The 4 Rs of Fertilizer Application, by Sheila Dunning UF/IFAS Extension Agent

fertilizer_bag_in_grassThe cliche is “April showers bring May flowers,” but April deluges create weak plants and yellow grass.

Pictures this: You were following the University of Florida/Institute of Food and Agricultural Sciences’ recommendations and waited until April 15 to fertilize.

You followed the Urban Turf Rule and applied low-phosphate fertilizer with slow-release nitrogen.

Yet, your grass is yellow, and the shrubs haven’t grown any. What happened?

The 18-plus inches of rainfall we experienced at the end of April flushed nearly everything, including fertilizer, out of the soil. Nitrogen and potassium are highly leachable. Phosphorus is also depleted under saturated soil conditions.

If you haven’t submitted a soil test since the storms of April, now is the time to do so. It’s time to apply a summer fertilizer, but it needs to address all the nutrient deficiencies created from excess rain. Soil test kits can be obtained from the Okaloosa County Extension office.

Fertilizer Selection

Best Management Practices have been developed so individuals can make fertilizer selection decisions that reduce the risk of water contamination.

When you get soil test results from the University of Florida Lab, remember the “4 Rs” when applying fertilizer:

  • Right source. A BMP compliant fertilizer contains a portion of slow-release (water insoluble) nitrogen with little to no phosphorus, and a potassium level similar to the nitrogen percentage (e.g. 15-0-15, that contains 5 percent coated nitrogen). A soil test is the only way to accurately identify specific nutrients your landscape lacks. Many soil tests indicate a need for phosphate, and currently, it is illegal to apply more than 0.25 pounds per 1,000 square feet without a soil test verifying the need.
  • Applied at the right rate. Know the square footage of your property and how much fertilizer you can spread using your equipment’s settings. Individuals walk at varied speeds and the product-recommended rates are based on 1,000-square-foot areas. Using 15-0-15 fertilizer, the right rate for one application would be 3 pounds per 1,000 square feet. That 35-pound bag is all that is needed for an almost 12,000-square-foot yard (a large corner lot). Information on calibrating your fertilizer spreader.
  • At the right time. This is when plants are actively growing and beginning to show nutrient deficiencies. Summer, when rainfall and irrigation are frequent, is a typical application time.
  • Over the right place. That is, only on living plant areas. Avoid getting fertilizer on the sidewalk, driveway, and street. A deflector on your spreader is helpful. Otherwise, sweep or blow the fertilizer back onto the grass or into the landscape beds. Avoid having fertilizer end up in a water body.

The final factor is irrigation. To obtain the most benefit from fertilizer, the 4 Rs must also be applied to irrigation. The water source, application rate, frequency and duration of application,a nd uniformity of the sprinkler system on the application site dramatically affect the results of fertilizer applications.

Information on calibrating irrigation equipment.

Nutrient and irrigation management are critical to conserve and protect Florida’s natural resources. We must meet the needs of the present without compromising the ability of future generations to meet their own needs.

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