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Previous studies highlighted the significance of optimizing the cutting blade for crop harvesting and size reduction. This study investigated the effect of blade sliding cutting angle and stem level on cutting energy of single rice stem using a cutting apparatus that combined with texture analyzer. The cutting energy was determined for four blade angles. The results showed that the average cutting energy was the highest for cutting stem upper level and the lowest for cutting stem lower level. It was found that the peak cutting force per unit stem area decreased with blade sliding cutting angle increased. However, the least average cutting energy was 9.12 J/mm 2 of 45° sliding angle when cutting without counter support blade and 32.3% less than that of 60° sliding angle. When cutting with counter support blade, the cutting energy per unit stem area varied from 6.57 to 12.54 J/mm 2 as the sliding angle varied from 0° to 60°, whereas the peak cutting force per unit stem area varied from 2.46 to 0.98 N/mm 2 . It was concluded that the optimal sliding cutting angle was 45° without support blade and 30° with support blade, respectively. The experiments on rice stems in this study indicated that optimization of sliding cutting angle and stem level have a significant effect on cutting energy savings. Also this study emphasized the need to further investigate the effect of the case of more moisture content and cutting speed on the cutting energy to help in selection of optimum cutting speed and harvesting time. Citation: Zhang C L, Chen L Q, Xia J F, Zhang J M. Effects of blade sliding cutting angle and stem level on cutting energy of rice stems. Int J Agric & Biol Eng, 2019; 12(6): 75-81.

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Straw returning into field is a direct and effective measure to reduce the straw burning and improve the soil organic matter content. Straw returning directly to field needs higher performance machines, especially under the condition of large amount of straw in the field is more difficult. Therefore, the model of conservation tillage by combination of subsoiling and straw returning was studied. Experiments on combined tillage machine for effect of subsoiling on working quality and total power consumption for high stubble straw returning were carried out. The high stubble rape field was used as the test field; forward speed and PTO speed of tractor were taken as the test factors. Straw coverage rate and straw proportion of the lower half burying layer were taken as the test indexes of the working quality. Subsoiling and rotary burying (SRB) returning operation was used as experimental group and direct rotary burying (DRB) returning operation was the control group. The results showed that under different working conditions, the mean value of straw coverage rate of SRB was 93.0%, straw proportion of the lower half burying layer was 52.8%, these values were better than DRB. The straw proportion of the lower half burying layer of SRB compared with DRB increased by 10.5%. Two factors all had a significant effect on it under the SRB and DRB conditions. Subsoiling could significantly reduce the PTO torque. Under low speed, the total power consumption of SRB was slightly smaller, while under high speed, the total power consumption of DRB was slightly smaller. Under the SRB and DRB conditions, two factors both had a significant effect on total power consumption. The optimal working combination (working quality as the primary index) was 1.5 km/h of forward speed and 720 r/min of PTO speed. Under this condition, the straw coverage rate was 94.1%, the straw proportion of the lower half burying layer was 59.0%, and the total power consumption was 35.62 kW. The research confirmed that subsoiling is beneficial to the working quality and total power consumption of high stubble straw returning machine. It could meet the working requirements, and provide a reference for optimizing straw returning machine and improving working quality.

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