Tillage and tilth
Tillage is as old as agriculture. Jetho Tull – Father of tillage
• After the harvest of the crop the soil becomes hard and compact because of:
1. Beating action of raindrops.
2. Irrigation and subsequent drying
3. Movement of implements and labourers.
• TILLAGE: The physical manipulation of soil with the implements and tools to result in good tilth for better germination and growth of crops.
• TILTH: It is the physical state of soil resulting from tillage.
CHARACTERISTICS OF GOOD TILTH
1. A soil should be friable, crumbly, mellow and adequately aerated.
2. A soil in good tilth is porous. Capillary and non-capillary pores are equal. This facilitates free movement of air and water.
i. Higher per cent of larger aggregates (more than 5 mm in diameter) are necessary for irrigated agriculture and a higher percentage of smaller aggregates (1 to 2 mm diameter) is advisable for dryland agriculture.
ii. Tilth can be coarse or fine. Fine kind of tilth is required for sandy soils and coarse tilth or rough cloddy conditions is enough for heavy black soils.
iii. With very fine tilth, the surface gets packed up when it dries after a rain. because of this, the soil is incapable to absorb rainwater and it results in water loses.
Objectives of Tillage:
1. To produce enough seedbed for good germination and good crop growth.
2. To make the soil loose and porous.
3. To aerate the soil
4. To control weeds
5. To remove the stubbles. (that may harbour pests)
6. To expose the soil-inhabiting pathogens and insect pests to the sun and kill them.
7. To break hardpans in the soil
8. For deep tillage and inversion of soil
9. For incorporating bulky organic manures
10. To warm up the soil11. To increase the infiltration rate.
Effects of tillage on soil physical properties:
1. Soil Structure: Compositions of soil particles with granular and crumbly nature is considered good. For good growth, the best size of soil aggregate is 1-5 mm. Smaller soil aggregates may clog soil pores and larger ones may have large pore space. When done at optimum soil moisture level, tillage improves the soil structure. Tilling a soil when it is too wet soils spoils the structure.
Ploughing a dry soil is difficult and not helps in improving the structure.
2. Soil texture: Relative proportion of different soil particles i.e. sand, clay and silt.
Coarse sand - 2.0 - 0.2mm.
Fine sand - 0.2 - 0.02mm.
Silt - 0.02 - 0.002mm.Clay - <0.002mm.
• Tillage has no effect on soil texture.
3. Pore space: After ploughing a field the soil particle gets loosely arranged and pore space is increased. When the soil is in good tilth, the capillary and non-capillary would be approximately equal. This facilitates free movement of moisture and air in the soil.
4. Bulk Density: (B.D) When the soil is loosened, the soil volume increase without any change on weight. BD of Clay soils is low (1.05 m3) that of sandy soils are high (1.25 – 1.30 m3) and BD of tilled soil is less than that of untilled soil. Particle density is always more than BD.
5. Particle density: Particle density is not changed by tillage.
6. Soil Colour: Organic matter is chiefly responsible for the dark brown to dark grey colour of the soil. Tillage increases the oxidation and decomposition of organic matters which results in fading of colour.
Types of tillage
Tillage operations are classified into two types based on the time at which they are carried out.
1. Preparatory cultivation – carried out before sowing the crop
2. After cultivation – practised after sowing the crop.
→ Primary tillage – Ploughing
→ Secondary tillage – harrowing
→ Seedbed preparation – country plough can be used.
Factors influencing preparatory tillage:
1. The previous crop is grown: Stubble of previous crop influence the tillage (Redgram, cotton stubbles are very deep-rooted and require deep tillage to remove them)
2. The crop to be grown: Some crops can be grown with rough tilth for very small-seeded like sorghum while for crops like tobacco, chillies etc fine tilth is required. Deep tillage is needed for crops like sugarcane and tuber crops.
3. Types of soil: Clay soil can be ploughed only within a narrow range of soil moisture and the power of drought required is high. Light textured soils can be ploughed under a broad range of soil moisture and need less drought.
4. Climate: Deep tillage is not permitted in shallow soils in low rainfall areas as it drives to rapid drying and loss of stored soil moisture. Deep cultivation is possible in high rainfall areas.
5. Type of farming: Intensive cropping needs intensive tillage.
Inter cultivation:
Tillage operations done in the crop rows with the objectives of
• Destroying the weeds
• To form a soil mulch
• To prevent cracking of soil
• To prevent crust formation
Intercultivation starts from the very early stage of crop i.e., two to three weeks from sowing. Short duration crops require two-three intercultivation while long duration crop requires 3-4 weeks.
After cultivation:
It covers intercultivation and various other special operations carried out in a standing crop.
They include.
1. Thinning and Gap-filling.
2. Rogueing in crops for seed purpose.
3. Earthing up in crops, banana, groundnut and sugarcane.
4. Cropping in banana
5. Desuckering oper in banana
6. Wrapping and propping in sugarcane
7. Nipping in castor
8. Topping, Trimming and desuk in tobacco basal leaves are removed
9. Defoliation in cotton
10. Hand pollination in sunflower.
Fertilizer application in irrigation also comes under after cultivation.
PUDDLING
When grown under submerged conditions Rice has higher growth and yield. Keeping standing water throughout the crop period is not possible without puddling. Puddling is ploughing the land with standing water so as to create an impervious layer below the surface to reduce deep percolation losses of water to provide a soft seedbed for planting rice.
Puddling method consists of ploughing repeatedly in standing water until the soil becomes soft and muddy. Initially, Water is filled at 5 to 10cm depending on the water status of the soil to bring it to the saturation and above and then first ploughing is carried out.
After 3 to 4 days, another 5 cm of water is filled and later after 2 to 3 days second ploughing is carried out. By this operation, most of the clods are crushed and the majority of the weeds are incorporated. In Next 3 to 4 days, another 5 cm of water is given and third ploughing is done in both the directions. The third ploughing can be done by a wetland plough or with a wetland puddler. Planking or levelling board is operated to level the field.
To know whether puddling is thoroughgoing or not, a handful of mud is taken into the hand and pressed. If it flows freely through fingers and if there are no hard lumps, puddling is supposed to be thorough. Unlike other tillage operations, puddling destroys the soil structure. The individual soil particles that are sand, silt and clay are separated during puddling operation.
Puddling is done with various implements depending on the availability of equipment and nature of the land. Soils with a bulk density less than 1.0 are regarded as problem soils as puddling with animal-drawn implements is difficult. The feet of the animals sink very deep while puddling. Under such a situation, puddling is achieved with spades by manual labour. Most of the farmers use wetland plough or mouldboard plough or worn out dryland plough. Wetland puddler consists of a set of blades attached to a beam at an angle. When it is worked, the soil is churned and puddling operation is finished quickly compared to the country plough. Generally, green manure is used at rice field which is incorporated by green manure trampler. Tractor drawn implements can be used for puddling by adding cage wheels to prevent sinking.
Types of tillage
Tillage operations may be grouped into-
1. On season tillage 2. Off-season tillage
1. On-season tillage
Tillage operations that are done for cultivating crops in the same season or at the start of the crop season are known as on-season tillage. They may be preparatory cultivation or after cultivation.
A. Preparatory tillage: This refers to tillage operations that are made to prepare the field for raising crops. It consists of deep opening and loosening of the soil to produce about a desirable tilth as well as to incorporate or uproot weeds and crop stubble when the soil is in a workable condition.
Types of preparatory tillage
a. Primary tillage
b. Secondary tillage
a. Primary tillage: The tillage work that is done after the harvest of the crop to bring the land under cultivation is known as primary tillage or ploughing. The opening of compact soil using different ploughs is called as Ploughing. Country plough, power tiller, tractor, mouldboard plough and bose plough drawn implements are used for primary tillage.
b. Secondary tillage: The tillage operations that are done on the soil after primary tillage to bring good soil tilth are known as secondary tillage. Secondary tillage consists of lighter or finer operation which is performed to clean the soil, break the clods and incorporate the fertilizers and manure. Harrowing and planking are done to serve the purposes. Planking is done to crush the hard masses, level the soil surface and to compact the soil lightly. Harrows, cultivators, spade & Guntakas are used for secondary tillage.
c. Layout of seedbed: This is also one of the segments of preparatory tillage. Levelling board, buck scrapers etc. are used for levelling and markers are used for the layout of the seedbed.
B. After cultivation (Inter tillage): The tillage that is done on the standing crop after sowing or planting and before the harvesting of crop plants is called After Tillage. Also called as inter cultivation or post-seeding. It includes Driling, weeding, earthing up, hoeing, a harrowing or side dressing of fertilizers etc. Spade, hoe, weeders etc. are used for inter cultivation.
2. Off-season tillage:
Special purpose tillage: Tillage operations meant to serve special purposes are said to be special-purpose tillage. They are,
a. Sub-soiling: To break the hardpan underneath the plough layer, special tillage operation (chiselling) is performed to reduce compaction. Sub-soiling is necessary once in four to five years where heavy machinery is used for field operations, harvesting, seeding and transporting. Advantages of sub-soiling are, the greater volume of soil may be obtained for the cultivation of crops, excess water may percolate down to recharge the permanent water table, reduce soil erosion and runoff & roots of crop plants can penetrate deeper to extract moisture from the water table.
b. Clean tillage: It refers to working of the soil of the whole field in such a form that no living plant is left undisturbed. It is practised to control weeds, soil-borne pathogen and pests.
c. Blind tillage: It refers to tillage operations done after seeding or planting the crop either at the pre-emergence stage of the crop plants or when they are in the early stages of growth so that crop plants (potato, sugarcane, etc.) do not get damaged, but, extra plants and broad-leaved weeds are removed.
d. Dry tillage: Dry tillage is practised for crops that are sown or planted in dryland condition having sufficient moisture for germination of seeds. This is suitable for crops like broadcasted rice, jute, potato, wheat, pulses oilseed crops and vegetable crops. Dry tillage is done in a soil having enough moisture (21-23%). Dry tillage makes the soil more porous and soft.
Also, the water holding capacity of the soil and aeration is increased. These states are more favourable for soil micro-organisms.
e. Wet tillage or puddling: It refers to tillage that is done in a land with standing water. Puddling consists of ploughing repeatedly in standing water till the soil becomes soft & muddy. Puddling forms an impervious layer below the surface to decrease deep percolation losses of water and to provide a soft seedbed for planting rice. It is done in both the directions for the incorporation of green manures and weeds.
Wet tillage destroys the soil structure and the soil particles that are departed during puddling settle later. Wet tillage is the only land preparation for transplanting semi-aquatic crop plant such as rice. Planking after wet tillage makes the soil compact & level.
Puddling hastens transplanting operation as well as the establishment of seedlings. Wetland ploughs or worn out dry land ploughs are commonly used for wet tillage.
Depth of ploughing
The desirable depth of ploughing is 12-20 cm for field crops. The ploughing depth varies with the effective root zone of the crop. The depth of ploughing is 10-20 cm for shallow-rooted crops & 15-30 cm for deep-rooted crops.
Number of ploughing
The number of ploughing depends on three factors- soil conditions, time available for cultivation between two crops and type of cropping systems. Zero tillage is followed in rice fallow pulses. A minimum number of ploughing is taken up at an optimum moisture level to bring useful tilth depending on the need of the crop.
Time of ploughing
The most optimum soil moisture content for tillage is 60% of field capacity.
Modern concepts in tillage:
Conventional tillage includes primary tillage to break open & turn the soil accompanied by secondary tillage to prepare the seedbed for sowing or planting. With the start of herbicides in intensive farming systems, the concept of tillage has been changed. Constant use of heavy ploughs create hardpan in the subsoil, results in poor infiltration. It is more sensitive to run-off and soil erosion. It is capital intensive and increases soil degradation. To evade these ill effects, modern concepts on tillage is in the practice.
1. Minimum tillage: It aims at decreasing tillage operations to the minimum necessary for ensuring a good seedbed. The advantages of minimum tillage above conventional tillage are,
• The cost and time for field preparation are reduced by decreasing the number of field operations.
• Soil compaction is relatively less.
• The structure of the soil not gets destroyed.
• Water loss by runoff and erosion is minimum.
• Water storage is increased in the plough layer.
Tillage can be reduced in 2 ways
a. By eliminating operations which do not give many benefits when compared to the cost.
b. By combining agricultural operations like seeding & fertilizer application. The minimum tillage systems can be grouped into the subsequent categories,
(i). Row zone tillage- Primary tillage is done with mouldboard plough in the whole area of the field; secondary tillage operations like harrowing & discing are reduced and done just in row zone.
(ii). Plough plant tillage- After the primary tillage, a special planter is used for sowing. In one run over the field, the row zone is pulverized & seeds are sown by the planter
(iii). Wheel track tillage- Primary ploughing is done normally. The tractor is used for sowing; the wheels of the tractor pulverize the row zone in which planting is done.
In all these systems, primary tillage is done normally. Though, secondary tillage is substituted by direct sowing in which sown seed is covered in the row zone with the tools used for sowing.
2. Zero tillage (No-tillage): In this, a new crop is planted in the residues of the former crop without any prior soil tillage or seedbed preparation. It is possible when the weeds are controlled by the usage of herbicides. Zero tillage is suitable for soils with a coarse-textured surface horizon, good internal drainage, the high biological activity of soil fauna, favourable initial soil structure and an adequate quantity of crop residue as mulch. These conditions are usually found in Alfisols, Oxisols and Ultisols in the humid and sub-humid tropics.
Till planting
Till planting is one method of exercising zero tillage. A wide sweep & trash bar clears a strip over the prior crop row and planter opens a thin strip into which seeds are planted and covered. Here, herbicide functions are extended. Before sowing, the vegetation present has to be destroyed for which broad-spectrum non-selective herbicides like paraquat, glyphosate and diquat are used.
• Zero tilled soils are homogenous in structure with the higher number of earthworms.
• Organic matter content increases because of less mineralization.
• Surface run-off is decreased because of the presence of mulch.
Disadvantages
• Higher amount of nitrogen has to be used for mineralization of organic matter in zero tillage.
• Perennial weeds can be a problem.
• High no. of volunteer plants and buildup of pests.
3. Stubble mulch tillage or stubble mulch farming
At all times, Soil is preserved either by growing a crop or by leaving the crop residuals on the surface during fallow periods. Sweeps or blades are generally used to cut the soil up to 12-15 cm depth in the first operation following harvest and depth of cut is reduced during subsequent operations. When a large number of residues are present, a disc type tool is used for the first operation to incorporate some of the residues into the soil. This accelerates the decomposition but still keeps enough residues on topsoil.
The 2 methods for sowing crops in stubble mulch tillage are,
a. Similar to zero tillage, a wide sweep & trash bars are utilised to clear a strip & a narrow planter shoe opens a thin furrow in which seeds are placed.
b. A narrow chisel of 5-10 cm breadth is worked through the soil at a depth of 15-30 cm moving all plant residues on the surface. The chisel smashes the tillage pans & surface crusts. Planting is done with special planters.
Disadvantages of stubble mulch farming
• The residues left on the surface intervene the seedbed preparation and sowing operations.
• The traditional tillage and sowing implements or tools are not suitable under these conditions.
4. Conservation tillage: The major purpose is to conserve soil and soil moisture. It is a system of tillage operations in which organic residues are not altered into the soil so that they remain on the surface as a protective cover against erosion and evaporation losses of soil moisture. The stubble forms the protective cover on the surface, it is normally referred to as stubble mulch tillage. The residues left on the soil surface interfere with seedbed preparation & sowing operations. It is a year-round system of managing plant deposit with implements that undercut residues, losses the soil and kills the weeds.
Advantages
• Energy conservation by lessened tillage operations.
• Improves soil physical properties.
• Reduce the water runoff of fields.
Main field preparation:
Tillage operations are usually classified into two, preparatory cultivation and after cultivation. The preparatory cultivation or tillage is operations that are done prior to the cultivation. This preparatory cultivation is commonly called as main field preparation. The main field preparation includes three processes,- primary tillage, secondary tillage and lay-out for sowing.
Some of the major primary tillage implements are country plough, disc plough, mouldboard plough, chisel plough etc. Cultivators and harrows are usually used for secondary tillage purpose.
Though, in practical means, the first two (primary and secondary tillages) may not have any key difference, because both operations are mainly carried out with the same implement. Country plough & cultivators are used for both purposes. After thorough ploughing, the field modified into a proper way for planting such as ridges and furrows or beds and channels or pit according to the necessity of the crops. Such field modifications are necessary for better crop production.
Crop density and geometry
Competition – types of competition, plant population, intraplant and interplant growth and yield, optimum plant density and planting pattern.
What is competition?
Competition is the conflict between individuals within a population for available resources when the level of resources is below the combined need of the members of the population.
How does competition occur in plants?
Crop plants are grown in closely spaced populations. In the early phase of growth, individual plants are small and widely spaced and do not hinder each other. As the plants grow at some point in time, they start to interfere with their neighbours and competition begins. No matter how close two plants are, they do not compete with each other so long as the growth resources are in excess of the needs of both. When the immediate supply of a single necessary factor falls below the combined demand of the two plants, the competition begins.
TYPES OF COMPETITION
1. Competition for nutrients: Nutrient uptake increase with increasing plant population. Higher population under low fertility conditions leads to the development of nutrient deficiency symptoms because of competition.
2. Competition for light: Competition for light occurs when one plant casts a shadow on another or within a plant when one leaf shades another leaf. In early plant growth stages, there will be little mutual shading and also at relatively low light intensities, the plant will be able to photosynthesize with full efficiency. As the plants develop, mutual shading increase and the light become a limiting factor.
3. Competition for water: The success of any plant in the community for water depends on the rate and competitiveness with which it can make use of the soil water supply.
4. Intra-specific and inter-specific competition: In populations of similar genotypes, in the absence of weeds, the competition is intra-specific (within species), where different species of crops are grown, in mixtures and wherever weeds are present, the competition is inter-specific (between species).
Plant population and growth
• High plant density leads to certain modifications in the growth of plants.
• Plant height increases with increase in plant population because of competition for light.
• Sometimes it may happen that a moderate increase in plant population may not increase but decrease plant height due to competition for water and nutrients but not for light.
• Leaf orientation is also changed due to population pressure. The leaves are straight, narrow & are arranged at longer vertical intervals under high plant densities.
This is a desirable architecture.
Plant population and yield
• Decrease in yield of an individual plant at high plant density is due to the reduction in the no. or earls or panicles.
Ex: - Redgram produces about 20 pods/plant at 3.33 lakh plants/ha (30x10cm) & produces more than 100 pods per plant at 50,000 plants/ha (80x25cm).
• Under very high population levels plant become barren, hence the optimum plant the population is necessary to obtain the maximum yield.
Optimum plant population
Optimum plant population for any crop varies considerably due to the environment under which it is grown. It is not possible to suggest a generalized plant population since the crop is grown in different seasons with different management practices.
E.g.:- Redgram plants sown in the winter season will have half the size of those produced in monsoon season. Optimum plant population is 55,000 plants/ha. For monsoon season crop of red gram and this is increased to 3.33 lakh plants/ha for winter crop; as low temperature retards the rate of growth, the higher population is established for quicker ground cover.
In sorghum, the climate is desirable throughout the pre-anthesis period, the optimum population is two lakh plants/ha & when it is not congenial for growth during pre-anthesis, it is four lakh plants/ha.
PLANTING PATTERN
Planting pattern affects crop yield through its influence on light interception, rooting pattern & moisture extraction pattern. Different planting patterns are followed to suit various weed control practices & cropping systems. Plant geometry refers to the shape of the plant while crop geometry refers to the shape of space available for individual plants. Crop geometry is modified by changing inter and intra-row spacing.
Square planting
It is fair to expect that squares arrangement of plants will be more efficient in the utilization of light, water & nutrients available to the individuals than in a rectangular arrangement. In wheat, decreasing inter-row spacing below the standard 15-12 cm i.e., reducing rectangularity usually increases yield slightly. In crops like Tobacco, inter cultivation in both directions is possible in square planting & helps in the efficient control of weeds. But, square planting is not advantageous in all crops. Groundnut sown with a spacing of 30 x 10cm (3.33 lakh/ha) generated higher pod yield than with the same amt. of the population in square planting. Pod yield is reduced either by increasing rectangularity or approaching square planting.
Rectangular planting
Sowing the crop with seed drill is the conventional practice. Wider inter-row spacing & closer Intra row spacing is very common for most of the crops, thus achieving rectangularity. This rectangular arrangement is chosen mainly to facilitate inter cultivation. Sometimes only inter-row spacing is maintained & intra-row spacing is not followed strictly & seeds are sown almost as solid rows.
Miscellaneous planting arrangements
Crops are sown with seed drills in two directions to contain more number of plants & mainly to reduce the weed population. Crops like finger millet, rice are transplanted at the pace of 2-3 seedlings per hill. Transplanting is done in rows or randomly. Skipping of every alternative row is skipped, & the population is improved by decreasing intra-row spacing, it is known as paired row planting. It is usually restored to introduce an intercrop.