Zhaoyan You, Ya Gao, Huichang Wu, Xuemei Gao, Jianchun Yan, Huanxiong Xie

(Nanjing Institute of Agricultural Mechanization, Ministry of Agriculture and Rural Affairs, Nanjing, 210014, China)

Abstract: To solve the problems of low seeding operation quality, low applicability of seeding apparatus and low production efficiency existing in current sowing methods of green manure crops, a 2BFLA-200 type multi-variety green manure intelligent mixer was developed in this paper. Key components such as the pyramid seed box, the electric through-hole combined type seeding apparatus, the evenly-sowed component, and adaptive seeding quantity intelligent control system were designed. The sliding friction angles of 4 main green manure varieties were measured, and the minimum inclined surface angle of the designed pyramid seed box was 35°. Based on the seed size, one thousand grain weight, and seed consumption of per unit area, the seeding channel of the electric through-hole combined type seeding apparatus can be selected and the effective opening of the channel can be set. The 4 varieties and 12 channels adaptive seeding quantity intelligent control system is able to react to real-time adjustments of seeding parameters and show the on-line monitoring of seeding status. Take planting Chinese milk vetch as an example. The multifactorial experiments as well as the regression analysis of the test data were carried out, and the results show that among the three factors in the experiment, the rotation speed of sowing wheel had the greatest influence on the germination rate and variation coefficient of sowing uniformity. On the other hand, machine forward speed had the least influence on the germination rate and the variation coefficient of sowing uniformity. The optimal combination of factors and parameters which affected the sowing quality of multi-variety green manure intelligent mixer was as follows: the machine forward speed was 5 km/h, the rotation speed of the sowing wheel was 44 r/min, and the even-distributed cylinder diameter was 5.5 mm. Verified by field experiments using the optimal parameter combination, the Chinese milk vetch germination rate was 96.71% and variation coefficient of sowing uniformity was 7.95%. Compared with optimal values predicted by the model, the relative errors were all below 5.5%. This validates the optimal values of the three parameters, which has a good prospect for application.

Keywords: green manure; multi-variety; mixer; seeding quantity intelligent control

0 Introduction

Planting green manure crops has the advantages of changing soil’s physical and chemical properties, increasing soil organic matter, and improving crop yield and quality. At the same time, it is also an important green production mode of crop rotation and fallow, improving cultivated land quality and reducing chemical fertilizer application[1-5]. The mixed sowing of leguminosae, gramineae, cruciferae, and other green manure crops can not only develop tourism agriculture, but also make full use of space and light energy. This has the advantage of enhancing plant stress resistance and reducing rotten stems and yellow leaves[6-8]. The planting scale of green manure abroad is large, and the production equipment suitable for green manure sowing has begun to develop in the direction of automation. For example, the Romanian company Moreni has developed an orchard green manure sowing and fertilization machine, which can complete the operation links such as shallow rotation, sowing, fertilization, and suppression at one time autonomously. In addition, the synchronous planter with double row seeders produced by the company Simba Horsch in the UK can sow Chinese milk vetch and other green manure varieties at one time. The existing domestic green manure sowing methods mainly include manual sowing, hand-rocking sowing, electric spraying, UAV aerial seeding, and so on[9-15]. There are two problems that need to be solved when using the above sowing methods. One issue that we face is that the key indicators such as green manure seed utilization rate, germination rate, and sowing uniformity cannot fully meet the quality requirements of production operation. The second issue that must be addressed is that the applicability of seeding apparatus in sowing equipment is not enough. The current sowing methods available can only sow one kind of green manure variety, which can’t meet the operational requirements of the sowing of multi-variety green manure crops in the field at one time.

To address the issues of the production needs and the disadvantages of the existing green manure sowing methods in China, a multi-variety green manure intelligent mixer was developed in this paper. This mixer could improve the sowing quality and meet the seeding quantity intelligent mixed sowing demands of green manure crops with 4 varieties and 12 channels. The best combination of factors and parameters which affected the sowing quality of the green manure mixer was determined through an optimization test, providing a new method for efficient and high-quality mixed sowing of green manure crops.

1 Overall structure and working principle

1.1 Machine structure

The structure diagram of the developed 2BFLA-200 type multi-variety green manure intelligent mixer is shown in Figure 1. The structure of the multi-variety green manure intelligent mixer is composed of a cover plate, fertilizer box, pyramid seed box, left mounting plate, middle partition plate, right mounting plate, main slot plate, electric through-hole combined type seeding apparatus, evenly-sowed component, adaptive seeding quantity intelligent control system, etc. 12 groups of independent pyramid seed boxes stand side by side, which are fixed and installed on the main slot plate and middle partition plate. Each pyramid seed box is independently controlled by an electric through-hole combined type seeding apparatus. The lower discharge port of each electric through-hole combined type seeding apparatus is connected with an evenly-sowed component. The adaptive seeding quantity intelligent control system is fixedly installed on the main slot board. The control interface of the handheld terminal is located in the cab, which is convenient for the driver to adjust the sowing parameters in real time and monitor the sowing status online.

Fig. 1 Diagram of the 2BFLA-200 type multi-variety green manure intelligent mixer1.Adaptive seeding quantity intelligent control system 2.Evenly-sowed component 3.Through-hole combined type electric seeding apparatus4.Main slot plate 5.Right mounting plate 6.Middle partition plate7.Cover plate 8.Fertilizer box 9.Pyramid seed box10.Left mounting plate

1.2 Technical parameters and working principle

The key technical parameters of 2BFLA-200 type multi-variety green manure intelligent mixer are shown in Table 1. When the multi-variety green manure intelligent mixer is used in the field, the pyramid seed boxes is first filled with the green manure seeds according to the sowing quantity requirements and the mixed sowing agronomic requirements of the sown green manure varieties. The positions of the seed-metering rollers and operation parameters of electric through-hole combined type seeding apparatuses are adjusted on the control interface of the handheld terminal. The electric through-hole combined type seeding apparatus realized intelligent sowing with the adaptive seeding quantity intelligent control system. The green manure seeds are released from the seed dropping mouth of the seeding apparatus, then placed into the evenly-sowed component through the seed conveying pipe, and finally evenly spread to the surface after passing through the evenly-sowed component to complete the sowing operation.

Tab. 1 Key technical parameters of 2BFLA-200 type multi-variety green manure intelligent mixer

2 Design of main components

2.1 Pyramid seed box

In order to solve the problem of seeds piling up near the dropping mouth of the seed box, which results in poor seed delivery and incomplete seed metering, the sliding starting angle measuring device was designed as shown in Figure 2(a). The starting angle measuring device is mainly composed of a shaking handle, frame, pull wire, and seed dropping plate. The seed dropping plate can rotate from 0° to 90° with the rotation of the shaking handle. In order to ensure the accuracy of the measured parameters, the steel used for the seed dropping plate should be consistent with the actual seed box material. The sliding starting angles of four kinds of green manure seeds, theastragalussinicusL,orychophragmusviolaceus,loliummultiblorumLam, andraphanussativusL were measured in turn. When the green manure seed began to slide continuously on the seed dropping plate, the angle between the seed dropping plate and the horizontal plane was recorded, which was the sliding starting angles of the tested green manure seed[16]. According to the measurement, among the four green manure varieties, the sliding starting angle ofloliummultiblorumLam seed was the largest at 30°. Therefore, the pyramid seed box was designed as shown in Figure 2(b).Yminin the figure was the minimum inclination angle of the seed box and is set to 35°. The inclination angle is greater than the maximum measured sliding starting angle ofloliummultiblorumLam seed, which ensures that the sowed green manure seeds entered the seeding apparatus smoothly.

(a) Sliding starting angle measuring device

(b) Pyramid seed box

2.2 Electric through-hole combined type seeding app-

aratus

The main structure andpracticality picture of the electric through-hole combined type seeding apparatus are shown in Figure 3(a). Each seeding apparatus had a built-in metal seed metering roller. Each electric through-hole combined type seeding apparatus is driven by a single speed regulating motor to achieve separate control. The opening adjustment bolt can adjust the seed dropping port size of the seeding apparatus along thexdirection and acted simultaneously with the adjustment of the projection surface of the seed metering roller along theydirection. This further improves the adjustment accuracy of seed metering quantity[17]. The seed metering roller is divided into two sections. The outer surface of one section is set as socket type, and the outer surface of the other section is set as cogging type. By adjusting the position of the seed metering roller along theydirection, the opening size of the holes on the seed metering roller can be adjusted. Figure 3(b) is a schematic diagram of projections at different positions when the socket type seed metering mode is used. Figure 3(c) is a schematic diagram of projections at different positions when the cogging type seed metering mode is used. In Figure 3(b) and Figure 3(c), the effective opening of the seed metering roller decrease gradually from left to right.

(a) Main structure and practicality pictures of the electric through-hole combined type seeding apparatus

(b) Diagram of different positions of seed metering roller with socket type mode

(c) Diagram of different positions of seed metering roller with cogging type mode

2.3 Evenly-sowed component

The structure of seed evenly-sowed component is shown in Figure 4, which is composed of 10 uniform equally spaced horizontal seeding cylinders arranged in 4 rows up and down in the seed chute. The parameters of the seed evenly-sowed component are designed as follows: the lengths of the upper and lower sides of the blanking chute areL1=60 mm andL2=200 mm respectively; the longest side of the chuteL3=600 mm; the height difference of the evenly-sowed cylinders between two adjacent rowsL4=150 mm， andL5is the gap distance between two adjacent uniform cylinders, which changes with the diameter of the uniform cylinder.

Fig. 4 Structure of the evenly-sowed component

2.4 Adaptive seeding quantity intelligent control system

The adaptive seeding quantity intelligent control system of the multi-variety green manure intelligent mixer is an embedded control system based on an ARM microprocessor. The main components of the adaptive seeding quantity intelligent control system are shown in Figure 5, consisting of an onboard controller and handheld setting terminal.

(a) Onboard controller

(b) Handheld setting terminal

Anopto-isolator is used in the core control circuit of onboard controller equipped with a CAN bus motor control interface, giving frequency of up to 100 kHz. The handheld setting terminal is equipped with a 7-inch color LCD touch screen and light touching buttons which can choose from a selection of 4 varieties and 12 channels of green manure varieties, set sowing quantity setting and channel configuration, perform real-time adjustment of seeding parameters, and show on-line monitoring of seeding status. The sowing operation parameter setting interface and sowing operation condition display interface of multi-variety green manure intelligent mixer are shown in Figure 6 and Figure 7 respectively.

Fig. 6 Setting interface of the sowing operation parameter

Fig. 7 Display interface of the sowing operation condition

3 Field performance test

3.1 Test condition

The field experiment of the 2BFLA-200 type multi-variety green manure intelligent mixer was conducted in Yijiang Town, Nanling County, Wuhu City. The experiment took place from September 26 to 29, 2020. The stubble height of rice in the experimental field was about 100-250 mm according to the grass grain ratio of rice, which was 1.09[18]. The amount of straw was about 8 770 kg/hm2. The soil moisture content measured by a TZS soil moisture tester was 25.4%, and the soil bulk density was 1.26-1.32 g/cm3. The Chinese milk vetch variety used for the experiment was Yijiang No.1, and the weight of one thousand seeds was about 3.5 g. The supporting power was Zoomlion RM904-2 tractor.

3.2 Test method

During the experiment, the field was divided into three plots, each of which was 30 meter long and 20 meter wide. A total of 10 rows were sowed in each route. After the test, the test area was framed in each sowed row with a 30 cm wide iron frame, and the same experiments were carried out in the remaining two plots in turn. In order to investigate the sowing quality of the multi-variety green manure intelligent mixer, GB/T 9478—2005 “Test method for grain drill planter”, GB 8080—2010 “Green manure seeds” and actual sowing conditions[19-20]were referred to. Germination rate and variation coefficient of sowing uniformity were selected as the evaluation indexes of sowing performance.

The germination rate is the percentage of the healthy seedlings out of the total number of seeds. 15 days after the test sowing, 5 test areas were randomly selected for each sowing row, and a total of 5 sowing rows were measured. The calculation method was shown in formula (1).

(1)

Where,Geis germination rate, %,N1is the emergence number of seedlings, andNis the total seed number in the test area.

Variation coefficient of sowing uniformity refers to the distribution uniformity of seeds sown by the multi-variety green manure intelligent mixer in the same sowing row and the same distance. After the test, 5 test areas were randomly selected in each sowing line, and a total of 5 sowing lines were measured, the calculation formulas of test index (2)-(4) were as follows.

(2)

(3)

(4)

3.3 Test scheme of response surface method

Based on the previous sowing test results and analysis, the three-factor quadratic regression Box-Behnken test scheme was adopted[21-25]with the machine forward speed, rotation speed of the seeding wheel and the diameter of the evenly-sowed cylinder as variables and germination rate of Chinese milk vetch and variation coefficient of sowing uniformity as response values. Machine forward speed was set at 4-8 km/h, the rotation speed of seeding wheel was between 44-52 r/min, and the adjustment diameter range of the evenly-sowed cylinder was 3.2-6.8 mm. The codes of various test factors were shown in Table 2 (X1,X2andX3were factor code values). A total of 17 groups of response surface analysis tests were carried out, as shown in Table 3. Design-Expert 8.0.6.1 software was applied for data processing.

Tab. 2 Table of factor and level

3.4 Results and analysis of performance test

3.4.1 Establishment and verification of regression model

Using the Design-Expert 8.0.6.1 software, the variance analysis of regression models was carried out for germination rateY1and uniformity variation coefficientY2of Chinese milk vetch, as shown in Table 4.Y1andY2quadratic regression models were obtained respectively as follows.

Y1=95.28+0.025X1-2.70X2+0.78X3-

0.35X1X2-0.20X1X3+0.30X2X3-

0.22X12-1.42X22-1.46X32

(5)

Y2=10.82+0.66X1+2.13X2-0.66X3-

0.13X1X2+0.35X1X3-0.27X2X3+

1.32X12-1.21X22+2.02X32

(6)

Through the analysis of Table 3, the regression models of germination rateY1and uniformity variation coefficientY2showed thatP<0.001. The determination coefficientsR2ofY1,Y2were 0.983 2 and 0.969 0 respectively. This showed that the model error was small, and it was reasonable to analyze and predict germination rate as well as the sowing uniformity variation coefficient of the multi-variety green manure intelligent mixer.

Tab. 3 Experiment design and response values

3.4.2 Analysis of model interaction items

As can be seen from theFvalue of each factor, the rotation speed of seeding wheel and diameter of the evenly-sowed cylinder have a significant effect on germination rate of Chinese milk vetch. The descending order of influencing factors is: rotation speed of seeding wheel > diameter of evenly-sowed cylinder > machine forward speed. According to the established regression model, the response surface of the interactions between various factors on germination rate of Chinese milk vetch was obtained, as shown in Figure 8. It can be seen from the contour density and response surface shape that the interactions of various factors had no significant effect on germination rate of Chinese milk vetch, which was the same as the result of variance analysis.

Tab. 4 Variance analysis of regression model

Meanwhile, it could be seen from theFvalue of each factor that rotation speed of seeding wheel and diameter of evenly-sowed cylinder had a significant effect on variation coefficient of sowing uniformity. The rotation speed of the seeding wheel had the most significant effect on the variation coefficient of sowing uniformity. Using the established regression model, the response surface of the interactions between various factors on uniformity variation coefficient was obtained. In Figure 9, it can be seen from the contour density and response surface shape that the interactions of various factors had no significant effect on variation coefficient of sowing uniformity, which was the same as the result of variance analysis.

4 Parameter optimization and verification test

4.1 Parameter optimization

In this article, in order to meet requirements of highest germination rate and the lowest variation coefficient of sowing uniformity of Chinese milk vetch, parameter optimization of the multi-variety green manure intelligent mixer was carried out. Data analysis software was used to optimize the established total factor quadratic regression model of the three indexes, and constraint conditions were established in equation (7) as follows.

(7)

The optimal parameter combination of the multi-variety green manure intelligent mixer was obtained as follows: machine forward speed was 5.12 km/h, rotation speed of the seeding wheel was 44.12 r/min, diameter of the evenly-sowed cylinder was 5.45 mm. With these parameters, germination rate and variation coefficient of sowing uniformity were 96.42%, and 7.52%, respectively.

4.2 Verification test

In order to verify the accuracy of the above model, a validation test was carried out in another paddy stubble-field in Yijiang Town, Nanling County, Wuhu City from Oct 17 to 18, 2020. Considering the feasibility of the tested parameters, the optimized parameter combination was adjusted to as follows: machine forward speed was 5 km/h, rotation speed of seeding wheel was 44 r/min, diameter of evenly-sowed cylinder was 5.5 mm. Three tests were carried out and the average value was taken as the test verification value. The validation test results showed that the average germination rate of Chinese milk vetch was 96.71%, the average variation coefficient of sowing uniformity was 7.95%, and the relative errors with the optimization results predicted by the model were all less than 5.5%. The operation indexes of the optimized multi-variety green manure intelligent mixer met the operation requirements.

5 Conclusions

1) A 2BFLA-200 type multi-variety green manure intelligent mixer was designed, which could meet the requirements of mixed sowing of various green manure varieties such asastragalussinicusL,orychophragmusviolaceus,loliummultiblorumLam, andraphanussativusL. The precision seeding was achieved and the seeding uniformity was improved, which had a good prospect of popularization and application.

2) Using field experiments combined with the Box-Benhnken central composite design theory, the effects of main operation parameters of multi-variety green manure intelligent mixer on germination rate and variation coefficient of sowing uniformity were explored, and the response surface method was used to analyze the test results. The order of importance of the influencing factors was determined. The descending order of influencing factors which affected germination rate and variation coefficient of sowing uniformity is: rotation speed of seeding wheel, diameter of the evenly-sowed cylinder, and machine forward speed.

3) According to regression analysis, the optimized parameter combination of multi-variety green manure intelligent mixer was obtained as follows: the machine forward speed is 5 km/h, rotation speed of seeding wheel is 44 r/min, and the diameter of the evenly-sowed cylinder is 5.5 mm. The validation test results showed that the average germination rate of Chinese milk vetch was 96.71%, the average variation coefficient of sowing uniformity was 7.95%, and the relative errors with the optimization results predicted by the model were all less than 5.5%.