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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. [ABSTRACT FROM AUTHOR]

Pollination is a key process in the hybrid rice seed production. At present, the traditional artificial assisted pollination is still the main method of hybrid rice seed production in China. Traditional artificial assisted pollination methods have some disadvantages, and they are not conductive to the realization of full mechanization of hybrid rice seed-making. In order to find a more efficient and more reliable auxiliary pollination method to facilitate the full mechanization of hybrid rice seed production, a ducted-fan pollination machine based on high-clearance chassis for hybrid rice was designed in this paper. The flow field characteristics of ducted-fan-pollinator were simulated and analyzed by using computational fluid dynamics technology (CFD). The simulation and measurement airflow field results showed that, when the motor velocity of ducted-fan pollinator was 9 000 rad/min, the uniformity of air velocity distribution was better and the average wind velocity was 4 m/s at 6.0 m from the air outlet. It satisfied the minimum requirements for pollen lifting and suspension transportation during hybrid rice pollination. In addition, the ducts played a certain role in enclosing the airflow formed by the rotor rotation, and avoided the airflow formed by the rotor rotation to diffuse around in a certain area. A prototype had been trial-produced accordingly. Field validation tests were carried out by optimizing the parameters of the device. The ducted-fan pollination machine was composed of high ground clearance power chassis, micro gasoline generator, DC power supply, truss, truss automatic leveling device, ducted-fan start-up controller, truss lifting mechanism and several ducted-fan-pollinators. The chassis clearance was 1.7 m, the wheelbase was 2.4 m. The tread was 2.5 m, which could span one compartment of male parent. And the truss width was 11.0 m. The coverage width of single pollination operation could reach 31.5 m. Under the walking velocity 1.5 m/s, the operation efficiency could reach 7 hm2/time (30 minutes for each pollination). The results showed that under the conditions of 1.5 m/s walking velocity and 9 000 rad/min motor revolving velocity of the pollination machine, the average number of pollen grains was 8.39 grains in the pollen collection point of the female parent compartment in the unit visual field, which satisfied the minimum requirement of hybrid rice seed production and pollination (at least 3 grains of pollen were required in the agronomy of hybrid rice seed production). A comparative experiment was conducted on the actual production of hybrid rice pollination by ducted-fan pollination machine based on high-clearance chassis and agricultural UAV. The results showed that the seed-setting rates of the 2 pollination methods were 44.2% and 42.7% respectively. The results of the 2 operations were similar, which showed that the designed ducted-fan pollination machine based on high-clearance chassis for hybrid rice could meet the actual production requirements of hybrid rice seed-making. This study provides a reference for the mechanization of hybrid rice seed production. [ABSTRACT FROM AUTHOR]