phytotechnie
Soil Preparation and Tillage in Agriculture
Soil Preparation
TILLAGE
Historical importance:
Effects of Tillage on Soil
1. Physical Effects
1. Primary Tillage (الحراثة الأولية)
Introduction to Tillage
• Definition: Tillage is the agricultural preparation of soil by mechanical agitation.
• Objectives:
• Enhance soil aeration.
• Facilitate seedbed preparation.
• Control weeds and manage crop residues.
Factors Determining the Depth of Ploughing
• The depth of ploughing is influenced by various factors, ranging from soil type to crop requirements.
• Proper ploughing depth is essential for optimizing soil preparation and ensuring healthy plant growth.
Soil Type
• Light Soils (Sandy or Loamy):
• Require shallow ploughing (5–15 cm) to avoid excessive dryness and maintain moisture.
• Heavy Soils (Clay or Compacted):
• Need deeper ploughing (20–30 cm) to break hardpan layers, improve aeration, and enhance water drainage.
Crop Type
• Shallow-Rooted Crops (e.g., Wheat, Rice):
• Require shallow ploughing (10–15 cm) as roots don’t penetrate deep.
• Deep-Rooted Crops (e.g., Sugarcane, Cotton):
• Need deeper ploughing (25–40 cm) to allow roots to grow and access nutrients and moisture.
Moisture Conditions
• Dry Soil:
• Deep ploughing helps break compacted layers and allows moisture penetration.
• Moist Soil:
• Shallower ploughing is sufficient since the soil is already loose.
Primary Tillage
Definition: The first operation after the harvest of the previous crop, involving deep soil penetration.
Aims for deeper ploughing (15–25 cm) to loosen soil and incorporate crop residues.
Purpose:
• Break up compact soil layers.
• Improve soil structure and drainage.
• Incorporate organic matter into the soil.
Tools Used: Moldboard plow, chisel plow, disc plow.
Examples: deep plowing, subsoiling
Year-Round Tillage
Definition: Tillage operations carried out throughout the year.
Repeated tillage operations are carried out until sowing of the crop. Even after harvest of the crop, the field is repeatedly ploughed or harrowed to avoid weed growth in the off season.
Subsoiling
Subsoiling is breaking the hard pan without inversion and with less disturbance of top soil. A narrow cut is made in the top soil while part of the subsoiler breaks the hard pans. This implement can penetrate to a depth of 50 cm to loosen deep soil layers and promote water movement and root growth. Chisel ploughs are also used to break hard pans present even at 60-70 cm.
Secondary Tillage
Definition: Follows primary tillage and refines the soil for planting. Involves shallow ploughing (5–15 cm) for seedbed preparation and leveling.
After ploughing, the fields are left with large clods with some weeds and stubbles partially uprooted.
Definition: Follows primary tillage and refines the soil for planting.
Purpose:
• Leveling the soil surface.
• Breaking clods and pulverizing the soil.
• Weed control and moisture conservation.
Tools Used: Harrows, cultivators, rollers.
Examples: Harrowing, disking.
Harrowing
Harrowing is done to a shallow depth to crush the clods and to uproot the remaining weeds and stubbles. Disc harrows, cultivators, blade harrows etc., are used for this purpose.
Planking
Planking is done to crush the hard clods to smoothen the soil surface and to compact the soil lightly. Thus the field is made ready for sowing after ploughing by harrowing and planking. Generally sowing operations are also included in secondary tillage.
Layout of Seedbed and Sowing
"Why Prepare a Seedbed?"
• Create a favorable soil structure
• Facilitate seed germination
• Promote root development
"How to Prepare a Seedbed"
Steps:
• Land Clearing – Remove weeds and debris.
• Tillage – Loosen soil using plows or tillers.
• Leveling – Ensure uniform soil height.
• Moisture Management – Ensure adequate soil moisture.
Sowing Methods
• Broadcasting: Suitable for large fields.
• Drilling: Ensures even spacing.
• Transplanting: For certain crops or pastures.
• Direct Seeding: Economical and efficient.
Layout of Seedbed and Sowing
• After the seedbed preparation, the field is laid out properly for irrigation and sowing or planting seedlings.
• These operations are crop specific.
• For most of the crops like wheat, soybean, millet, groundnut, etc., flat levelled seedbed is prepared.
• After the secondary tillage, these crops are sown without any land treatments.
Layout of Seedbed and Sowing
• For some crops like maize, vegetables etc., the field has to be laid out into ridges and furrows.
• Sugarcane is planted in the furrows or trenches.
• Crops like tobacco, tomato, chillies are planted with equal inter and intra-row spacing so as to facilitate two-way intercultivation.
• After field preparation, a marker is run in both the directions. The seedlings are transplanted at the intercepts.
Primary Implements
One of the most common and essential tools used in tillage, particularly for turning over the soil in preparation for planting. It is known for its ability to effectively break up soil, incorporate organic matter, and create a suitable seedbed.
The Moldboard Plough
The moldboard plow breaks loose, inverts the soil and breaks it into lumps.
Mechanism of Action
• The share cuts into the soil, breaking it into smaller pieces.
• The moldboard then lifts the soil, turning it over and exposing fresh soil underneath.
• The turned soil is left in ridges or furrows, providing aeration and preparing the land for planting.
The Disc Plough
• Because of its inclined disc blades, disc plough does not cut, invert or pulverize the soil as deeply as the mouldboard plough.
• The disk plows are important for use in loose soils on soils that are too dry and hard for easy penetration of moldboard plows.
Mechanism of Action
• The discs rotate and cut through the soil, breaking it into smaller pieces.
• Unlike the moldboard plough, the discs do not turn the soil over completely but break it up and invert it slightly.
• This method helps incorporate crop residues and improves soil structure.
In some sticky soils neither type of plow will be effective when the soil is wet. In this case, scrapers behind each disk will keep the disks clean. The disk plow could be used when there are sufficient stubble, straw, weeds or aftermath available to leave the residues mixed with the surface soil enough to check soil erosion, except on light soils.
The advantages of plow disk are:
⮚ with the same tractor it will cover about 3 times as much ground as the moldboard plow.
⮚ The work done is less, because the soil is moved a shorter distance.
⮚ The speed of operation makes early plowing possible, even when some snow is still found.
⮚ Because of the rough surface left, soil blowing is reduced.
The Chisel Plough
• The chisel plow breaks the soil without inverting or pulverizing the soil.
• The Chisel Plow performs the initial loosening of the soil while leaving the trash on top.
• Some soil clumps could be formed, but it cuts the vegetation under the soil surface and the roots of plants. It is usually set at 20 to 30cm deep. The maximum depth is 60cm.
Such plows are suited for the following types of soils:
I. the alkaline and the saline soils, since plowing with such an implement does not invert the soil layer where the salts are accumulated to the zone where the roots are mostly distributed.
II. the shallow soils that do not exceed 20-25cm.
III. the soils that are characterized by a very dry surface layer and wet deeper layers.
IV. soils with fertility concentrated in the surface layer.
V. some modified chisels could be used for harrowing the soil.
Subsoiler
• It is a form of a chisel plough designed to penetrate to a greater depth.
• This implement can penetrate to a depth of 50 cm to loosen deep soil layers and promote water movement and root growth.
• A lot of power (40-60 hp) is needed to pull one shank of a subsoiler at a depth of 50 cm in heavy soil.
Secondary Implements
The land after being plowed is not yet ready for planting. After plowing, the field must be tilled with harrows, cultivators or other implements with disks, shovels, teeth, spikes, sweeps or knives (Following figures).
Under most conditions, a smooth finely pulverized seedbed should not be prepared until just before seeding.
Disc harrow
Spike tooth harrow
For light tillage with little surface disturbance. For Pulverizing cloddy soils in friable state, it breaks soil crust and be used together with a plough or harrow).
Chain link harrow
Mounted harrow
Plowing Under Lebanese Conditions
⮚ Do not plow heavy soils unless they are friable enough, otherwise soil clumps will be formed that are difficult to mellow, beside the great resistance that will face the plow.
⮚ Add the organic fertilizers before plowing. Low organic matter content leads to the adhesion of clay and silt particles, which results in bad aeration, bad drainage and weak growth of plants. Organic fertilizers in light soils will improve physical and chemical properties.
⮚ Light soils should not be plowed deeply. After plowing rolling would be desirable.
⮚ Early fall plowing is desirable for growing crops of winter or spring habit, such operation promotes the moisture accumulation during winter. If the land is intended to be fallowed, then shallow plowing to control weeds may be practiced but without inverting the soil.
⮚ Seeds of smaller size require better mellowing of the soil.
⮚ If a hard pan is formed as result of continuous use of heavy machinery and plowing to a constant depth, then chiseling when the soil is dry might be beneficial as well as planting of leguminous crops may improve the structure of the soil.
⮚ For growing small grains, plowing to a depth of 15-25cm is enough and 25cm for cotton.
⮚ The depth of plowing heavy soils must be changed from year to year.
⮚ On lands with a slope, plowing should be done perpendicular to the slope and not parallel to it in order to prevent soil erosion. On such soils, early plowing is not desirable.
⮚ The borders of the field are plowed in perpendicular direction to the furrows.
⮚ The runs of the machinery must always be straight.
⮚ The depth of plowing must be the same in all parts of the field.
Deep plowing has a great influence on the oxidation of organic matter, especially in rainfed cropping system, as well as it increases the costs of production. It was found that by increasing the depth of plowing for 1 cm, then the mass of the soil to be moved is 150 tons/ha, which will require more power and eventually more fuels and greater cost.
From data presented in table 1, it is shown that depth of plowing did not increase grain yield of wheat.
| Depth of plowing (cm) | 12.5 | 20.0 | 25.0 | 37.5 | 45.0 |
|---|---|---|---|---|---|
| Grain yield (Bushels*/acre) | 22.7 | 25.2 | 25.0 | 24.1 | 23.9 |
*one bushel of wheat is equal to 27kg. 1 bushel = 0.35 m³
In the Bekaa valley, an experiment was conducted on wheat and potato also did not reveal significant differences in yield between the different depths of plowing.
In semi-arid and semi-humid areas, deep plowing should not be practiced unless in the case of the first fall plowing for spring crops or fields to be fallowed. All other practices should be surface tillage to a depth of 10cm without inverting the soil.
On irrigated areas with bad drainage, plowing to a depth of 30cm is adequate if hard pans are not found. If hard pans do exist, then plowing to a depth of 50cm might be necessary.
What are the four types of tillage? Types
• Primary and secondary tillage. Primary tillage is usually conducted after the last harvest, when the soil is wet enough to allow plowing but also allows good traction.
• Reduced tillage.
• Intensive tillage.
• Conservation tillage.
• Zone tillage.
Reduced or Zero Tillage Practices
Tillage system is an important management variable that influences long-term agricultural sustainability. Inversion tillage systems are effective in loosening soil, but the effect is usually short-lived and causes accelerated decomposition of organic matter. Conservation tillage practices, such as no tillage (NT), reduced tillage, and minimum tillage, were developed to protect soil from wind and water erosion. The intensive soil tillage, will end in gradual soil degradation and loss of crop productivity (Figure 1).
Inversion tillage is commonly practiced by ploughing almost 70% of the topsoil and sowing the seeds within it. This soil inversion has immediate benefits in yield and weed control, but it also damages the integrity of the soil, hampering its ability to retain moisture and necessitating heavy usage of fertilisers. The topsoil stores the majority of soil nitrogen, and destroying this layer through tillage removes necessary nutrients from the seedbed. Alongside serious environmental impacts, the longevity of the soil as a viable means of production is also threatened.
Soil degradation is due primarily to soil erosion and the loss of organic matter associated with conventional tillage practices that leave the soil bare and unprotected in times of heavy rainfall and wind.
No- tillage and reduced tillage have been used since ancient times by the so called "primitive cultures" for the cultivation of crops, simply because man has not the muscle force to till any significant area of land to a significant depth by hand.
Few years ago, about more than 95 Million hectares are found under No- tillage world wide. Since 1987, the technology has experienced a 59 fold increase in Latin America from 670.000 ha to 40.6 million ha in the year 2004 against a 5.6 fold increase in the USA.
Influence of No-Tillage on Different Soil Properties
There is enough scientific evidence from warmer areas that shows that no- tillage has positive effects on chemical, physical and biological soil properties compared to conventional soil preparation.
a) Influence of No Till on Soil Physical Properties
Conservation agriculture dramatically reduces soil erosion maintains or even increases the organic matter content in the soil and keeps the soil temperature at low levels. It is well assumed that cultural practices mainly affect macro-porosity, i.e. pores larger than 30 micrometer (in diameter) that can be formed by soil tillage, soil fauna and roots of crops. It was found that, after four years under no tillage, the macro-porosity decrease. Tillage system influences on soil bulk density are variable. An increase in soil density in no-till system was found in near the soil surface layers when compared to plowing. Under no-tillage, higher infiltration rates have been measured compared to conventional tillage and this results in a drastic reduction of erosion. In no- tillage a higher soil moisture content and lower soil temperatures as well as higher aggregate stability have been measured.
b) Influence of NT on Soil Chemical Properties
Compared to conventional tillage, no- tillage has positive effects on the most important chemical properties of the soil. Under no- tillage, higher values of organic matter, nitrogen, phosphorus, potassium, calcium, magnesium and also a higher pH and cation exchange capacity, but lower Al values are measured. The maintenance of a vegetal cover reduces soil erosion and improves soil infiltration and Organic matter content. Minimizing soil disturbance reduces mineralization of organic matter (OM) and can result in larger storage of soil OC relative to conventional tillage.
c) Influence of NT on Biological Soil Properties
Reduced tillage affords limitation of erosion by increasing structural stability and resistance against stress from vehicle load and by permitting the development of earthworm community. It is reported, however, that reduced tillage practices raise soil compaction inducing a decrease in macrofauna activity.
Due to the fact that no mechanical implements are used that destroy the "nests" and channels built by micro- organisms, higher biological activity occurs under the no- tillage system. Also, micro- organisms do not die because of famine under this system (as is the case under bare soils in conventional tillage) because they will always find organic substances at the surface to supply them with food. Finally, the more favorable soil moisture and temperature conditions under no- tillage also have a positive effect on micro- organisms of the soil.
For these reasons more earthworms, arthropods, (acarina, collembola, insects), more micro- organisms (rhyzobia, bacteria, actinomicetes), and also more fungi are found under no- tillage as under conventional tillage. Despite the fact that chemicals are used to kill weeds, higher biological activity occurs under no-tillage, an indicator of a healthier soil.
الزراعة الحافظة في خليط الشعير-بيقية والشوفان-بيقية
مصلحة الأبحاث الزراعية - تل عمارة تجربة الخلائط 2008 – 2009
لم تختلف الإنتاجية بين طريقة الزراعة الحافظة والزراعة التقليدية لخليط الشعير مع البيقية حيث بلغت الانتاجية 18 طن/هـ. أما في خليط الشوفان مع البيقية فقد تفوقت الإنتاجية في طريقة الزراعة الحافظة فبلغت 20 طن/هـ بينما بلغت الانتاجية 13 طن/هـ في الطريقة التقليدية
مصلحة الأبحاث الزراعية - تل عمارة تجربة
الخلائط - النتائج 2008 – 2009
نتائج المحتوى الرطوبي 2009
Moisture % (May 2nd)
Field Crop Production (Seeds and Seedlings)
SEEDS and SEEDLING
Seeds could be considered as a form of existence of living plants, adapted to reproduce and to help the species to survive despite the seasonal unfavorable growth conditions.
The seeding material is not necessarily the true seed in the botanical sense.
From agronomic point of view:
Seeds are called those parts of plants that are seeded in order to obtain yields.
In botanical sense:
A seed is a developed fertilized ovule that includes the embryo and its food reserves and a protective seed coat.
SEEDS and SEEDLING
High quality seed is essential for successful crop production.
High quality seed should be healthy, of high germination capacity and purity.
Poor seed contaminated with foreign seed will:
• increase the labor cost for production and
• reduces the crop yield and
• contaminates the current crop as well as the seed and the soil in the following seasons.
Factors Promoting Seed Germination
In general, a good seed should express a germination of 90 to 100% in laboratory conditions.
Small grains may express 90% germination when sown in good field conditions. Sorghum and cotton give lower germination rate because of higher susceptibility to attack from seed-rotting fungi. A sorghum seed of 95% germination capacity will produce about 75% germination if the seed was treated and about 50% of untreated seed.
The most important factors necessary for germination are ample humidity, oxygen and appropriate temperature. A deficiency in any factor may prohibit germination.
Moisture
Abundant water is necessary for rapid germination.
Field crop seeds may start to germinate when their moisture content (on dry basis) reaches 25 to 75% or more. Seeds of sorghum, millet and sudangrass will germinate when the moisture content of the seed is about 26%, while those of most legumes will require as high moisture content as about 75%.
The water usually enters the seed through the hilum or directly through the seed coat. The imbibed water causes the protein and starch of the seed to swell. Wheat seeds may absorb water from a saturated atmosphere to reach a moisture content of 30% on wet basis, which is still not enough for germination.
Oxygen
Many dry seeds are impervious to gases including oxygen. Yet, absorption of water may render the seed permeable to oxygen. Seeds planted too deeply in a moisture saturated soil may prevent germination due to the lack of oxygen. Rice is an exception where the seed may germinate under a water surface level of 15cm.
Temperature
In general, cool-season crops germinate at lower temperatures than warm-season crops. Wheat, oat, barley and rye may germinate at the temperature of ice melting point. Crops such as field peas, red clover may germinate at a temperature of 9°C or even less. Tobacco seeds germinate slowly below 17°C. Starchy seeds appear to be more easily infected by rots and they are less likely to produce sprouts at low temperature than oil crops.
At temperatures too high for germination, the seeds may be killed or be merely forced into secondary dormancy. The killing has been ascribed to the destruction of enzymes and coagulation of cell proteins.
Light
Most field crops germinate in either light or darkness.
Many grasses germinate better in the presence of, or after exposure to light, especially when the seeds are fresh.
The light requirement in all cases is small. Even a flash of light may induce germination in seeds that are swollen.
Most weed seeds require light for germination, whereas the absence of light enables such seeds to remain dormant in the soil.
Process of Germination
When placed under appropriate conditions, seeds gradually absorb water for about 3 days until when the moisture content may reach about 60% of dry weight in cereals and 100% or more in legumes. Meanwhile the seeds become swollen.
Glucose will be transported to the growing sprout by diffusion from cell to cell.
Proteins are broken into amino-acids then build protein in the seedling.
Fats which occur mainly in the cotyledons of oil-bearing seeds and in the embryos of cereal seeds will split by lipases into fatty acids and glycerol, which in turn undergo chemical changes to form sugars to build up carbohydrates and fats in the seedling.
Energy is supplied by respiration and the oxidation of carbon and hydrogen into carbon dioxide and water.
The energy consumed during germination may amount to ½ the dry weight of the seed. The germination of 35 kilograms of wheat utilizes the equivalent of oxygen found in 25 M³ of air.
In germinating seeds, the embryo ruptures the seed coat (about 2 days after being wetted) and the radicle or the embryonic root is the first organ to emerge, which is soon followed by the plumule or the young shoot.
In grasses (monocots) and some legumes (dicots) such as the pea and the vetches, the cotyledons remain in the soil. The plumule is pushed upward by the elongation of the epicotyl (subcrown internode). This type of germination is called hypogeal germination.
The coleoptile of grasses emerges from the soil as a colorless tubelike structure that encloses the first true leave protecting it from the mechanical resistance of the soil.
In many cotyledons such as beans and flax, the cotyledons are pushed over the soil surface by elongating the hypocotyl. This is called epigeal germination.
Aspects of Seed Quality for Germination
Whole seeds: A marked decrease in germination will be noticed in almost all crops if the germ of the seed is injured. Broken or cracked seeds mold more than whole seed. The viability of seed may be destroyed quickly by molding or heating as a result of the growth of fungi and bacteria, which break down and absorb the constituents of the seed, thus starving the young sprouts. The best protection against rotting is the treatment of the seed with disinfectants.
Seed maturity: Immature seed, because of small size, has a low reserve food supply and usually produce weak plants and may fail to germinate. Because of high moisture content they are vulnerable to frost injury.
Seed size: Large seeds usually produce more vigorous seedlings than those of smaller size. Such plants may survive adverse conditions better and they will produce greater yield when equal numbers of seeds are planted. This difference in yield may not be sound when equal weights are seeded due to the greater number of plants obtained from the smaller fraction of seed.
Seed Dormancy
Growth of the embryo is arrested in the ripe seed, but starts again on germination. The requirements for germination are water, oxygen and temperature. A newly ripe seed, is not germinating-ripe, but is in a state of dormancy and fails to respond to these conditions. The duration of dormancy period may vary from only a few days to several years.
Dormancy could be due to more than one factor, and after-ripening may therefore involve more than one process.
In some legumes, hard seeds are produced which are incapable of absorbing water; after a time the testa loses its waterproof character and the seed can germinate. In other cases the testa is impermeable to gases, so that oxygen cannot enter and carbon dioxide cannot escape; eventually the testa becomes permeable and the embryo can respire freely. In other cases, the testa or fruit wall forms a physical barrier, which constrains the embryo, and germination could not take place.
However, in most species it seems to be a block to the physiological processes involved in germination. The block may be the presence of an inhibitor or the absence of a hormone or other growth-promoting substance; both inhibitors and promoters may be present, with the former predominating. In after-ripening the balance is changed either by the loss of the inhibitor by leaching, evaporation or oxidation, or by the production of a promoting substance. The best-known dormancy-breaking agents are:
Leaching
Temperature – dry heat, chilling or night-and-day alternations of temperature
Physical abrasion or softening of integuments
Nitrates in solution
Carbon dioxide
Light
Field Crop Production (Fertilizers)
• What are Field Crops?
• Crops grown on a large scale for food, fiber, feed, or industrial use.
• Examples: Cereals (wheat, maize, rice), pulses, oilseeds, and fiber crops (cotton).
• Why Fertilizers Are Essential
• Replenish soil nutrients removed by intensive cropping.
• Support high-yield crop varieties.
• Enhance overall crop quality (e.g., protein content, oil yield).
2. Essential Nutrients for Field Crops
a. Macro-Nutrients
• Nitrogen (N):
• Stimulates vegetative growth and chlorophyll synthesis.
• Essential for cereals and leafy crops.
• Common sources: Urea, ammonium nitrate, anhydrous ammonia.
• Phosphorus (P):
• Aids in root development, flowering, and seed formation.
• Critical during early crop growth stages.
• Common sources: Single superphosphate (SSP), diammonium phosphate (DAP).
• Potassium (K):
• Improves disease resistance, water use efficiency, and crop quality.
• Common sources: Potash (Muriate of Potash - MOP).
b. Secondary and Micro-Nutrients
• Secondary Nutrients: Calcium (Ca), Magnesium (Mg), Sulfur (S).
• Sulfur improves oil content in oilseeds like mustard and sunflower.
• Micro-Nutrients: Zinc (Zn), Boron (B), Iron (Fe), Copper (Cu).
• Zinc: Important for cereals (e.g., wheat, rice).
• Boron: Vital for flowering and fruiting in cotton and pulses.
Types of Fertilisers
a. Inorganic Fertilizers
• High nutrient concentration; quick release.
• Examples: Urea, DAP, MOP, ammonium sulfate.
b. Organic Fertilizers
• Manure, compost, and green manure.
• Improve soil structure and microbial activity.
c. Biofertilizers
• Rhizobium for nitrogen fixation in legumes.
• Azotobacter, Azospirillum, and Phosphorus-Solubilizing Bacteria (PSB).
d. Specialty Fertilizers
• Slow-release and controlled-release fertilizers (e.g., sulfur-coated urea).
• Nano-fertilizers for precision nutrient delivery.
4. Fertilizer Management Strategies
a. Soil Testing
• Importance of analyzing soil nutrient levels and pH.
• Avoid over-fertilization to reduce environmental risks.
b. Fertilizer Application Methods
• Broadcasting: Spreading fertilizers evenly over the soil surface.
• Band Placement: Applying fertilizers in rows or near plant roots for efficient uptake.
• Foliar Feeding: Spraying liquid fertilizers on crop foliage for quick absorption.
• Fertigation: Applying water-soluble fertilizers through irrigation systems.
c. Timing of Fertilizer Application
Split applications for better nutrient uptake (e.g., basal and topdressing in rice). Matching fertilizer use with crop growth stages:
Nitrogen during vegetative stages.
Phosphorus and potassium during reproductive stages.
d. Crop-Specific Fertilization
Cereals (e.g., Wheat, Rice, Maize): High nitrogen demand during vegetative growth.
Legumes (e.g., Soybean, Chickpea): Focus on phosphorus and potassium due to nitrogen fixation.
Oilseeds (e.g., Mustard, Sunflower): Sulfur and boron are critical for high oil yield.
Cotton: Requires balanced NPK with emphasis on potassium for fiber quality.
5. Benefits of Fertilizers in Field Crop Production
Yield Increase: Higher productivity of staple crops (e.g., rice, maize).
Quality Enhancement: Protein content in cereals and oil content in oilseeds.
Economic Benefits: Better returns on investment with improved crop yield.
6. Challenges and Environmental Concerns
Nutrient Loss: Leaching, volatilization, and runoff lead to lower efficiency.
Soil Degradation: Imbalanced use of fertilizers causes soil acidity and nutrient depletion.
Water Pollution: Nitrate leaching leads to eutrophication of water bodies.
7. Sustainable Fertilizer Use
Integrated Nutrient Management (INM): Combining organic, inorganic, and biofertilizers for balanced nutrient supply.
4R Nutrient Stewardship: Right source, right rate, right time, right place.
Crop Rotation and Cover Crops: Enhances soil fertility and reduces the need for external fertilizers.
• Fertilizers are critical for maximizing yield and quality in field crops.
• Sustainable practices reduce environmental risks and improve long-term soil health.
Fertilizers are compounds given to plants to promote growth and better crop quality; they are usually applied either via the soil, for uptake by plant roots, or by foliar feeding, for uptake through leaves.
Fertilizers can be:
▪ organic (composed of organic matter, i.e. carbon based)
▪ or inorganic (containing simple, inorganic chemicals).
They can be :
• naturally-occurring compounds such as peat or mineral deposits (Chilean sodium nitrate, mined "rock phosphate" and limestone)
• or manufactured through natural processes such as composting)
• or chemically-synthesized inorganic fertilizers such as ammonium nitrate, potassium sulfate, and superphosphate, or triple superphosphate.
Fertilizers and Manure
Fertilizers typically provide, in varying proportions,
▪ the three major plant nutrients (nitrogen, phosphorus, and potassium)
▪ the secondary plant nutrients (calcium, sulfur, magnesium)
▪ and sometimes trace elements (or micronutrients) with a role in plant nutrition: boron, chlorine, manganese, iron, zinc, copper and molybdenum.
Fertilizer needs are established by field experiments for each soil type, environment, crop and variety. They could be estimated by laboratory tests of soils and plant tissues, by pots cultures and by observation of deficiency symptoms in plants.
Soluble compounds of nitrogen are leached downward into the soil and may reach the water supplies if they reach a drainage outlet or the underground water table. Although nitrates leach downward deep into the soil, the total nitrogen is mostly in the organic residues of the upper horizons.
Phosphorus compounds become fixed in the upper soil levels and they may enter streams or ponds only from fields subjected to water erosion.
Potash is also uniformly through out the different soil horizons except in sandy soils and under high rainfall conditions, where the potash content increases with depth.
Few fertilized fields are as high in fertility as they were in their virgin state. The chemical elements have been entering the seas and ponds ever since the earth was found.
Macronutrients and Micronutrients
Fertilizers can be divided into macronutrients or micronutrients based on their concentrations in plant dry matter.
There are six macronutrients: nitrogen, potassium, and phosphorus, often termed 'primary macronutrients' because their availability is often managed with NPK fertilizers, and the 'secondary macronutrient', and calcium, magnesium, and sulfur, which are required in similar quantities but whose availability is often managed as part of liming and manuring practices rather than fertilizers. The macronutrients are consumed in larger quantities.
There are many micronutrients, and their importance and occurrence differ somewhat from plant to plant. In general, most of them are present from 5 to 100 parts per million (ppm) by mass. Examples of micronutrients are as follows: iron (Fe), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo), and zinc (Zn).
Macronutrient Fertilizers
Synthesized materials may be described as straight, where the product predominantly contains the three primary ingredients of nitrogen (N), phosphorus (P) and potassium (K), which are known as N-P-K fertilizers or compound fertilizers when elements are mixed intentionally. They are named or labeled according to the content of these three elements, which are macronutrients.
The mass fraction (percent) nitrogen is reported directly. However, phosphorus is reported as diphosphorus pentoxide (P₂O₅), the anhydride of phosphoric acid, and potassium is reported as potash or potassium oxide (K₂O), which is the anhydride of potassium hydroxide.
An 18-51-20 fertilizer would have 18% nitrogen as N, 51% phosphorus as P₂O₅, and 20% potassium as K₂O. The other 11% is known as ballast and has no value to the plants. If nitrogen is the main element, they are often described as nitrogen fertilizers.
In general, the mass fraction (percentage) of elemental phosphorus, [P] = 0.436 x [P₂O₅] and the mass fraction (percentage) of elemental potassium, [K] = 0.83 x [K₂O].
An 18−51−20 fertiliser therefore contains, by weight, 18% elemental nitrogen (N), 22% elemental phosphorus (P) and 16% elemental potassium (K).
In many countries there is the public perception that inorganic fertilizers "poison the soil" and result in "low quality" produce. However, there is very little (if any) scientific evidence to support these views. When used appropriately, inorganic fertilizers enhance plant growth, the accumulation of organic matter and the biological activity of the soil, while reducing the risk of water run-off, overgrazing and soil erosion. The nutritional value of plants for human and animal consumption is typically improved when inorganic fertilizers are used appropriately.
Nutrient Uptake
The mechanism of nutrient uptake by plants is still debatable. The most commonly accepted theories are the following:
Soil solution theory. The capillary water or the soil solution is considered the environment where ionic exchange takes place. CO₂ released by roots with water will form carbonic acid H₂CO₃ which ionizes to give hydrogen ions that replace the adsorbed ions on the surface of the clay particles that will be transferred to the soil solution to be absorbed by the plant fine roots.
Contact theory assumes that on the root hairs that carry negative charges hydrogen ions are found which will be directly exchanged with the ions found on the surface of the soil particles without movement to the soil solution. It is also assumed that this exchange requires energy and the absorption will be stopped when the activity of cells is ceased due to the absence of oxygen or significant reduction in temperature.
It could be noticed that there is a certain level of selectivity for the absorbed ions, and the cations and ions are absorbed independently, as well, some of them are absorbed more readily than others such as the ammonium, potassium and nitrates that could be absorbed in greater quantities than needed for normal growth. Such consumption is called Luxury consumption. It should be aware that excessive consumption of nitrates by some forage crops may cause poisoning to animals. The same could be noticed for selenium when excessively consumed by some Astragalus spp.
Soil-Nitrogen Relations
Most crops respond very well to nitrogen fertilizers on most soils of the humid, sub-humid and irrigated areas. Sufficient nitrogen has a tendency to encourage stem and leaf development. Deficiency of this element results in plants of poor color, poor quality and low productivity. At the same time, excessive nitrogen tends to cause lodging of plants, late maturity, poor seed development in some crops and greater susceptibility to diseases. On semi-arid lands, surplus available nitrates cause excessive plant growth that exhausts the soil moisture in dry seasons before grain is produced.
Soil-Nitrogen Relations
The nitrogen in the soil is derived originally from the air, which contains about 70,000 tons over each hectare of land. A great part of the gaseous nitrogen is fixed through the activities of soil bacteria. It is introduced to the soil as organic nitrogen of plants or plant residues. Upon decomposition, some of the nitrogen is released into the air as elemental nitrogen or ammonia, while the part that remains in the soil is converted into ammonia and nitrites and finally into nitrates.
Ammonia and nitrogen oxides in the air are returned to the soil in rain and snow. Ammonia and nitrates are used by plants and some are lost in drainage waters. Some of the nitrogen remains in the soil for a long period in the organic matter that is not fully broken down. Nitrogen supply may be maintained by the growth of legumes, use of manure and by the addition of nitrogen fertilizers.
The nitrogen uptake by plants is in the form of NH₄⁺ or NO₃⁻. NO₃⁻ is consumed more readily by plants, whereas NH₄⁺ is caught by the clay particles or the organic of the soil. Therefore, the use of fertilizers containing 25% nitrates and 75% ammonia will be much useful for winter cereals which will benefit from the nitrates in early growth stages and from ammonia in advanced stages.
According to the nitrogen content, soils could be divided into:
▪ Very poor soils with less than 0.5g/kg (<500ppm).
▪ Poor soils with 500-750ppm
▪ Moderate soils with 750-1000ppm
▪ Rich soil with 1000-2000ppm
▪ Very rich with nitrogen content >2000ppm.
In general, organic matter is supposed to contain about 5% nitrogen.
Role of Bacteria in Nitrogen Fixation
Bacteria that multiply in nodules on the roots of legumes fix nitrogen from the air into forms that the plant can utilize. This is called symbiotic fixation of nitrogen. An average of 50 to 250 kg of nitrogen per hectare is added to the soil by legume bacteria annually if the crop is plowed under. In general, alfalfa and clovers may fix more nitrogen than large-seeded legumes. The interior of an effective nitrogen-fixing nodule is pink or red.
Rhizobium bacteria require molybdenum, cobalt and iron to function normally. They are more effective in soils low in nitrogen. A number of leguminous fix nitrogen by specific Rhizobia strains. Some strains form nodules but fix no nitrogen. The interior of an effective nitrogen-fixing nodule is pink or red.
Effective legume inoculation is provided by using the correct, fresh, refrigerated culture applied to the seed along with a little water, milk or sirup or other adhesive substance by thorough mixing. The treated seed should be sown in moist soil that is pressed around the seed within 24 hours if possible.
Some 15 other genera of bacteria including Azotobacter and Clostridium are reported to convert nitrogen into organic combinations by a process called nonsymbiotic fixation. A number of blue green algae growing in ponds or flooded rice may also fix nitrogen.
Soil-Phosphorus Relations
Adequate amount of phosphorus favor rapid plant growth and earliness, thus avoiding damage by early freezes in temperate regions.
On acid clay soil low in organic matter, a better response to phosphorus fertilization could be noticed. Calcareous soils that are rich in both phosphorus and calcium will express low phosphorus availability due to high calcium content.
According to phosphorus content, soils are classified as:
Poor soils with phosphorus content less than 50ppm
Moderate soils with phosphorus content 50-350ppm
Rich soil with phosphorus content greater than 350ppm.
Soil-Potassium Relations
An adequate amount of potassium in the soil improves the quality of the plants, insures greater efficiency in photosynthesis, and increases resistance to certain diseases.
It also insures the development of well filled kernels and stiff straw in cereals, encourages growth in legumes, assists in chlorophyll formation and is particularly helpful in the production of starch or sugar-forming crops.
Potassium is beneficial to tobacco, potatoes, cotton and sugarbeets. Potatoes grown with little potassium are low in starch, watery and generally poor in quality. Insufficient potassium in tobacco will reduce the burning quality. The leaves will have a poor color and flavor. Potash usually is abundant in soils of volcanic origin.
COMMERCIAL FERTILIZERS
a) Nitrogenous fertilizers
Nitrate fertilizers are materials with the nitrogen combined in the nitrate form that is readily utilized by plants such as in sodium nitrate. Sodium nitrate tends to make the soil alkaline.
Ammonium fertilizers such as ammonium sulfate, ammonium phosphate and others carry the nitrogen in the ammonium form, which is less readily leached in the soil than the nitrate form although soluble in water. Ammonium sulfate tends to make the soil acid because of the sulfate ion.
Fertilizers that contain nitrogen in the amide form include urea and calcium cyanamide. These simple nonprotein compounds dissolve in water, while the nitrogen is converted to ammoniacal or nitrate forms by bacteria.
b) Phosphate fertilizers
Phosphorus usually is in the form of phosphate, mostly of calcium. It must be dissolved in the soil solution to be taken up by the plants. Phosphorus uptake by the plants is in the form of orthophosphate (H₂PO₄⁺) or in the form of HPO₄⁻⁻.
The phosphatic fertilizers are:
Triple superphosphate with 23 to 48% phosphoric acid.
Ammonium phosphate, chiefly monoammonium phosphate with 11% nitrogen and about 48% phosphoric acid. It has a tendency to increase soil acidity.
Superphosphate with 16 to 20% of P₂O₅.
other materials such as bone meal and finely ground raw-rock phosphate.
c) Potassium fertilizers
The principal potash fertilizer materials are potassium chloride with 47-61% potash (K₂O), potassium sulfate with 47 to 52% and the manure salts with 19 to 32%.
According to potassium content, soils could be classified as:
▪ Poor soils with potassium content less than 100ppm
▪ Moderate soils with potassium content of 100-300ppm
▪ Rich soil with potassium content greater than 300ppm.
Another classification is also used, where soils are divided into:
• Poor soils with potassium content less than 250ppm
• Moderate soils with potassium content of 250-400ppm
• Moderately rich soils with potassium content of 400-550ppm
• Rich soils with potassium content greater than 550ppm.
d) Mixed fertilizers
A mixed fertilizer contains 2 or more fertilizer elements. The fertilizer formula indicates the composition of the mixture indicated as NPK. For example, a 10-10-10 or N10P10K10 contains 10 per cents of each of nitrogen (N), phosphoric acid (P₂O₅) and potash (K₂O). The other consists of other elements such as calcium, sulfates, chlorides, inert material and some micro-nutrients.
MANURES AND MANURING
The term "manure" originated from Fr. manoeuvre "worked by hand", but gradually came to apply to any process by which the soil could be improved. Among such processes was that of directly applying "manure" to the land, or what we now call "farmyard manure" or "dung," the excreta of farm animals mixed with straw or other litter.
Manures could be: (a) what may be termed "natural manures", and (b) "artificial manures". Manures, again, may be divided according to the materials from which they are made - e.g. "bone manure", "fish manure", &c.; or according to the constituents which they mainly supply - e.g. "phosphatic manures", "potash manures", "nitrogenous manures", or there may be numerous combinations of these to form mixed or "compound manures".
GREEN MANURE
Green manure crops are mostly annual legumes that are grown and turned under as a replacement for manures or soil amendments. In green manuring, the following should be considered:
If the green manure competes with the artificial nitrogen fertilizers and the alternative use of the land.
Green manure has a little benefit in soils that are rich in nitrogen.
Green manure is of little value in dry areas.
The factors that influence the decomposition of green manure and the release of the nutritive elements to the soil are:
Temperature, Humidity, Tillage practices, Aeration, pH, The ratio of carbon to nitrogen C/N, Soil texture and structure.
The influence of green manure on nitrogen content in the soil depends on:
▪ The used crop
▪ The prevailing environmental conditions
▪ The strain of Rhizobia used for inoculation of the seed
▪ The quantity of biomass produced
▪ The growth stage, when the crop was turned under.
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