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To solve problems of non-adjustable fertilizer and low fertilization precision in the precision hole fertilization of dry direct-seeding rice, an adjustable socket-wheel precision hole fertilizer apparatus for rice was designed. The basic structure and working principle of the fertilizer apparatus were expounded, the structural parameters of key components were determined. The numerical simulation experiments based on the discrete element method were carried out by using sulfurized urea as the research object. Selecting the rotation speed of the socket-wheel, the length of the trough, the depth of the socket as the experimental factors, and taking the average amount of fertilizer discharging and the coefficient of variation of fertilization uniformity as evaluation indicators, the orthogonal rotation combined experiments with three factors and five levels were carried out. A multi-objective optimization method was used to determine the best parameter combination under the constraint of the target value of the hole fertilizer discharging of 1.500 g. The simulation results show that the coefficient of variation of fertilizer uniformity was the smallest and the coefficient of variation was 15.80% when the rotation speed of socket-wheel was 26.57 r/min, the length of the trough was 5.36 mm and the depth of socket was 5.64 mm. By using slow-release urea, sulfurized urea and bio-organic fertilizer as test materials, the bench test and field test was carried out on the fertilizer apparatus and the reliability of the simulation results and the adaptability of the fertilizer apparatus were verified.

Returning straw to the field is currently the main treatment method for straw, which reduces the environmental pollution caused by the burning of straw, and also improves the structure and fertility of soil. The uniaxial RBR with the function of forward-rotation is generally used in the operation of the returning straw to field presently. However, the effect of returning straw to the field and the quality of rotary tillage are poor, which affects the seed germination and emergence (Yonglei et al., 2013;Haishui et al., 2015). Although the biaxial straw returning cultivator (SRC) has a good effect of returning straw to the field, the cultivator has a long longitudinal structure, which causes poor stability of field operation, and affects the quality of rotary tillage. The CSRC, which is widely used in southern paddy fields, has the advantages of good effects of returning straw to the field and high quality of rotary tillage. However, the horizontal CSRC still uses the standard forward-rotating rotary blades at present. The arrangement of the rotary blades is the same as that of the forward-rotating rotary blades, which results in the problem of that the power consumption of the counter-rotating RBR being significantly higher than that of the forward-rotating RBR.In recent years, many scholars have explored the energy consumption and working performance of SRC. Because the DEM can be used to simulate the formation and destruction of contact between granular materials (Li et al., 2016;Zeng and Chen, 2016), it is suitable for simulating the interaction between rigid body and elastomer (Huimin, Changying and Chandio et al., 2016; Huimin, Changying and Tagar et al., 2016). The DEM has been widely used in the study of the interaction between of straw, soil and RBR. Chandio et al. used the DEM to establish a simulation model of the interaction between straw, disc plough and soil, and analyzed the displacement, acceleration and displacement changes of soil particles and straw particles during the work of the tillage (Farman, 2013). Momozu et al. deeply carried out research on

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