Tillage and Types of tillage

Definition

Tillage refers to the mechanical manipulations of the soil that are used to provide necessary soil conditions favourable for the growth of crops. 

Tillage includes all operations and practices that are used for the purpose of modifying soil physical characters. Tillage is the most difficult and time consuming operation in crop production. About 30 per cent of the total cost of cultivation goes for tillage operations.

Tillage is as old as agriculture. Primitive man used to disturb soil for placing seeds. Jethrotull, who is considered as Father of Tillage proposed a theory that plant absorb minute soil particles and suggested thorough ploughing and other operations to make the soil into finer particles. Though this theory is not correct, tillage operations are carried out to prepare a fine seed bed for sowing of crops.

Objectives of tillage

• To prepare seed bed to a satisfactory level which promotes good germination and establishment of seedlings.

To control weeds and improve close plant soil interaction in the rooting zone.

To manage the plant residues for incorporating into the soil or to retain on the top layer to reduce erosion.

To improve soil physical condition for rain water harvesting and minimizing soil erosion.

To establish specific surface configurations for sowing, irrigation, drainage etc.

To incorporate and mix the applied fertilizers into the soil.

To expose weeds and soil borne pathogens to heat and killing them.

Tilth : Tilth is the term used to express the physical condition of soil resulting from tillage. The physical condition is related to the soil structural changes which promote good seed germination and crop establishment. Tillage operations are aimed at producing and maintaining good tilth. A soil with good tilth will be mellow, friable and adequately aerated. Such soils have high retentive capacity of rain water and good aeration with adequate infiltration. The soil tilth is not static and varies with time.

Influence of tillage on soil physical properties

Tillage has considerable influence on soil physical properties like pore space, structure, bulk density, soil water, soil colour and temperature. Hence, tillage influence germination, seedling emergence and crop stand establishment.

i) Pore space : Soil are made up of particles of different sizes. Air and water filled spaces between these particles constitute pore space. When a field is ploughed, the soil particles are loosely staked in a random manner and pore space increases. 

 Under good tilth condition, capillary and non-capillary pores are in equal proportion and facilitates free moment of air and water and increases infiltration.

ii) Soil structure : Soils with crumbly or granular structure are good for crop production. When soil is subjected to tillage at optimum moisture leads to crumb like structure which reduce the erosion greatly. Soil structure will destroy when tillage is carried at inappropriate soil moisture. 

iii) Bulk density : When the soil is loosened with tillage, the soil volume increases without any effect on weight. Therefore, the BD of tilled soil is less than untilled soil.

iv) Soil colour : Tillage increases the oxidation of iron and manganese, decomposition of organic matter resulting in fading of colour.

v) Soil water : The available soil water depends on soil porosity, soil depth and random roughness. Roughness is the measure of micro-elevations and depressions caused bu ridges and furrows. All these characters are influenced by tillage. It also influences infiltration and water holding capacity.

vi) Soil temperature : Tillage loosens the soil surface resulting in decrease of thermal conductivity and increase heat exchange.

Types of Tillage 

Tillage based on the timing of operation, is broadly divided into 

a) Preparatory cultivation : Operations carried before sowing

b) After cultivation / inter tillage : Operations carried after sowing

Preparatory cultivation :Tillage operations that are carried from the time of harvest of a crop to the sowing of the next crop or the operations carried in any cultivable land to prepare seed bed for sowing / planting of crops are known as preparatory cultivation. 

Preparatory cultivation consists of 

a) Primary tillage

b) Secondary tillage

c) Layout of seed bed

A) Primary tillage / Ploughing : Ploughing is the opening of the compacted soil with the help of different ploughs. Ploughing is done to cut open and invert the soil, uproot the weeds and stubbles.

 The optimum time for ploughing is decided on soil moisture status. 

If the soil is ploughed when dry, 

(a) there will be formation of big clods 

(b) demands enormous energy and 

(c) it is difficult to operate.

Too wet condition also unfavourable for ploughing as 

(a) the soil sticks to plough, 

(b) there will be formation of hard pan in sub soil layer 

(c) the clods formed will be very hard after drying.

 Optimum range of soil moisture for effective ploughing is 25-50% depletion of available soil moisture. Light soils can be ploughed in a wide range of soil moisture condition while, heavy soil have narrow range.

 Depth of ploughing mainly depends on effective root zone. Tap rooted crops have deep roots and require deep ploughing while shallow fibrous roots demand shallow to medium ploughing.

 The number of ploughings necessary to obtain good tilth depends on soil type, weed problem and crop residue on the soil. In heavy soils, 3-5 ploughings are necessary while, 1-3 ploughings are sufficient in light soils. When weeds and plant residues are higher, repeated (more) ploughings are necessary.

 Selection of ploughs depends on the purpose, soil condition and nature of weed problems.

Types of primary tillage

i) Deep ploughing

One cm of surface soil over one hectare of land weighs about 150 MT. Therefore,  deep ploughing demands enormous energy. Cenral Research Institute for Dryland Agriculture (CRIDA), Hyderabad classified ploughing as 

Shallow ploughing   5 to 6 cm depth

Medium ploughing   15 to 20 cm depth

Deep ploughing   25 to 30 cm depth

Summer deep ploughing expose weeds and other soil borne pathogens to heat and turns out into large sized clods. The clods crumble due to alternate heating and cooling and due to occasional summer rains which will disintegrate clods gradually. Deep tillage improves soil moisture content due to enhanced wetting zone.

A deep tillage of 25  30 cm is necessary for deep rooted crops like pigeon pea (Cajanus cajana), while moderate tillage of 15-20 cm is required for maize (Zea mays), wheat (Triticum aestivum). 

ii) Sub soiling 

Sub soiling is the breaking of hard pans without inversion and with less disturbance to surface soil. Hard pans in the soils may be formed because of silt load, Fe & Al blocking, clay particles or man made will restrict the root growth of crops. Men made pans are induced because of repeated tillage at same depth or ploughing under excess soil moisture condition.

iii) Year round tillage 

Tillage operations carried throughout the year are known as year round tillage. In dryland areas, field preparation is initiated with summer shower and repeated till sowing and even after harvest of crop, the field is repeatedly ploughed to avoid weeds and soil erosion.

B. SECONDARY TILLAGE

 Lighter or finer operations performed on the soil with harrows and cultivators after primary tillage are known as secondary tillage. They are carried to

a) Break clods and create smooth surface for seed germination and establishment

b) Uprooting of weeds and stubbles of previous crop

c) Mixing of applied manures and fertilizers in to the soil

d) Covering of seeds

Generally, sowing operations are included in secondary tillage.

C. LAYOUT OF SEED BED

 Certain crops like wheat (Triticum aestivum), Soybean (Glycine max), Castor (Ricinus communis) can be sown directly after secondary tillage, certain crops like Maize (Zea mays), Sugar cane (Saccharum Sp), vegetables need ridges and furrows, certain crops can be sown with seed drills while, seeds of certain crops needs covering with harrows / plank / roller for necessary germination.

 It is essential to prepare ideal seed bed suiting to the particular crop for proper germination and establishment. 

 An ideal seed bed should provide the essential conditions for good germination and favourable environment for emerging seedlings. Such conditions include aeration, moisture and allow easy penetration of roots. Its should also free for weeds and soil borne pathogens.

 A firm seed bed may be required to ensure close contact between seed and soil where as, a loose seed bed may be desirable for good aeration. Smaller the seed greater will be its sensitivity (eg. Tobacco  Nicotiana tobaccum) to seed bed condition which demand fine seed bed. Crops with bold seeds are not demanding fine seed bed (eg. Castor - Ricinus communis).

II. After cultivation

The tillage operations that are carried out in standing crop are called after tillage. It includes

a) Top dressing : Drilling / dressing of fertilizer in standing crop and covering

b) Earthing up : Carried with ridge plough or wooden plough to form ridges at the base of the crop rows to provide anchorage / support and irrigation.

c) Inter-cultivation : Working with harrows, hoes, cultivators in between crop rows to control weeds, aeration and to conserve moisture.

Implements used for different operations

Primary tillage : Wooden plough, sub soil plough, chisel plough, ridge plough, MB plough etc

Secondary tillage : Cultivators, harrows, plank, roller

 Layout of seed bed : Country plough, seed drill

Inter-cultivation : Wooden plough, blade harrows, ridger, spade, hand hoes etc.