Development of Customized Production Machine for Flue-cured Tobacco Formula Nutritional Soil

Jianyong LI, Jianwen WANG, Mengxiang PENG, Li LI, Jiongjiong ZHAO, Liangjiao LIU, Dewu ZENG

Liuyang Branch of Changsha Tobacco Company, Changsha 410302, China

Abstract On the basis of full investigation and repeated trials, nutritional soil composed of cake fertilizer, mushroom residue, cow dung and calcium magnesium phosphate fertilizer was determined as an alternative for traditional flue-cured tobacco fired ash soil. In accordance with the feed grinding, mixing and processing integrated principle, processing machine for flue-cured tobacco nutritional soil was developed. The clogging problem of mixing box was solved by improving grinding and stirring method of mixing system. Mechanized and large-scale production and commercialized supply of flue-cured tobacco nutritional soil was piloted to simplify the production process and reduce the production cost of nutritional soil for flue-cured tobacco and meet the needs of green development of tobacco production, thereby creating good social and economic benefits.

Key words Flue-cured tobacco, Nutritional soil, Formula, Processing machinery

1 Introduction

Nutritional soil is a specially formulated bed soil containing a variety of mineral nutrients to meet the growth and development of seedlings. It has the characteristics of loosening, aeration, strong water and fertilizer retention, and no pests and diseases. The nutritional soil for flue-cured tobacco is generally prepared by fully mixing fired ash or fertilizer and finely crushed soil. Nutritional soil encircling can significantly increase the contact area between tobacco seedling roots and soil, and enhance the retention and absorption capacity of tobacco seedling roots for water and fertilizer. Simultaneously, a certain quantity and quality of nutritional soil can isolate the unmixed fertilizer in the soil and soil contaminated by pathogens and pesticides, can reduce the risk of tobacco seedling injury caused by fertilizer, pesticides and diseases, and is a guarantee to promote early growth and rapid growth of tobacco seedlings, and increase yield and quality. Flue-cured tobacco nutritional soil encircling technology has low cost and great effect. It is one of Liuyang’s traditional high-quality cultivation techniques and is widely used in tobacco-producing areas across China.

Traditional flue-cured tobacco nutritional soil is generally completely or mostly prepared with burnt ash soil. When burning ash soil, the surface structure of the soil will be destroyed, causing soil erosion, the smoke from burning will pollute the air, and even worse, it is easy to cause forest fire, not meeting the needs of green development of tobacco production. Therefore, this technique is strictly restricted or prohibited by laws and regulations on forestry, soil and water conservation and environmental protection. Article 12 (6) of

Several

Provisions

on

Forest

Fire

Prevention

in

Hunan

Province

, which was passed on November 30, 2018, stipulates that during the period of forest fire prevention, mountain burning, miscellaneous burning, manure burning and grass, crop straw and orchard weeds burning are prohibited in the forest fire prevention zone. Article 25 of the

Regulations

on

the

Prevention

and

Control

of

Air

Pollution

in

Hunan

Province

passed on April 5, 2017 stipulates that it is forbidden to burn straws, fallen leaves and garbage in the open air in densely populated areas, around the airport and near the main traffic lines,

etc.

, which may cause smoke and dust pollution. At the same time, with the continuous development of modern tobacco agriculture in China, the scale of tobacco planting is getting bigger and bigger, and the amount of nutritional soil required by a single household is increasing significantly. Tobacco growers need to prepare their own nutritional soil through the following steps: burning ash, piling, sieving, taking soil, transporting, adding fertilizer, mixing and bagging. For large-scale flue-cured tobacco growers, the preparation of nutritional soil has many links, and require much labor and high cost. The contradiction of the limited range of the place for firing ash soil has become increasingly prominent. The problem of poor implementation of nutritional soil encircling technology is also becoming more and more prominent. Therefore, it is necessary to replace the traditional formula nutritional soil with the new formula nutritional soil without burnt ash soil to meet the requirements of green development and environmental protection in tobacco production. Research and development of soil making machinery to promote the specialized production and commercial supply of flue-cured tobacco nutritional soil can simplify the production process, reduce the production cost, and improve the implementation rate of flue-cured tobacco nutritional soil encircling technology, so that the traditional nutritional soil encircling technology can be maintained and carried forward.

2 Investigation on the implementation of the technology of planting tobacco with nutritional soil in Liuyang City

At present, there are three kinds of tobacco nutritional soil in Liuyang City. The first one is the traditional nutritional soil with fired ash soil as the main material. In most cases, it is completely composed of sieved ash soil; and in few cases, it is added with 20%-40% mountain soil and 0.5% seedling fertilizer. Most of the users are middle and small-scale old growers. The second one is nutritional soil with mountain soil as the main material. Generally, it is composed of 92%-94% loess and 6%-8% cake fertilizer. Most of the users are tobacco growers who do not burn the ashes. The third one is 100% mountain soil. Although the stump encircling effect of this type of soil is worse than that of the former two, it is better than the field soil. The number of users of this type of nutritional soil is small, but it is distributed all over China.

In recent years, due to the rise of labor prices and the limitation of the burning of ashes, it is more and more difficult to implement the flue-cured tobacco nutritional soil stump-encircling technology. In order to explore a new way to improve the implementation rate of tobacco nutritional soil stump-encircling technology, the technical staff of Liuyang Branch of Changsha Tobacco Company envisioned that the formulated nutritional soil without burnt ash soil could be manufactured mechanically, and supplied commercializedly to tobacco growers who do not prepare the nutritional soil for flue-cured tobacco, so as to improve the implementation rate of the flue-cured tobacco nutritional soil stump-encircling technology. The project first focused on Yangtian Village, the base unit of Liuyang City, and the purchase intention of tobacco growers for commercial flue-cured tobacco nutritional soil was surveyed. The results are shown in Table 1.

Table 1 Investigation results of nutritional soil preparation for flue-cured tobacco

Among the 17 farmers who did not prepare flue-cured tobacco nutritional soil, 7 expressed that the price was acceptable, and they were willing to give up the plan of using local field soil to encircle stumps, and instead, to buy nutritional soil for encircling stumps. Based on the demand of 1.8 t/ha, a total of 49.7 t of commercial nutritional soil was needed by only the village. The results of sampling survey in other tobacco growing areas were similar. Therefore, it is concluded that it is feasible to carry out mechanized production and commercial supply of flue-cured tobacco nutritional soil in the whole city, taking the village as a pilot.

3 Formula determination

As the functions of nutritional soil is to protect tobacco seedlings and promote the early growth of tobacco seedlings, only when the physical and chemical properties of flue-cured tobacco nutritional soil are significantly better than those of field soil, can the functions of flue-cured tobacco nutritional soil be brought into full play. The results showed that the effect of traditional fired ash soil on flue-cured tobacco seedling growth in the early period was significant. The main reason is that the ash soil had lower bulk density and higher permeability, and rich mineral nutrition significantly promoted root growth and nutrient absorption of tobacco seedlings. However, there is also problem of insufficient water and fertilizer conservation, and it is easy to burn seedlings in hot weather and lack of water in soil. Therefore, it is speculated that the nutritional soil made with unpolluted mountain soil as the main material, supplemented with a large amount of organic fertilizer can achieve the same effect through improving nutrient content and reducing bulk density.

Although the stump-encircling effect of flue-cured tobacco nutritional soil and the alternatives for traditional fired ash soil have been studied, there is currently no report on the large-scale application of nutritional soil as an alternative for formulate fired ash soil. Xu Wei

et

al.

proved that coal ash can replace fired ash soil, but coal ash contains heavy metals and is difficult to remove, so it does not have the conditions for further inspection. Zhou qianya

et

al.

proved that the flue-cured tobacco seedling raising effect of composed rice straw was better than that of fired ash soil. But the results show that after 2 months of composting with fermentation agent, the rotting degree of rice straw had not yet reached the state of processability. In addition, the cost of collection is slightly higher, the stacking site must be large, and there is a fire risk, so it does not have the conditions for large-scale application at present. Through repeated trials and comparison, the formula of flue-cured tobacco nutritional soil for large-scale production was determined. The cost of formula ingredients is shown in Table 2.

Table 2 Cost of commercial production of (1 t) nutritional soil

The formula is mainly composed of uncontaminated loess below the surface of the mountain. It is added with commercial cake fertilizer, mushroom residue, cow dung and calcium magnesium phosphate fertilizer without pest pollution, to omit the cost of disinfection. The contents of organic matter, nitrogen, phosphorus, potassium and C/N ratio of the nutritional soil are higher than those of 6% cake fertilizer, and the bulk density of the nutritional soil is lower than that of 6% cake fertilizer, making use effect better and cost lower.

4 Development of machinery for making nutritional soil

4.1 Design idea

Since there is no special machinery on the market, flue-cured tobacco nutritional soil has been produced by manual mixing, characterized with low efficiency and high cost. Therefore, it is designed to use excavator to collect soil, loader to load soil, agricultural transporter to haul soil, and use loader to put the premixed soil into the feed box for processing. According to the working principle of feed processing machine, a processing device for flue-cured tobacco nutritional soil, integrating grinding and mixing, was designed and manufactured. The feed box is installed above the grinding and mixing device. A customized extended discharge chute is installed under the grinding and mixing device. A fixed support frame is installed at the bottom. After grinding and mixing, the nutritional soil falls to the ground along with the rolling central shaft with blades installed in the middle of the extended discharge chute. After bagging and weighing, the nutritional soil is sealed with electric portable packer. The design diagram of flue-cured tobacco nutritional soil production machine is shown in Fig.1.

Fig.1 Design of production machine for flue-cured tobacco nutritional soil

4.2 Main structure

The flue-cured tobacco nutritional soil production machine is produced by Liuyang Fengshun Planting and Breeding Cooperative, under the guidance of Liuyang Branch of Hunan Tobacco Company. The machine is mainly composed of control system, feeding system, mixing system and packaging system (Fig.2).

Fig.2 Production machine for flue-cured tobacco nutritional soil

4.2.1

Control system. The power of the control system is 7.5 kW motor, with PLC controller and leakage protector.

4.2.2

Feeding system. The power of feeding system is 42 kW. The raw materials are fed into the feeding box by a tyre type loader with an unloading height of 3.2 m. The feeding box is a chamfered platform made of 2 mm thick stainless steel plate. The inlet of the feeding box is 62 cm long and 42 cm wide, which is consistent with the size of the loader bucket.

4.2.3

Mixing system. In the grinding device, the hammer of grinding box was originally designed as multi-column grinding type. Several columns fixed on the disc in the grinding cavity rotate under the drive of the central shaft. Thus, the raw materials are mixed and impacted to complete grinding and stirring. During the test, it is found that this grinding pattern is prone to failure, and the failure frequency is up to 6 times/h. The production efficiency of nutritional soil is only 0.5 t/h. The fixed grinding-shaped columns were replaced by long cutting-shaped chippers for grinding and stirring. The results show that the failure frequency was 4 times/h and the production efficiency of nutritional soil was 0.7 t/h. Although the mechanical efficiency had been improved, the fault had not been eliminated fundamentally. The reason is that the raw materials, such as mountain soil and organic fertilizer, which are used to make tobacco nutritional soil, are easy to be stuck to the grinding box under certain moisture content, and they accumulated continuously on the surface of the fixed columns and long chippers, and then compacted and expanded after sticking into blocks, resulting in the blockage of the grinding box and the blocking of the impact columns or the long chippers. The grinding box, impact columns and long chippers needed to be cleared repeatedly to continue. The complete drying of mushroom residue, organic fertilizer and cake fertilizer not only require drying equipment, but also needs to consume a lot of energy, which will significantly increase the cost and prolong the production cycle. Through the redesign of the technical personnel, two auxiliary shafts were installed on both sides of the main shaft of the grinding box, the striking head was changed into a plurality of rectangular cutter boards, and the rectangular cutter boards are sheathed in the middle of the auxiliary shafts. When the auxiliary shafts rotate around the main shaft, the rectangular cutter boards can also rotate around auxiliary shafts to strike. When encountering obstacles, they can still maintain the impact and rotary excavation on the nutritional soil, so as to eliminate the phenomenon that the main shaft stops due to the blockage in the grinding chamber (Fig.3). The test results show that the machine worked continuously for 2 h without failure, and the processing efficiency of nutritional soil increased from 0.5 and 0.7 to 3.0 t/h.

Note: a. Multi-column grinding; b. Linear cutting; c. Multi-chipper flail.

4.2.4

Packaging system. The mixed flue-cured tobacco nutritional soil directly flows into the open storage box, or lifted from the ground by the loader to the open storage box, drops from the hopper (controlled by valve) under the open storage box into the packaging bag, and is sealed with portable packer after weighing.

5 Validation of results

5.1 Cost comparison

The cost of the machine-made flue-cured tobacco nutritional soil was compared with that of the local traditional fired ash soil and that of the mixture of mountain soil and cake fertilizer. As the bagged nutritional soil is easy to carry and can be easily transported to the field, compared with the bulk nutritional soil to the roadside, the loading and unloading time and the transportation distance between the field and the roadside are saved, so that the releasing efficiency is improved, and the total cost of flue-cured tobacco nutritional soil is not increased. Therefore, the cost of the above three kinds of flue-cured tobacco nutritional soil was calculated according to the bagging method. The total cost of commercial production of nutritional soil was 278.5 yuan (soil collection, 10 yuan; fertilizer, 132 yuan; mixing, 48.5 yuan; packaging, 40 yuan; loading and unloading, 25 yuan; transportation, 25 yuan). The cost of flue-cured tobacco nutritional soil made by different methods is shown in Table 3 and Table 4.

Table 3 Cost of (1 t) nutritional soil made of traditional fired ash soil

Table 4 Cost of (1 t) nutritional soil made from man-made cake fertilizer

As shown in Table 3-5, although the cost of artificial soil was all labor cost, due to the low efficiency of manual operation, the total cost was still 51.5 yuan/t higher than that of the formula nutritional soil made by machine. Compared with the single-household small-scale artificial production of flue-cured tobacco nutritional soil, mechanization and large-scale production significantly reduced the fertilizer, soil collection, mixing and packaging cost. The reason is that under the condition of mechanized, large-scale and commercialized production of flue-cured tobacco nutritional soil, we can choose to purchase more cost-effective fertilizers such as mushroom residue and cow dung to replace cake fertilizer, in order to reduce cost. At the same time, mechanical soil sampling, mechanical mixing and the use of hand-held packer significantly improved work efficiency. Although the cost of mechanical production of flue-cured tobacco nutritional soil increased by 90 yuan/t (the cost of packaging materials, loading and unloading and transportation), the total cost was still 143 yuan/t lower than that of manual production of cake fertilizer nutritional soil.

5.2 Application effect

In 2019, Liuyang Fengshun Planting and Breeding Cooperative produced 80 t of flue-cured tobacco nutritional soil by machine according to the order. After being subsidized by tobacco companies, it was supplied to tobacco farmers at the price of 200 yuan/t. Among them, 49.7 t was supplied to 7 tobacco farmers in Yangtian Village according to 18 t/ha. The results of observation and feedback from tobacco farmers show that the formula nutritional soil made by machine had the same effect as the traditional fired ash soil and the artificial mountain soil-cake fertilizer nutritional soil. Among the 7 tobacco growers who used commercial nutritional soil to surround stumps in the pilot villages surveyed, the yield and purchase price of 5 of them were higher than the average yield and average purchase price of the pilot village. In 2020, 312 t of nutritional soil was made and supplied to 109 farmers, with an application area of 206.4 ha. According to the feedback of the application effect survey, in 2020, among 109 tobacco farmers using commercial flue-cured tobacco nutritional soil, 66 were very satisfied, 41 were quite satisfied, 107 expressed their willingness to continue to purchase and use the commercial nutritional soil in 2021, accounting for 98.2% of the total.

6 Conclusions

Based on the principle of feed grinding and mixing integrated processing machinery, the flue-cured tobacco nutritional soil processing machinery was made. The grinding and stirring methods of the mixing system were improved. Mechanized and large-scale production and commercial supply of flue-cured tobacco formula nutritional soil can significantly improve the production efficiency and reduce the cost of nutritional soil, omit the production process of tobacco farmers, and improve the implementation rate of flue-cured tobacco nutritional soil stump-encircling technology. The successful development of flue-cured tobacco nutritional soil processing machinery promotes the replacement of nutritional soil with traditional fired ash soil as the main material by new formula nutritional soil in flue-cured tobacco production, and avoids the damage to the ecological environment of tobacco production area. At the same time, the production of new formula nutritional soil needs a lot of organic fertilizer such as mushroom residue, improving the collection and utilization of waste organic matter such as mushroom residue. The application of a large amount of nutritional soil with high organic matter content will also improve the soil fertility of tobacco fields. After adopting the mechanical production method, the soil collection is intensive, which is convenient for supervision and management. If the soil is collected from the vicinity of development zone, after cutting off the top of the mountain, the value of the land will be improved. To sum up, in the nutritional soil made by machinery, the utilization rate of raw material lumps is higher, and the uniformity of the finished product is better, which are more conducive to the early growth and rapid development of tobacco seedlings. Through unifying formula and dosage of nutritional soil, the phenomenon of seedling burning caused by improper preparation of nutritional soil will be avoided, the standard production level of flue-cured tobacco will be improved, and the quality of tobacco will be improved as well.