2. Soil is the unconsolidated cover
What on the surface of the earth.
Soil is made up of mineral
is particles, organic particles,
air, and water.
soil? Soil is capable of supporting plant
growth.
4. Functions of agricultural soils
• Anchor plant roots
• Supply water to plant roots
• Provide air for plant roots
• Furnish nutrients for plant
growth
• Release water with low levels of
nutrients
5. There are five components of soil:
• 1. Rock
• 2. Sand
• 3. Silt
• 4. Clay
• 5. Humus
• Can you match each type of soil to its picture?
7. Sand
Sand is tiny grains of worn down rock. It doesn’t
hold water or have many nutrients.
8. Silt
Silt is very small, broken pieces of rock. It is
larger than clay, but smaller than sand. It is
powdery when dry.
Sand ------------Silt---------------Clay
9. CLAY
Clay holds water well. It is sticky and can be
shaped when it is wet. But, it is very hard
when dry.
Clay has many nutrients.
Clay is used for adobe or brick houses.
10. Humus
Humus is made of leaves, twigs, small
animals, or other decayed substances.
Humus adds many nutrients to the soil.
Humus is in the topsoil.
11. TYPES OF SOIL
Indian Council of Agricultural Research ( ICAR )
has divided Indian soils into eight major groups :
1.Alluvial Soil
2.Black Soil
3.Red Soil
4.Laterite Soil
5.Forest Soil
6.Desert Soil
7.Saline Soil
8.Marshy Soil
12. Soil Structure
The arrangement of sand, silt, and clay particles to
form larger aggregates.
• Organic matter is the glue that
holds the aggregates together
• Large pores (spaces) between
aggregates are filled with air in
a moist soil.
• Small pores are filled with
water in a moist soil. Even
smaller pores inside the
aggregates (not shown) are also
filled with water.
1/10 inch
13. Supplying Plant Nutrients
Nutrients that plants obtain from the soil
Macronutrients: Micronutrients:
(needed in large amounts) (needed in small amounts)
• Nitrogen (N) • Chlorine (Cl)
• Phosphorus (P) • Cobalt (Co)
• Potassium (K) • Copper (Cu)
• Calcium (Ca) • Iron (Fe)
• Magnesium (Mg) • Manganese (Mn)
• Sulfur (S) • Molybdenum (Mo)
• Nickel (Ni)
• Zinc (Zn)
14. Where do plant nutrients come
from?
• Decaying plant litter
• Breakdown of soil minerals
• Addition by humans
– Commercial fertilizer
– Manure
– Lime
– Other
17. Nutrient additions by humans
• Commercial fertilizers
– Nutrients are in a form that is available to plants
– Dissolve quickly and nutrients go into soil water
• Lime
– Dissolves slowly as it neutralizes soil acidity
– Releases calcium and magnesium
• Organic nutrient sources
– Manure, compost, sewage sludge
– Decay and nutrient release is similar to crop litter
18. Characteristics of the Soil
Horizons
• 0 Horizon-located on
surface, mostly O.M.
• A Horizon-Called
Topsoil, good amounts
of O.M. and minerals.
• B Horizon- Known as
Subsoil, Less O.M.
• C Horizon- Mostly parent
material, does little for
plant growth.
Editor's Notes
1. Alluvial Soil in IndiaThey are by far the largest and the most important soil group of India. They are composed of sediments deposited by rivers and the waves. Their chemical composition makes them one of the most fertile in the world. Usually deficient in nitrogen and humus ( thus fertilizers are needed ).Occupy the plains ( from Punjab to Assam ) and also occur in the valleys of Narmada and Tapti in M.P. & Gujarat, Mahanadi in the MP and Orissa, Godawari in A.R and Cauvery in T.N.Can be divided into Khadar ( new ) and Bhangar ( older, more clayey and kankary ) alluvium.2. Black Soil in IndiaAlso called Regur and is ideal for cotton crop. These soils have been formed due to the solidification of lava spread over large areas during volcanic activity in the Deccan Plateau, thousands of years ago.They are black due to compounds of iron and aluminium ( also because of titaniferous magnetite ).Mainly found in Deccan Plateau – Maharashtra, Gujarat, M.P, Karnataka, Andhra Pradesh, Tamil Nadu.Apart from cotton cultivation, these fertile soils are suitable for growing cereals, oilseeds, citrus fruits and vegetables, tobacco and sugarcane.They have high moisture retention level.Lack in phosphorus, nitrogen and organic matter3. Red Soil in IndiaThey are mainly formed due to the decomposition of ancient crystalline rocks like granites and gneisses and from rock types rich in minerals such as iron and magnesium. The term ‘red soil’ is due to the wide diffusion of iron oxides through the materials of the soil.Covers almost the whole of Tamil Nadu, Karnataka, Andhra Pradesh, S.E. Maharashtra, Chhatisgarh, parts of Orissa, Jharkhand and Bundelkhand.Generally deficient in nitrogen, humus and phosphorus, but rich in potash.Suitable for rice, millets, tobacco and vegetables ( also groundnuts and potatoes at higher elevations ).4. Laterite Soil in IndiaFound in typical monsoon conditions – under conditions of high temperature and heavy rainfall with alternate wet and dry periods. The alterations of wet and dry season leads to the leaching away of siliceous matter and lime of the rocks and a soil rich in oxides of iron and aluminium compounds is left behind.Found in parts of Western Ghats, Eastern Ghats, Rajmahal hills, Maharashtra, Karnataka, Kerala, Orissa, West Bengal, Assam, Tamil Nadu, etc.Poor in nitrogen and minerals.Best for tea, coffee, rubber, cinchona, coconut and suitable for rice and millet cultivation if manured.5. Forest and Mountain SoilsSuch soils are mainly found on the hill slopes covered by forests. The formation of these soils is mainly governed by the characteristic deposition of organic matter derived from forest growth.In the Himalayan region, such soils are mainly found in valley basins, depressions and less steeply inclined slopes. Apart from the Himalayan region, the forest soils occur in higher hills in south and the peninsular region.Very rich in humus but are deficient in Potash, phosphorous and lime and needs fertilizers.Plantation of tea, coffee, spices and tropical fruits.6. Arid and Desert SoilsA large part of the arid and semi – arid region in Rajasthan and adjoining areas of Punjab and Haryana lying between the Indus and the Aravallis receiving less than 50 cm of annual rainfall is affected by desert conditions.This area is covered by a mantle of sand which inhibits soil growth.The phosphate content of these soils is as high as in normal alluvial soils. Nitrogen is originally low but its deficiency is made up to some extent by the availability of nitrogen in the form of nitrates. Thus the presence of phosphates and nitrates make them fertile soils wherever moisture is available.The changes in the cropping pattern in the Indira Gandhi Canal Command Area are a living example of the utility of the desert soils.7. Saline and Alkaline SoilsIn the drier parts of Bihar, Up Haryana, Punjab, Rajasthan and Maharashtra, are the salt – impregnated or alkaline soils. Known by different names : Reh, kallar, USAR, etc.Some of the salts are transported in solution by the rivers and canals, which percolates in the sub – soils of the plains.The accumulation of salts makes the soil infertile and renders it unfit for agriculture.8. Peaty and Marshy SoilsOriginate in the humid regions as a result of accumulation of large amounts of organic matter in the soil. They contain considerable amounts of soluble salts and 10 – 40% of organic matter.Peaty soils are found in Kottayam and Alappuzha districts of Kerala, where it is called Kari.Marshy soils, high in vegetable matter, are found in northern Bihar, coastal parts of Orissa, Tamil Nadu and West Bengal and parts of UP
Nutrient cycling is an extremely important function of soils. Living plants contain all the nutrients essential for plant growth. When crops are harvested some of those nutrients are removed, but many remain behind in plant litter. When the litter falls onto the soil or is plowed under, those nutrients are returned to the soil. Some of the nutrients in plant litter dissolve into the soil water like salt would. Most of the nutrients in plant litter are bound up in complex organic molecules and are not available to plants. The litter must first be broken down, or decomposed, by soil microbes. The ferocious looking critters in this cartoon are meant to be soil microbes. These are actually microscopic organisms and cannot be seen with the naked eye. Nor do they look anything like this under the microscope. Hungry soil microbes, mainly bacteria and fungi, use the carbon in the litter for food. They consume some of the nutrients in the litter and release what they don’t need into the soil water. The feeding of soil microbes turns fresh plant litter into stable soil organic matter. When the microbes die the nutrients in their bodies are also released to the soil water and are available for plants to take them up again.
Nutrient cycling is an extremely important function of soils. Living plants contain all the nutrients essential for plant growth. When crops are harvested some of those nutrients are removed, but many remain behind in plant litter. When the litter falls onto the soil or is plowed under, those nutrients are returned to the soil. Some of the nutrients in plant litter dissolve into the soil water like salt would. Most of the nutrients in plant litter are bound up in complex organic molecules and are not available to plants. The litter must first be broken down, or decomposed, by soil microbes. The ferocious looking critters in this cartoon are meant to be soil microbes. These are actually microscopic organisms and cannot be seen with the naked eye. Nor do they look anything like this under the microscope. Hungry soil microbes, mainly bacteria and fungi, use the carbon in the litter for food. They consume some of the nutrients in the litter and release what they don’t need into the soil water. The feeding of soil microbes turns fresh plant litter into stable soil organic matter. When the microbes die the nutrients in their bodies are also released to the soil water and are available for plants to take them up again.
Farmers routinely add nutrients to soils to boost crop yields. Commercial chemical fertilizers like urea, ammonium nitrate, triple super phosphate, and muriate of potash are designed to be in a form that plants can take up and use. Most fertilizers are also designed to be very soluble, that is they quickly dissolve and release nutrients into the soil water.Lime is added to “sweeten” the soil as the old timers used to say. Lime increases soil pH by neutralizing acidity in the soil. As it reacts the lime dissolves and releases calcium and magnesium into the soil water.Farmers also add organic nutrient sources such as manures, composts, sewage sludge and others. These materials are similar to plant litter in that many of the nutrients are not available to crops. The materials must first be decomposed by soil microbes. As they decompose the nutrients are released into soil water.Notice that with each of these various nutrient sources I have repeated the phrase “nutrients are released into the soil water.” So we have all these nutrients moving into the soil water. What happens to them now?
