2. Introduction
• The selection of tractor and the matching implements has become more
difficult than ever before.
• In India more than 75 Models of tractors ranging from 10hp to 75 hp and
more have put number of problems in front of the buyers.
• The economic selection of field equipment’s is a complex problem as
compared with other industries. They are
Most of the farms are small, diversified and are subjected to local
conditions, hence each farm has to be considered as special problems.
Agricultural production is seasonal (equipment will stand idle most of
the time).
The supply and ability of the operators and farm labours is quite varied.
The need of the timely operations because of the seasonal requirements
of the crops.
3. Introduction
• To overcome this problem a systematic approach is to be made which
includes many considerations.
• Land holding, type of soil, cropping pattern, weather conditions, no. of
working days available in the season etc. are some of the primary
considerations to compute the required hp of tractor and the matching
implements.
• Once the tractor hp is set, to choose a better tractor, there are few more
factors such as:
Economic viability of the maintenance cost, operation and repair
cost.
Availability of after sales services.
Suitable gear ratio to meet out the requirements of any part load etc.
5. PRIMARY CRITERIA
• Size of land holding and type of operation
• Working time available
• Type of soil
6. Size of land holding and type of operation
• Amongst the primary criteria of the tractor selection, the size of land holding
is very important.
• Very high hp tractor purchased may remain under- utilized causing financial
loss in terms of depreciation and interest,
• where as a low hp tractor may not be able to complete the work in time ad
the purpose of procuring a tractor, is not met.
• The tractor is used for various operations starting from land preparations,
sowing to harvesting, threshing and transportation work. Of these
operations, some are difficult and the output in terms of hectares per hour is
less than others.
• Therefore, it is always recommended that while determining the hp of the
tractor we should consider the field operation which is toughest and time
consuming (normally primary tillage operations).
7. Working time available
• The time available for a particular field operation is another
important factor in deciding the hp range.
• In the whole year if more than one crop are to be taken then the
time available after harvesting of one crop and the seedbed
preparation of the second crop is to be calculate very precisely
based on past records.
• While calculating availability of time, one should refer at least 4-5
years records and consider the year in which the worst weather
condition was prevailing and thus obtain number of calendar days
available for various operations.
8. Working time available
• Even the entire period calculated as above will not be really
available for continuous field operations due to unforeseen reasons
viz. break down, non- availability of man power, sudden weather
interruptions, fatigue etc.
• however, experience reveals that at most 80% of the available time
is spent in the field. In addition to above, field efficiency of the
tractor implement combination is only 70% to 80%, which means
the actual operational time for field use is less and the rest is used
for making headlines, turns etc.
9. Type of soil
• The soil resistance in different soil conditions varies. In heavier soil it is
high and in light soils low.
• An implement which can give a desired depth of operation in light soil
at certain given speed will not be able to do the same quantum of work
in the same period of time in heavier soil.
• In other words, a tractor capable of performing all operations timely for
specified size of field in light soil will not be able to do so in heavy soil
for the same size of the field.
• The tilth for heavier soil is achieved later than the lighter soil which
means, total no of hours available for heavier soils will be less than the
lighter, which indicates that for heavier soil a higher hp tractor will be
more suitable compared to a tractor needed for same size field of
lighter soil.
10. SECONDARY CRITERIA
Selection of tractor within known hp range depends on the following plus
points:
The no. of gears is more and the gear ratio spaced in such away
that any part of the drawbar pull within its maximum range can be
obtained in comparatively high speed.
The running cost of the tractor with respect to its specific fuel
consumption.
After sales services and repair facilities.
The provision of automatic draft control system is preferred.
Lower turning radius to increase the field efficiency.
Ergonomical aspects.
11. COMPUTATION OF HORSEPOWER RANGE OF TRACTOR
• The maximum hp required for any type of field operation will be the
hp of the tractor needed. The approach follows as bellows:
Find out the optimum size of the implement which can complete
the operation during available time.
Find out the hp requirement for above implement.
12. To find out the size of the implement:
• Having known the total area and working time, the capacity of the desired
implement can be given by:
• Theoretical field capacity (ha/hr) = area (ha)/ time (hrs)
Also, {speed (km/hr)* width (m)}/ 10
• Effective field capacity (ha/hr) = theoretical field
capacity(ha/h)* field capacity
• Therefore, width of implement (m) = {theoretical field capacity*10}/
{speed* field efficiency}
14. Draft Estimation
• In order to determine the draft requirement of an implement it is
necessary to use a pull meter. Estimation of likely draft
requirements can be taken from the table provided.
• However, these values will vary according to soil type, soil
moisture, depth of working, ground speed and manufacturer.
15. • total draft can be calculated by simply multiplying implement
width by draft per unit width. Considering the example using the
chisel plough, then:
Total draft = width (m) x draft / metre (kN/m)
= 7.8 x 5
= 39 kN ( approx. 3900 kgf)
16. Estimation of drawbar power
• Drawbar power can be related to draft and speed, by using the formula below. Any one drawbar
power level may be attained by a combination of pull and speed. That is, a large pull at a low speed
could produce the same drawbar power as a small pull at high speed.
• Drawbar power = pull (kN) x speed* (km/hr)
3.6 (constant)
Using the same chisel plough as in the previous example, the power requirements become:
Drawbar power = 39 x 8
3.6
= 87 kW (116hp).
*Speed has been determined by the initial assumption when working out the required implement
width.
• Note: Kilowatts (kW) x 1.34 = Horsepower (hp)
Horsepower (hp) x 0.746 = Kilowatts (kW)
• At this point, it would pay to work through all of the tillage operations and determine the
requirements for each, after closely considering the time available and field efficiency. The
largest power requirement would be then used in determining engine power.
17. • The dbhp depends upon various factors viz. soil conditions, speed of
operation, tire size, ballasting etc. hence to designate the hp of the
tractor, we have to choose a standard which remains unaffected by
above factors.
• The PTO hp is accepted yard stick to designate the tractor hp.
• On recommendations of the Budni Institute, mention of PTO hp on
tractor specification plate has been made necessary by BIS.
18. Estimating engine power
• Once drawbar power has been calculated, a decision needs to be
made about what type of tractor is to be used.
• The selection decision between wheels or tracks is far too complex a
topic to be covered in this chapter.
• Suffice to say that if set-up and matched correctly, the operating
costs should be similar for either tractive type.
• The decision between two wheel drive and four wheel drive is much
simpler as it is determined by the minimum available size of a 4WD
and the maximum size of a 2WD (that is approximately 150 kW or
200 hp).
