Effect of coating thickness on spreader damage to encapsulated controlled-release fertilizer granules

Coated controlled-release fertilizer granules can be damaged when applied by fertilizer spreaders. Physical damage to the coated granules can change the release rate of the nitrogen because the damaged coating will allow water to pass through the coating and dissolve the nitrogen. Six controlled-release fertilizers with nominal release rates from 70 to 700 days were applied with six spreaders, and samples of the applied products were tested for coating damage. There were highly significant differences in the amount of damage caused by different spreaders, with a rotary spreader causing the most damage and a fluted-wheel metering system and a drop spreader with a bar-type impeller causing the least damage. Nominal release rate had a significant effect on amount of damage, with the longer release rates (thicker coatings) having less damage. Even the highest damage levels were under 10%, thus observable differences in crop response are unlikely.