Introduction
Chinese cabbage (Brassica rapa L. ssp. Pekinensis) is one of the most popular vegetable crops in several Asian countries, especially in Korea, because of a high demand of Kimchi production (Jang et al., 2015). Chinese cabbage is usually harvested annually or biennially. It forms either a straight head of similarly overlapping leaves or a loosen head in some cases with more distinct leaves. The form and the dimension of the cultivar differ greatly, and height and weights of head can range from 10 to 50 cm and 0.5 to 5.0 kg, respectively. The leaf colors are usually between dark and light green.
Cabbage cultivation has increased in recent years in Korea. In 2020, the total production of cabbage increased by 26.4% as well as the cultivation area by 26.3%, when compared with those of 2019 (KOSTAT, 2020). However, the increase of domestic cabbage production draws the interest of labor-saving and mechanized harvesting and collecting cabbages from the field. The cabbage cultivation fields are mostly in rural and middle of the mountain areas, and field sizes are mostly less than 0.5 ha. Therefore, cabbage harvest and collection depends mainly on manpower, which is labor- and time consuming. Sometimes it takes several days to collect and transport cabbages from the field, causing damage and post-harvest losses.
Operation performance and economic feasibility are important criteria for productive farm operations for tractor and tractor mounted machinery. Cost-effectiveness of tractor and tractor mounted machinery is advised to identify the corresponding risks during the development (Zubko et al., 2018). Moreover, the farm machines are strongly affected by climatic zones and the terrain. Thus, a research of factors of work effectiveness of tractor mounted machines should be conducted in each region.
Several studies showed performance and economic analysis of tractor and tractor mounted machinery. da Cunha et al. (2011) compared two types of potato harvesters, i.e., mechanised and semi-mechanised units. They analysed operational capacity, production losses, as well as the cost effectiveness of the harvesters. The mechanized harvest showed a loss of 2.35%, relative to a semi-mechanized harvest loss of 6.32%. A field study for the efficiency of a rotary disk spreader mounted on a tractor was reported by Laghari et al. (2014). The study revealed that ground velocity had little effects on propagators and was operational at higher ground velocities to meet better field capacities. Performance evaluation research was presented by Balas et al. (2018) for a tractor mounted drip installer. The performance was measured on the basis of different metrics, such as field performance, operating parameters, and performance parameters. Venzon et al. (2020) also performed a performance test of a tractor mounted soil monolith collector. Bosrotsi et al. (2017) studied the technical performance and economic viability of a yam harvester. The harvester performance was evaluated based on speed, field efficiency, fuel consumption, and wheel slip, and the economic analysis based on the harvesting cost.
The key focus of this study was the performance assessment on the basis of the field capacity and field efficiency of the tractor mounted cabbage collector under development. The economic analysis focused on annual costs, partial costs, and fixed costs to evaluate the total operating cost of the collector.
Materials and Methods
Study site
The research was conducted on 17th and 18th November, 2020. The experimental site was located at Jeungpyeong-gun, in Chungcheongbuk-do, Korea Republic (36.7855° N, 127.5817° E). This research was conducted under the supervision of department of Agricultural Machinery Engineering, College of Agriculture and Life Sciences, Chungnam National University, Daejeon and Rural Development Administration (RDA), Korea Republic. Total field area was 2,912 m2 (Fig. 1). The Chinese cabbage (Brassica rapa subsp. Pekinensis) was cultivated in the field and during the tests, the cabbages were 12-week old. Cabbage was cultivated on the ridge of each rows and the average row to row distance and the row width was 0.9 m and 0.5m, respectively. The field seemed to be good shape during the harvest time.
Chinese cabbage collector
A tractor (MX100, Daedong, Daegu, Korea) was equipped with a front loader and a Chinese cabbage collector. The major components of the collector was a belt type conveyor, a hydraulic motor system to operate the conveyor belt, and three hydraulic cylinders to fold and unfold the conveyor. The dimension of the Chinese cabbage collector was 7×1×1.24 m and the total weight of the machine was 4,555 kg, with the tractors, loaders, and cabbage collector weight were 3,600, 134 and 850 kg, respectively. The Chinese cabbage collector attached with a three-point hitches in the field is shown in Fig. 2. The Chinese cabbages were harvested manually and then loaded it on the conveyor belt and it carried the cabbages into the polypropylene bags for final transportation. Table 1 shows the technical specifications of the test tractor.
Field test
In the Chinese cabbage field, four 5 m×5 m plots (Fig. 3a) were randomly selected for the cabbage harvest trails with the cabbage collector. Each plot was isolated from each other by removing the cabbages between the plots. Then the number of cabbages in each plot were counted manually and then calculated the harvest loss. Fig. 3 shows different measurements in the field during the test. Cabbage height and diameter were measured from each test plots and calculated the heightdia-1 ratio. The row spacing, row width, number of cabbages in each row, were also measured from the field during the tests. A measuring tape was used to determine the field measurements prior to the start of the field test.
For the performance test, total eight men power were used. Four men power (A, B, C, and D) (Fig. 4) were used to harvest and collect the cabbages onto the collector from the field. One man power (E) (Fig. 4) was used to operate the hydraulic system to control and adjust the collector conveyor speed. Two men power (F and G) (Fig. 4) were used to take care of the big poly bag to collect the cabbages into the bag and performed loading and unloading of bags when it is full. Another one man power (H) (Fig. 4) was used as a tractor operator who was able to control the tractor speed and other functions as well as shut down the whole system in case of emergency. The performance test was conducted on each test plots with a tractor speed of 0.39, 0.50, 0.56 and 0.82 kmh-1, where we considered the standard tractor forward speed of 0.50 kmh-1. The cabbage conveyor speed was 1.98 kmh-1 for all the tests. The primary observations, measurements and other parameters are mentioned in Table 2. The damage percentage rate of cabbages was separately investigated by calculating the number of split cabbages from the collector and the number of damaged cabbages by the conveyor belt.
Chinese cabbage collector field capacity and efficiency test
The parameters used for assessing the performance of the Chinese cabbage collector were the Theoretical and effective field capacity (TFC, EFC) and field efficiency (FE). While the FC presented an area of land processed per unit time for a particular site operation, FE defined effective and theoretical site capacity as the ratio of expected and actual time required to complete the site operation (ASABE, 2008). The collector's ability to work was measured by the amount of data collected over time. The material capacity of this machine can be expressed by equation (Agu, 2020; Dauda et al., 2013):
(1)
where, S = operating speed (kmhr-1)
W = row width (m)
(2)
where, A= Field area covered at specific time (ha)
T = Total time required for the operation (hr)
(3)
(4)
where, Y = Total yield (t)
In order to evaluate the effect of tractor forward speed, machine capacity (MC) and effective field capacity (EFC) were calculated at different forward speed. Statistical analysis was performed conducted to determine the correlation between MC, EFC and FE with respect to tractor forward speed. Cutting damage and the split of the cabbages from the collector belt were observed and calculated as performance of the collector.
Tractor slip calculation
Agricultural tractors play a significant role in drawback operation and the drawpull force and speed are used to describe it (Janulevicius et al., 2019). Drawpull force is strongly influenced by the interaction between wheel and soil surface. About 20-55% feasible tractor power is wasted due to slippage and tires and soil deformation (Taghavifar & Mardani, 2015). An important task for combining the tractor units is the preliminary calculation of the slippage. Fig. 5 shows the speed, forces, and wheel torque that are normally measured on a tractor during tractive performance tests.
To measure the wheel slip of the tractor, driving wheel speed and the body speed should be calculated. The driving wheel speed is generally easier to be measured and the body speed of tractor can be obtained from the rotating speed of non-driving wheels. According to the original definition of the wheel slip (Zhixiong et al., 2013):
(5)
where, S is wheel slip,
ω is wheel angular velocity (ms-1),
r is wheel dynamic radius (m),
v is vehicle translational velocity (ms-1).
By calculating the wheel rotation speed n, ω can be replaced as follows:
(6)
Soil mechanical test
Soil samples were collected from the study site before the performance test of the cabbage collector. Cone penetrometer was used to test the soil type. Cone penetration testing (CPT) is an in-situ test that is used to identify the soil type. In this test a cone penetrometer is pushed into the ground at a standard rate and data are recorded at regular intervals during penetration. A cone penetration test rig pushes the steel cone vertically into the ground. The cone penetrometer is instrumented to measure penetration resistance at the tip and friction in the shaft (friction sleeve) during penetration. Core sampler and Cone penetrometer used in test field are shown in Fig. 6.
To measure the wheel slip of the tractor, driving wheel speed and the body speed should be calculated. The driving wheel speed is generally easier to be measured and the body speed of tractor can be obtained from the rotating speed of non-driving wheels. According to the original definition of the wheel slip (Zhixiong et al., 2013):
Nine sampling points were located at the study area and mid-sections of the fields were used to measure soil penetration resistance, bulk density and moisture contents in the 0-40 cm layer at 10 cm intervals. Soil moisture content was determined gravimetrically from bulk density samples. The measurements were made in each points on the same day.
Chinese cabbage collector economic analysis
In order to measure the feasibility of the Chinese cabbage collector, the economic analysis was carried out. The total cost of cabbage collector was calculated by the following equations (RDA, 2019):
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
The economic feasibility of tractor mounted cabbage collector was determined by comparing the total cost in the traditional method and mechanical method.
Results and Discussion
Field capacity and field efficiency test
The forward speed of the tractor is computed for machine capacity, effective field capacity, and field efficiency. The effect of tractor forward speed on machine capacity and effective field capacity is determined as shown in Fig. 7a and 7b. Under same cabbage collecting condition with resultant increase in machine capacity from 120 tday-1 to 250.5 tday-1 with the increase of tractor forward speed. The correlation showed a positive high correlation indicating a significant contribution to the mechanical capacity of tractor forward speed. The effective field capacity indicated that with the increase of tractor forward speed from 0.39 kmhr-1 to 0.82 kmhr-1 increased the effective field capacity from 1.48 to 3.07 haday-1. Meanwhile, the effect of tractor forward speed on field efficiency is shown in Fig. 7c. The effect of forward speed revealed that with the increase of forward speed, field efficiency was decreased from 95.1% to 93.75%. The highest field efficiency was found at 0.50 kmhr-1 and the lowest was found at 0.82 kmhr-1.
The average (%) accuracy of total number of collected cabbages by the collector was found 96.88% as shown in Table 3. The accuracy decreased with high and very high forward speed of tractor. From all the tests, the medium speed of tractor provided highest (%) accuracy of cabbage collection (Fig. 8). The split of cabbages was because of vibration and collector’s belt movement. In addition, we also checked the cutting damage of the cabbage. As, the cutting of cabbage was done by the workers, some cabbages were cut insufficiently. There was no excess of cutting or broken of cabbages. The cutting damage of the cabbage was around 20.5%. There was no mechanical damage done by the machine during the test of cabbage collector.
Soil mechanical analysis
Table 4 shows the mechanical properties and the soil texture results. As it is shown, the average moisture content was around 30% (volumetric water content) and the average bulk density was 1.55 gcm-3. The soil moisture content was little bit affected as it was rained day before harvesting. The soil texture was found “loamy sand” soil in the test field.
Table 5 provides the cone penetration results in different point in the test field. The average penetration energy required was 2,630.55 kPa. As the soil texture and the moisture content was very similar to the test field area, the cone penetration rate was also very similar to all the points in the field.
Slip calculation
For four-wheel drive tractor, when it operates, the front axle wheel slip is not equal to the rear axle wheel slip, because there are different load conditions, and the tire size, the tire structure, and the instantaneous soil conditions are various, too. Moreover, the slip from the left and right wheels on the same axle will vary, regardless of the differential surface soil conditions. In order to know the overall slip of tractors, four tires’ slip should be obtained first, and then the mean which is the tractor’s overall slip can be calculated. From our estimation, the slip was very low. The average slip was found 1.6%, which is negligible.
Moreover, the slip (%) was increased with the increase of tractor forward speed shown in Fig. 9. The slip was calculated during the loading condition, the cabbage collector was mounted with the tractor and in operation. We did not consider different gear or different loaded conditions. Also the drawbar pull refers to the amount of force required to move a wheel on a slope. Because of the kind of terrain, the weather condition, and the mechanical behavior, the larger wheel load led the drawbar pull higher, despite the fact that the traction coefficient decreased.
Economic analysis
We estimated the total cost of tractor and Chinese cabbage collector used in this study. The total cost of mechanical method was assessed as fixed and mechanical costs along with existing costs as shown in Table 6. The conventional cost were also calculated based on the number of manpower used and the labour cost.
The analysis showed that the mechanical method for the Chinese cabbage collector was more cost effective than the conventional method. The variable cost for the cabbage collector was 146,224 wonhr-1, which is slightly higher than the conventional method (140,000 wonhr-1). The total cost required for the Chinese cabbage collector was 639,910 won10a-1, which is 74 % less than the conventional collection method of 2,450,000 won10a-1. The cost factors suggested the modification of buying and operating expenditures by effective and exacting tractors and skilled operators. This economic analysis presented that the Chinese cabbage collector is economically feasible for the field application.
Conclusion
In this study, field test was conducted to evaluate the performance and economic analysis of tractor mounted Chinese cabbage collector. The test was conducted in the 12-week old Chinese cabbage field. During the test, four different tractor forward speed was observed with an average fuel consumption of 23.95 lh-1. The theoretical field capacity, effective field capacity and field efficiency were calculated and the effect of forward tractor speed was evaluated. With the increase of forward speed the machine’s field capacity was also increased with a high correlation coefficient (R2=0.99). The field efficacy was found slightly decreased with the increase of forward speed. The damage percentage of the collector was estimated 20.5%. The soil properties was determined as loamy soil and the slip was calculated as 1.6% which is very much negligible. Different kind of terrain, the weather circumstances, and the mechanical behavior, the larger wheel load led the drawbar pull higher. The economic analysis was found to be 74% cost effective than the conventional cabbage collection method. The cost factors suggested the modification of buying and operating expenditures by effective and exacting tractors and skilled operators. The analysis also presented that the collector was economically feasible for the filed application.