2.2. Design Considerations
To eliminate the interference of other factors, developed earthing up machine was deliberated following variable considerations such as line to line distance of sugarcane in the field, tyne selection and adjustment for soil pulverization, depth of expected furrow after soil removal and compaction of piled up soil at sugarcane root.
i) Line to Line Distance of Sugarcane
In sugarcane field, various line to line distances are generally practiced in Bangladesh. So, the maximum width of earthing up machine should be smaller than the minimum practiced distance between lines of sugarcane in the field. The minimum line to line distance being practiced most in Bangladesh is approximately 0.75 m. So, the maximum width of earthing up machine was kept 0.61m.
ii) Tyne Selection and Adjustment for Soil Pulverization
In earthing up operation, soil between two adjacent lines was pulverized and then the soil was needed to move away to form a furrow and that soil was piled up at the root zone of sugarcane. Hence R-type or J-shaped Tyne blades helped to displace the loose soil, this type of Tyne blades was selected for this machine. The blades adjustment should be in such a way that the half of the shaft of the earthing up machine was fitted with these sorts of blades facing one direction, while the other half with blades facing the opposite direction. The half of pulverized soil moved towards one side and other half of it towards other side and a furrow was formed.
iii) Diameter of Soil Compactor of Earthing up Machine
The diameter of soil compactor was kept higher than the depth of furrow created by earthing up machine. The furrow depth was kept 0.15 m. So with some clearance for bearing, the diameter of soil compactor was kept 0.38 m. In addition to some other points were also considered before design and development. Such as- motion of the parts, materials selection, workshop facilities, cost of construction, assembling and safety of operation.
2.5. Different Parts of Earthing up Machine
The earthing up tool did not have its own power supply. As a result, the earthing up machine (
Figure 3) was powered by a small to medium-sized 2WT (two-wheeled tractor), locally named power-tiller. The earthing up machine was mounted behind the power tiller, which wrenched it through the gap between two lines of sugarcane tillers.
Earthing up machine consisted of some stationary and moving parts excluding the power source (power tiller engine or tractor) as shown in
Figure 4. Design and development of different parts of the earthing up machine are shown in
Figure 4,
Figure 5 and
Figure 6.
a) Rotary Tiller
The rotary tiller (
Figure 5) was the nearest moving element to the power source, receiving direct power from the engine via the chain and sprocket power transmission system. The rotary tiller's provided power was used to rotate the tiller-shaft (rotary-shaft) in a forward direction, allowing Tyne to pulverize the soil. To wrap Tyne around the shaft, there were 22 Tyne holders (
Figure 5). The main functions of a rotary tiller were to hold and rotate Tyne for breaking soil clods, pulverizing ridge soil, and sending soil backwards to the ratoon root region for earthing up.
b) Tyne
R-type, or J-shaped Tyne blades, were employed for earthing up operations because of their functional benefits. This sort of Tyne blade sent the cut dirt both side and backward during rotating movement. To take advantage for earthing up operations, half of the shaft of the created earthing up machine was fitted with these sorts of blades facing one direction, while the other half blades facing the opposite direction (Figure-5b). The soil of the ridge between two sugarcane ratoon was swept from the center to both sides of the ridge and a furrow was produced for such facing of the blades.
c) Furrower cum Soil Compactor
The furrower cum soil compactor is just after the rotary tiller and Tyne blades. It is a drum configuration with two cone-shaped cylinders as shown in Figure-6. The drum revolved around a separate shaft. These two cone-shaped cylinders were fitted to the shaft such that the diameter in the center of the drum remains bigger than the diameter on the side. The crushed earth was rolled over this structure, which generated a V-shaped furrow. This drum structure also compacted material that had already replaced to the root area of sugarcane tillers, prevented soil from sweeping away from the cane root area and also provided wind resistance to the ratoon soil.
d) Casing or Body
Casing (
Figure 1 and
Figure 2) is the frame of an earthing up machine that holds the shaft of the furrower cum soil compactor. It kept the furrower linked to the rest of the earthing up equipment. In addition, the casing acted as a dead weight for the soil compactor, allowing it to make a furrow. Because of the casing was so near to the furrower cum soil compactor, it also cleaned mud, grass, and other debris from the furrower drum.
2.8. Performances of Earthing up Machine
i) Soil Moisture Content
In this study, a digital soil moisture meter was used to measure the soil moisture content. The probe of digital moisture meter was put to a specified depth into the soil of the trial field as shown in
Figure 7a. The moisture content of the soil was promptly displayed on the digital screen after insertion of the moisture meter. The "Hold" button was pushed to prevent unnecessary change in reading.
Ii) Soil Disturbance
While testing the earthing up machine in the sugarcane field, the soil was turned over and the disturbed soil was earthen up, resulting in two ridges on both sides of the furrow. In
Figure 8 W
st denoted the distance between the outside margins of the two ridges. The ridge to ridge distance is a distance between the two summits of the ridges on both sides of the furrow (RRC). The rest of the disturbed soil created the furrow's shallow groove. In
Figure 8, the second line (the damaged soil surface) represents the groove's profile. The disturbed dirt was meticulously cleaned until the furrow's contour was seen clearly. The disturbed soil surface and the furrow's shape were meticulously measured. The top width of furrow (W
sb) on the original soil surface was determined the disturbed soil cross-sectional area. The height of the ridge was measured from the top of the ridge to the original soil surface (H
r).
Figure 8 depicted the aforementioned soil disturbance characteristics.
Now, the area of furrow after earthing up A
f was calculated with following equation:
where, A
f = Area of furrow (m
2); W
sb = Top width of furrow (m); w = Bottom width of furrow (m);t = Depth of furrow (m)
Soil disturbance efficiency,
where, s =Soil disturbance efficiency (%); A
f = Area of furrow (m
2); w
c = Soil compactor middle width (m);W
c = Soil compactor edge to edge width (m); t
c = Soil compactor depth (m)
iii) Effective Field Capacity
Effective field capacity of the earthing up machine was calculated using the following equation:
Effective field capacity (ha/hr),
where, A= Area covered at time T (m
2); T = Operational time (min)
iv) Theoretical Field Capacity and Field Efficiency
Theoretical field capacity of the earthing up machine was calculated using the following equation:
Theoretical field capacity (ha/hr),
where, S= Speed of machine (km/hr);W = Width of machine (m)
Field efficiency of the earthing up machine was calculated using the following equation:
Field efficiency (%),
where, C
th = Theoretical field capacity (ha/hr); C
eff = Effective field capacity (ha/hr)
2.9. Economic Analysis of the Machine
Like other farm machinery, the costs of earthing up machine was categorized into two: annual ownership costs, which occurred regardless of machine use, and operating costs, which varied directly with the amount of machine use [
11].
i) Ownership Costs of Earthing up Machine
Ownership costs (also called fixed costs) included depreciation, interest (opportunity cost), taxes, insurance, and housing, repair & maintenance cost.
a) Depreciation
The annual depreciation cost of earthing up machine was computed in the straight-line method using following equation [
11]. Depreciation (BDT/yr.),
where, P = Machine price (BDT); S = Salvage value (BDT) = 5% of P; M = Economic life of earthing up machine (yr.)
b) Annual Interest
Annual interest cost of earthing up machine was computed in the straight-line method using following equation [
1].
Annual interest (BDT/yr.),
where, P = Machine price (BDT); S = Salvage value (BDT) = 5% of P;
i = Interest rate (decimal/yr.)
c) Total Ownership or Fixed Costs
The estimated costs of depreciation and annual interest were added together to find the total ownership cost. In the cost calculation of earthing up machine, taxes, insurance, and housing cost were negligible. So,
where, FC = Total ownership or fixed costs (BDT/yr.); D = Depreciation (BDT /yr.); I = Annual interest (BDT/yr.)
ii) Operating Costs of the Machine
Operating costs or operational costs (also called variable costs) of earthing up machine included all costs for successive machine operation such as repairs & maintenance cost, fuel cost, lubrication cost, and operator or labor cost.
a) Repairs and Maintenance Cost
Repair costs occurred because of routine maintenance, wear and tear, accidents etc. Many experts mentioned that total repairs and maintenance costs of most farm machines averaged about 1-2 percent of machine price or manufacturing cost for rotary tiller. So,
where, R&M =Repairs and maintenance cost (BDT/hr); P = Machine price (BDT.)
b) Fuel Cost
Earthing up machine required a power tiller or small two-wheeled tractor for the power supply. As for the developed machine, the power source was the diesel engine of that power tiller. So, there was a fuel cost which was calculated using following equation:
Fuel cost (BDT/hr),
where, f= Fuel consumption (liter/hr); p = Price of fuel (BDT/liter)
c) Lubrication Oil Cost
Surveys indicated that total lubrication costs on the most farms average about 15 percent of fuel costs (William et. al., 2015). The lubrication oil cost was calculated using following equation,
Lubrication cost (BDT/hr),
where, F = Fuel cost (BDT/hr)
d) Labor (Operator) Cost
Again at least one operator was required to operate this earthing up machine. So, for earthing up operation, the operator cost was calculated using following equation:
Operator cost (BDT/hr),
where,
l = wages of operator (BDT /hr) =
e) Total Operating or Variable Costs
Repair and maintenance, fuel, lubrication and labor costs were added to calculate total operating cost of the developed machine. So,
where, VC = Total operating or variable costs (BDT/hr); R&M = Repairs and maintenance cost (BDT /hr); F = Fuel cost (Tk. /hr); O = Lubrication oil cost (BDT./hr); L = Labor or operator cost (BDT /hr)
iii) Total Cost of the Machine
After all costs being estimated, the total operating cost per hr was converted to cost per year and then this was added to the total ownership cost per year to calculate total cost per year to own and operate the developed earthing up machine. So, the total cost of earthing up machine was calculated as follows:
where, TC =Total cost of earthing up machine; FC = Total ownership or fixed costs (BDT/yr.); VC = Total operating or variable costs (BDT /hr); H
ye = Expected total operational time in a year (hr/yr.); C
eff = Effective field capacity (ha/hr)
Finally, total cost per year was divided by the hourly work rate in ha/hr to calculate the total cost/ha as shown in equation (xvi).
iv) Net Cash Flow (NCF)
Net cash flow (NCF) refers to either the gain or loss of funds over a period. As the earthing up machine was developed to reduce the human labor for earthing up operation, there was a difference between these two methods of earthing up operation and the difference was the revenue of using the earthing up machine. So,
Net cash flow (BDT /ha),
where, TC
ha = Total cost of earthing up machine (BDT /ha);
Cmanual = Total cost by manual method (BDT/ha) =×Hym;
Hym = Man-hr required (hr/ha)= no. of labor (nos./ha) × no. of day × working time (hr/day)
v) Net Present Value (NPV)
A technology or machine is said to be financially feasible when the net present value is positive. The bigger the net present value, the project is the more profitable. The following formula was used for calculating the net present value of developed machine (Rahman et. al., 2018).
Net present value (BDT),
where, NCF =Net cash flow (BDT);
i = Interest rate (decimal/yr.); P = Machine price = Initial capital investment (BDT)
vi) Internal Rate of Return (IRR)
Internal rate of return is a discount rate that makes the net present value (NPV) of all cash flows equal to zero in a discounted cash flow analysis. The net present value of the developed earthing up machine was calculated using the following equation (Rahman et. al., 2018):
Internal rate of return (decimal),
where, NCF = Net cash flow (BDT /yr.); P = Machine price = Initial capital investment (BDT)
vii) Benefit-Cost Ratio of the Machine
The important tool of cost-benefit analysis is the benefit-to-costs ratio (BCR), which is the total cost of the benefits or outcomes divided by the total monetary costs of obtaining them. So, the benefit-to-costs ratio of earthing up machine was determined by following equation:
Benefit-cost ratio (decimal),
where, NCF =Net cash flow (BDT/ha); TC
ha = Total cost of earthing up machine (BDT/ha)
vii) Pay-Back Period of the Machine
Payback period means the period of time that a project requires recovering the money invested in it. Therefore, the payback period of the earthing up machine was computed using the following equation:
where, NCF =Net cash flow (BDT); TC
hr = Total costs of earthing-up machine (BDT/hr); P = Machine price = Initial capital investment (BDT); H
ye = Expected total operational time in a year (hr/yr.); C
eff = Effective field capacity (ha/hr)