Drop-type spreaders distribute materials between the wheels of the spreader as it is pushed or pulled across the turf. Drop-type spreaders operate by gravity flow of the material through the spreader opening. The rate of application is controlled by the width of the opening on the spreader and the speed of the applicator. To calibrate a drop-type spreader the operator weighs the amount of material dispersed per unit area at a specific spreader setting and constant speed. The person who will make the actual application should be pushing the spreader or driving the tractor so that the speed during the actual application will be the same as the speed used during the calibration.
Some drop spreaders have a calibration tray that attaches beneath the spreader discharge.
In this case, the operator simply makes a pass over a given distance, weighs the product collected in the tray and calculates the rate of application per 1,000 sq. In the absence of a calibration tray, the operator must either collect the material over plastic or concrete to obtain a weight or determine the loss of weight from the spreader when making a pass over a given area. This process is repeated until the setting is found that distributes the targeted amount of material. Measurements required to calibrate a drop-type spreader include the distance the operator covers and the weight of material applied. Obviously, a scale or balance of some type is required to determine weight.