Introduction

China ranks third in sugarcane production around the world. Most of the sugarcane plantations are located in Guangxi, Guangdong, Yunnan, and Hainan province (Song and Ou 2004; Zhu 2010). In China, only 1.42% of canes are harvested mechanically (National Bureau of Statistics of China 2018) but most of the canes are still harvested manually (Ou et al. 2013). Mechanical operations have been proved to be superior over manual operations. It reduced cost of production and enabled efficient utilization of resources with better work output (Murali and Balakrishnan 2012). However, it is very challenging to promote mechanical harvesting in South China due to the hilly terrains and severe cane lodging conditions. Cane lodging could greatly hinder mechanical harvesting in terms of high loss and low field efficiency (Ma et al. 2014a, b). In recent years, a large number of foreign brand sugarcane harvesters that have been manufactured outside China have entered Chinese market; however, a few domestic harvesters have been successfully commercialized (Ou et al. 2010). Sugarcane harvesters are mainly categorized into two groups: whole stalk harvesters and chopper harvesters (Chen et al. 2009; Ma et al. 2014a). At present, the chopper harvester is widely used because of its good adaptability and better performance in harvesting lodged canes (Liang et al. 2014). A typical chopper harvester mainly consists of a topper, crop dividers, a feed roller, a base cutter, a butt lifter roller, choppers, an elevator, a primary extractor, and secondary extractor. The crop divider, which consists of inside scrolls, outside scrolls, crop divider toes, and floating sidewalls (Fig. 1), is the key mechanism which has a great impact on cane cutting quality. During harvesting, the crop divider is capable of separating and lifting the intertwined stalks, which facilitates the cane being fed to the harvester smoothly (Ma et al. 2014a, b).

Fig. 1
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Crop dividers of sugarcane chopper harvester

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There are two major types of crop dividers: spiral crop dividers and finger-chain crop dividers. The efficiency of finger-chain crop divider in harvesting lodged canes is not satisfactory. It does not perform well for lodged sugarcane with lodging angle of 60°~90°. The efficiency of chain drive is relatively low and the cane stalk lifting process is not smooth, which makes canes often slip off the fingers (Liao et al. 2012). The spiral crop divider is composed of two symmetrical spiral scrolls (inside scrolls and outside scrolls), which are usually driven by hydraulic motors. With the harvester moving forward, the intertwined and lodged sugarcanes can be effectively separated and lifted to a certain height from the ground which greatly facilitates the stalk feeding operation that follows. With the simple & compact structure and good adaptability, the spiral crop divider had been widely used in various sugarcane harvesters (Gao and Ou 2004).

In the literature, few studies are focused on sugarcane crop dividers and most of the design works have been based on previous references (Deng et al. 2003). Therefore, the spiral flightings were designed only as a mechanism for transporting materials and ignored their efficiency for lifting the lodged canes. Only a few studies have been carried out on the contact friction between sugarcane stalks and crop dividers (Dong et al. 2010; Song et al. 2012b). Therefore, it is meaningful and necessary to investigate the lifting performance of the crop dividers in the sugarcane harvesters.

To improve the lifting performance of crop dividers in harvesting lodged canes, the key is to investigate the lodging conditions and the interacting mechanism between crop dividers and cane stalks (Mou et al. 2010). The recorded parameters for different lodging conditions were used to calculate the corresponding lifting performance parameters. The results are expected to provide constructive guidance for the design of spiral crop dividers.

Materials and Methods

Sugarcane Harvester Crop Dividers

In this study, a sugarcane chopper harvester (4GQ-180, Liugong Machinery Co., Ltd, Liuzhou, Guangxi province, China) was employed to harvest sugarcane crop, in March 2019. As shown in Fig. 1, the crop dividers consisted of inside scrolls, outside scrolls, crop divider toes, and floating sidewalls. The sugarcane field was located at Quli Town, Fusui County, Chongzuo City, the Guangxi Zhuang Autonomous Region, China.

Material

Before the field test, the critical parameters of sugarcane and cane field were recorded (Table 1). The harvesting runs were randomly selected, and each test zone was about five meters long (Fig. 2). The third-year ratoon crop (Variety Guitang 43) was used for the field test, and the field had 60% of lodged canes. The basic parameters of soil and sugarcane are shown in Table 1.

Table 1 Sugarcane and test field conditions
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Fig. 2
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Five-meter test run

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During these test runs, a high-speed camera (FR-Stream Usb Camera of Guangzhou Yuanao Instrument Co. Ltd, Guangdong province, China) was used to record the lifting process of lodged canes with 500 fps. Before the field test, the sugarcane stalks were labeled for identifying the targeted canes during the analysis of high-speed videos. Moreover, a staff gauge was set up as a reference to facilitate the observation of the lifting process. After the test, the corresponding lifting height was recorded (Fig. 3).

Fig. 3
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The equipment for lifting height measurement

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In this study, the lifting height of sugarcane was calculated according to the Eq. (1) and the absolute lifting height of lodged canes as shown in Fig. 4.

$$h = h_{1} - h_{2}$$
(1)

where \(h\) is the absolute lifting height of lodged canes, \(h_{1}\) is the reading of staff gauge when sugarcane is at the highest contact point between sugarcane and the crop divider and \(h_{2}\) is the reading of staff gauge on the ground.

Fig. 4
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The absolute lifting height of lodged canes

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Sugarcane Lodging Levels

The lodging angle \(\alpha\) and side angle \(\beta\) are two important indicators for sugarcane lodging levels. The lodging angle \(\alpha\) refers to the angle between center line of sugarcane stalk and the plumb line, and the side angle \(\beta\) refers to the angle between the stalk vertical projection and the forward direction of the harvester (Fig. 5). Depending on the values of lodging angle \(\alpha\), the cane lodging levels can be divided into three categories: slight lodging (\(\alpha\) = 0–30°), medium lodging (\(\alpha\) = 30°–60°) and severe lodging (\(\alpha\) = 60°–90°). Based on the values of side angle \(\beta\), the cane lodging can be divided into five categories: forward lodging (\(\beta\) = 0), side and forward lodging (0 < \(\beta\) < 90°), side lodging (\(\beta\) = 90°), side and inverse lodging (90° < \(\beta\) < 180°), and reverse lodging (\(\beta\) = 180°) (Song et al. 2011).

Fig. 5
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The schematic diagram of crop divider with cane stalks

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The Cartesian coordinate system was established, and a schematic diagram of crop divider contacting with cane stalks was made, as illustrated in Fig. 5 (Song et al. 2012a). The XOY plane was aligned with the ground surface, O1 was the crossing point of cane stalks and the ground surface, and the centerline of inside scroll was parallel to the XOZ plane. The harvester moved forward the positive direction of x-axis. In the harvesting process, the distance from ground to contact point became larger with lodged canes being lifted that made the lodging angle and side angle decrease gradually. Among these, \(h\) was the height of lodged canes lifted by the crop divider, and the lifting height was measured as the vertical distance from the ground to contact point (between the cane stalk and the inside scroll); \(\alpha\) was the lodging angle of cane stalk; \(\beta\) was the side angle of cane stalk; and \(\gamma\) was the installation angle of the inside scroll. The inside scroll rotated clockwise.

Experiment Design

During the test, the following operational parameters were fixed: the rotational speed of the inside scrolls was 100 rpm, the forward speed of harvester was 0.2 m/s, and the installation angle of the spiral scroll was 55°. In the harvesting trials, the crop divider toes were always kept in contact with ground surface.

The influence of lodging angle and side angle on crop divider was an important factor studied. For this, the lodging angle and side angle of sugarcane were selected as the experimental factors, and the lifting height of sugarcane stalks was considered as the evaluation indicator. The single factor test of the crop divider was carried out. To study the effect of the lodging angle and side angle on the lifting height, different levels of these experimental factors were tried and these formed the test treatments. Four levels of lodging angle (α) at 30°, 60°, 75°, and 90° and six levels of side angle (β) at 30°, 60°, 90°, 120°, 150°, and 180° were studied (Table 2). Each test treatment was repeated five times, and the results were averaged for analysis.

Table 2 Settings of factor levels
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For data analysis, the ANOVA was carried out using IBM SPSS Statistics (SPSS Inc., Chicago, IL, USA) and the high-speed video was analyzed using Troublepix x64 Edition software (Norpix Inc., Quebec, Canada).

Results and Discussion

Sugarcane Lodging Measurement

The lodging levels of sugarcane were measured and recorded for each test zone. As shown in Fig. 6, the lodging angles of most test canes ranged from 30° to 60°, accounting for about 45% of the lodged canes, followed by the canes with 0–30° lodging angles, accounting for 30% of the lodged canes, and only 25% of test canes were lodged at an angle of 60°–90°. Because the side angle was defined relative to the forward direction of harvester, we recorded the angle from 0° to 90° (Fig. 7). It was found that most test canes were in forward and reverse lodging, accounting for about 50% of the lodged canes.

Fig. 6
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Distribution of sugarcane with different lodging levels

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Fig. 7
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Distribution of sugarcane with different side angle levels

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It was observed that, when the lodging angle was less than 75°, the lifting performance of the spiral crop divider was better. Song et al. (2012a) also observed that the performance of single spiral crop divider was poor, with the lodging angle greater than 75°. Therefore, in future, the performance of crop dividers needs to be improved so that these can give a better performance when the canes lodge at angles greater than 75°.

The Single Factor Test

With the increase in the lodging angle \(\alpha\) and side angle \(\beta\), the corresponding lifting height recorded is listed in Table 3. Figure 8 illustrates the lifting performance as affected by various levels of lodging. When the side angle \(\beta\) was fixed, the lifting height of sugarcane was directly proportional to the lodging angle \(\alpha\). When the lodging angle \(\alpha\) was from 75° to 90°, the lifting height was about 125–135 cm; when \(\alpha\) was from 0° to 30°, the lifting height increased to 140–150 cm. However, when the lodging angle \(\alpha\) was fixed, the lifting height of sugarcane increased initially and then decreased with the increasing side angle \(\beta\).

Table 3 The lifting height of the different lodge angles and side angles
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Fig. 8
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The effect of the lodging angle and side angle

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When the side angle \(\beta\) of sugarcane was about 90°, the lifting height of sugarcane reached the maximum indicating the best performance of the crop divider in harvesting side lodged sugarcanes. When the cane was in the forward lodging and reverse lodging state, the crop divider did not give a satisfactory performance because the lodged sugarcane was in the gap between the inside and outside scrolls. The vertical projection of the cane stalk was almost the same as the forward direction of the harvester. On the whole, during the entire harvesting process, sugarcane had little contact with the crop divider. The spiral scrolls cannot gently lift and feed cane into the harvester throat resulting in unsatisfactory lifting effect. In addition, multi-blade cutting occurred frequently resulting in more cutting losses.

In this investigation, it was found that when the side angle \(\beta\) was less than 15°, the crop divider did not have a satisfactory lifting effect because the side forward lodged sugarcane was always pushed away from the inside scroll and even cut directly without being lifted by the harvester. A similar conclusion was also derived by Mou et al. from their studies (Mou et al. 2010). In addition, it was also found that the crop divider could not effectively separate and lift the lodged sugarcane when canes get intertwined due to lodging. Furthermore, intertwined canes also caused large-scale uprooting problems.

Two-Way ANOVA

The result of two-factor test for the lodging angle \(\alpha\) (A) and side angle \(\beta\) (B) is illustrated in Fig. 6. The two-way ANOVA was conducted by IBM SPSS Statistics (Table 4). The results indicated that both the lodging angle \(\alpha\) and side angle \(\beta\) had significant influence on the height to which canes are lifted. When either A or B is reduced, the canes can be easily pushed away, with a significant change in the height to which the cane can be lifted. The results also indicated that the effect of the lodging angle \(\alpha\) was greater than that of the side angle \(\beta\). The larger the angle at which the canes are lodged, more will be the area of contact of the sugarcane with the spiral scrolls, and the height to which the canes are lifted will be more.

Table 4 The results of two-way ANOVA
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High-Speed Photographic Analysis of Lifting Process

The operational parameter setting of the crop divider was just as aforementioned experiment design. To observe the lifting of lodged sugarcane in detail, the whole lifting process was recorded using a high-speed camera. The experimental results are shown in Fig. 9.

Fig. 9
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The high-speed photography images

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The targeted cane stalk was labeled as No. 4 (Fig. 9). In Fig. 9a–d, it showed that lodged sugarcane was gradually being lifted up: image (a) illustrated that the spiral scroll just started contacting the cane stalk; images (b) and (c) showed cane stalk was lifting along the spiral flights of inside scrolls; image (d) showed that the cane stalk gradually moved from the outside to the inside of the spiral scroll; image (e) and (f) showed the cane stalk was successfully lifted up to the highest point with the crop divider. During the lifting process, it was observed that the targeted cane stalk bounced up and down on the spiral scrolls. The reason was that cane stalk always moved from scroll surface to spiral flightings or vice versa resulting in bumped sliding.

In addition, it was observed that the spiral crop divider was not effective in lifting the canes if the problem of lodging is severe. In the experiment, it was also found that the lodged sugarcane could be easily lifted up to the appropriate height by targeting the cane leaves which have greater friction coefficient than the stalk. A similar conclusion was obtained by Song et al. (2012b) with their findings that the friction coefficient of the self-trashing varieties of sugarcane was lower than that of the varieties which have the leaves adhering to the stalks, so the leafless cane stalks slip off from the spiral scrolls more easily (Song et al. 2012b). Therefore, future designs should exploit the sugarcane leaf friction properties to improve lifting performance.

Conclusions

In this paper, the lifting performance of crop dividers in harvesting lodged canes was tested and analyzed. The conclusions were as follows:

  • When the side angle \(\beta\) was fixed, the lifting height was directly proportional to the lodging angle \(\alpha\). However, when the lodging angle \(\alpha\) was fixed, the lifting height of sugarcane increased first and then decreased with the increasing side angle \(\beta\).

  • When the side angle \(\beta\) of sugarcane was about 90°, the lifting height of sugarcane reached the maximum, indicating the best performance of the crop divider.

  • When there was forward and reverse lodging of the canes, the performance of crop divider was not up to the mark. It was also found that when the side angle \(\beta\) was less than 15°, the crop divider did not lift the canes satisfactorily.

  • The crop divider could not effectively separate and lift the lodged sugarcane when the cane stalks and leaves intertwined, which sometimes even resulted in large-scale uprooting problems.

The present study suggests that modifying the design of crop dividers would be critical to increase their harvesting efficiency for lodged sugarcanes. Future research need to focus on the design of crop divider so that it can cope up with the problem of larger lodging angles and separating intertwined leaves in the case of severe lodging.