Purpose of soil tillage

Develop a desirable soil structure for a seedbed or a root bed (solid, water, air + organic matter)

Control weeds or remove unwanted crop plants (thinning)

Manage plant residues. Thorough mixing of residue is desirable for decomposition

Minimize soil erosion by following such practices as contour tillage, listing

Establish specific surface configurations for planting, irrigating, drainage, or harvesting

Incorporate and mix fertilizers, manure, pesticides, or soil amendments into the soil

Accomplish segregation. Moving from one layer to another, removal of rocks, or root harvesting

Tillage methods and equipment

Tillage implement

Process system: tillage tools (e.g., plow bottom, disk blade)

Support system: frame, wheels, hitch, control and protection devices

Three hitching configuration: integral (mounted), semi-integral (semi-mounted), drawn (pull-type)

Tillage operation

Primary tillage: initial, major soil-working operation to reduce soil strength, cover plant materials

Secondary tillage: final tillage operation prior to planting a crop

Tillage practices

Conservation tillage: leaves plant residue on the soil surface, reduce the time and energy for tillage

Conventional tillage: whole field tillage

Chapter 8. Soil Tillage

Primary tillage in conventional tillage system

Moldboard plow, disk plows and tiller, chisel plows, subsoiler, stubble-mulch plow, tiller, rotary tiller, lister, and bedder

Moldboard plows

Equipped with tillage tools called plow bottom (share 보습, landside 지측판, moldboard)

Function of plow bottom: cut the furrow slice, shatter the soil, and invert the furrow slice

Rolling coulters: help cut the furrow slice and cut through plant residue

Moldboard plows

Attachment: integral, semi-integral, and drawn, depending how plows are mounted to a tractor through 3 point hitch and

draw bar

Automatic reset standards allow a plot bottom to move rearward and upward to pass over an obstacle. Hydraulic cylinder

or spring mechanism automatically moves the bottom to its original position

Moldboard plows

Most moldboard plows are designed to turn the furrow slices only to the right

Two-way plow has two sets of opposed bottoms that can be used selectively

Eliminates dead furrows

Advantageous for terraced fields or contour plowing

Disk plows

Consists of a series of disk blades mounted individually on a frame

Disk angle (원판각, 42~45 도), tilt angle (경사각, 15-25 도)

Disk diameter: 60 ~ 70 cm

Disk shape: conical or spherical

Conical blade: has outside surface flattened to a specific cone angle

Spherical blade: tangent at the edge surface area of the blade

Suitable for hard, dry soils, and sticky soils where a moldboard plow will not scour

Disk tillers

Similar to a disk plow in regard to the frame, wheels, and depth control

But the disk tiller blades are uniformly spaced along one axle or gang bolt and clamped together so the entire gang

rotates as a unit

Used in dryland grain-growing regions for shallow tillage (8 ~ 13 cm)

Diameter: 51 ~ 61 cm, smaller than those of a standard disk plow

Gang angle: 35 ~ 55 degrees, no tilt angle, disk angle: 35 ~ 55 degrees

Chisel plows

Primary tillage at depths from 15 to 46 cm, good for dry soils

Shanks equipped with replaceable points or shovels little

inversion of soil

Requires ½ of the draft of a moldboard plow

Spring-cushion, spring-reset, or spring-trip mountings to protect

the tool and frame from impacts

Subsoilers

Used to break through and shatter compacted or other

impermeable soil layers and to improve rainfall penetration

Operating depths 45 ~ 75 cm

Little soil mixing and so soil inversion

Effective under dry and firm soil conditions

Rotary tillers (also called power tiller)

Power transfer to the tiller via PTO(power-take-off) drive

Main purpose is soil pulverization

Pushes the tractor forward (CCW rotation of blades)

Secondary tillage

Any tillage operations performed after the primary tillage

For preparation of planting. Break down large clods and prepare an ideal seedbed for planting

Ideal seedbed: allow for good seed-to-soil contact, conserve moisture needed for germination, allow vigorous root growth

Equipments are generally called harrows: disk harrow, spring time harrows, spike tooth harrows, cultivators, rotary hoes

Disk harrows

Differ from disk plows: no tilt angle, blades mounted on a common axis called the gang

Lighter and have smaller wheels than disk tiller

Arrangements: single-acting, tandem, offset…. In pairs with opposite disk orientation to balance the side draft

Narrow disk spacing (about 18 cm) for final seedbed preparation

Disk spacing (about 23 cm) for mixing of chemicals or cutting of surface trash

Spacing greater than 28 cm for harder soils or when heavy surface residue is present

Gang angle: 15 ~ 35 degrees

Spike tooth, tine-tooth, and spring-tooth harrows

Used in the final seedbed preparation, and also for post-planting operations to breakup soil crust and remove weeds

Cultivators

Types: field cultivators, row crop cultivators, rotary cultivators

Field cultivators for seedbed preparation, similar to chisel plows but operate at much shallower depths

Row crop cultivators: times spaced to go between the crop rows, for cultivation and weed control

Rotary cultivators: not powered, for weed control in row crops, break soil crests for better seedling emergence and mixing

of fertilizers

Rotary hoes: made of several star wheels

Culti-packers, roller, and finishing boards

Break up soil clods and conserve moisture for better seed germination

Bedders

Used to make ridges or beds

Made of disk implements to form the ridges

Listers

Look like double moldboard plow

Used to create furrows for planting

Planters are attached to listers to accomplish planting in the same operation

Tillage in conservation tillage systems

Conservation tillage systems to conserve soil, water, and/or energy (e.g., in areas prone to wind soil erosion)

Level of conservation tillage: minimum tillage, strip tillage, and zero tillage

Soil texture

Percent of particles in various size classes (sand, silt, and clay)

Mechanics of Tillage Tools

Physical properties of soils

Mechanical properties of soils – Shear strength

Shear stress-strain diagram for a given normal stress (Fig. 8.25)

Shear strength: shear stress on a plane within the soil sample where soil failure has taken place

Increase in the normal stress would cause an increase in maximum shear

Coulomb’s experiments (1776)

fs

tan cs

Determination of shear strength – direct shear test, tri-axial test

Field measurements of soil shear strength

Tools are inserted into the soil, rotated, and required torque was measured

Round shear box Narrow annulus shaped box Vane shear apparatus

32

3

r

Ms

3

2

3

12

3

rr

Ms

328

3

r

Ms

Friction