1. the Physical Manipulation of Soil with Tools and Implements to Result in Good Tilth

TILLAGE

Definitions

1. The physical manipulation of soil with tools and implements to result in good tilth for better germination and subsequent growth of crop (Reddy and Reddi, 1992). 2. Tillage refers to mechanical manipulations of the soil that provide necessary conditions favourable for the growth of crops. It includes operations and practices that are used for the purpose of modifying the physical character of the soil ( Balasubramaniyan and Palaniappan, 2004) 3. Those mechanical, soil-stirring actions carried on the soil for the purpose of nurturing crops 4. Manual or mechanical soil-stirring actions necessary for the proper establishment and growth of crops.

Tilth the physical condition brought about by a tillage operation.

Characteristics of good tilth

1. Good soil tilth should be mellow or friable (mellowness or friability of soil is that property of the soil by which the clods when dry, become more crumbly; crumbling of soil = gradual disintegration of clods) 2. Soil with good tilth is quite porous and has free drainage up to the water table. The capillary and non-capillary pores are about equal so that sufficient amount of water is retained in soil as well as free air. Soil aeration, activity of microorganisms and chemical reactions in the soil increase with increase in non-capillary pores. Total porosity and pore size distribution are important to improve moisture retention and availability of oxygen in the rooting zone. 3. Powdery soil encourages surface crusting when the soil dries after wetting 4. Soil aggregate should be stable enough to withstand water and wing erosion Note: Soil tilth is not static- it changes with time.

Goals and purposes of tillage

A. Seedbed preparation: aim is to provide an optimum environment for seed germination and subsequent growth and development of crops. The seedbed preparation must be suitable for the crop –ensure tilth allows seed the to be placed at the proper depth The tilth must also supply: 1) adequate soil temperature 2) soil aeration 3) soil moisture 4) seed –soil contact, to facilitate rapid seed germination and seedling growth

Lecture notes_Makuvaro.V_2011 Page 1 B. Inco-orporation and mixing of applied fertilizers - Used to incorporate and mix lime, fertilizer or pesticides into the soil.

C. Weed control Weed control operations can be done before planting; between planting and crop emergence and after crop emergence. . Weeds are buried in the soil with tillage operations (deep tillage)

D. Erosion control

Tillage operations employed differ with situation: e.g leave residue on the soil surface to prevent water and wind erosion, or provide rough soil surfaces which help prevent wind and water erosion (To improve the physical condition of the soil so that rainwater could be absorbed easily and erosion minimized ).

Some of tillage e.g tied ridging and other conservation tillage techniques guard soil against erosion

Other objectives

- Insect pest control: Most pests in their different developmental stages cannot survive if buried beyond 20cm. Eggs and larvae of insects and their breeding places are destroyed

- Temperature control: (bare unploughed soils have higher temperature fluctuations than tilled soils)

- Management of crop residues; The residues are inco-orperated into the soil to allow them an optimum environment for decomposition

- Improvement of plant –soil interactions/contact in the root zone and to improve soil physical condition to promote good root penetration.

- Moisture management ( under both drought and flood situations ) e.g tied ridging, pot-holing etc)

- Removal of soil crust

Types of tillage

 Primary and Secondary tillage are the two general catergories of tillage referring to/based on depth of tillage, type of implement and goals in preparing a seedbed.

 Two types of tillage can also be identified, based on time (with respect to crop) at which they carried out viz; i) Preparatory cultivation (seedbed prep): consists of primary tillage, secondary tillage and lay-out of seedbed

Lecture notes_Makuvaro.V_2011 Page 2 ii) After cultivation –tillage operations are carried out in the standing crop e.g drilling or side dressing of fertilizers.

A. Primary tillage:

 It is tillage which cuts, inverts and /or shatters the soil to a depth 15-36 cm. It may bury trash by the inversion and it usually leaves the surface rough.

 It is a more aggressive , relatively deeper operation and implements tend to be heavier and more strongly constructed than for secondary tillage.

The aims of primary tillage may include: i) loosening and aerating the soil surface layer; ii) incorporating fertilizer iii) covering plant residue from previous crop or mixing the residue into the surface layer of the soil

Examples of primary tillage implements:

 Mouldboard ploughs, chisel ploughs  Disc ploughs  Sub-soilers  Chisels  Rippers  Offset and heavy tandem disc harrows and ploughing discs  Rotary tillers

Ploughs:

These can be classified according to four criteria:

1. Type of plough body (disc or moudboard) 2. type of operation (conventional or reversible) 3. hitching system (trailed, mounted, semi-mounted) 4. number of plough bodies

Thus a plough may be called for example; a mounted conventional two-disc plough.or a semi-mounted reversible thee disc plough.

Disc or mould board ploughs are used according to the required tilth (soil inversion, uniformity, water conservation and growing conditions are the 4 aspects to be considered ), the existing field conditions ( two aspects are considered namely obstacles and soil moisture)and the draft and maintenance requirements ( these are related to the type of operations of the disc and mouldboard ploughs).

Lecture notes_Makuvaro.V_2011 Page 3 Note: Under normal conditions farmers use a mounted conventional or reversible three disc plough., but in hard conditions(e.g………..), the three disc plough may be changed for a two-disc plough. For very powerful tractors, a semi-mounted five or six disc plough can be used. Disc ploughs are basically tractor drawn because of their weight and size.

Mould plough( action): Cuts slices of soil and inverts them. A layer of soil is separated from the underlying sub-soil and is inverted.. Degree of cover of trash on surface layer depends on depth of ploughing, setting of plough and amount of plant residue.

Components of a mould plough::

Practical / class demonstration –

a) Draw a clearly labelled sketch diagram of a mouldboard plough and describe the functions of any three components of this plough. b) Write brief notes on the following aspects of the mouldboard plough - plough height - hand suction - pitch

1.Plough bottom: contacts with the soil and contains main working parts which are:

a) the share – has a sharp cutting edge which sinks into the soil making passage for the plough bottom. It is made up of steel or cast iron; the former preferred since it is less liable to damage and can be repaired /builtup and hard surfaced when worn. b) Mouldboard ( also called “breast” or “wing” ) – helps in inverting the furrow slice – has atwisting and inverting action which causes breaking and pulverization of the soil depending on curvature of the mouldboard. ( gentle curvature leaves furrow slice unbroken, while short, broad board with abrupt curvature causes much pulverization).

c) Land side ( also called “slad or “heel” )

- Positioned on the side opposite the mould board and is usually rectangular in shape - Helps to resist the side pressure exerted by the furrow slice and helps in stabilizing the plough during the plouging operation

d) Frog – An irregular piece of metal to which the share, mould board and land side are attached. e) Coulter - Knife or disc –like attachment fixed to the beam. It helps in separating the furrow slice from the unploughed land.

Lecture notes_Makuvaro.V_2011 Page 4 2. Handle – helps in guiding the plough

3. Beam – fixed to the plough bottom and extends forward. It is connected to the yoke by means of chains or ropes. 4. Clevis or bridle or hake - these are provisions for horizontal or vertical adjustments for regulating the width and depth of the furrow. A number of holes are provided to facilitatate hitching at the correct/desired point E.g. if hitching is done to the hole nearest to the mould board, widest furrow is formed and opposite true.. In vertical bridle, if the draft chain is fixed at the top-most holes, furrow will be deeper.

5. Wheels: assist the plough woman in steadying heavy ploughs This makes ploughing easier and less tiring.

Disc plow (action):

Action is similar to that of the mould board plough and the soil inversion is only partial. It can be used in situations where the mouldboard may not function well properly/satisfactorily e.g. i ) hard and dry soil ii ) sticky soils iii) highly abrasive soils iv) hardpan soils v) new ground with remaining stumps, roots etc.

Chisel plough:

- It does not plough. The desired action of the chisel plough is to break and shutter the soil while leaving enough residue on the surface to help control soil erosion. - It is a heavy cultivating implement - It is also used to breakdown plough pans or plough soles caused by mouldboard ploughing at the same depth for years - Useful in hard conditions and in reclaiming rough lands and orchards - It is heavy structured

Stubble mulch tiller

- Combines the operations of chiselling and disking. It consists of disk blades and in front to cut and loosen trash and a chisel plough in the rear section to break and shatter the soil

Powered rotary tiller

- Require engine power to rotate the blades for cutting/lifting and loosening the soil. Depth of cut is up to 12-15 cm. - Effective in chopping and incorporating trash and preparing a fine tilth bed. They are often used for secondary tillage at shallower depths Note: excessive use may lead to soil pulverization- limiting water infiltration and increasing the erosion hazard. Rotary tillers are suitable for light soils

Lecture notes_Makuvaro.V_2011 Page 5 Subsoilers:

- Used to penetrate the soil deeper than with conventional cultivation machinery. - There is no soil inversion and this differentiates the practice/process from deep ploughing (where depth of tillage can go beyond that considered adequate for primary tillage. Deep ploughing can be done to invert soil in special circumstances such as sanitation , improvement of soil structure and control of some perennial weeds. It should be done when the soil is completely dry. Depth of ploughing is generally deeper than 50cm). - Break up relatively impervious layers of soil which have arisen as a result of compaction from tillage operations ( movement of heavy machinery or as a result of ploughing at the same depth for a long time). Impervious layers can also form naturally. The impervious layers can limit root growth and nutrient and water holding capacities of soil. - May have one or more heavy tines which break the through the impervious layer causing a shatter. - Sub-soiling refers to pulling a chisel type implement through the soil to a depth of 30cm or deeper to shatter impervious layers (Depth of work is approximately 50 cm) - Sub-soiling should be carried out under very dry conditions or when internal drainage beneath the impervious layer should be good. Sub-soiling is not effective when subsequent tillage operations re-compact the soil

B. Secondary tillage

It refers to tillage operations that follow primary tillage and are for the purpose of preparing a final seedbed suitable for planting, seed germination seedling estabilishment and weed control It works the soil to shallower depths -5-15 cm

Aims include:

1) Levelling and firming the soil 2) Further pulverising of the to ensure good seed –soil contact 3) Control

Note: excessive secondary tillage may increase the evaporation of water from the surface layers of soil resulting in sub-optimum moisture levels for proper germination.

Examples of secondary tillage equipment:

1) Disk harrow

- e.g. tandem disk harrow(can be used for primary tillage depending on size) - Action: pulverze soil clods, levels and firms soil

Lecture notes_Makuvaro.V_2011 Page 6 2) Field cultivators(usually have conditioners).

- Resembmles chisel plough except that it is lighter constructed and designed for shallower tillage. - They are widely used for seedbed preparation and weed control.

3) Spring, spike and tine-tooth harrows - These implements vary in design but they have similar purpose of levelling, pulverising, firming soil and sometimes weed control. They may be operated separately or pulled behind ploughs, disc harrows or field cultivators

4) Roller packers and roller harrows? - Can be made from stone, iron or wood - Implelement consists of heavy rollers designed to crush soil clods and the soil surface- good for small-seeded grasses and legumes - General principle involved is the rotation of massive material round the axle - It should not be used on wet soils otherwise severe crusting results

5) Row-crop cultivators

Tillage practices /systems.

There are three main tillage systems/practices. These include: a) Conventional tillage; b) Conservation tillage; c) Minimum /reduced tillage.

Conventional tillage includes both primary tillage and secondary tillage. A number of operations are performed systematically depending on the requirements of the crop and area for example: a) shredding or disking crop residues (preliminary operation) b) primary tillage(ploughing) c) secondary tillage –may inolve disc harrowing followed by spike-, spring- or tine-tooth harrowing, one or two times d) planting e) cultivating/weeding

Several passes of different operations leave the soil with a fine tilth that is ideal for planting. It also eliminates the risk of trash interfering with the planting opration, but may have the disadvantage of rendering the soil highly erodible.

Conservation tillage is broadly defined as any practice[trash farming, mulch farming, stubble farming as opposed to clean tillage] that leaves at least 30% of crop residue over the soil surface after planting ( Oliver, 1989; Vowles,1989 cited by Nyakanda, 2000).

Lecture notes_Makuvaro.V_2011 Page 7 The main objectives of conservation tillage( and mulch tillage) are: a) Soil and moisture conservation; b) Energy conservation. Conservation tillage has a number of advantages. Some of the advantages include: a) Reduced soil erosion; b) Increased water availability; c) Moderation of temperature; d) Timeliness of operations; e) Improved soil structure; f) A better root system develops closer to the surface; g) This is a cheaper system. These advantages are generally on long term.

The disadvantages of conservation tillage are: a) It is difficult to rectify compaction layers: b) The mulch created may reduce temperatures c) High C/N ratio of the common crop residues may depress nitrification.

Minimum tillage (reduced /optimum/economy tillage). This system concentrates on the minimum disturbance of the soil, mostly introducing the seed into the soil. There are several methods of introducing seed into the soil used in this case. They include: a) Strip tillage; normally, the farmer works on strip/row of previous crop b) Direct planting in stations. The system has been made possible of late, by the use of special equipment and the use of herbicides

Tillage can be reduced in two ways – a) omitting less beneficial operations b) combining operations

These systems involve principles rather than well defined practices.

System objectives include:

a) Reducing energy input and labour requirement for crop production b) Conserving soil moisture and reducing erosion c) Providing optimum seedbed and rootbed growth area, rather than homogenizing the entire soil surface d) Keeping trips over the field to minimum

Limitations of the system: - Weed infestation especially early weed infestation : more of a problem for the smallholder farmers. Weed pressure under reduced tillage can be reduced by controlling the late weeds in the previous crop. - Pests and diseases are likely to be a problem especially where residues remain in the field (what is the situation with smallholder farmers. How do they manage crop residues? – grazing in situ; removal and storage at cattle kraals etc ) Use of resistant varieties and good crop rotations will reduce pest and disease problems.

Lecture notes_Makuvaro.V_2011 Page 8 Other tillage terms/practices

Clean tillage: Cultivation of a field so as to cover all plant residues and to prevent the growth of all vegetation except the particular crop desired, e.g. conventional tillage.

Mulch tillage: Soil tillage that employs plant residues or other material to cover the ground surface.

Combined tillage: Reduces number of secondary tillage operations by combining secondary tillage and planting into one operation. Several secondary tillage implements may be hooked together and used in conjunction with a planter

Zero tillage (No-till) - An extreme form of minimum tillage . Primary tillage is done away with and secondary tillage is restricted to seedbed preparation in the row zone only. - It is recommended in high erosion prone areas and in multiple cropping systems/areas where there is inadequate time for any tillage operations - Weed control is a problem - Practice reduces loss of soil moisture through evaporation which would result from conventional tillage of stubble.

Tillage for weed control

1) Tillage before planting Most tillage operations prior to planting provide some measure of weed control especicially secondary tillage operations immediately before planting. Delayed seedbed preparation utilizes delayed secondary tillage to kill weeds on previously ploughed land. 2) Tillage after planting and before crop emergence Tillage of large seeded crops e.g. maize and soyabean can be done before emergence to i) weed control ii) break soil crust for better crop emergence.

Ten (10%) crop stand can be destroyed , but loss in stand is usually less severe than loss of stand resulting from soil crusting. Can use rotary hoe soon after crop emergence.

3) Cultivation after crop emergence. Although chemicals provide some weed control, cultivation of row crops often provides the most economical and surest method for controlling troublesome weeds. Cultivation should be shallow to minimize root injury otherwise it can lower yields compared to other methods of weed control if roots are severely pruned.

Lecture notes_Makuvaro.V_2011 Page 9 Agronomic considerations in adopting tillage practices.

When deciding to use a tillage practice we have to consider several factors. These considerations are:

a) Seed and fertiliser placement; Although surface crop residues prevent soil erosion, they present problems in seed and fertilizer placement. Heavy trash can interfere with proper seed placement, covering of seed with soil and seed –to-soilcontact. In no-plough systems, cooler soil temperatures under mulch and relative immobility of P, K and micro-nutrients in soils can reduce nutrient uptake efficiency of plants growing in low fertility soils.

b) Pest control; Weeds accumulate near soil surface in reduced tillage systems. Crop residues also interfere with weed control equipment. Need for chemical weed control at increased herbicide rates, but limiting the use of pre-plant, soil-incorporated herbicides. Surface residues may harbour pest organisms which can become major problems compared to clean tillage systems. c) Soil conservation. Crop residues save loss of top soil.

Field efficiency

With tillage the farmer is striving for more field operation capacity and efficiency. The weather can prevent tillage from being completed in time for optimum planting dates.

Field efficiency of any implement is the ratio of effective field capacity to theoretical field capacity

Field efficiency (FE) = Effective field capacity(EFC) * 100 Theoretical Field Capacity (TFC)

EFC is the actual amount of work done while TFC is the amount of work which would be done if no time was lost.

Example; W is the width of implement in feet and S is the speed at which implement is working in miles /hour

TFC = W *S (convert to acres/hour) 8,25

Where 8.25 is a constant.

Lecture notes_Makuvaro.V_2011 Page 10 Consider a plough, 20 ft(approx. 6m) wide and at 6 miles /hour (app. 10km/hr)

TFC = 20 * 6 = 14.5 acres/hr 8,25

Under actual working conditions we might expect 12 acres/hour, i.e. EFC

Therefore, FE = EFC * 100 = 12 * 100 = 82,76* TFC 14,5

Field Efficiency in practice considers:

a) general machine performance b) the use of time c) factors affecting machine capacity N.B Many machines/implements are used because of tradition or because farmer already has them but nowadays ECONOMIC CONSIDERATIONS are a must.

Machinery selection on the basis of capacity and performance:

Three factors control machine capacity and performance:

a) machine width or size b) operating speed c) time spent in operation

Compaction

a) Most soils compact more severely if worked b) If soil is tilled when moisture is too high and then permitted to dry, extremely hard clods are formed which are hard to break later. c) Tillage when soil moisture level reaches proper levels i) reduces the potential for compaction ii) make pulverization easier iii) weeds are easier to kill when soil is dry

Compaction can be caused by tools and tractor wheels during i) ploughing ii) cultivation iii) planting and spraying of row crops.

Compaction effects root development (overall plant development) – too hard to penetrate or soil may be too dense for normal root growth, i.e. no air, poor moisture penetration , etc.

Lecture notes_Makuvaro.V_2011 Page 11 Compaction may be reduced by:

1). Working dry soil

2). Controlling (reducing) traffic in fields

a) Using machinery with bigger wheels;

b) Reducing the number of trips over the field;

c) Pulling two or more implements if several operations are to be carried out;

d) Working the widest swath through the field;

e) Driving tractors at maximum recommended speed over the field;

f) Ploughing down stover.

Lecture notes_Makuvaro.V_2011 Page 12