Development of layered fertilizer amount adjustment device of pneumatic centralized variable fertilizer system

Fertilizer is essential to safeguard food security, and rationalizing fertilization and improving fertilizer use efficiency can reduce its detrimental impact on environment and sustain agriculture production. Current corn fertilization in China is largely growth stage-based with a base fertilization coupled with a number of topdressings. This is inefficient in fertilizer use and labor-intensive, difficult to meet the requirements for sustainable agriculture. Delivering the fertilizer to the location in soil where the crop mostly demands for is a technology to effectively improve fertilizer use efficiency and increase crop yield. In this paper we present a pneumatic centralized device to stratifying fertilizer in soil based on the demand of crop roots. The structure and working parameters of the key components in the device were calculated theoretically; the diameter of the conveying pipe in the device was 76 mm, the inlet airflow velocity should be higher than 25 m/s, and the distribution ratio of the fertilizer can be adjusted arbitrarily from 1:1 to 1:2. The performance of the device was analyzed using the discrete element method coupled with the computational fluid dynamics by taking the rotational speed of the rotary cone (A), the inlet airflow velocity (B) and the fertilization velocity (C) as determinants, and the coefficient of variation (CV) of the fertilizer amount at each fertilizer outlet as an performance index. A quadratic-regression rotation orthogonal simulation test was used to link the performance index to the determinants. The results showed that both rotational speed of the rotating cone and the inlet airflow velocity had a significant effect on the CV. When rotational speed of the rotary cone was 735-1 196 r/min, the inlet airflow velocity was 36-41 m/s, the fertilization velocity was 0.14-0.42 kg/s and the distribution ratio was 1:2, the associated CV at different fertilizer outlets varied from 3.7% to 4.9%. The influence of all determinants on the CV was ranked in the order of A>B>C. Bench test of the device was conducted in the Conservation Tillage Research Center of the Ministry of Agriculture and Rural Areas, with rotational speed of the rotary cone being 735 r/min, the inlet airflow velocity being 36 m/s, the fertilization rate being 0.42 kg/s and the distribution ratio being 1:2. The results showed that the CV was less than 5.18% and the deviation of the distribution ratio was less than 2.68%, consistent with the results obtained from simulation and meeting the requirements for fertilization operation. This work provides a new technology with theoretical support to optimize pneumatic centralized device for stratifying fertilizers into soil.