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Broadcasting application of nitrogen at returning green stage results in ammonia volatilization and low nitrogen use efficiency. At present, the mechanized topdressing equipment is lacking in China, the precise fertilizer deep applicator was designed to meet the demand of mechanized subsurface topdressing fertilization for wheat, the precise row-following and accurate deep fertilizing method were studied based on autonomous navigation system. The applicator was driven by tractor mounted with autonomous navigation system to realize specific row-following operation, the speed of applicator was resolved by taking advantage of RTK-GNSS technology, the fertilizer application was driven by hydraulic system, double-disc opener opened a ditch to realize deep fertilizing, closed-loop PID control system was used to control motor speed and realize real-time rotation rate adjustment to achieve accurately control fertilizer amount. Field experiments were conducted to examine the performance of applicator, results indicated that: when the fertilizer amount was preseted to be 200kg/hm2, tractor speed at 5km/h, the row-following deviation within ±6cm, the dynamic deviation of fertilizer amount deviation within 9%, which met the practical demand;compared with broadcasting application by fertilizer distributor, the amount of nitrogen was decreased by 25kg/hm2, grain yield was increased by 486.5kg/hm2. The applicator could achieve precise deep topdressing fertilization for wheat and be equipped for precision agriculture.