are targeted according to locally determined requirements. Yield monitors are a recent development in agricultural machinery that allow grain producers to assess the effects of weather, soil properties, and management on grain production. While yield mapping has become an important part of precision farming strategies the goal of this project was to plot a yield map by the application of yield monitoring components. The best location to evaluate productivity levels, by measuring yield and quality of grain and straw, is the combine harvester. The system consists of an impact flow sensor determining the mass flow of grain, the GPS receiver determining position of the machine, two shaft encoders measuring the speed of the combine, an ultrasonic sensor measuring the actual cutting width, and a data logger which displays values and saves them on a MMC card. The cornerstone of a yield monitoring system is the mass flow sensor, used to measure the mass flow rate of clean grain through a combine which is accomplished by assessing the impact force of grain hitting a plate. The mass flow sensor consists of a load cell and an impact plate which is exposed to the predominant grain flow from the clean grain elevator. This sensor was positioned in the transition housing between the clean grain elevator and the loading auger of the clean grain tank. The calibration of the sensor relates the force on the sensor to the mass flow rate of grain. The GPS receiver was used to provide GPS data that finally identifies the spatial properties of the field. The incremental steel shaft encoders were fixed on the back wheels to eliminate wheel slippage effect. The distance traveled by the combine during a sampling period was determined by multiplying the ground speed by the time of the sampling period. A JD 955 combine equipped by yield mapping components harvested two wheat fields in Fereidoonshahr, Isfahan Province, Iran. The yield data were used with information generated by the GPS receiver and a yield map was created by the use of ArcGIS 9.3 software. Pre-harvest yield hand sampling from parts of the fields were performed and the yield was determined to validate the system. After harvesting wheat, soil samples were collected from various locations and analyzed for soil spatial variability across the fields. Analysis were mainly soil texture, soil potassium content, phosphorus content, nitrogen content and soil electric conductivity. The correlation analysis of the soil data and yield data of the two fields showed only height and phosphorus content had significant effect on yield. For farm1, height had a negative correlation (r= -0.371, p 0.05) and phosphorus content (r= -0.296, p 0.05). For farm 2, height had a