Site specific crop management is a technology by which agricultural inputs such as seed, fertilizer and herbicide are adjusted to match the requirements of specific field areas. Agricultural machines must apply the correct application rate at each field location. One possibility is to add a controller to obtain variable rate capability from conventional metering mechanisms for uniform application. Information contained in the geographic information system related to the seeding rate in each field area is downloaded to the system computer before field operations commence. The computer/controller will continuously control variable application rates based upon knowledge gained both from the geographic information system (GIS), and knowledge of field location as provided by DGPS. The process of changing the application rate while the machine traveling across the field takes some time and it accompanies by some misapplication. The severity of this misapplication depends on the characteristics of the metering control mechanism which one of them is the response time. The specific objectives of this research were: 1) to examine and evaluate the seeding uniformity of a grain drill units, 2) to selecting the appropriate control system for changing the uniform rate of Hassia grain drill to a variable rate one, 3) to determine the response time of the variable rate grain drill, 4) to write appropriate software for gathering data associated with position, ground speed and sending command automatically to the control system base on variable rate seeding map and ground speed, 5) to evaluate the variable rate grain drill base on ASABE standard. The closed loop control system was composed of: 1) a 250 Watt DC motor with a constant ratio gearbox, 2) two encoders (one for sensing the travel speed of the grain drill and the other for sensing the speed of the DC motor), 3) a GPS receiver, 4) Pulse-With-Modulation DC motor controller, and 5) a laptop as a data logger. The seeding rate command obtained from GIS is adjusted by considering the actual ground speed of the drill before it is translated into a target motor speed. The controller then generates an electrical signal which is proportional to the target speed. The interface software was written in Visual Basic which could read data from both encoders and the GPS receiver. The results of initial grain drill evaluation showed that all outlets on the drill did not deliver the same number of seeds. Increasing rotational speed of metering device significantly increased tendency of metering mechanism to damage wheat seeds. Outlets were not different in seed damaging. Results showed that all outlets data were not autocorrelated and selecting 24 or 12 random data from 36 autocorrelated data were not essentially