Rice seedling segmentation is a fundamental process of extracting the guidance line for automated rice transplanters with a visual navigation system, which can provide crop row information to ensure the transplanter plants seedlings along the crop row without damaging seedlings. However, obtaining accurate rice seedling segmentation in paddy fields is still a challenging task. In this paper, a rice seedling segmentation method in paddy fields is proposed. The method mainly consists of two steps: image graying and threshold segmentation. In the procedure of image graying, the RGB (Red Green Blue) seedling image is first converted into the YCrCb color space and a Cg component is constructed. A color-index 2Cg-Cb-Cr is then constructed for image graying based on the excess green index (2G-R-B), which can reduce the influence of illumination variation on the equality of image graying. For the second step, an improved Otsu method is proposed to segment rice seedlings. With respect to the improved Otsu method in this research, the background variance of within class variance is weighted by a probability parameter to ensure that the method works well for both bimodal and near-unimodal histogram images, and the search range of gray levels is constrained to reduce the time to search the segmentation threshold. Experimental results indicate that the proposed method achieves better segmentation results and reduces the computational cost compared with the traditional Otsu method and other improved Otsu methods.

To improve the adaptability and precision of the slider-hole-wheel seed-metering device to meet the requirements of precision sowing, the single factor simulation experiments and the three factors three levels of orthogonal simulation experiments were carried out based on the discrete element method. The rotation speed of the seeding shaft, the shape of the hole, and the depth of the hole were set as experiment factors. The results of simulation experiments showed that the qualified rate was the highest when the rotation speed of the seeding shaft was 30 r/min, the shape of the hole was oval, and the depth of the hole was 9 mm. The qualified rate, replay rate, and miss-seeding rate were 89.09 %, 3.64 %, and 7.27 %，respectively. The hybrid rice seeds of Zhongnong 2008, Chuangliangyou 4418, and Gangyou 898 were chosen as the materials for the bench and field seeding performance tests to verify the reliability of the simulation results. The test results showed that the qualified rate of Zhongnong 2008, Chuangliangyou 4418, and Gangyou 898 seed in bench tests were 85.07 %, 85.20 %, and 82.13 %, and the qualified rate of Zhongnong 2008, Chuangliangyou 4418, and Gangyou 898 seed in field tests were 82.13 %, 82.27 %, and 80.53 %. The seeding performance with the three kinds of rice seeds could meet the agronomic requirements for precision sowing of hybrid rice. The paper provided the basis for the structure optimization and seeding performance improvement of the slider-hole-wheel seed-metering device.

In order to realize automatic steering controls of rice transplanters in paddy fields, an automatic steering control algorithm is essential. In this study, combining the fuzzy control with the proportional-integral-derivative (PID) control and the kinematics model, a compound fuzzy PID controller was proposed to adjust the real time data of the PID parameters for the automatic steering control. The Kubota SPU-68C rice transplanter was then modified with the new controller. Next, an automatic steering control experimental with the modified transplanter was carried out under two conditions of linear tracking and headland turning in verifying the automatic steering effect of the transplanter in different steering angle situations. The results showed that the deviation with the new controller and the modified transplanter was acceptable, with maximum deviation in linear tracking of 7.5 cm, the maximum headland turning a deviation of 11.5 cm, and the average a deviation of less than 5 cm. In conclusion, within the allowable deviation range of the field operation of the rice transplanter, the proposed algorithm successfully realized automatic steering controls of the transplanter under different steering angles.

In this study, discrete element method (DEM) simulations of straw-soil rotary blade roller (RBR) were established based on the EDEM software. The forward speed, the rotational speed of the RBR shaft, and the rotary tillage depth were set as the operating parameters, while the straw coverage rate and operational energy consumption were set as the evaluation indexes for the straw returning cultivator (SRC). A three-factors three-level optimization simulation was carried out using the quadratic regression orthogonal combination design method to obtain the optimal values for these parameters. Finally, a series of field experiments was carried out to verify the performance of the SRC by using the optimal parameters. The results of these experiments showed the SRC outperformed a traditional cultivator. In conclusion, the optimization of the selected parameters significantly improved the utilization of stubble and greatly reduced the energy consumption.

To investigate the impact of different seedling transplanting times on rice growth, the present study evaluated seedling age and root pruning using treatments consisting of root pruning (RC20, RC30, and RC40) and no root pruning (CK20, CK30, a...