Burying uniformity in soil is often required during rice straw returning. In this study, a burying roller was designed with an internal and external opposed double-screw using the straw crushing-rotary tillage and burying returning machine. A single-factor discrete element simulation (two-factors and ten-levels) was conducted to analyze the influence of the straw length (6-15 cm) and the screw angle (30°-75°) of the external screw belt in the burying roller on the coefficient of variation of the straw mass distribution. The parameters of the burying roller were optimized on the patterns after simulation. The field experiments were conducted to verify the performance of the device. The simulation results showed that the coefficient of variation of the straw mass distribution initially decreased and then increased as the screw angle increased at the constant straw length. The quadratic function was used to fit the relationship between the coefficient of variation of the straw mass distribution and the screw angle under different straw lengths. The curves of 10 straw lengths were determined for the minimum coefficient of variation of the straw mass distribution in the range of 55°-62°. Once the screw angle was constant, the coefficient of variation of the straw mass distribution was linearly related to the straw length. Specifically, the coefficient of variation of the straw mass distribution decreased by 3.255 percentage points for every 1 cm reduction in the straw length. The straw length was positively correlated with the resistance encountered in the soil. Shorter straw also encountered less resistance in the soil. It was more easily buried in the deeper soil layer, thereby reducing the coefficient of variation of the straw mass distribution. When the screw angle of the screw blade was 55°, and the straw length was 6 cm, the coefficient of variation of the straw mass distribution reached its minimum of 27.59 percentage points, and the straw burying uniformity was the highest, which was the optimal working parameter on the simulation. And the spatial distribution of the straw in the soil showed a decreasing distribution along the depth of the soil. The proportion of straw mass in the upper soil layer (>0-50 mm) was greater than that in the middle soil layer (50-100 mm). In turn, there was more than that in the lower soil layer (100-150 mm). The reason was that the straw was initially distributed on the soil surface, and then moved to the depth of the soil under the action of the burying roller. The greater the downward movement was, the greater the displacement and the stronger the resistance encountered, and the less the straw distribution was. In the two factors of the screw angle and straw length, the percentage of the straw mass in the upper soil layer (>0-50 mm) and the lower soil layer (100-150 mm) shared the opposite trends, while the percentage of straw mass in the middle soil layer (50-100 mm) fluctuated slightly. Since the increasing straw mass in the lower soil layer was mainly from the upper soil layer, the straw mass in the upper soil layer improved the uniformity of the straw mass distribution. Field experiments showed that the percentage of straw mass in the soil layers at the depth of >0-50 mm, 50-100 mm and 100-150 mm were 40.91%, 34.58% and 24.51%, respectively, while the coefficient of variation of the straw mass distribution was 25.35 percentage points, when the screw angle of the external screw belt was 55° and the straw length was 6 cm. Compared with the simulation, the percentage deviations of the straw mass in the different soil layers and the coefficient of variation of the straw mass distribution were 0.04-2.24 percentage points, with the relative errors of 0.2%-8.8%. The simulation was basically consistent with the experiment, indicating the effectiveness of the parameter optimization on the burying roller and the better uniformity of the rice straw returning and high seedbed quality after the machine operation. The findings can provide sound support to improve the straw returning quality for the straw crushing-rotary tillage and burying returning machine.

To mitigate the damage rate of Camellia oleifera seeds during the process of Camellia oleifera fruit dehulling, a Camellia oleifera fruit cutting and compression machine was developed. This machine operates on the principle that the shell-breaking stress of Camellia oleifera fruit is reduced following cutting, thereby integrating the steps of grading, cutting, compressing, and separating for the dehulling of Camellia oleifera fruit. Utilizing the electronic universal testing machine, a 4-factor single-factor test was conducted, including the number of cutting knives, cutting direction, compressing direction, and Camellia oleifera fruit size. The results showed that the average breaking force of Camellia oleifera seeds was 196.33 N. Compared with direct separating without cutting, the shell-breaking of Camellia oleifera fruit with 1, 2, 3, and 4 cuts decreased 30.14%, 38.62%, 45.05%, and 47.74%, respectively. Compared with cutting along the long axis, the shell-breaking force of Camellia oleifera fruit cutting along the minor axis decreased 8.1%; however, the effect of cutting direction on shell-breaking force is not significant. The shell-breaking force of Camellia oleifera fruit compressing along the long axis was 24.11% lower than that of Camellia oleifera fruit compressed along the minor axis. With the increase of Camellia oleifera fruit size, the shell-breaking force of Camellia oleifera fruit also increased. The shell-breaking force of 25-30 mm, 30-35 mm, and 35-40 mm was 85.62%, 127.34%, and 178.69% higher than that of 20-25 mm, respectively. In conclusion, using grading measures, making one cut along the long axis and compressing along the long axis is a suitable method for husking of Camellia oleifera fruit.

In order to improve the crushing efficiency and spreading uniformity of rice straw incorporation, considering its characteristics of high stubble, dense structure, and strong toughness, a rice straw incorporation machine by crushing-rotary tillage-burying with a crushing roller equipped with straight blades and L-shaped blades was designed. This design leveraged the crushing and kneading action of the straight blades and the cutting and crushing effect of L-shaped blades. With the qualification rate of crushing straw and straw spreading uniformity as evaluation indicators, a mixed-level orthogonal experiment (four levels for two factors and two levels for two factors) was conducted to analyze the effects of radial angle, L-shaped blade bending angle, rotational speed, and forward speed on the qualification rate of crushing straw and straw spreading uniformity. The results showed that the factors affecting the qualification rate of crushing straw, in descending order of significance, were radial angle, rotational speed, and L-shaped blade bending angle. Those affecting straw spreading uniformity, in the same order of significance evaluation, were radial angle, L-shaped blade bending angle, forward speed, and rotational speed. The optimal parameter combination was determined as a radial angle of 70°, an L-shaped blade bending angle of 135°, a rotational speed of 2400 r/min, and a forward speed of 0.60 m/s. The experiment was conducted using the optimal parameter combination, the qualification rate of crushing straw reached 92.41%, and the straw spreading uniformity was 87.44%. Compared with the best-performing experimental group, the qualification rate of crushing straw increased by 1.86 percentage points, while the straw spreading uniformity was only 0.75 percentage points lower than the maximum value. Compared to China’s national standard requirements, the optimized results show a 2.41 percentage point increase in straw crushing qualification rate and a 12.44 percentage point increase in straw spreading uniformity, thus meeting and exceeding China’s national standards. The qualification rate of straw crushing and the uniformity of straw spreading were better than other combined blades. This study provides both theoretical and technical support for reducing the adverse effects of rice straw incorporation on subsequent crops.

Rape straw is characterized by high stubble, thick stalks and difficulty to decompose. In this study, the opposing double-screw burying device was designed to combine the crushing-rotary tillage-mulching machine for the rape straw returning. The coefficient of variation of straw mass distribution and the percentage of straw mass in different soil layers were taken as the evaluation standard of straw returning. A four-factors and four-level orthogonal test was then conducted to determine the influencing parameters, such as the helix angle of the opposing double-screw burying device, rotary speed, forward speed, and the length of the straw. The results show that the coefficient of variation of straw mass distribution in different soil layers slowly decreased and then sharply increased with the increase of the helix angle. The better uniformity was obtained for the rape straw returning when the helix angle was below 60°. Furthermore, the coefficient of variation of straw mass distribution in different soil layers decreased and then increased with the increase of the rotary speed. Specifically, the displacement of the straws increased, when the rotary speed was below 210 r/min. The reason was that the kinetic energy of the straws increased with the increase of the rotary speed. Once the rotary speed exceeded 210 r/min, the displacement of the straws increased with the increase of the straw kinetic energy, and then the straw was screened and aggregated from the soil. Different specific gravity thus caused the uneven distribution of the straw in the soil. There was a similar trend of decreasing and then increasing in the coefficient of variation of straw mass distribution in different soil layers, as the forward speed increased. The straw was separated from the soil under excessive disturbance at the low forward speed, where the machine stayed put. By contrast, the variation coefficient also increased at the high forward speed with the weak function of the opposing double-screw mulching device. There was a positive relationship between the variation coefficient and the straw crushing length, indicating the shorter the length was, the smaller the variation coefficient was. The significant degree in the coefficient of variation of straw mass distribution was ranked in the descending order of the straw length, helix angle, rotary speed, and forward speed. The highest proportion of straw mass was in the upper layer (0-50 mm). There was a gradual decrease with the deepening of the depth. The uniformity of rape straw returning was also achieved to increase the straw in the deep soil (＞100-150 mm). The percentage of straw mass varied in the different soil layers with the four factors between the upper layer (0-50 mm), indicating the opposite in the deep soil (＞100-150 mm). But there was a small change in the percentage of straw mass in the intermediate soil layer (＞50-100 mm). The uniformity of the mixed straw mulching was improved to reduce the length of straw crushing reducing, while improving the degree of mixing between the straw and the soil without excessive disturbance. In terms of the helix angle of 60°, the rotary speed of 210 r/min, the forward speed of 0.6 m/s, and the length of straw of 6 cm, the percentages of straw mass in the depth of 0-50, ＞50-100, and ＞100-150 mm were 43.97%, 33.28%, and 22.75%, respectively, where the coefficient of variation of straw mass distribution of straw mass was 26.43%. The percentage of straw mass in the upper layer was reduced by 2.36 percentage points, whereas, the percentage of straw mass in the deep depth increased by 7.18 percentage points, and the coefficient of variation of straw mass distribution was reduced by 12.6 percentage points, indicating the best uniformity of rape straw returning and the best quality of the seed bed, compared with the orthogonal experiment groups. The finding can provide a strong reference to improve the quality of rape straw returning.

To solve the difficulty in ditching for the deep fertilization in tea gardens caused by the high quantity of tea branches and stubbles, a new ditching device combined with a kind of rotary tillage and chisel shovel was designed. The combined ditching device worked by the following steps: Firstly, the stubble, such as fallen leaves and weeds between the rows, was cleaned up and thrown away by the rotary tillage. Then, the chisel-shaped fertilizing shovel forcefully dug into the soil, realizing the deep fertilization groove. The parameters of the rotary tillage and stubble-throwing device and the chisel-shaped fertilizing shovel were optimized by single factor test and quadratic regression orthogonal rotation test, respectively. The optimization results showed that when the number of stubble-throwing blades of the rotary tillage and stubble-throwing device was five, and the blade installation inclination angle was 16°, the stubble removal rate was the highest at the high speed of the cutter (300 r/min), which was 91.64%. When the entry angle of the chisel-shaped fertilizing shovel was 30°, the entry clearance angle was 8°, and the operating speed was 0.7 m/s, the stability coefficient of the groove depth was 94.9%, which was the optimal parameter of the chisel-shaped fertilizing shovel. The field experiment showed that the average width of the ditching was 224 mm (between 202-248 mm), the average depth of the groove was 194.9 mm (between 173-218 mm), and the stability coefficient of the groove depth could reach 92.78%, realizing stable lateral deep fertilization in the tea garden.

Rapeseed straw returning has been widely used in the rape-corn rotation area in the middle and lower reaches of the Yangtze River. However, there are adverse effects on the corn sowing quality at present. indicators are often used to evaluate the quality of straw return to the field, such as the coverage rate (the proportion of straw covering the surface) and burial rate (the proportion of straw buried in the soil). It is still unclear to fully express the spatial distribution of straw in the soil. In this study, a systematic investigation was implemented to explore the effects of length and spatial distribution on corn sowing quality in rapeseed straw returning. The corn germination rate and plant height were also taken as the evaluation indexes in the experiment. A 2-factor, 10-level, and one-way test was conducted to investigate the effects of rape straw length (6-150 mm) and the spatial distribution of straw in different depths of the soil (0-15 cm) on the corn emergence rate and plant height. The results showed that the emergence rate and plant height of maize decreased gradually and linearly with the increase in rape straw length. Specifically, the emergence rate and plant height increased by 3.83 percentage points and by 1.32 cm for every 1 cm decrease in straw length. The reason was that the long straw caused the soil to shelf, and the large void in the soil led to the aeration and breathability. The moisture conservation reduced emergence and survival rate during seeding and seedling rooting. The shorter the straw was, the greater the displacement of the straw movement was. Correspondingly, there was a higher decomposition rate of short straw than that of long one, indicating more contribution to mixing with the soil. The decomposition of nutrients promoted the development and growth of seedlings; Furthermore, the corn emergence rate reached 100%, and the plant height grew up to 55.84 cm when the length of the straw was taken as the minimum of 6 mm under the same straw mass of the upper (≥0-5 cm), middle (≥5-10 cm) and bottom (≥10-15 cm) straw, (coefficient of variation of the straw mass was 0). At the same time, the corn emergence rate and plant height were determined by the proportion of straw mass in the upper soil layer at the same length of rapeseed straw during uneven mulching. The greater corn emergence rate and plant height were achieved for the lower mass fractions of straw in the upper soil layer; Meanwhile, the corn emergence rate and plant height were determined by the proportion of straw mass in the middle soil layer, particularly in the same proportion of straw mulching mass in the upper soil layer. The smaller stover mass share was observed in the middle soil layer. There was a greater emergence rate and plant height of corn seedlings. The reason was that the straw stacking and clumping often occurred after returning the straw to the field and burying it in the shallow layer of soil because the straw and soil failed to mix sufficiently. The experiment demonstrated that the uniform spatial distribution of straw mass shared a significant effect on the seeding performance. However, there was no correlation between the uniform mulch and the performance of seeding. As such, the burying depth of straw greatly contributed to the water and fertilizer retention in the soil, even the distribution of roots. The continuous growth of roots promoted water and nutrients for the better growth of crops. The degree of straw crushing was improved to reduce the straw mass in the middle and upper layers. While there was an increase in the proportion of straw mass in the bottom layer of the soil. The deep burying of straw was realized to improve the seedling emergence rate and the height of the plant. The finding can provide theoretical support to construct high-quality seed beds for straw return.