduced the time required to complete data collection and data entry by 58% compared with human visual evaluation. "The GreenSeeker was relatively inexpensive and required less total combined time for data collection and entry than visual evaluation. The handheld sensor was very stable and did not require routine maintenance, update, and recalibration. It provided a consistent, objective evaluation of overall turfgrass quality," stated Bell.
Training personnel to use the handheld sensor, including data entry, took less than one hour; training a visual evaluator can require several days, and evaluators can take months to become proficient.
The researchers added that although the sensor has distinct advantages, there are still reasons to include the human element in turfgrass assessment. Bell noted that "the handheld optical sensor alone cannot provide necessary information about turfgrass texture or density that can be effectively determined by human evaluators. However, it does provide a consistent measure of reflectance that is primarily affected by a combination of turfgrass color and percent live cover."
- Bell, Gregory E., Martin, Dennis L., Koh, Kyungjoon, Han, Holly R. Comparison of Turfgrass Visual Quality Ratings with Ratings Determined Using a Handheld Optical Sensor. HortTechnology, 2009; 19: 309-316 [link]
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