DRAFT OF PLOWS

Draft of Plows -  determined by the resistance of the soil to tillage operation, the speed of plowing, sharpness of the cutting edge and over-all adjustment of the plow.

    Ø     Resistance of the soil is expressed as specific draft.  This is the force required to cut a unit cross-sectional area of soil as shown in Table 1.  The specific draft is multiplied by the width and depth of cut to get the draft.

    Ø     The increase in draft due to speed as shown in Table 2 is applied to that part of the total required for turning and pulverizing the furrow slice.

Table 1.            Specific draft of different soils

SOIL TYPE	SPECIFIC DRAFT, SD
	Lbs/in2	Kg/cm2
Sandy soil Sandy loam Silty loam Clay loam Heavy clay Virgin soil, clay Gumbo, moist Dry adobe	3 3-6 5-7 6-8 10-11 12-15 16-18 18-20	0.21 0.21-0.42 0.35-0.49 0.42-0.56 0.70-0.77 0.85-1.06 1.13-1.27 1.27-1.41

Table 2.            Increase in draft due to speed

SPEED		DRAFT, %
MPH	KPH
1 2 3 4 5 6	1.6 3.2 4.8 6.4 8.0 9.6	100 114 128 142 156 170

Sample Problem 1:                 Determine the hectares plowed per hour when a tractor is operating at 6.4 kph and is pulling four 36-cm moldboard bottoms at a depth of 20 cm.  How many hectares can be plowed in 10 hours if field efficiency is 78 percent?  If the soil is clay loam, what is the draft required to work the soil? Draft hp requirement? Tractor hp requirement?

Solution:

a.             Hectares plowed in 10 hours:

    where:       C = Field Capacity, Ha/hr

S = Speed, Kph

W = Width of cut, m

Eff = Field Efficiency, decimal

b.         Draft requirement based on soil type:

                   where:

D_s = Draft, kg

Specific Draft = Kg/cm² from Table 1

W = width of cut, cm

D = depth of cut, cm

D_s = (0.49 Kg/cm²)(4x36 cm)(20 cm) = 1,411 Kg

c.          Adjusted draft requirement due to speed of plowing (from Table 2):

D_a = 1,411 kgx1.42 = 2,004 Kg

d.         Draft horsepower requirement:

     where:  D_a = Adjusted Draft, Kg

S = Speed, Kph

     =          46.8 hp

e.         Tractor Horsepower:

FARM MECHANIZATION

Tillage

- any physical soil manipulation which changes the structure of the soil, kills weeds, and rearranges dead plant materials

Classification of Tillage

     1. Primary tillage - initial cutting, breaking and usually inversion of the soil.  Implements used are moldboard, disc and chisel plows and subsoilers cutting the soil to a depth of 6” to 36”.  Often referred to as plowing.

     2. Secondary tillage - subsequent breaking, pulverization and leveling of the soil making it ready for planting. Implements used are disc, spike-tooth and spring-tooth harrows preparing the soil to a depth of 3” to 6”.  Often referred to as harrowing.

     3. General-purpose tillage – Combined primary and secondary tillage in one operation.  Implements used are the rotavators and floating tillers cutting the soil to a depth of up to 6”.  Often referred to as rotavating.

Terms Used in Plowing

     1. Land – unplowed soil.

     2. Furrowslice – soil cut, lifted, inverted and thrown to one side of the plow bottom.

     3. Furrow – trench or canal left by the furrowslice.

     4. Backfurrow – raised ridged when two furrowslices overlap each other.

     5. Deadfurrow – trench left equal to two furrows when furrowslices are thrown on opposite sides.

     6. Furrow wall – unbroken side of the furrow.