Central-hopper spreaders are widely used to apply dry fertilizer. Uniformity of distribution is severely limited by the centrifugal-fan and boom-type distributors used on these spreaders.

The purpose of this study was to investigate the application of automatic control principles to an experimental auger-boom-type distributor. To facilitate the use of automatic controls, a distributor of special design was developed, It consisted of an auger conveyor with a U-shaped cross section. Eighteen discharge openings were Located on 6-inch centers along its length. Small compartments at the location of each opening, agitators on the auger flighting, and a control slide along the length of the boom, controlled the discharge from the boom. The control system consisted of a flow-level detector at the outboard end of the boom and a controller and linear actuator to operate the control slide.

Basic performance characteristics of the distributor were measured on a laboratory test stand using manual-remote control. Coefficients of variation for discharge patterns along the length of the boom varied from 4.63 to 12.22 percent under various combinations of auger speed, discharge opening size, and boom inclination. Discharge rate was more sensitive to opening size than auger speed. Regression coefficients and tests of independence indicated that discharge rate waa not greatly influenced by fertilizer flow level. Minor segregation of dry-blended fertilizere was noted.

In tests with automatic control, errors in slide position were corrected. However, slow oscillation of the slide occurred after the initial correction. An improved flow-level detector and controller are needed for acceptable field performance of the system,