Agriculture for Engineers 4 (3+1)

Lesson 22. Principal of Tillage

22.2 PURPOSE OF TILLAGE

The purpose of tillage is to prepare a seedbed, break weed, insect and disease cycles, burry plant residues, incorporate fertilizers and amendments, break surface crust and fracture plough pans or hard subsoil horizons.

 22.3 OBJECTIVES OF TILLAGE

There are several objectives of tillage of which the most important are suitable seedbed preparation, weed control and soil and water conservation. The other objectives are:

(i) Adequate seed-soil contact to permit water flow to seed and seedling roots. Intimate contact between the soil particles is necessary to facilitate movement of water for quick germination.

(ii) Tillage improves soil aeration, which helps in multiplication of microorganism. Organic manures decomposition is enhanced resulting in higher nutrient availability. Increased aeration also helps in degradation of herbicides and pesticides residues and harmful allopathic chemicals exuded by roots of previous crop or weeds.

(iii) Weed control is an important object of tillage. Two or three deep ploughing in during summer controls problematic weeds like nutsedge orchido (Cyperus rotundus. L.)

(iv) Proper tillage results in soil and moisture conservation through higher infiltration, reduced runoff and increase depth of soil for moisture storage. When compact soil is plough, it becomes fluffy (soft or loose or friable) and can hold more amount of water. Removal of hardpans increases the soil depth for water absorption, surface roughness and furrow dikes slowdown the velocity of runoff and provide more time for infiltration of water.

(v) Break the compacted layers to increases soil permeability and helps to increase of root penetration due to breaking hard pans and compacted layers.

(vi) Tillage helps to incorporate weeds, crop residues, green manures and other organic manures and fertilizers, soil amendment anti other agro chemicals applied for the control of weeds, insect and pest etc. to reduce volatilization losses.

(vii) Tillage exposes the lower soil to weather and replaces the surface soil under earth. Many of the insects remain dormant as pupae in the top layer of the soil. As a result of tillage insect-pest come out and destroy by beat and birds and predatory animals.

(viii) Tillage helps to check loss of water through percolation in low land paddy fields by making an impervious soil low layer (hard pan) and also makes the soil level and flat those are suitable for uniform movement of irrigation water.

(ix) The tillage prepares good seed bed which is necessary for early seed germination and initial good stand of the crop and improves the soil structures.

(x) The stubbles of previous crop, which harbors insect pests, arc removed following tillage resulting in reduced pest attack on the succeeding crop.

(xi) The improve soil structure can be produced by tilling the soil at proper time when the soil moisture is optimum. Tillage operation carried out at improper soil moisture damage soil structure and leads to develop hard pans.

(xii) Control of soil erosion on sloppy land, tillage across the slope of field will create furrow dikes, which slow do the velocity of runoff rain or irrigation water and consequently reduced soil erosion. Before rainy season the fields are left cloddy, to prevent erosion and increase the water storage in the soil. This is the good practice under dry farming situation,

 22.4 TILLAGE INFLUENCE ON PHYSICAL PROPERTIES OF SOIL

Tillage has considerable influence on soil physical properties like pore space, structure, bulk density, water content and colour. These effects of tillage lost for about a month. Tillage practices have therefore, greatest effect on seed germination, seedling emergence and stand establishment.

22.4.1 Pore Space

Soils are made up of particles of different sizes. Air filled spaces between these particles constitute pore space. When a field is ploughed, the soil particles are loosely stacked in a random manner and pore space is increased, When the soil is in good tilth, the, capillary and non-capillary pores would be roughly equal. This facilitates free movement of air and moisture in the soil and increases infiltration.

22.4.2 Soil Structure

Soil with crumbly and granular clods is considered as soils with good structure. When the soil is subjected to tillage at optimum moisture, crumb structure is developed so that loss of soil by erosion is greatly reduced. Rain Water is held in the large pores, between the aggregates and also in the Microspore pores of the aggregates. It is considered that soil aggregates of 1 to 5 mm in size are favourable for growth of plants. Smaller aggregates may clog the soil pores and larger ones may have large pore space between them and affect the development of rootlets of the young seedlings. Soil structure is destroyed when tillage is carried out at inappropriate soil moisture.

22.4.3 Bulk Density

When the soil is loosened, the soil volume increase without any effect on weight. Therefore, bulk density of tilled soil is less than the untilled soil.

22.4.4 Soil Colour

Organic matter is mainly responsible for the dark brown to dark grey colour of the soil. Tillage increases oxidation and decomposition resulting in fading of colour.

22.4.5 Soil Water

Tillage improves soil water in different ways. The amount of available water depends on soil porosity, soil depth and random roughness. All these characters are increased by tillage. Roughness is a measure of micro elevations and depression caused by furrows and ridges, clods and depression. Random roughness indicates elevation and depressions of the field without a pattern as it happens after ploughing. It influences the volume of surface-depression storage or temporary storage of rainfall. Tillage also increases rate of infiltration, water holding capacity and hydraulic conductivity.

22.4.6 Soil Temperature

Tillage creates soil temperature optimum for seed germination and seedling establishment. Tillage loosens the soil surface resulting in decrease of thermal conductivity and heat capacity.

 22.5 TYPES OF TILLAGE

Tillage operations are grouped into two types based on the time (with reference to crop) at which they are carried out. They are:

22.5.1 Preparatory cultivation

Tillage operations that are carried out to prepare seedbed before sowing of crop from the time of harvest of a crop to the sowing of the next crop are known as preparatory cultivation. Preparatory cultivation consist of three distinct operations viz. primary tillage, secondary tillage and layout of seedbed.

22.5.1.1 Primary tillage or ploughing

Ploughing is opening of the compacted soil with the help of different ploughs. Ploughing is done mainly to open the hard soil. In addition, ploughing should ensure inversion (whenever necessary) of soil, uprooting of weeds and stubbles and less cloddy soil surface.

Optimum time of ploughing:  The correct time for ploughing depends on soil moisture. When the soil is dry it is difficult to open the soil, more energy is used and large sized clods result. When the soil is ploughed under wet conditions, the soil sticks to plough, the soil below the plough sole becomes compacted and on drying becomes a hard pan, soil structure is destroyed and the clods on drying become very hard. The optimum range of soil moisture for effective ploughing is 25 to 50 per cent depletion of available moisture. Light soils can be ploughed in a wide range of soil moisture conditions while the range is narrow for heavy soils.

Depth of ploughing: Depth of ploughing mainly depends on the effective root zone depth of the crops. Generally crops with tap root system require greater depth of ploughing, while fibrous, shallow rooted crop require shallow ploughing.

Number of ploughings: The number of ploughings necessary to obtain a good tilth depends on soil type, weed problem and crop residues on the soil surface. In heavy soils, more number of ploughings are necessary, the range being 3 to 5 ploughings, Light soil requires 1 to 3 ploughings to obtain proper tilth or the soil. When weed growth and plant residues are higher, more number of' ploughings are necessary.

Selection of ploughs: Depending on the purpose, soil condition and nature of weed problem, different ploughs are used.

 Table 20.1 Suitable ploughs for different situations

Plough	Situation or purpose
Mouldboard plough (M.B.Plough) (Tractor drawn)	Deep ploughing and inversion
Mouldboard plough (Animal drawn)	Incorporation of manures, fertilizer and plant residue
Disc plough	Cutting of creeping or spreading grass and inversion
Country plough	Multipurpose

 

Types of primary tillage: Depending on the purpose or necessity, different types of tillage are carried out. They are deep ploughing, subsoiling and year round tillage.

Deep tillage or deep ploughing : In western countries, deep ploughing is 50 cm depth for rainfed conditions and 70 cm depth for irrigated conditions. Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad classified ploughing according to depth as under:

Table 20.2: Different types of ploughing categories

Depth	Categories
5-6 cm	Shallow ploughing
15-20 cm	Medium deep ploughing
25-30 cm	Deep ploughing

 

Deep ploughing turns out large sized clods that are baked by the hot sun when it is done in summer. These clods crumble due to alternate heating and cooling and due to occasional summer showers. This process of gradual disintegration of clods improves soil structure. The rhizomes and tubers of perennial weeds (World's problematic weeds viz, Cynondon dactylon and Cyperus rotundus) die due to exposure to hot sun. Summer deep ploughing kills pests due to exposure of pupae to hot sun and attack of birds and predators.

Deep tillage also improves soil moisture content; however the advantage of deep tillage in dry farming condition depends on rainfall pattern and crop. There is no yield advantage if rainfall below normal. The residual effect of deep tillage is marginal. Therefore, it is advisable to go for deep tillage ploughing only for long duration, deep rooted crops.

Sub soiling: Hard pans may be present in the soil, which restrict root growth of crops. These may be slit pans, iron or aluminum pans, clay pans or man made pans are tillage pans induced by repeated tillage at the same depths. These are present in most of the Indian soils.

Root growth of crops is confined to top few cm of soil where deep penetration of roots is inhibited by hard pans. For example, cotton roots grow to a depth of 2 m in deep alluvial soil without any pans when hard pans. They grow only up to hard pan, say 15-20 cm. Similarly vertical root growth of sugarcane is restricted due to hard pans and it is not compensated by horizontal spread. Sub soiling is breaking the hard pan without inversion and with less disturbance of top soil.

Year round tillage: Tillage operations carried out throughout the year are known as year round tillage. In dry farming regions, field preparation is initiated with the help of summer showers. Repeated tillage operations are carried out until sowing of the crop. Even after harvest of the crop, the field is repeatedly or harrowed to avoid weed growth in the off-season.

22.5.1.2 Secondary tillage

Lighter or finer operations performed on the soil after primary tillage is known as secondary tillage. After ploughing, the field is left with large clods with some weeds and stubbles partially uprooted. Harrowing is done to a shallow depth to crush the clods and to uproot remaining weeds and stubbles. Disc harrows, cultivators, blade harrow etc., are used for this purpose. Planking is done to crush the hard clods to smooth the soil surface and to compact the soil lightly. Thus, the field is made ready for sowing after ploughing by harrowing and planking. Generally sowing operations are also included in secondary tillage.

Layout of seedbed and sowing: After the seedbed preparation, the field is laid out properly for irrigation and sowing or planting seeding. These operations are crop specific. For most of the crops like wheat, soybean, pear millet, groundnut, castor etc., flat leveled seedbed is prepared. For some crops like maize, vegetables etc., the field has to be laid out into ridges and furrows. Sugarcane is planted in the furrows or trenches. Crops like tobacco, tomato, chilly are planted equal inter and intera-row spacing so as to facilitate two way inter-cultivation. Setline planting is adopted in Gujarat for sowing cotton and groundnut. Every year, seed rows are in the same place, since the seed lines are set permanently at wider spacing. The inter-row space is not cultivated.

After field preparation, sowing is done with seed drills. These seeds are covered by running blade harrow to a shallow depth followed by planking so as to level and impart necessary compaction. Sowing is also done by dropping seeds behind the country plough.

22.5.2 After Tillage or After Cultivation

The tillage operations that are carried out in the standing crop are called after tillage. It includes drilling or side dressing of fertilizers, earthing up inter-cultivation. Earthing up is an operation carried out with country plough or ridge plough so as to form ridge at the base of the crop. It is done either to provide extra support against lodging as in sugarcane or to provide more soil volume for better growth of tubers as in potato or to facilitate irrigation as in the vegetables. Inter-cultivation is working blade harrows, rotary hoes etc., in between the crop measure by closing deep cracks in black soils.

 22.6 MODERN CONCEPT OF TILLAGE

In conventional tillage, the soil is opened with mouldboard plough for primary tillage. Subsequently, a fine seedbed is prepared by secondary tillage. In this process, energy is often wasted and sometimes, soil structure is destroyed. Recently, considerable change has taken place in tillage practices and several new concepts have been introduced, namely, minimum tillage, zero tillage, stubble mulch farming etc.

22.6.1 Minimum Tillage 

The concept of minimum tillage is started in USA. Minimum tillage is aimed at reducing tillage to the minimum necessary for ensuring good seedbed, rapid germination, a satisfactory stand and favourable growing conditions.

Minimum tillage has certain advantages: Improved soil condition due to decomposition of plant residues in situ; higher infiltration caused by the vegetation present in the soil and channels formed by the decomposition of dead roots; less resistance to root growth sue to improved structure; less soil compaction by the reduced movement of heavy tillage vehicles and less soil erosion compared to conventional tillage. However, these advantages are evident on coarse and medium textured soils and appear after two to three years of practicing minimum tillage.

There are certain disadvantages of minimum tillage. Seed germination is lower minimum tillage. In minimum tillage, more nitrogen has to be added as rate of decomposition of organic matter is slow. Nodulation is affected in some leguminous crops like peas. Sowing operations are difficult with ordinary equipment. Further, continuous use of herbicides causes pollution problems and dominance of perennial problematic weeds.

Minimum tillage can be practiced by different methods as given below:

Row zone tillage : After primary tillage with mouldboard plough, secondary tillage operations like discing and harrowing are reduced. The secondary tillage is done in the row zone only.

Plough-plant tillage :  After the soil is ploughed, a special planter is used and in one run over the field, the row zone is pulverized and seeds are sown.

Wheel track planting : Ploughing is done as usual. Tractor is used for sowing and the wheels of the tractor pulverize the row zone.

22.6.2 Zero Tillage

Zero tillage is an extreme form of minimum tillage. Primary tillage is completely avoided and secondary tillage is restricted to seedbed preparation on the row zone only. It is also known as no-till and is resorted to where soils are subjected to wind and water erosion, timing of tillage operation is too difficult and requirements of energy and labour for tillage is too high. Zero tilled soils are homogenous in structure with more number of earthworms. The organic matter content increases due to less mineralization. Surface runoff is reduced due to the presence of mulch. The favourable effects of zero tillage on soil physical properties are apparent after two years of its practice.

Till planting is one method of practicing zero tillage. The machinery accomplishes four tasks in one operation: clean a narrow strip over the crop row, open the soil for seed insertion, place the seed and cover the seed properly. A wide sweep and trash bars clear a strip over the previous crop row and planter-shoe open a narrow strip into which seeds are planted and covered.

In zero tillage, herbicide functions are extended.  Before sowing, the vegetation present has to be destroyed for which broad spectrum, nonselective herbicides with relatively short residual effect (paraquat, glyphosate etc.,) are used. During subsequent stages, selective and persistent herbicides are needed. The herbicides applied should not cause injury to the succeeding crop.

The seedling establishment in zero tillage is 20 per cent less than in conventional methods. High dose of nitrogen has to be applied as mineralization of organic matter is slow in zero tillage. Large populations of perennial weeds appear in zero tilled plots. Higher number of volunteer plants and build up of pests are the other problems.

22.6.3 Stubble Mulch Tillage

The traditional methods of tillage developed in temperate moist climates based on mouldboard plough, often increase soil erosion when adopted indiscriminately in arid land cultivation. A new approach was developed for keeping soil protected at all times whether by growing a crop or by crop residues left on the surface during fallow periods. It is known as stubble mulch tillage or stubble mulch farming. It is a year round system of managing plant residue with implements that undercut residue, loosen the soil and kill weeds. Soil is tilled as often as necessary to control weeds during the interval between two crops. Good management of stubble mulch farming system begins with harvest of the crop. Sweeps or blades are generally used to cut the soil up to 12 to 15 cm depth in the first operation after harvest and the depth of cut reduced during subsequent operations. When unusually large amount of large amount of residues are present, a disc type implement is used for the first operation to incorporate some of the residues into the soil. This hastens decomposition, but still enough residues on the soil.

Stubble mulch tillage, however, presents practical problems. The residues left on the surface interfere with seedbed preparation and sowing operations. The traditional tillage and sowing equipment is not suitable under these conditions. Two methods are adopted for sowing crops in stubble mulch farming.

Similar to zero tillage, a wide sweep and trash-bars are used to clear a strip and a narrow planter-shoe opens a narrow furrow into which seeds are placed.

A narrow chisel of 5 to 10 cm width is worked through the soil at a depth of 15 to 30 cm leaving all plant residues on the surface. The chisel shatters tillage pans and surface crusts. Planting is done through residues with special planters.