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It has come to our attention that some golf course superintendents may be somewhat lax in calibrating their fertilizer spreaders. Bad idea.

“Lack of or improper calibration won’t affect the efficacy of the fertilizer itself, but can certainly affect efficacy of the fertilizer application,” says Dr. Eric Miltner, agronomist for Koch Turf & Ornamental. “Proper application depends in part on nutrient application rate, so without knowing the rate through calibration, you are taking a big risk. Also, through the act of calibration you can observe the distribution pattern of a spreader. This can be critical in ensuring that your fertilizer is applied evenly and consistently, so that you don’t end up with streaking or fertilizer burn.”

Dr. David Han, associate professor and extension specialist of turfgrass management at Auburn’s Department of Crop, Soil, and Environmental Sciences, “hopes” superintendents are not being lax with spreader calibration, for it is vital for maintaining turf health and the environment. “Many nutrients are harmful – either to the turf, the environment or both – when applied in excessive amounts and when they are deficient, so putting out the right amount is critical.” He adds applying unnecessary fertilizer wastes money and fertilizes weeds without benefitting the turf. Improperly calibrated spreaders can also cause unsightly cosmetic effects when they apply fertilizer unevenly, causing streaks or a checkerboard pattern of different color grass when different areas do not receive the same amount of nutrients.

Dr. Tamson Yeh, pest management and turf specialist at the Cornell University Cooperative Extension, cautions that failure to calibrate can result in over application and thus fertilizer burn if using a rapid release, high salts formulation or excess nitrogen that will result in juicy overgrowth and increased susceptibility to disease and insects. “Insufficient application due to poor calibration can also result in disease issues – like dollar spot,” Yeh says. “When fertility crashes, dollar spot moves in.”

Improper calibration leads to leaching when excess nitrogen is applied followed by rain or irrigation, and can lead to runoff when excess prills are applied and moved across compacted soil, hardscape or over irrigated turf, resulting in nitrate runoff into surface water bodies as it is attached to water, and phosphorous runoff because it is attached to sediment.

Han cites some scary numbers: “Fertilizer is expensive. If your calibration is over applying at 30 percent, for example, and a bag of greens grade fertilizer 30-0-15 is $40 for a 50-pound bag … If you need one pound of actual nitrogen/1000 square feet, then you need 3.3 pounds of product/1000 square feet. If you are applying 30 percent more (3.3 X 0.3), you are essentially applying 0.9 pounds more, almost a pound. A 50-pound bag properly calibrated fertilizes 15,000 square feet. A 30 percent over delivery only covers about 12,000. That adds up quick. Plus, that means going from one pound of actual nitrogen to 1.3 pounds, which can also add a lot of environmental stress.”

Spreader calibration can be a pain in the neck, Miltner says, thus the lax attitude toward the task. “You have to have a good space and the right tools,” he says. “And it takes time and maybe a lot of trial and error. But having your equipment in tune is as important to good fertilization as having sharp mowers is to mowing – but you don’t have to do it as often.”

The task should be done at least annually for each product you use, Miltner says. If you have had to replace any of the critical parts on your spreader (impeller, drive gears, open/shut valves, etc.), then you should re-calibrate. In a nutshell, the person doing the calibrating needs to measure the amount of product spread over a known area, and adjust until the rate is right. Various online resources are available, often through the state’s extension service.

Calibration is only time consuming “when learning to do it the first time,” says Dr. Aaron J. Patton, associate professor of horticulture and turfgrass extension specialist at Purdue’s Department of Horticulture and Landscape Architecture. “After the first time and when organizing the resources needed to calibrate, calibration can be quick and easy.”

Every time a new product is used, the spreader should be calibrated because no two fertilizers have the same prill size and weight. This is especially true with rotary spreaders, because small, light granules will fly farther than bigger, heavier ones. The operator also affects calibration since no two people walk at exactly the same rate. Calibrate the spreader for each operator and each product, which can be time-consuming.

Practice makes perfect and a single individual will be able to quickly tell when something is "off" with the spreader. “Making calibration part of a routine for a single individual and even making it part of the job description insures that it does not get pushed to the back burner during multitasking as so often happens,” Miltner says.

John Torsiello is a writer based in Torrington, Conn., and a frequent GCI contributor.