With increasing demand for food and, consequently, increasing consumption of chemical fertilizers, sustainable development methods are used in developed agriculture. Site-Specific Crop Management (SSCM) known as a method in which the farm is divided into several different areas and using variable rate technology (VRT), the application of inputs is changed according to the needs of special area. One way to access variable rate capability in agricultural machinery is to add controllers to distributers which uses a constant rate. In this research, the input variable rate is applied using the map-based method. The stages of this research were: 1) design and construction of closed-circuit television control system for variable rate fertilizer, 2) write a suitable program to collect data related to the position and speed of progress in order to send controlling commands to the fertilizer’s rate-control circuit (Code vision software was used), 3) Static eva‎luation of the device and measurement of system’s time responses and the error’s rate, 5) eva‎luation of fertilizer fields in order to achieve accuracy according to ASABE standard. Centrifugal distributer was used as a variable rate distributer using a close-loop control system. The Pulse Width Modulation (PWM) method was used to change the speed. Components used in the control system include: 1) 370watt DC motor with coupling and gearbox, 2) encoder (connected to the tractor wheel to calculate the linear speed of the tractor), 3) rate control system, 4) GPS receiver, 5) Two 12-volt batteries (control system and motor power supply). Before entering the field, the control system was calibrated for actual spraying rates and the encoder connected to the tractor was calibrated for speed. Superphosphate (SP) fertilizer was used for spraying. The size of the boxes for collecting fertilizer grains was 10×40×50 cm and the dimensions of the test area were 20×30 m. The relationship between output flow rate, manure spraying per hectare and engine rotational speed was calculated with a coefficient of determination of 0.98. distributer’s eva‎luation was performed in longitudinal and transverse distribution test for fixed rates of 150 and 57 kg/ha. In the longitudinal test, for a rate of 150 kg / ha, the coefficient of variation was 16.02% and the standard deviation was 22.80, and for the rate of 57 kg/ha, the coefficient of variation was 26.68% and the standard deviation was 15.06. With increasing application of fertilizer rate, we saw a decrease in the percentage of coefficient of variation (CV) and uniformity in the distribution pattern. In the transverse test, a three-dimensional distribution pattern was designed for each rate and the average effective spray distribution width of the distributer’s was calculated 8 m. In the case of manual variable fertilization, the soil was divided into two cells with dimensions 15×12 m and the rate change Was done by the control system. The S-shaped diagram was fitted to both response time of seed rate change from high to low and vice versa and the response time equations were obtained with a coefficient of determination of 0.98. In manual control mode and in rate transfer from high to low, the delay time was 1.84 seconds, and the response time was 7.36 seconds. In transmitting the rate from low to high, the delay time was 2.48 seconds and the response time was 9.2 seconds. The reason for the increase in response time in the second case is the dominance of the motor over the resistant torque. The mean cell size was considered to be 11 m according to the response time. In the case of automatic variable fertilization, the rate of transfer from high to low response time was 8 seconds and from low to high the response time was 9.76 seconds. The best place to apply the rate to increase accuracy at a distance of about 3.2 meters at the end of the first cell 6 meters at the beginning of the second cell.

مرتضي صادقي

عباس همت، مهرنوش جعفري

امين اله معصومي، آقافخر ميرلوحي