Tillage and Tilth

B.Sc Agriculture 1st semester notes(Agronomy, AGR-111) 

Based on ICAR 5th Dean

TILLAGE

The word tillage is derived from the anglo-saxon (cultural group which inhabited England from the 5 "century) words ‘tilian’ or ‘teolian’ meanng ‘to plough and prepare soil for seed to sow, to cultivate and to raise crops’. Jethrotull, who is considered as father of tillage suggested that thorough ploughing is necessary so as to make the soil into fine particles.

Tillage refers to the mechanical manipulation of soil to provide favourable condition for
crop production. It breaks the compact surface of earth to certain depth and loosens the soil
mass so that roots of the crop penetrate and spread into the soil. This includes ploughing,
harrowing, mechanical destruction of weeds and breaking of soil crust.

Tilth: Tilth is the physical condition of soil obtained out of tillage (or) it is the result of tillage. The tilth may be a coarse tilth, fine tilth or moderate tilth.

Objectives of Tillage:

Main objectives of tillage are to ensure

 - adequate soil aeration for proper gaseous exchange in the root zone,

 - adequate seed soil contact to permit water flow to seed and seedling root,

 - anon-crusted soil to permit seedling emergence,

 - alow density soil that permits root elongation and proliferation,

 - a weed free environment,

 - proper mixing of applied fertilizers and manures in the soil,

 - apest and pathogen free environment,

 - removing the hard pan, if any, to increase the soil depth for water absorption,

 - toimprove soil structure

Characteristics of Good Tilth

(i) A-soil in good tilth should be mellow, friable, crumby and adequately aerated.

(ii) A soil in good tilth is porous. Capillary and non-capillary pores are equal. This facilitates
free movement of air and water.

(iii) Higher percent of larger aggregates (more than 5 mm in diameter) are necessary for
irrigated agriculture, while higher percentage of smaller aggregates (1 to 2 mm diameter) is desirable for dry land agriculture.

(iv) Tilth can be coarse or fine. For sandy soils fine kind of tilth is required and for heavy black soils rough cloddy conditions or coarse tilth is enough.

Effects of Tillage on Soil Physical Properties:

1) Soil Structure: Arrangements of soil particles with crumby and granular nature is
considered good. Best size of soil aggregate for good growth of crop is (1-5 mm) smaller
aggregates may clog soil pores and larger ones may have large pore space. Tillage
improves soil structure when done at optimum soil moisture level. Tilling a soil when it
is too wet spoils the structure. Ploughing a dry soil is difficult and will not help in
improving structure.

2) Pore space: When a field is ploughed the soil particles are loosely arranged 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 soil.

3) Bulk Density (B.D.): When the soil is loosened, the soil volume increase without any
effect on weight. BD of Clay soils is low (1.05 metric cube and that of sandy soils is high (1.25 —1.30 metric cube) and Bulk density of tilled soil is less than that of untilled soil. Particle density is always more than BD.
 

4) Particle density (PD): Particle density is not altered by tillage.
 

5) Soil Texture: Soil texture is not altered by tillage

6) Soil Colour: Organic matter is mainly responsible for the dark brown to dark grey colour of the soil. Tillage increases oxidation and decomposition of organic matter resulting in fading of colour.

TYPES OF TILLAGE

 
 
A) On Season Tillage: All the tillage operations that are aimed at cultivation (growing) of a
particular crop and start from seed bed preparation and end with the harvesting of crop are known as on season tillage operations. It includes preparatory tillage and inter-tillage.

1) Preparatory Tillage: Preparatory tillage simply means the tillage operations carried
out for the field preparation for sowing/planting of the crop. It includes all the tillage operations which are carried out till the sowing of the crop. It is again of two types
primary and secondary tillage.

i. Primary tillage: The operation performed to open up any cultivable land with a view to prepare a seedbed for growing crops, is termed as primary tillage. It is normally
designed to reduce soil strength, cover plant materials and rearrange aggregates. The various equipments used for primary tillage are mould board plough, disc plough, heavy- duty disc harrow, chisel plough, etc. In primary tillage, generally the soils are ploughed twice, each time in diagonally opposite directions. Primary tillage loosens the soil and mixes in fertilizer and/or plant material, resulting in soil with a rough texture. The objective is to cut, lift, twist and turn the soil while incorporating
organic and animal wastes into ploughed layer.

ii. Secondary tillage: Lighter and finer operations performed on the soil after primary tillage for obtaining good seedbed for sowing, are termed as secondary tillage. These operations are generally performed on surface soil. Very little inversion and shifting of soil take place and consequently less power requirement per unit area. Secondary tillage produces finer soil and sometimes shapes the rows. It can be done by using various equipment like plough, disk plough, harrow, dibble, hoe, shovel, rotary tiller, sub-soiler, ridge or bed forming tillers, roller etc. Blade harrows are also worked once or twice to kill the weeds, break up clods and to obtain relatively smooth and levelled surface for subsequent sowing. 

2) Inter-tillage: Alter the crop is sown, the soil may need further tillage to control weeds, break up crusting or create soil mulch. All such tillage operations which are carried out after sowing till harvesting of the crop are known as inter-tillage or intercultural operations.

B) Off-Season Tillage
       Tillage operations during un-cropped season for special purposes other than that for immediately raising the crop in the season are known as off-season tillage.
Depending upon the purpose of tillage, the off-season tillage may be of three types, viz.
summer tillage, sub-soiling and clean tillage.

1) Summer tillage: Taking advantage of summer rains, the field is ploughed deep (deep
ploughing) to eradicate perennial weeds and to destroy soil borne pathogens, pests and parasites, and to check erosion. This tillage is known as summer tillage.

2) Subsoiling: To break the hard plough pans, reduce soil compaction and to improve
drainage, the field is ploughed very deep or sometimes subsoil plough is also used.
This tillage is usually known as subsoiling.

3) Clean Tillage: Vertisol (Black clay soils) are often left un-cropped during a part of the
rainy season due to unfavourable weather or soil conditions or both. The soil is tilled
during this period to control weeds and to create soil much for conserving moisture for subsequent crops grown during post rainy season. This tillage is called fallow, mulch tillage or clean tillage.
 

Year-round Tillage
      In dryland agriculture, tillage initiated with the onset of summer showers is continued
periodically until sowing during crop period and even after the crop harvest to avoid weed
growth, hard pans and soil water erosion besides conserving soil moisture; such tillage is usually referred to as year-round tillage.
 

Puddling
   Manipulation of soil under water with tools and implements to break down the soil
aggregates is called puddling and the soil is called puddled soil. It disrupts the continuity of the pore spaces, reduces pore space and increases bulk density. Dispersed clay breaks transmission of pores and forms a thin layer over the surface. As a consequence of all these changes, deep percolation is greatly reduced. The three main objectives of puddling are ideal soil condition for planting seedlings, reducing deep percolation losses of water and weed control. Standing water in the field due to puddled soil has several advantages in rice production. Unlike other tillage operations, puddling aims at destroying soil structure. The individual soil particles viz., sand, silt and clay are separated during puddling operation. The soil layer with high moisture below the plough sole is compacted due to the weight of the plough. The soil particles separated during
puddling settle later. The sand particles reach the bottom, over which silt particles settle and
finally clay particles fill the pores thus making impervious layer over the compacted soil.

MODERN CONCEPT OF TILLAGE

In conventional tillage, the soil is opened with mould board 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 or conservation tillage etc.
 

Conservation Tillage
     The conservation tillage refers to any tillage or planting system in which at least 30% of the crop residue is retained and spread all over the field in such a way that at least 30% of the soil surface is covered by the plant residues after planting. Conservation tillage leaves plant
residue at the soil surface, which reduces run-off, increases the surface soil organic matter
(SOM), promote greater aggregate stability and restricts soil erosion. Other beneficial aspects
of conservation tillage are preservation of soil moisture and increase of soil biodiversity;
reducing the intensity of soil tillage decreases energy consumption and the emission of carbon dioxide, while increasing carbon sequestration. The most common forms of conservation tillage are no-till system or zero tillage and reduced or minimum tillage.
 

Minimum Tillage
    The concept of minimum tillage 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 due 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 after two to three years of practicing minimum tillage.

There are certain disadvantages of minimum tillage. Seed germination is lower in 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.

Zero Tillage
    Zero tillage is an extreme form of minimum tillage. In zero tillage, primary tillage is
completely avoided and secondary tillage is restricted to seedbed preparation in 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. Different types of zero-till seed drills are available for sowing in no-till fields. This machinery accomplishes four tasks in one operation: cleans a narrow strip over the crop row, opens the soil for seed insertion, places the seed and covers the seed properly. 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 buildup of pests are the other problems.

Stubble Mulch Tillage
    The traditional methods of tillage developed in temperate moist climates based on
mould board plough, often increase soil erosion when adopted indiscriminately in arid land cultivation. A new approach was developed for keeping soil protected at all times either by growing a crop or by leaving crop residues on the surface during fallow periods. It is known as stubble mulch tillage or stubble mulch farming. 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.