Tillage and seeding practices in drylands
5.1 Tillage
The mechanical manipulation of soil with tools and implements for obtaining
conditions ideal for seed germination, seedling establishment and growth of crops is
known as tillage. Tillage may be described as the practice of modifying the state of
the soil in order to provide conditions favourable to crop growth, (Cuplin, 1986). The
objectives of tillage in drylands are
(1) Develop desired soil structure for a seed bed which allows rapid
infiltration and good retention of rainfall.
(2) Minimize soil erosion by following practices such as contour tillage,
tillage across the slope etc.
(3) Control weeds and remove unwanted crop plants.
(4) Manage crop residues
(5) Obtain specific land configurations for in- situ moisture conservation,
drainage, planting etc.
(6) Incorporate and mix manures, fertilizers, pesticides or soil amendments
into the soil.
(7) Accomplish segregation by moving soil from one layer to another,
removal of rocks or root harvesting.
Hence, attention must be paid to the depth of tillage, time of tillage, direction
of tillage and intensity of tillage.
5.1.1 Depth of tillage – It depends on soil type, crop and time of tillage
a) Deep tillage: of 25-30 cm is beneficial for deep heavy clay soils to improve
permeability and to close cracks formed while drying. In soils with hard pans, deep
tillage once in 2-3 years with chisel plough up to 35-45 cm depth at 60-120 cm
interval will increase effective depth for rooting and moisture storage. Deep tillage is
preferable for cotton, redgram and other deep rooted crops. It is not to be
recommended for shallow, gravelly, light textured soils.
b) Medium deep tillage: of 15-20 cm depth is generally sufficient for most soils and
crops. It is recommended for medium deep soils, shallow rooted crops, soils with
pan free horizon and for stubble incorporation.
c) Shallow tillage: up to 10 cm is followed in light textured soils, and shallow soils
and in soils highly susceptible to erosion. In soils prone for surface crusting, shallow
surface stirring or shallow harrowing is useful.
As depth of tillage increases, soil moisture storage from rainfall also increases
from about 7-8 % with shallow tillage to 9-10% with medium deep tillage and 11-
12% with deep tillage.
5.1.2 Time of tillage
Early completion of tillage is often helpful to enable sowing immediately after
rainfall and before the soil dries up. Summer tillage or off-season tillage done with
pre season rainfall causes more conservation of moisture and also enables early and
timely sowing. It is particularly useful for pre-monsoon sowing.
a) Year round tillage: Here the tillage operations are carried out throughout the
year in dry farming areas. The tillage operations are started immediately after the
receipt of summer showers and continued till sowing of the crops. After harvest of
the crop, by taking the advantage of the residual soil moisture the soil is ploughed
once or twice to retain the soil moisture in the lower layers. The advantages of year
round tillage are reduced weed growth, better tilth, adequate soil moisture, and
timely sowing.
5.1.3 Direction of tillage
For moisture conservation, ploughing across the slope or along the contour is
very effective. Plough furrows check the velocity of runoff, promote more infiltration
and improve soil moisture storage.
5.1.4 Intensity of tillage
It refers to the number of times tillage is done. Frequent ploughing in shallow
light textured soils will pulverize the soils into fine dust and increase the
susceptibility to erosion. In heavy soils, leaving the land in a rough and cloddy stage
prior to sowing is useful for more depression storage.
The concept of minimal tillage is also practiced in dry lands. Here tillage is
confined to seeding zone only and the inter-space is not tilled. It not only saves time,
energy and cost but also helps in moisture conservation. The practice of “set line
cultivation” adopted in some dry regions is an example of minimum tillage. Here the
seed row space is fixed and season after season, tillage is done only in this seeding
strip. The intervening strip is not tilled.
5.2 Modern concepts of Tillage
In dry lands, rainfall is received simultaneously over a large area. In order to
ensure timely sowing before soil dries up, the interval between land preparations
and sowing must be narrowed down. This calls for completion of tillage over a large
area in quick time. Dependence on bullock power and traditional wooden plough
may not help in this regard. Use of more efficient tillage implements and
mechanization of tillage operations are warranted.
Tillage in drylands also encompasses land shaping for in situ soil moisture
conservation. Implements that can carryout tillage and land shaping in one single
operation will help in saving time and cost. If land preparation, land shaping and
sowing can be done in one single operation it can save considerable time. This is
termed as once over tillage, plough planting or conservation tillage. Suitable tractor
drawn machinery like a broad bed former cum seeder, Basin lister cum seeder which
can complete the land shaping and sowing simultaneously can be used.
a) Minimum/optimum/reduced tillage: It is the tillage system aimed at reducing
the number of tillage operations to the minimum level i.e. necessary for better seed
bed preparation, rapid germination for maintenance of optimum plant stand. It not
only saves time, energy and cost but also helps in moisture conservation. The
objectives of these systems include (1) reducing energy input and labour
requirement for crop production (2) conserving soil moisture and reducing erosion
(3) providing optimum seedbed rather than homogenizing the entire soil surface,
and (4) keeping field compaction to minimum .The advantages are:
i) Reduction of soil compaction
ii) Reduction of soil erosion
iii) Increases infiltration of water
iv) Increased soil fertility due to decomposition of crop residues
v) Less cost of production because less number of tillage operations
Disadvantages are
i) Reduced seed germination
ii) Root nodulation is affected in certain crops
iii) More nitrogen is required to enhance mineralization process
iv) Require specially designed equipment
Forms of minimum tillage
i) Row zone tillage: After the primary tillage with plough, the harrowing is done
only in crop row zone
ii) Plough plant tillage: After primary tillage special planter is used for pulverising
the soil, sowing the seed and covering the seed
iii) Wheel track planting: After primary tillage the tractors are used by their
wheels, for pulverisation, sowing and covering of seed.
b) Conservation/mulch tillage: The objectives are to achieve soil and water
conservation and energy conservation through reduced tillage operations. Both
systems usually leave crop residue on the surface and each operation is planned to
maintain continuous soil coverage by residue or growing plants. The conservation
tillage practices may advance some of the goals of alternative farming such as
increasing organic matter in soil and reducing soil erosion, but some conservation
tillage practices may increase the need for pesticides. Conservation tillage changes
soil properties in ways that affect plant growth, and reduce water runoff from fields.
The mulched soil is cooler and soil surface under the residue is moist, as a result
many conservation tillage systems have been successful.
c) Zero tillage or no-till system It is an extreme form of minimum tillage where
primary tillage is completely avoided and secondary tillage is is resricted to crop
zone.In this method use of mechinery and hebicides with relatively low or no
residual effect on the crop to be established will play a major role.The mechinery
should have attachments for four operations namely, cleaning the narrow strip over
crop row,open the soil for seed insertion,placing the seed and covering the seed.
Advantages are
i) Increases the biological activity in the soil
ii) Organic matter content of the soil is increase due to decomposition of crop
residues
iii) reduction of suface runoff
Diadavantages are
i) poor seed germination
ii) High dose of N required for mineralisation
iii) Some perennial weeds and voluntary plants predominate
iv) More disease and pest incidence
5.3 Seeding practices
5.3.1 Establishment of optimum population
Poor or suboptimal population is a major reason for low yields in rainfed
crops. Establishment of an optimum population depends on
a) Seed treatment
b) Sowing at optimum soil moisture
c) Time of sowing
d) Depth of sowing
e) Method of sowing
f) Crop geometry
a) Seed treatment
Seed treatment is done for many purposes such as protection against pests
and diseases, inoculation of bio-fertilizers and inducing drought tolerance.
i) Seed hardening
It is done to induce drought tolerance in emerging seedlings. It is the process
of soaking seeds in chemical solution and drying to induce tolerance to drought. Soil
moisture stress immediately after sowing affects germination and establishment.
Seed hardening enables seedlings to survive this early moisture stress.
During seed hardening, seeds are subjected to partial hydration followed by
dehydration before sowing. Seeds are soaked for specified time in chemical solutions
of prescribed concentration. Soaked seeds are then dried in shade back to original
moisture content. During soaking, seeds imbibe water and germination process is
started but not completed. The hardened seeds are thus in a ready state for
germination. When sown in moist soils, seeds germinate immediately. Such early
germination helps in seedling emergence before surface soil dries up.
b) Sowing at optimum soil moisture
An effective rainfall of 20-25 mm which can wet a depth of 10-15 cm is needed
for sowing. Moisture stress at or immediately after sowing adversely affects
germination and establishment of seedlings. To ensure adequate soil moisture at
sowing, sowing has to be done as early as possible after soaking rainfall is received.
Sowing methods and implements play a crucial rile in this regard.
c) Time of sowing
Optimum time of sowing is indicated by adequate rainfall to wet seeding
depth and continuity of rainfall after sowing. The probable sowing time in a rainfed
area is the week which has a rainfall of not less than 20 mm with coefficient of
variability less than 100% and the probability of a wet week following wet week.
Timely sowing ensures optimal yield besides it may also help pest avoidance. In
Maharastra kharif sorghum cultivated in 30 lakh hectares and more than 70% under
hybrid prone to shoot fly. If sown at early July, the pest incidence can be avoided.
Pre-monsoon dry seeding
In some regions, where heavy clay soils dominate, sowing after rains is
impossible due to high stickiness of soil. Here sowing is done in dry soil, 2-3 weeks
before the onset of monsoon (pre-monsoon). Seeds will remain in soil and germinate
only on receipt of optimum rainfall.
The advantages of pre-monsoon dry seeding are
i) Early sowing
ii) Uniform germination and good establishment
iii) Utilization of first rainfall itself for germination instead of for land
preparation in post monsoon sowing
iv) Early maturity before closure of monsoon and avoidance of stress at
maturity.
The success of pre-monsoon dry seeding depends on the following
i) It is recommended for bold seeds like cotton and sorghum only and not for
all crops.
ii) Time of advance sowing must be fixed based on rainfall analysis for date of
onset of monsoon and continuity of rainfall after sowing.
iii) Seeds must be hardened to ensure quick germination and drought
tolerance
iv) Seeding depth must be such that seeds will germinate only after receipt of
rainfall to wet that depth is received. Surface sowing may lead to
germination with less rainfall and death due to subsequent soil drying.
v) Off season tillage is necessary to enable sowing in dry soil before monsoon
vi) Seed damage by soil insects has to be prevented
Examples of pre-monsoon sowing
1. For sorghum in black soils, pre-monsoon dry seeding is recommended 1-2
weeks before onset of monsoon with depth of sowing at 5 cm and seed hardening
with 2 per cent potassium di-hydrogen phosphate or potassium chloride.
2. For cotton in black soils, pre-monsoon dry seeding is recommended at 2-4
weeks before commencement of monsoon, with a sowing depth of 5 cm and seed
hardening with CCC (500 ppm) or potassium chloride or DAP at 2% level.
d) Optimum depth of sowing
When seeds are sown on surface or at very shallow depth, germination and
seedling growth are affected when surface soil moisture dries up. Sowing at a depth
where soil moisture availability is adequate, ensure early and uniform germination
and seedling establishment. Optimum depth of’ sowing varies with crop, especially
seed size and penetration power of plumule.
Sesamum 1-2 cm
Pearl millet and minor millets 2-3 cm
Pulses, sorghum, sunflower 3-5 cm
Cotton, maize 5 cm
Coriander 7 cm
e) Method of sowing: In dry lands, it is important to sow the seeds in moist soil
layer to ensure proper germination and seedling emergence. It is therefore
necessary to sow immediately after rainfall to avoid sowing in dry soil. It is also
important to sow the seeds at correct depth, neither on the surface nor too deep.
Establishment of an optimum population also depends on proper spacing between
plants. The density, geometry, and depth of sowing are dependent on method of
sowing. The sowing methods usually adopted in dry lands include broadcasting,
sowing behind plough and sowing by seed drills. Dibbling of seeds and planting of
seedlings are also adopted for some crops (Cotton, tobacco, chillies). Each method
has advantages as well as limitations. The choice of sowing method depends on seed
size, soil condition, time available, cropping system, crop geometry, sowing depth,
source of power, cost of sowing, etc.
Merits and limitations of sowing methods
Sowing
method
Merits Limitations
Broadcasting Quick coverage for small seeds
like – ragi, sesamum, minor
millets, medium sized seed like
sorghum, pulses can also be
broadcasted
Spacing and depth not ensured
High seed rate, intercrop sown
separately
Sowing behind
plough
For medium and bold seeds like
cotton, sorghum, maize,
groundnut, pulses, castor,
sunflower etc., Seeding requires
wooden plough only. Easy
operation, row spacing can be
ensured
Low coverage-spacing between
plants and depth of sowing not
ensured. Intercrop has to be
sown separately. Only monsoon
sowing is possible
Local seed drill
(gorru)
For medium and bold seeds
wooden implement, easy
maintenance, less cost, row
spacing is ensured, more
coverage than broadcasting and
sowing behind plough. Sowing
depth and row spacing is
uniform
Spacing between plants is not
uniform and depends on
experience of seed dropper.
Intercrop has to be sown
separately. Cannot be used for
pre-monsoon sowing.
Mechanised
seed drill
(Bullock
drawn/tractor
drawn)
Large coverage, row and plant
spacing ensured, uniform depth
of sowing. Base crop and
intercrop sown simultaneously.
Enables early sowing in large
area, saves cost and time. Pre
monsoon sowing is possible.
Initial cost is high, needs skill
for operation and maintenance.
f) Crop geometry: Crop geometry refers to the shape of land occupied by individual
plants as decided by spacing between rows and between plants. It depends on the
root spread and the canopy size of the crop and the cropping system.
Crop Crop geometry (cm)
Sole crop in solid row Intercropping
Sorghum 45 x 15 (60+30) x 15 paired row
Pearl millet 30 x 15
Ragi 30 x 10
Small millets 30 x 10
Black gram, green gram,
Soybean, horsegram
30 x 10
Redgram 60 x 30
Cowpea 30 x 15
Cotton 45 x 30 (60+30) x 15 in paired row
Cotton (Arboreum) 45 x 15
Groundnut 30 x 10
Sesamum 30 x 30
Sunflower 45 x 15
Sunflower hybrids 45 x 20
Sunflower varieties 30 x 15
Coriander 30 x 15
bengalgram 45 x 15
Maize 45 x 30
5.4 Setline cultivation: It is a form of minimum tillage practice predominant in
saurastra region of India where farmers are adopting the practice of continuously
cultivating, manuring and sowing wide spaced crops in the same line or row year
after year. In between the rows the soil is worked with blade or harrowed only for
weed control. The crops like sorghum, bajra, cotton, and groundnut are cultivated by
this method. The advantages are
i) Reduced cost of cultivation
ii) As the crops are raised in the same row, the rhizosphere is loose with good
aeration and permeability without development of hard pans in the sub
soil
5.5 Soil crusts: Soil crusts are hard layers that develop at the soil surface due to
action of rain drop or irrigation water and subsequent drying. Soil crusts often
hinder the emergence of seedlings and hence establishment of crop stand.
Crust formation: The impact of rain and or irrigation disrupts the soil aggregates,
reduces the mean size of the structural units and causes resorting and repacking by
water movement in splash flow and sedimentation process. On subsequent drying it
results in the development of continuous layer of closely packed soil particles. The
crust has high bulk density, lower macro porosity and higher mechanical strength
than below.
Effects of crust on soil and crop
i) Reduce infiltration rate
ii) Increase runoff and erosion
iii) Impede emerging seedling
iv) Injure the young seedling by movement of large blocks of crusts during
cultivation
Management practices to avoid crust problem
i) Shallow and dense sowing
ii) Use of thorny bush harrowing
iii) Mulching
iv) Light harrowing after rain
v) Planting on shallow furrows and on sides of ridges