Evaluating How Accurately Lawn Fertilizers Are Applied Using Homeowner Equipment

Abstract

Inappropriate use of fertilizers in urban environments has been implicated in increased nutrient loads in Florida water bodies. We tested how accurately lawn fertilizers were applied by 36 master gardeners and other volunteers. Subjects were asked to apply a label rate of fertilizer [30% fine granular slow-release formulation (32–0–10) at 1.37 kg/100 m2 (2.81 lb/1000 sq ft) and a coarse granular readily available nitrogen fertilizer (10–0–10) at 3.17 kg/100 m2 (6.5 lb/1000 sq ft)] using three spreaders [a hand-held rotary, a broadcast rotary (push), and a drop spreader]. Results showed that under the test conditions applications using the hand-held rotary spreader were the most accurate (averaging 98% of target rate over two tests), while applications using the push rotary spreader tended to be over-applied (138% to 301% of target rate), and those of a drop spreader tended to be under-applied (31% to 48% of target rate). Our simple study highlights that lawn fertilizers are not always accurately applied. Sources of error included variability in applicator walking speed, inaccurate swath widths (e.g., too narrow with push rotary or too wide with drop spreader), and the amount of fertilizer loaded into hoppers. A good approach to provide a quick check of overuse or underuse is for applicators to determine the area to be treated and calculate and weigh the required amount of fertilizer before application. The inclusion of a volumetric measurement on the bag label (in addition to weight) would facilitate calibration for homeowners without requiring access to weigh scales.