Precision fertilization can greatly contribute to the utilization rate of chemical fertilizers and ecological safety. The amount of chemical fertilizer can also be reduced for the rational demand of agricultural production. Among them, the fertilizer ejector is one of the most important components during precision fertilization. Its performance is of great significance to improve the quality of granular fertilizer application. However, the existing research focuses mainly on the structural optimization of the fertilizer ejector for the better fluidity of fertilizer particles. It still lacks the precision, the lag of fertilizer discharge, and easy clogging of granular fertilizer at the same time. In this study, a variable-diameter pneumatic-driven discharger of precision fertilizer was developed to integrate "discharge opening adjustment + rotational speed control + pneumatic forced discharge". The high accuracy was achieved to mitigate the fertilization hysteresis under varying operational speeds, in order to fully meet the agronomic requirements across different field plots during mechanized direct seeding of rapeseed. A systematic optimization was also carried out on the key parameters of the variable diameter structure, air-fertilizer mixing device, airflow distribution, and fertilizer guiding structure. The discharge tests were also conducted to calibrate the system. A control model was established to correlate the fertilizer discharge rate with the rotation speed and discharge opening. Dual-variable precision fertilization was implemented. The tests demonstrated that the optimal discharge range of 4.27-61.41 g/s was achieved with rotation speeds of 30-120 r/min and openings of 15-25 mm, fully meeting the operational requirements for the rapeseed direct seeding at the speeds of 2.5-12.0 km/h and the fertilization rates of 225-600 kg/hm². There was a high accuracy of fertilizer discharging of 96.30%-98.66%. The coefficient of variation for the consistency and stability of displacement in each row (C_v1) of 2.58%-8.62% and the same industry (C_v2) of 2.81%-6.85% fully met the national standards. Furthermore, the pneumatic-driven discharger eliminated the blockages in the operational range of 3.25-61.25 g/s. Specifically, the fertilizer particle velocity was enhanced by 44%, whereas, the discharge time was reduced by 44%, compared with the non-pneumatic ones. A field test confirmed that the high accuracy of fertilization was achieved over 95.07% via the precise control of opening and rotation speed, particularly under the fertilization rates of 300-600 kg/hm² and the operational speeds of 3.2-12.1 km/h. These findings can provide the technical references to develop the variable-rate fertilization equipment in rapeseed direct seeding.

Precision fertilization is one of the key technologies to control non-point source pollution in agriculture. Fertilizer reduction and efficiency technology can greatly contribute to green and sustainable agriculture in the rice-oil rotation region in the mid-lower reaches of the Yangtze River. Among them, fertilizer apparatus s have been focused mainly on the performance and optimization of structural devices. It is relatively lacking in the high speed and precision of fertilizer apparatus for rapeseed in real time. It is a high demand to optimize the precision fertilizer discharging for the reference value. The performance of fertilizer apparatus can depend directly on the accuracy of working components, in terms of uniformity and rational fertilization. However, the existing fertilizer apparatus cannot fully meet the range of direct seeding rapeseed of high-speed machines, due to the jam, low stability and distribution, as well as the serious crushing of particle fertilizer. In this study, an extrusion fertilizer apparatus for rapeseed was designed with a centrifugal cavity disc with high speed and precision. According to the agronomic requirements of high-speed direct seeding, the movement analysis of fertilizer particles was combined to determine the key parameters, such as fertilizer inlet, centrifugal cavity disc, fertilizer outlet, and power system. The discrete element software (EDEM) was used to establish the simulation model of fertilizer discharging. A systematic investigation was implemented to clarify the influence of the speed of the fertilizer apparatus on the torque of the centrifugal cavity disc, the average load, and the crushing rate of fertilizer particles. The results showed that the torque of the centrifugal cavity disc increased, whereas, the average load of fertilizer particles in the cavity disk decreased gradually, and the crushing rate increased below 0.80%, with the increase of the speed of fertilizer apparatus. The performance test showed that the speed of the fertilizer ejector was 30-120 r/min, and the displacement was 15.0-58.1 g/s, fully meeting the demand of high-speed direct seeding when the maximum fertilization amount was 600 kg/hm². The coefficient of variation was less than 8.58% for the consistent displacement in each row of fertilizer discharging, less than 6.45% for the stability of the displacement in the same industry, and the crushing rate was less than 0.89%; Specifically, the coefficient of variation was below 8.72% for the displacement consistency of each row shall under normal field operation with 0°~5° inclination. The comparative test showed that compared with the spiral perturbation, the fertilizer discharging with a centrifugal cavity disc was suitable for high-speed operation, where the crushing rate was reduced by 63.82%. There was no fertilizer jam when discharging fertilizer at high speed and large displacement. The field test showed that when the operation speed was in the range of 4.1-10.1 km/h, the coefficient of variation was not more than 6.72% for the consistent discharge in each row of the fertilizer ejector, while the coefficient of variation for the stability of the same row during fertilizer discharging was not more than 4.84%, and the relative error between actual and theoretical fertilizer discharging was less than 4.54%. The fertilizer discharging shared a wide range of displacement, smooth and stable operation, in order to effectively avoid the fertilizer sticking and the crushing rate in the process of fertilizer discharging. The fertilizer apparatus also fully met the demand for the high-speed direct seeding and precision fertilizer discharging of rapeseed.