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3. Study on the mechanization of sweet sorghum cultivation

3.1. Process and machinery
3.2. Pneumatic sprayer
3.3. The plan and effect of deep plow
3.4. Sweet sorghum leaf stripping device

From 1984 to 1986, based on the study of mechanization of cultivation, considering the growing features of sweet sorghum and the present agricultural situation, sorghum cultivation was studied to get the high yield of the stems and seeds and to reduce the field working times. A suitable process of sweet sorghum mechanization cultivation and a series of farm machinery which was used in the process was obtained. The critical field operation in the procedure such as sowing, spraying and deep plowing at the same time; mechanical harvesting and stripping leaf at the same time were studied with a lot of farm attachment machines. The most suitable layout, structure, and parameters of the machines were obtained.

The three year study proved that this technology was suitable for the mechanization development level of China; the pneumatic sprayer which was designed according to the procedure showed a stable and usable performance, and it reduced the field working time of the machine; the deep plowing plan arranged with the procedure had a notable effect on promoting the growth of sweet sorghum root, on preventing the plant from falling over, and on the raising yield of the stems and seeds. Study of the device, which was used to harvest the stems and cut the leaves of the sweet sorghum at the same time, provided a reliable reference for the further perfection of the procedure.

3.1. Process and machinery

3.1.1 Experimental Conditions

The experimental field was at Shenyang Agricultural University test farm and the terrain was hilly. The soil was brown loess with the character of viscosity. There is a large area of this kind of soil in Liaoning Province and the soil is a representative for China.

The varieties of the sweet sorghum were: in 1984, 7 species such as Rio, Keller, Wroy and so on; in 1985, 5 species, Rio, Keller, Wroy, etc; in 1986, only 2 species, Rio and Wroy. The experimental area was as follows: 0.2 ha in 1984; 11.3 ha in 1985; 1.7 ha in 1986. In the sweet sorghum mechanization cultivation, the distance between rows of plants was 70 cm. The last year crop was corn.

3.1.2 Process and machinery

The process in the sweet sorghum mechanization cultivation was as follows: plowing in fall -> harrowing in fall applying farm manure -> harrowing and land smoothing in spring -> sowing, applying fertilizer, spraying weed killer -> compacting -> thinning out seedlings -> final thinning out seedling -> weeding and subsoiling -> spraying insecticides -> stripping out the useless branch of the plant -> applying additional fertilizer -> stripping out the leaves -> harvesting the stems -> nipping off the ear -> transporting.

In the above process, plowing and harrowing in fall, spring harrowing, smoothing, sowing, applying fertilizer, spraying weed killer and insecticides, subsoiling, and transporting had been accomplished by means of mechanization, while the others were still done by hand. Table 3.1 shows the machines that were used.

Table 3.1 Cultivation Procedure and Machinery

Working items



1. plowing in fall 2. harrowing in fall

hydraulic lift type 5 furrow trail plow trail-type tandem - disk harrow

Dong FangHong-75 (DFH-75) DFH-75

3. harrowing and smoothing in spring

trail-type random disk harrow; land smoother


4. sowing; applying fertilizer; spraying weed killer

toolbar single-unit planter; pneumatic sprayer


5. cultivating; weed killing; subsoiling; molding

compactor; cultivator fertilizer applicator

DFH-28 Tienieo-55 (TN-55)

6. spraying

knapsack sprayer-duster

7. transport

3T farm trailer


3.1.3 The Working Course of Mechanization

A. Tillage: included plowing and harrowing in fall, harrowing and smoothing in spring. Plowing and smoothing used DFH-75 tractor equipment with the hydraulic lift type of 5 furrow trailed plow or with the trail-type tandem disk harrow to carry out both operations. Harrowing and smoothing in spring when the soil had not completely melted employed the method of combined operations, harrowing the farm manure, which had been applied previously, under the ground. The work of plowing, harrowing and smoothing ensured that the soil was loosened and that the surface of the earth was smooth; that the soil was made loose at the upwards and tight at the downwards; and that the soil moisture was conserved.

B. Plant seeds, apply fertilizer, and spray weed killer: a general tractor was used with all-purpose frame equipment with six sets of single-unit planters at the back and mounting pneumatic sprayer in front of the tractor to do the work of sowing, applying fertilizer and spraying weed killer at the same time. seeds were sown with a wider row spacing of 70 cm. This had the advantage of good winding and lighting; cultivating and weed killing easily; deep plowing conveniently; and resisting drought, waterlogging and plant lodging. Planting seeds and applying phosphate fertilizer at the same time not only accelerated the growth of the plants and increased the yield of stems and seeds, but also impelled the plant to mature quickly. Meanwhile spraying weed killer efficiently and early, could help the plant to grow and help to control insect pest and plant diseases.

The combined operation saved energy and reduced soil damage by machine. The design of the pneumatic sprayer equipment with planter meant that the three items of work could be done simultaneously.

C. Field management: this included cultivating and weeding, thinning out and final thinning out seedlings, removing superfluous branches or shoots, loosening soil and applying additional fertilizer, etc. Field management was caried out during the last ten day of May to the beginning of July. The management which cooperated with mechanization and manual work had to be completed by the beginning of the rainy season. The thinning out of seedlings was done when the seedlings were 12 to 15 days old and had reached a height of 3 cm high. The final thinning out was done when the seedlings were 12 cm high. It was important to chop and thin out seedlings in time.

Because sweet sorghum is a plant which grows to between 3.5 and 4 m, it was necessary to promote the growth of roots to prevent the plants from lodging. The plan of subsoiling when the seedlings were young was adopted to reduce root damage. Subsoiling at a depth of more than 25 cm not only broke the subsoil, accelerated the growth of roots, impelled the plants to mature quickly and accumulated more sugar, but also helped prevent waterlogging and stopped the surface soil from being washed away during the rainy season.

The studied chisel type of ripping tine and subsoiling plan had a significant effect on preventing the plant from lodging, as well as increasing the stem and seed yield.

D. Plant Disease and Pest Control

The insects which damage sweet sorghum include aphids, army worm and corn borer. Observation over a period of several years showed that the army worm appeared during the planting of unilobed weeds, then migrated to the sweet sorghum plants. The more weeds there were or the nearer they were to the plants, the more the army worm appeared on the plants. Therefore, a comprehensive approach was adopted, combining prevention as primary and elimination as secondary method. In order to prevent the insect pest from occurring and spreading, the following measures were adopted: sowing sweet sorghum seeds and spraying weed killers at the same time, cultivating when the seedlings were young, planting soybean and spraying weed killers at the edge of the sweet sorghum field, and spraying insecticide when the army worm appeared.

To prevent and eliminate the other insect pest, the method of enhancing the forecast of insect pest situation was used in the early time.

E. Harvest: it was the most difficult work in the mechanization cultivation process so far, there were no suitable high stem plant harvester in china to harvest sweet sorghum plant. A common use type of Chinese sorghum harvester which was designed by Jinzou Farm Machinery Research Institute was studied. The harvester was equipped with a designed stripping leaf device. The results showed that the harvester had a good placing plant performance; the plan of designing the device was feasible and the device performed a high rate of stripping leaves. However, the stripping height of the machine was 25 to 30 cm, and there was the phenomenon of tearing stem. so that, the further experiment and study is still in need.

3.2. Pneumatic sprayer

Weed not only competes with sweet sorghum plants for space, water, fertilizer, air, and heat, and affects the output heavily, but also causes army worm to produce easily planting seeds and spraying weed killer at the same time could eliminate weeds which grew among seedlings and rows in the early time. so that, a pneumatic sprayer which accorded with the planter was developed to plant seeds, apply fertilizer and spray weed killer at the same time.

3.2.1 The Layout and Working Principle of the Pneumatic Sprayer

One of the largest feature of the machines was cooperated with the planter and fixed to the machine conveniently. Fig. 1 showed that the tank is mounted in the front of DFH-28 tractor. An air pump which is carried by the tractor presses the air, and the air enters the mixer which is in the tank through a pressure regulator valve. Then the air jets from the nozzle to the tank. The pressed air with a high speed makes the liquid to be mixed in the tank and establishes pressure in it. Finally, the pressed liquid gets into the sprayer nozzles which are placed at the planter and by which the weed killer liquid are sprayed.

Feeling mechanisms, and 6 sets of single unit planters are fixed at the general-purpose toolbar which is mounted at the back of the tractor.

3.2.2 The Main Parts and Parameters of the Sprayer

Mixer is one of the main parts of the sprayer. The mixing property is one of the most important indexes to evaluate the performance of a sprayer. Because of the sensitive difference between the sweet sorghum plants and weeds to the weed killer, certain herbicide could kill weeds or control the growth of weeds, but not injure the seedlings. If the density of weed killer is too high or the dosage is too heavy, then even the plants which show a stronger insecticide resistance will be killed or the growth of the plants will be restrained.

Fig.3.1 Layout of Pneumatic Sprayer

1. tank
2. inlet covering
3. Pneumatic mixer
4. Liquid level indicator
5. back valve
6. pressure gage (air inlet)
7-pressure regulator valve
8. air pump
9. valve joint
10. air tank
11. pressure gage (liquid outlet)
12. ball valve
13. liquid distributor
14. pipe
15. frame
16. nozzles

If the weed killer is mixed not very well, then it will cause some parts of the sorghum plants to be insecticide burned because of the higher density of the weed killer, while the other parts of the weeds not to be killed because of the lower density of the weed killer. Therefore, some countries have set up a standard which means after the weed killer has deposited 24 hour, let the mixer work 10 minutes; then measure the density of the weed killer, the difference should not be more than 5% to 15%.

Some material showed that; the shape of the tank cross section, the ratio of the length to the maximum width of the tank, the volume of the tank, the position of the mixer in the tank, the direction of the spraying, the working pressure and mixing volume of the mixer, etc, influence the performance of the hydraulic mixer. A pneumatic mixer was similar to a hydraulic mixer and the main parameters of a pneumatic mixer were as follows;

a. The ratio (e) of the length of vertical line to the length of horizontal line of the tank cross section
b. The horizontal position (Lb) of the tank
c. The vertical position (Lv) of the tank
d. The angle (&A) of the nozzle to the level
e. The diameter (d) of the nozzle
f. The air inlet volume (Q) which is the ratio of one unit volume of the tank to one unit time
g. The mixing time (T)

First, the single factor experiments were conducted on the special designed experiment table, and optimum value ranges were found out. Then, the geometric parameters (Lb, Lv, a and d) which effect on the performance of the mixer were studied and the optimum values were found out by means of liner regression orthogonal test. They are as follows:

d=1.5mm, Lv=45mm, Lb=40mm, µ =27

Fig. 3.2 Layout of Tank and Mixer

1. joint
2. mixer
3. liquid outlet
4. tank
5. liquid bypass
6. volume level indictor
7. safety valve
8. liquid inlet
9. covering

Last, the parameters (e, T, and Q) were studied by means of two time regression orthogonal test and computation models were obtained. According to the intensity condition of the tank, following optimum values were determined:

The tank length: L=1100 mm
The tank width: b=550 mm
The thick of the tank wall: t=3 mm

3.2.3 Result and Discussion

Experiments were carried out on a large area combining with the mechanization cultivation of sweet sorghum and corn. The results showed that no matter where to spray the weed killer (the seedlings nearby or overall the field) the weed killing rate was more than 80%. Especially when used alachlor + atrazine as the herbicide, more kinds of weeds were killed and the weed killing rate got 98%. No insecticide burn and weeds which appeared in girdle or piece was found. These proved that the distribution and the density of the herbicide were even.

3.3. The plan and effect of deep plow

Sweet sorghum plants grew slowly in the early time, but quickly in the later period when the plants grew quickly, they needed a lot of water and nutrient. Deep plow between the rows set a good structure of cultivation layer of soil; made the roots grow down through the plow pan; raised the amount, length, and the growth range of the roots; enabled the roots to absorb more water and nutrient; caused the roots to grow and develop quickly; furthered the plant ability to resist lodging. In order to get a optimum deep plow plan, some experiments were conducted.

3.3.1 Experiment condition and method

The used variety of the sweet sorghum was Rio. The space between two sprouts was 20 cm, and row spacing was 70 cm. planting was done on May 20th, the subsoiling was carried out on June 19th.

Fig. 3.3 Types of Ripping Tines

The experiments included a control plot and 8 treatment plots, and used complete random block test with three replications. The length of the plots was 5 m, and the number of the rows in a plot was 5.

Fig 3.3 showed that there were 8 types of ripping tines which were used in the test.

The working depth was 30 cm. The height and the height regularity of the plants in each plot were found out by means of correlation analysis. The optimum type of the ripping tines was comprehensively evaluated with fuzzily mathematics method.

3.3.2 Result and Analysis

A. The effect of deep plow on soil temperature

When it was clear, the soil temperature increased by 0.31 to 0.64°C in the plowing layer after subsoiling with each type of ripping tines. Compared with all other types of the tines, chisel with the width of 60 mm had the biggest increased temperature. The increasing time lasted about 70 to 80 days.

B. The effect of deep plow on the weight of one unit soil

Before deep plowing, soil apparently could be divided into three layers. 0 to 20 cm was called plowing layer, 20 cm to 30 cm was called subarable layer, more than 30cm was called soil pan. After deep plowing, the weight of one unit soil reduced by 0.3 to 0.6 g/cm3 in the subarable layer, and 0.2 to 0.4 g/cm3 in the plowing layer.

C. The effect of deep plow on the water content of the soil

Deep plow created a good water conservation condition for the soil. Every treatment increased available water by 1.31% to 4%. Deep plow raised water content in the working layer of the soil, solved the problem between the need and the supply of the water.

D. The effect of deep plow on solid degree of the soil

After deep plowing, the solid degree of the soil was reduced for every treatment, especially for the lower of the working layer. The reduced amount was about 10kg/cm3 These set a good condition for the growth of the plant roots.

E. The type of the ripping tine

It was suitable to use chisel type of ripping tine when the plants were young. It could cut down the drag resistance of the soil and move soil in the lower layer. The result showed that, type 60 was the best one in the chisel type ripping tine.

3.3.3 The effect of deep plow on sweet sorghum

Deep plow changed the physics and chemical character of the soil, set a good condition for the growth of the plants, promoted the development of the roots, raised the yield of the stems and seeds.

A. In the deep plowing range, the number of the roots increased by 30 to 50. The percentage was about 30. The length of the roots increased by 70%, and the root fresh weight of a plant increased by 18g and its dry weight increased by 2.4g.

In the deep plowing range, the root-room growth area of one plant increased. The roots concentrated area moved down by 10 cm. The horizontal width of the roots distribution expanded, and even some roots crossed the neighbour rows.

The root mass distributed well and properly, therefore reduced the affect of water and fertilizer competition among the plants.

This distribution state of the roots in the deep plow area apparently improved the growth condition of the sweet sorghum plants.

B. Because of the well and proper distribution of the roots, the plant grew luxuriantly, and the width in diameter increased in average by 10 to 30 cm. Compared with the control plot, in the deep plow area the single plant fresh weight increased by 100 to 200g and the dry weight increased by 11 to 16g .

Fig. 3.4. Left: roots in the deep plow area Right: roots in the control plot

The squeezing juice experiment results showed that the output of the juice was increased by 5% to 7% for every treatment.

Fig. 3.5. Left: stems in control plot Right: stems in deep plow area

C. The earhead grew luxuriantly and evenly, and the seeds yield increased by about 7%.

Fig. 3.6. Left: earheads in deep plow area Right: earheads in control plot

3.4. Sweet sorghum leaf stripping device

Sweet sorghum stem contains a lot of sugar, so that it is a good kind of raw material to refine ethanol. But the leaf of the sweet sorghum is useless in squeezing sorghum juice. The leaf not only decreases the amount and quality if the juice, but also increases the load in transportation. stripping leaves in the field not only solved the above problem, but also left the leaves in the field and fertilized the soil. The studied stripping leaf device working together with the harvester cut leaf and harvested stem at the same time. The results showed that; the plan, before stripping stems removed the leaves using elastic stripping finger, was available.

3.4.1 The construction and working principle of the stripping leaf device (Fig.3.7)

The stripping leaf device equipped with the high stem harvester, allows cut leaves and harvest stems to be done at the same time.

The stripping leaf device consisted of elastic stripping fingers, a frame, transmission and drive mechanisms.

Three sets of stripping leaf device fixed in the middle of three groups of plant lifters. Every stripping leaf device had two finger plates, and the distance between the two plates was 781 mm. The plate was made up of a joint plate, a base and elastic stripping fingers . The diameter of the plate was 750 mm, the available length of the finger was 275 mm. Each plate could be equipped with 4, 6, or 8 fingers.

Fig. 3.7 Stripping leaf device

Fig. 3.8 The transmission system

Three hydraulic motors which were positioned under the stripping leaf device driven the three plates to turn in the same direction (Fig.3.8). The leaves were cut in the available height of 2002 mm.

The motor employed the hydraulic pump of the tractor as power. The pressed oil was divided into two ways by a distributor valve. In one path, the pressed oil went through the distributor of tractor hydraulic lift to control the height of the stripping table. In another path, the pressed oil passed through a valve which was placed in the stripping leaf device hydraulic system to drive the motor. The three hydraulic motors were controlled by means of connected in parallel in the inlet way. To prevent the affect of load changing on rotation speed of the motor, a volume control value with a pressure compensation device was located at the inlet path of the motors. There was a flow restricting valve in the main oil path of the three motors to complete the infinitely variable control of the stripping finger rotation.

When the harvester was working, the stripping leaf device, which were placed in the middle of the plant lifters and drives by the motor rotated in a high speed and cut off the leaves from the sweet sorghum.

3.4.2 The experiment plan and result

The stripping leaf results of the device could be evaluated by stripping leaf rate. It was difficult to collect the broken leaves on the ground, so that the random sampling method was used. Before stripping the leaves, the average weight of the leaves of a plant (A) was measured; then after stripping the leaves, the weight of the leaf remains of a plant (B) was measured; finally the stripping leaf rate (C) was found out C= (A-B) /A.

The results showed that; the number of the stripping finger; the rotation and the direction of the stripping plate; the size, material and hardness of the fingers; the speed of the harvester; the angle between the rotation plane of the fingers and the ground level; the plant situation and its water content, all the factors above influenced the stripping leaf performance.

Considering of the effect primary and secondary of these factors on the stripping leaf rate; the reaction among these factors; and the effect of these factors on the type of stripping leaf device, the numbers of the finger plates were chosen as variable factors. The orthogonal tests were conducted on the following condition:

sweet sorghum variety: Rio
leaf water content: 59.9%
stem water content: 70.9%
harvesting speed: 3.5km/h

average stripped leaf weight within the device available working height range was: 95.55g.

The results showed that the plan using elastic stripping fingers before cutting the stems was feasible. The stripping leaf rate was by 67.1 to 73.7%. The test results and the layout of the prototype provided a useful reference for designing stripping leaf harvester.


The sweet sorghum mechanization cultivation was studied using the machines which were made in china. Although some work still needed to be done by hand, it was suitable to Chinese situation. The technology was available to grow sweet sorghum in large area.

The studied pneumatic sprayer, the deep plow method and its attachment machines, especially the designed stripping leaf device which was used in harvesting, provided dependable material for completing and modifying the cultivation procedure.


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4. F S Wright. Underrow pipping and irrigation effects on corn yield. ASAE, Vol, 27 (4), 1984.

5. F R Miller and R A Creelman. Sorghum - a new fuel. 1980 proceedings of the 25th Annual Corn and Sorghum Industry Research Conference. ASTA.

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