Design and testing of planting unit for rice dry-direct-seeding planter in cold region

: Rice dry-direct-seeding technology is a time-saving, cost-saving and efficient rice cultivation technique that increases the efficiency of seeding. In order to implement the specialization, light simplicity and scale of rice production, improve the level of mechanization of the whole rice production process, and solve the problems of uneven seed furrows, uneven number of seeds sown, shallow mulching and uncompact repression that occur during the promotion and application of dry-direct-seeding for rice in the cold region of northeast China. In this paper, a planting unit for rice dry-direct-seeding planter is designed. The working principles and structural parameters of the furrow opening components, the seeding apparatus and the soil covering-pressing device are described. The mechanical model of the key components of the seeding unit was established, and the forward speed, roller diameter and compacting strength were selected as the test factors. A three-factor, five-level quadratic rotation orthogonal combination test was conducted with the seed breakage rate, seeding depth qualification rate, seeding uniformity coefficient of variation and hole grain count qualification rate as the evaluation indexes. Field performance test and test results show that: at a forward speed of 4 km/h, a roller diameter of 427 mm and a compacting strength of 48.45 kPa, the seed breakage rate was 1.31%, the sowing depth qualification rate was 9.95%, the coefficient of variation of sowing uniformity was 3.75% and the number of holes was 86.75%. This accords with the agronomic requirements of dry-direct-seeding for rice and implements a combination of superior agronomy and modern farm machinery.


Introduction
As one of the world's most important food crops, rice is grown in the monsoon and tropical rainforest regions of East, Southeast and South Asia [1,2] .China is the largest rice producer in the world.In 2019, the planting area is 30.76 thousand hm 2 , and the rice yield is 21.86 million t, accounting for about 32% of the world's total rice production [3,4] .
At present, rice cultivation in China is still dominated by seedling cultivation, transplanting and irrigation, with low levels of cultivation mechanisation, low operational efficiency and serious wastage of water resources [5][6][7] .Dry-direct seeding for rice is a watersaving cultivation technique in which the land is prepared in a dry field state, the treated rice seeds are sown directly into the rice field, and the field is wetted by drip irrigation after sowing, with no or little irrigation in the early stage and scientific and reasonable irrigation in the later stage according to the law of rice physiological water demand [8][9][10][11] .
The rice growing area in the cold north-eastern region of China is flat and vast and suitable for large scale mechanized operations.However, due to the constraints of lower temperatures, shorter light hours, lack of water resources and backward supporting farm machinery and agronomic techniques, dry-direct-seeding technology for rice has not been applied in a large scale [12][13][14] .
To address the problems of poor stability of the depth and width of the seed furrow, poor uniformity and high volatility of seed discharge, low performance of mulching, soil breaking and suppression in the application of dry-direct-seeding machines for rice in cold regions [15][16][17][18] .In this paper, a planting unit suitable for drydirect-seeding of rice in cold regions of northeast China is developed with reference to the actual agricultural conditions of rice cultivation and the agronomic requirements of dry-direct-seeding technology for rice.This planting unit can complete the entire planting process of trenching, seeding and mulching in one operation.
This paper focuses on the structural principle and mechanical characteristics of dry-direct-seeding units for rice in cold regions, and investigates the stresses, movement laws and operational effects of seeding units through a combination of theoretical numerical analysis and field tests.This paper provides theoretical references for the optimal design of rice dry seeding machines in cold regions.

Structure and working principle of planting unit
The dry-direct-seeding unit for rice in cold regions mainly consists of imitation institutions, ditchers, seed meters, hillers and pressing rollers.The overall structure is shown in Figure 1.

Imitation institutions
Seed meter Ditcher Hiller and pressing roller The planting unit is attached to the crossbeam of the dry-directseeding machine for rice by means of the fixing seat of the imitation institutions.The dry-direct-seeding machinery for rice is connected to the tractor by means of a standard three-point suspension.When working, the tractor pulls the dry-direct-seeding machinery for rice forward, the parallel four-bar imitation institutions control the depth of furrow opening and seeding depth, the ditcher presses out the seed furrow through the rotating pressure roller, the ground wheel drives the seed rower through the chain drive to sow the rice seeds into the seed furrow at low speed, the soil covering-pressing device completes the suppressing and backfilling of the soil on the surface of the seeds in the seed furrow.

Structural design of the ditcher
The ditcher is the working part of the planting unit to construct the seed furrow.A superior quality seed trench should compact the subsoil for water and moisture storage.The structure of the ditcher directly affects the quality of the seeding operation [19,20] .The dither consisting of frame and pressing roller s.

Mechanical model of the pressing roller s
When the pressing roller is in operation, the raised outer edge of the wheel touches the soil first, compacting the subsoil and pressing out the seed furrow.The different curvature of the wheel edge has a soil breaking and drag reducing effect.When the outer wheel edge is completely sunk into the soil, the inner roller comes into contact with the soil and suppresses the soil on both sides of the seedling belt.The radius of curvature of the outer wheel edge is small in relation to the diameter of the roller and is negligible for force analysis.At the same time, neglecting the relative sliding of the pressure roller in the soil and treating it as a rigid roller body that only performs pure rolling, the simplified force on the pressure roller is shown in Figure 2c.
As shown in Figure 2, z 0 is the maximum depth of penetration of the pressure roller into the soil; z is the depth of entry corresponding to any point B on the edge of the pressure roller; θ 0 is the angle of the center of the circle corresponding to the maximum depth of soil entry z 0 ; R is the radius of the pressure roller; P is the traction force on the pressure roller; W is the pressure generated by the pressure roller in the vertical direction; x is the horizontal coordinate corresponding to point B; dQ is the compressive reaction force of the soil acting in a tiny section dl on the wheel edge.
where, p is the compacting strength of the soil; b is the width of the roller; dl is the arc length of a tiny section on the wheel edge. Therefore, where, , is a coefficient to be determined in relation to soil cohesion; is a coefficient to be determined in relation to soil friction; z is the depth of entry and n is the soil elastoplasticity index. Then, In ∆OAB, , namely .
After differential, , therefore, The equation shows that the lower limit of the press roll is related to the load applied, the radius, the width and the soil characteristic coefficient.Therefore, the desired soil compactness of the seed substrate can be obtained by varying the construction size and weight of the pressing roller .

Design of the seeding apparatus 3.2.1 Structural design of the seeding apparatus
The seeding apparatus is the core working part of the dry-directseeding unit for rice.A well-structured seed planter is capable of steadily, accurately and evenly discharging rice seed into the seed furrow [21,22] .There are two forms of dry-direct-seeding for rice: strip sowing and hole sowing.In this paper, a combination of a spiral external grooved wheel seeding apparatus and a type-hole wheel seeding apparatus is used.This meets the sowing requirements for both strip and hole sowing and facilitates comparative trials [23,24] .The combined seeding apparatus consists of a seed box, shell, seed cleaning brush, tranmission shaft, seed release plate, seed rowing tube, combined seed rowing wheel, seed protection belt, seed limiting plate and seed adjusting plate.The structure of the seeding apparatus is shown in Figure 3.The combined seeding wheel consists of a spiral groove wheel and a type-hole wheel.When the key of the seed row shaft is connected to the spiral groove wheel, the groove wheel rotates to complete the strip sowing; when the key of the seed row shaft is connected to the type-hole wheel, the type hole wheel rotates to complete the hole sowing.
(1) The seeding quantity of the spiral grooved wheel is given by Equation ( 10) where, , q is the amount of fertilizer applied per revolution of the spiral groove wheel, g; D is the diameter of the spiral grooved wheel, cm; L is the effective working length of the spiral groove wheel, cm; γ is the seed density, g/cm 3 ; k is the seed filling factor; f is the cross-sectional area of the individual spiral grooves, cm 2 ; t is the spiral groove pitch, cm; z is the number of grooves; λ is the driving layer characteristic coefficient of seeds.Due to the action of the seed discharge brush and seed guard belt, the slotted wheel drives a negligible amount of seed discharge, namely λ = 0. Therefore, From Figure 4, the cross-sectional area of a single spiral groove can be derived from the following equation.
Substituting the corresponding coefficients and grooved roller dimensions into the above equation gives the following values: q 1 =6.72 g (L=1 cm), q 2 =13.44 g (L=2 cm), q max =20.16 g (L max = 3 cm).The type hole consists of two circular arcs of radius R and r.To facilitate seed filling and sowing, the following equation should be satisfied.
where, r is the small arc radius, mm; R is the large arc radius, mm; L is the total length of the type hole, mm; l max is the maximum length of the rice seed, mm; w max is the maximum width of the rice seed, mm; t max is the maximum thickness of the rice seed, mm.The depth of the type hole and the number of seed-filled grains per layer can be expressed by the following equation.
where, H is the depth of the hole, mm; N is the number of seeds in the hole; n is the number of filled seeds per layer.
According to the agronomic requirements of dry-direct-seeding for rice in the cold regions of Northeast China, it is best to sow 5 to 7 seeds per hole.The dimensions of the rice seeds are as follows: lengths are mainly distributed between 6.1 and 9.1 mm, widths between 2.6 and 3.5 mm and thicknesses between 2.0 and 2.6 mm [27][28][29] .By substituting the statistical values into the corresponding equations and after smoothing, the following type hole dimensions are obtained: the small arc radius is 4.5 mm, the large arc radius is 5 mm, the total length of the type hole is 13 mm and the depth of the type hole is 7 mm.

Design of the soil covering-pressing device 3.3.1 Structural design of the soil covering-pressing device
The soil covering-pressing device is a key component in the construction of the seed bed by the seeding unit.A high quality seed bed has a reasonable soil structure, with an even mulch and firm soil, which facilitates the growth and germination of the rice seed.In this paper, a self-rotating extruding soil covering-pressing device with soil breaking function is designed.The edge of the suppression roller engages at the bottom of the trench, the position and angle of engagement is adjustable and the protruding structure on the outside of the edge has both suppression and soil breaking functions.The soil covering-pressing device consists of a connecting frame, a soil covering-pressing wheel, an angle adjustment mechanism and a pressure adjustment mechanism.The structure of the the soil covering-pressing device is shown in Figure 6a.The parameters of the soil covering-pressing device directly influence the suppression effect and slip rate.The smaller the diameter of the soil covering-pressing wheel, the greater the slip rate during operation, while soil dragging and soil congestion can occur.The conditions for proper operation and non-slip of the soil covering-pressing wheel are shown in the following equations.
where, R is the radius of the overburden ballast wheel, mm; M r is the frictional moment in the sleeve, N-m; Q is the total load on the overburden ballast wheel, N; f is the coefficient of friction between the soil and the overburden ballast wheel; h is the lower limit of the soil, mm; θ is the angle of the circle corresponding to the depth of entry h, (°).
In this paper, the structure of the outer edge of the soil coveringpressing wheel is effective in reducing the slip rate.The ditcher is capable of compacting the bottom of the trench during the construction of the seed trench.Therefore, the lower limit of the radius of the soil covering-pressing wheel, namely R = 128 mm, is desirable to meet normal operating conditions.
(2) Force analysis of the soil covering-pressing wheel When the soil covering-pressing wheel is in operation, it can be considered a rigid body.The contact area between the soil covering-pressing wheel and the soil can be expressed as the product of the width of the rigid wheel and the radial contact arc length.The pressure exerted on the soil by the soil covering-pressing wheel can be expressed by the following equation.
where, , p is the pressure exerted on the soil by the soil covering-pressing wheel during operation, kPa; F is the ballast pressure exerted on the soil by the soil covering-pressing wheel, N; S is the contact area between the soil covering-pressing wheel and the soil, mm 2 .As shown in Figure 6b, the ballast pressure generated by the soil covering-pressing wheel on the soil can be expressed by the following equation.
, G is the gravity of the soil covering-pressing wheel and its appendages, N; F N is the spring pressure, N; α is the angle between the soil covering-pressing wheel and the X axis (horizontal direction), (°); β is the angle between the mulching ballast wheel and the Z axis (forward direction), (°); k is the coefficient of elasticity, N/m; x is the deformation, m.
The agronomic requirements for the compacting strength after dry-direct-seeding of rice are generally 30-50 kPa, the requirements for soil bulk weight are 0.8-1.2g/cm 3 , and the thickness of the mulch above the seeds is 2 to 3 cm.

Test conditions and instrumentation
Field performance testing and trial evaluation were conducted at the Academy of Agricultural Sciences, Harbin, Heilongjiang Province, China, in May 2021-June 2021.The previous crop in the test area was rice and the soil type was a typical black clay loam with a fine, flat soil.The thickness of the crumbly layer was 6 cm, the soil moisture content was 23% and the average firmness of the soil was 1.1 MPa.Each section of the test area is 60 m long, of which the first 10 m is the test commissioning area (data for reference only), the middle 40 m is the test testing area and the last 10 m is the test adjustment area (data for calibration only).
Test equipment: one tractor, one force tester, one SZ-1 digital soil hardness tester, one TZS-I soil moisture content tester, one GSI-200 electronic balance, one ploughing depth ruler, one electronic stopwatch, one tape measure, one ploughing depth ruler and several marking rods.

Test method
The forward speed, pressing roller diameter and compacting strength were selected as the test influencing factors, and a threefactor, five-level quadratic rotational orthogonal test design was chosen based on the factor levels.Factor level codes are listed in Table 1 and data were analyzed using Design-Expert software.Seed breakage rate: Three data collection zones of 1 m in length were selected within the test area, and the total mass of rice seeds discharged from each data collection zone and the mass of broken, damaged or injured rice seeds were determined separately.The percentage of broken, damaged or injured rice seed mass to the total rice seed mass is calculated according to the following equation, and the arithmetic mean of the three measurements is taken as the seed breakage rate for the group.
where, y 1 is seed breakage rate, %; m pi is mass of broken, damaged or injured rice seeds, g; m zi is total mass of rice seeds, g.Sowing depth qualification rate: Fifty locations were selected in the test area and the thickness of the upper soil cover on the seeds was determined as the sowing depth.The sowing depth qualification rate was calculated according to the following equation (qualified sowing depth is 2-3 cm).
where, y 2 is the sowing depth qualification rate, %; B h is the number of sowing depth qualified; B z is total number of samples.Hole qualification rate: Three 1m long data collection zones were selected within the trial test area and the number of holes qualifying for the number of holes and the total number of holes in each data collection zone were determined separately.The percentage of holes with a qualified number of grains to the total number of holes is calculated according to the following equation, and the arithmetic mean of the three measurements is taken as the percentage of holes with a qualified number of grains for the combination (5 to 7 seeds per seed hole is a qualified hole).
where, y 3 is the hole qualified rate, %; S h is the number of holes qualified; S z is the total number of holes.Coefficient of variation of sowing uniformity: Twenty locations were selected in the test area and the number of seeds in each location was measured to calculate the coefficient of variation of sowing uniformity according to the following equation.
where, y 4 is the coefficient of variation of sowing uniformity, %; L i is the number of seeds; n is the number of samples.

Test results
In this test, the coded values for the level of each influencing factor were used as the independent variables and the seed breakage rate, sowing depth pass rate, coefficient of variation in sowing uniformity and hole qualification rate were used as the dependent variables.The test scheme and results are listed in Table 2.The trial process and rice growth are shown in Figure 7.

Regression analysis of the test results
Based on the test results in Table 2, the test data was processed using Design-Expert software to produce an analysis of variance (ANOVA) for the effects of forward speed, Pressing roller diameter and Compacting strength on seed breakage rate, Sowing depth qualification rate, coefficient of variation in sowing uniformity and hole qualification rate.The results of the analysis are listed in Table 3.
(1) Regression modeling and significance testing of the seed breakage rate According to the results of the ANOVA on seed breakage rate in Table 3, factors x 1 , x 3 and x 3 2 had a highly significant effect on seed breakage rate at confidence level α=0.01, factor x 1 2 was significant at confidence level α=0.05 and the other factors were not significant.The influence of each factor on the significance of seed breakage rate was in the order of forward speed, compacting strength and pressing roller diameter.A quadratic multiple regression was fitted to the data in Table 2 to establish a quadratic regression equation for seed breakage rate.

Table 3 Analysis of variance for the effect of factors on response indicators
(2) Regression modeling and significance testing of the sowing depth qualification rate According to the ANOVA results in Table 3, factors x 2 , x 3 , and had a highly significant effect on the sowing depth qualification rate at confidence level , while the other factors were not significant.The influence of each factor on the significance of sowing depth qualification rate was in the order of pressing roller diameter, compacting strength and forward speed.A quadratic multiple regression was fitted to the data in Table 2 to establish a quadratic regression equation for the sowing depth qualification rate.
(3) Regression modeling and significance testing for the coefficient of variation in sowing uniformity According to the ANOVA results in Table 3, factors x 1 , x 2 and x 3 have a highly significant effect on the coefficient of variation of sowing uniformity at confidence level , factors and are significant at confidence level , while the other factors are not significant.The influence of each factor on the significance for the coefficient of variation in sowing uniformity was in the order of forward speed, compacting strength and pressing roller diameter.A quadratic multiple regression was fitted to the data in Table 2 to establish a quadratic regression equation for the coefficient of variation in sowing uniformity.
(4) Regression modeling and significance testing of the hole qualification rate According to the ANOVA results in Table 3, factors x 3 have a highly significant effect on the coefficient of variation of sowing uniformity at confidence level , factors x 1 , x 2 and x 1 x 2 are significant at confidence level , while the other factors are not significant.The influence of each factor on the significance for the coefficient of the hole qualification rate was in the order of compacting strength, forward speed, and pressing roller diameter.A quadratic multiple regression was fitted to the data in Table 2 to establish a quadratic regression equation of the hole qualification rate.

Analysis and optimisation of response surface 5.3.1 Response surface analysis of the seed breakage rate
Since the diameter of the pressing roller had no significant effect on the seed breakage rate, the diameter of the pressing roller was fixed at zero level (x 2 = 400 mm) to investigate the effect of forward speed and compacting strength on the seed breakage rate and their interaction.The response surface for the two-factor effect on seed breakage rate is shown in Figure 8a.
As can be seen from Figure 8, the seed breakage rate increases and then decreases with increasing forward speed at a pressing roller diameter of 400 mm, and the maximum value occurring around x 1 =7.83 km/h.The seed breakage rate increases and then decreases with increasing compacting strength, and the maximum value occurring around x 3 =45.02km/h.

Response surface analysis of the sowing depth qualification rate
Since the forward speed had no significant effect on the sowing depth qualification rate, the forward speed was fixed at zero level (x 1 =6 km/h) to investigate the effect of pressing roller diameter and compacting strength on the sowing depth qualification rate and their interaction.The response surface for the two-factor effect on the sowing depth qualification rate is shown in Figure 8b.
As can be seen from Figure 9, at a forward speed of 6 km/h, the sowing depth qualification rate increases with the diameter of the pressing roller , and the maximum value occurs around x 2 =430 mm.The sowing depth qualification rate increases and then decreases with increasing compacting strength, and the maximum value occurs around x 3 =43.62kPa.Fixing any of the three factors of the regression model at the zero level and examining the effect of the other two factors on the coefficient of variation in sowing uniformity and their interaction.The response surface for the effect of each factor on the coefficient of variation in sowing uniformity is shown in Figure 9.
As can be seen from Figure 9a, the coefficient of variation in sowing uniformity increases with increasing forward speed and decreases with increasing pressing roller diameter at a compacting strength of 40 kPa.As can be seen from Figure 9b, the coefficient of variation in sowing uniformity increases with increasing forward speed and with increasing compacting strength at a pressing roller diameter of 400 mm.As can be seen from Figure 9c, at a forward speed of 6 km/h, the coefficient of variation in sowing uniformity decreases with increasing diameter of the pressing roller and increased with increasing compacting strength.

Response surface analysis of the hole qualification rate
Fixing any of the three factors of the regression model at the zero level and examining the effect of the other two factors on the hole qualification rate and their interaction.The response surface for the effect of each factor on the hole qualification rate is shown in Figure 10.
From Figure 10a, it can be seen that under the compacting strength of 40 kPa, the forward speed of 4.0-7.2km/h and the diameter of the pressing roller s of 370-377.4mm, the hole qualification rate decreases with the increase of the forward speed and decreases with the increase of the diameter of the pressing roller; when the forward speed is 4-7.2 km/h and the diameter of the pressing roller is 377.4-430mm, the hole qualification rate increases with the increase of forward speed and decreases with the increase of diameter of the pressing roller; when the forward speed is 7.2-8 km/h and the diameter of the pressing roller is 370-377.4mm, the hole qualification rate decreases with the increase of forward speed and increases with the increase of diameter of the pressing roller; when the forward speed is 7.2-8 km/h and the diameter of the pressure roller is 370-377.4mm, the hole qualification rate decreases with the increase of forward speed and increases with the increase of diameter of the pressing roller .From Figure 10b, it can be seen that under the condition that the diameter of the pressing roller is 400 mm, the hole qualification rate increases with the increase of the forward speed and increases with the increase of the compacting strength.As can be seen from Figure 10c, at a forward speed of 6 km/h, the hole qualification rate decreases with the increase in pressing roller diameter and increases with the increase in compacting strength.

Optimisation of the test programme
According to the promotion and appraisal standard of DG/T 0832021 direct seeding machine for rice, the following optimization constraints were selected, taking into account the actual working conditions, agronomic technical requirements and the analysis of test results.
The main objective function optimization method was used and optimized by the Design-Expert software to produce a better test solution.The optimum solution was determined according to the actual operating conditions and the detailed parameter combinations are listed in Table 4.

Verification test
Different measurement areas of the same plot were selected and verification tests were carried out according to the optimal combination of parameters, and the test photos are shown in Figure 11.The Verification results showed that the optimal combination for dry-direct-seeding for rice in cold regions resulted in a seed breakage rate of 1.35%, a sowing depth qualification rate of 90.22%, a coefficient of variation in sowing uniformity of 3.79% and a hole qualification rate of 86.88%.Comparison with the results of the quadratic regression orthogonal rotational combination test showed that the results of the verification test were similar to the results of the experimental analysis.This indicates that the planting unit for rice dry-direct-seeding planter in cold regions designed in this paper meets the design requirements.

Conclusions
(1) In this paper, a planting unit for rice dry-direct-seeding in cold regions was designed.This sowing unit used pressing rollers to open the furrow, combined strip and hole sowing, and employed a self-rotating extruding soil covering-pressing device with a soil breaking function for soil compaction.These design features effectively addressed the challenges faced during the dissemination of dry-direct-seeding technology for rice in northeast China.
(2) A three-factor, five-level quadratic rotational orthogonal combination test was arranged by analyzing the kinematics and working conditions of the key components.Regression modeling was established between each test index and the influencing factors.The effects of forward speed, pressing roller diameter, and compacting strength on seed breakage rate, sowing depth qualification rate, coefficient of variation in sowing uniformity, and hole qualification rate were analyzed.
(3) The factors that had a significant effect on the seed breakage rate were, in order of significance: forward speed, compacting strength, and pressing roller diameter.The factors that significantly affected the sowing depth qualification rate were, in order of significance: pressing roller diameter, compacting strength, and forward speed.The factors influencing the significance of the coefficient of variation in sowing uniformity were, in order of significance: forward speed, compacting strength, and pressing roller diameter.The factors that had a significant impact on the hole qualification rate were, in order of significance: compacting strength, forward speed, and the diameter of the pressing roller.
(4) According to the regression model, the parameters were optimized and the analysis yielded the optimal combination of parameters: forward speed 4 km/h, pressing roller diameter 427 mm and compacting strength 48.45kPa, at this point the seed breakage rate was 1.31%, the sowing depth qualification rate was 89.95%, the coefficient of variation in sowing uniformity was 3.75% and the hole qualification rate was 86.75%.The verification test results differed little from the optimized values, which are accurate and reliable, and this meets the agronomic requirements of dry-directseeding.

Figure 1
Figure 1 General structure of the planting unit

Figure 2 F
Figure 2 Structure of the pressure roller and the forces applied During operation, the equilibrium equation of the pressure roller in the xoz plane is ∑

Figure 3
Figure 3 Structure of the seeding apparatus 3.2.2Structural design of the combined seeding wheelThe combined seeding wheel consists of a spiral groove wheel and a type-hole wheel.When the key of the seed row shaft is connected to the spiral groove wheel, the groove wheel rotates to complete the strip sowing; when the key of the seed row shaft is connected to the type-hole wheel, the type hole wheel rotates to complete the hole sowing.(1)The seeding quantity of the spiral grooved wheel is given by Equation(10)

Figure 4
Figure 4 Schematic diagram of the cross-section of the spiral groove (2) The structural parameters of the type hole are important to ensure the accuracy of the hole sowing.Rice seeds are shaped like ellipsoidal spheres and fill the type hole in three forms: flat, lateral and vertical, as shown in Figure 5.

Figure 5
Figure 5 Structure of the type hole

Figure 6
Figure 6 Force analysis of soil subjected to suppression 3.3.2Modeling of the soil covering-pressing wheel (1) Parameters of the soil covering-pressing wheelThe parameters of the soil covering-pressing device directly influence the suppression effect and slip rate.The smaller the diameter of the soil covering-pressing wheel, the greater the slip rate during operation, while soil dragging and soil congestion can occur.The conditions for proper operation and non-slip of the soil covering-pressing wheel are shown in the following equations.
trial b.Rice emergence 30 d after sowing c.Rice emergence 60 d after sowing d.Rice emergence 80 d after sowing.

Figure 7
Figure 7 Trial process and rice growth

1 P
p a c ti n g s tr e n g th /k P a F o r w a r d s p e e d /k m • h − r e s s i n g r o l l e r d i a m e t e r / m p a c ti n g s tr e n g th /k P a Sowing depth qualification rate/% a. Seed breakage rate b.Sowing depth qualification rate

Figure 8
Figure 8 Response surface plots of the seed breakage rate and sowing depth qualification rate

Figure 9 1 F 1 CFigure 10
Figure 9 Response surface plots of different factors on coefficient of variation in sowing uniformity

Test methods of test indicators
In accordance with the relevant provisions of the National Recommended Standard GB/T 6973-2005 of the People's Republic of China and the Agricultural Machinery Promotion and Certification Standard DG/T 083 2021.In this test, seed breakage rate, sowing depth qualification rate, coefficient of variation of sowing uniformity (measured at strip sowing) and hole grain count qualification rate (measured at hole sowing) were used as response indicators.