1. TILLAGE
Tillage operation are carried out to prepare a fine seed bed for
sowing crops. Tillage is the physical manipulation of soil with
tools and implements to result in good tilth for better
germination and subsequent growth of crops. Tilth is the
physical condition of soil resulting from tillage.
CHARACTERISTIC OF GOOD TILTH:
Tilth indicates two physical properties of soil i.e. the size
distribution of aggregates and mellowness or friability of soil.
Friability is that property of soil by which when the clods
become dry they are more crumbly. A soil with good tilth is
quite porous and has free drainage up to water table. The
capillary and non-capillary pores should be in equal proportion
so that sufficient amount of water is retained in the soil as well
as free air.
2. OBJECTIVES OF TILLAGE
1. Suitable seed bed preparation
2. Weed control
3. Soil and water conservation
4. Improvement of soil structure
5. Soil permeability
6. Soil aeration
7. Root penetration
8. Destruction of pests.
Good seed bed is necessary for early seed germination and
initial good stand of the crop. The seed bed should be fine for
small seeded crops and moderate for bold seeded crops.
Intimate contact between the soil particles are necessary to
facilitate moment of water for quick germination.
3. Weed control is an important objective of tillage. Proper tillage
results in soil and moisture conservation through higher infiltration,
reduced run- off and increased depth of soil for moisture storage.
When the compact soil is ploughed it becomes fluffy and can hold
more amount of water. Removal of hard pans increases the soil depth
for water absorption. Surface roughness and furrow slow down the
velocity of run-off water and provide enough time for infiltration of
water.
Soil permeability is increased by breaking the compact layers.
Tillage improves soil aeration which helps in multiplication of micro-
organisms. Organic matter decomposition is hastened resulting in
higher nutrient availability. Increased aeration also helps in
degradation of herbicide, pesticide residues and harmful allelopathic
effect exuded by roots of previous crops or weeds.
4. Tillage has limited impact on root growth as its roots
occupy only a tenth of the soil mass. However, breaking of
hard pans and compact layers increase depth of penetration of
roots. The stubbles of previous crop are removed following
tillage resulting in reduced pest attack on the succeeding crop.
Crop residues and farmyard manure are incorporated into
the soil. Herbicides and fertilizers are also mixed and
incorporated into the soil to reduce the volatilization losses.
5. INFLUENCE OF TILLAGE ON SOIL PHYSICAL
PROPERTIES:
Tillage has considerable influence on soil physical properties
like pore space, structure, bulk density, water content and
colour. These effects of tillage last for about a month. Tillage
practices have therefore greatest effect on seed germination,
seedling emergence and stand establishment.
TYPES OF TILLAGE
a. Primary tillage
b. Secondary tillage
Tillage operations are carried out from the time of
harvest of a crop to the sowing of the next crop and is known as
preparatory cultivation. It consists of three distinct operations
like primary tillage, secondary tillage and layout of seed bed.
6. a. Primary tillage or Ploughing
It is the opening of compacted soil with the help of
different ploughs. Ploughing ensures inversion of soil,
uprooting of weeds and stubbles. The optimum time of
ploughing depends upon soil moisture. The depth of ploughing
mainly depends on the effective root- zone depth of the crops.
Crops with tap root system require greater depth of ploughing
than the fibrous roots. The number of ploughings necessary to
obtain a good tilth depends upon soil type, weed problem and
crop residues in the soil. Depending on the purpose, soil
condition and nature of weed problem different ploughs are
used, hence selection of plough is important. Mould board
plough is used for deep ploughing and inversion. Disc plough
is used for cutting of creeping or spreading grass and
inversion.
7. TYPES OF PRIMARY TILLAGE
Depending upon the purpose or necessity, different type of tillage are
carried out. They are deep ploughing, sub-soiling and year round
tillage.
Deep tillage: One cm of surface soil over one ha of land weight about
of 150 tonnes. Therefore, to plough deeper, enormous amount of
energy is required. CRIDA (Central Research Institute for Dryland
Agriculture) Hyderabad has classified of 5-6 cm depth as shallow, 15-
20 cm depth as medium and 23-30 cm depth as deep ploughing.
Deep ploughing when done in summer turns out large sized clods,
baked by the hot sun. These clods crumble due its alternate heating
and cooling due to occasional summer showers. This process of
gradual disintegration of clods improves soil structure. The rhizomes
and tubers of problematic weeds like cynodon dactylon, Cyprus
rotundus die due to exposure to the sun. It also kills insect and pests.
8. A deep tillage of 25- 30 cm depth is necessary for deep rooted
crop like pigeon pea, moderate tillage of 15- 20 cm is required for maize.
Deep tillage also improves soil moisture content. However, the
advantage of deep tillage in dry farming condition depends on rainfall
pattern and crop. It is advisable to go for deep ploughing only for long
duration and deep rooted crops.
SUB-SOILING
Hard pans may be present in the soil which restricts root growth
of crops. There may be silt pans, iron or aluminum pans, clay pans or
man- made pans. Man-made pans are tillage pans induced by repeated
tillage at the same depth. These are present in most of the Indian soils.
Root growth of crops is confined to top few centimeters of soil where
deep penetration of roots is inhibited by hard pans. Sub- soiling is
breaking the hard pans without inversion and with less disturbance of
top soil. Chisel ploughs are used for breaking hard pans even at 60-70
cm depth. The effect of sub- soiling does not last` very long.
9. Year round tillage:
Tillage operations carried out throughout the years 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
the harvest of the crop the field is repeatedly ploughed or
harrowed to avoid weed growth in the off season.
10. b. Secondary tillage:
Lighter or finer operations, performed on the soil after primary
tillage are known as secondary tillage. After ploughing, the fields
are 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 the remaining weeds and stubbles. Disc harrows,
blade harrows and cultivators are used for this purpose. Planking
is done to crush the hard clods to smoothen the soil surface and to
compact the soil lightly. Thus, the soil is ready for sowing after
ploughing by harrowing and planking. Generally, sowing
operations are also included in secondary tillage.
Secondary tillage also includes layout of seed bed and sowing. The
field has to be laid out for irrigation and planting. These
operations are crop specific. Tillage operation carried out in the
standing crop is called after tillage. It includes drilling or side
dressing of fertilizers, earthing up and inter cultivation.
11. MINIMUM TILLAGE:
Minimum tillage is aimed at reducing tillage to the minimum necessary
for ensuring a good seed bed, rapid germination, satisfactory stand and
favourable growing conditions. Tillage can be reduced in two ways.
1. By omitting operations which do not give any benefit when compared
to the cost.
2. By combining agricultural operations like seeding and fertilizer
application.
THE ADVANTAGES OF MINIMUM TILLAGE ARE--
1. Improved soil conditions due to decomposition of plant residues in
place.
2. Higher infiltration caused by the vegetation present on the soil and
channels formed by the decomposition of dead roots.
3. Less resistance to growth due to improved structure.
4. 4 less soil compaction by the reduced movement of heavy tillage
vehicles and less soil erosion compared to conventional tillage.
12. However, these advantages are evident only on coarse and medium
textured soils and is evident only after 2-3 years of practicing minimum
tillage.
THE DISADVANTAGES OF MINIMUM TILLAGE:
1. Seed germination is lower.
2. More nitrogen has to be added as rate of decomposition of organic
matter is slow.
3. Nodulation is affected in some leguminous crops like peas and
cowpea.
4. Sowing operations are difficult with ordinary equipment
5. Continuous use of herbicides cause pollution and perennial weed
problems.
13. MODERN CONCEPT OF TILLAGE
In conventional tillage the soil is opened with a mould board plough for
primary tillage. The soil mass is broken into a loose system of clods of mixed
sizes. Subsequently a fine seed bed is prepared by secondary tillage in which
operations like crushing of clods, repacking, incorporation of plant residues,
fertilizers, smoothing of soil surface etc. is done.
This process involves wastage of energy and destruction of soil structure. To
cut down cost of tillage researches were done to know whether several tillage
operation are needed or not. The concept of minimum tillage was conceived in
USA as repeated use of machinery resulted is destroying soil structure, causing
soil pans and also soil erosion. The important aspect of tillage is weed control and
this can be achieved by using herbicides.
The practice of inverting the top soil in order to bury the crop residues is less
important object of tillage in modern field management. Crop residues can and in
many cases be left over as stubble mulch to protect against soil erosion and
evaporation loss. Researchers have shown that frequent tillage is often rarely
beneficial and in fact detrimental. All these reasons led to the development and
practice of minimum tillage, zero tillage and stubble mulch farming.
14. The practice of inverting the top soil in order to bury the crop
residues is less important object of tillage in modern field
management. Crop residues can and in many cases be left over
as stubble mulch to protect against soil erosion and
evaporation loss. Researchers have shown that frequent tillage
is often rarely beneficial and in fact detrimental. All these
reasons led to the development and practice of minimum
tillage, zero tillage and stubble mulch farming.
Cont…
15. ZERO TILLAGE
Zero tillage is an extreme form of minimum tillage. In this primary
tillage is completely avoided and secondary tillage is restricted to seed bed
preparation in the row zone only. It is also referred to as no - till and is
resorted to where soils are subjected to wind and water erosion, timing of
tillage operation is too difficult and the requirements of energy and labour
for tillage is 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 presence of mulch.
The favourable effect of zero tillage is evident after two years of its
practices.
Till planting is one of the method of practicing zero tillage. The
machinery accomplishes four tasks in one operation.
1. Clean a narrow strip over the crop row
2. Open the soil for seed insertion and fertilizer application
3. Place the seed
4. Cover the seed properly
16. The seedling establishment in zero tillage is 20% less than in conventional
methods. Higher dose of nitrogen has to be applied as mineralization of
organic matters is slow. Large populations of perennial weeds appear. Build-
up of pest is also a problem.
STUBBLE MULCH TILLAGE
An approach to keep the soil protected at all times from erosion whether by
growing a crop or by crop residues left on the surface during fallow periods is
known as stubble mulching tillage or stubble mulch farming. It is a year
round system of managing plant residue with implements that induce residue,
loosen the soil and kill weeds. Soil is tilled as often as necessary to control
weeds during interval between two crops. Good management of stubble
mulch farming system begins with the harvest of the crop.
Stubble mulch tillage, however, presents practical problems. The residue
left on the surface interferes with seed bed preparation and sowing
operations. The traditional tillage and sowing equipment is not suitable under
these conditions.
