soil characters

1. By,
Pillai Aswathy viswanath
PG 1 Botany
St. Thomas college
kozhencherry
Soil characters influencing
nutrient availability

2.  Plants are unable to grow in pure water,
the reason is that in addition to water
plants also require a number of mineral
elements.These are take up as inorganic
ions from the soil solution.
 The soil support the plant and it is the
main reservoir of water and nutrients for
plant.

3.  The soil is a complex physical, chemical
and biological substrate which is made up
of mineral matter , air, water and
organic materials

4.  It is a heterogenous material containing
solid, liquid and gaseous phase
 All of these phase interact with mineral
elements
 The solid particles may be inorganic,
organic or a mixture of both.
 Inorganic particles, often called mineral
particles
 Organic particles was formed by the
decay of organism

5.  The inorganic particles of solid phases
provided a reservoir of pottasium,
calcium, magnesium, and iron
 Also solid phase are organic compounds
containing nitrogen, phosphorus and
sulphur
 The liquid phase of the soil constitutes
the soil solution, which contains dissolved
mineral ions

6.  Plants obtain most of their oxygen and
carbon from the air by photosynthesis
and hydrogen is obtained directly or
indirectly from the water in the soil
 These three element together make up
the 90%of fresh plant tissue
 How ever plants cannot survive with out
the much smaller quantity of essential
nutrients

7.  So the nutrients like nitrogen,
phosphorous, pottassium,calcium
magnesium and sulphur obtained from
the soil
 So the characters of the soil play a big
part in the plants ability to extract
water and nutrients
 Soil characters like size , charge of
soil particles and soil pH will influence
the nutrient availability for plants

8. Soil particles are classed on their size :
 Anything over 2mm in diameter is referred
to as gravel, pebbles or stones
 Particles from 2mm to 0.5mm are called
sand particles
 0.5mm to 0.002mm are called silt particles
 Any particle under 0.002 mm is referred to
as clay

9.  Sand and silt are similar in composition
and are formed by physical and chemical
break down of rocks

10.  The texture of a soil depends on the
reletive mixture of sand ,silt and clay
particles
 Soil texture has an important role in
nutrient management because it
influences nutrient retention.
 For instance, finer textured soils tend
to have greater ability to store soil
nutrients

11.  More nutrients can be adsorbed by gram
of clay particles than by a gram of
sand or silt particles
 Because the clay particles provide a
much greater surface area for
adsorption
 Also soil texture influence in water
holding capacity and water infiltrating
rates

12.  In the soil ,the larger portion of plants
nutrients is bound up in complex compounds
that are unavailable to plants
 The complex compounds are gradually
changed in to the simpler compounds by
chemical weathering
 Thus the fertility of a soil depends in parts
on how easily the complex compounds be
change to simpler forms this is referred to
as the availability of a nutrients

13.  Plant nutrients are composed of single
elements eg;phosphorus
 compound of elements eg; ammonium
nitrate
 Most of the soil nutrients that a plant
take up must be in a soluble form (mixed
with water)
 When an atom is in water it is usually
becomes electrically charged and is called
an ion
 An ion with positive charge is called a
cation
 An ion with a negative charge is called an
anion

14.  Cation include sodium ,potassium,
calcium magnesium and aluminium
 Anions include chloride ,nitrate,
sulphate, carbonate and borate
 Both organic and inorganic soil particles
have predominantly negative charge on
their surfaces

15.  As a result
mineral cations
become adsorbed
on the negative
surface of soil
particles
 And also found
dissolved in the
soil solution and it
will later
absorbed by the

16.  This cation absorption is an important
factor in the soil fertility
 Mineral cation adsorbed on the surface
of soil particles are not easily lost when
the soil is leached by water and they
provide a nutrients reserve available to
plants roots

17.  Mineral nutrients adsorbed in this way
can be replaced by other cations in a
process known as cation exchange

18.  The degree to which a soil can adsorb
and exchange ions is termed its cation
exchange capacity and is highly
dependent on the soil type
 The soil with higher cation exchange
capacity generally has a larger reserve
of mineral nutrients

19.  Mineral anions such as nitrate and
chloride tend to be repelled by the
negative charge on the surface of soil
particles and remain dissolved in the soil
solution
 Thus the anion exchange capacity of
most agricultural soil is small compared
to the cation exchange capacity

20.  Among anions, sulphate in the presence
of calcium forms gypsum
 Gypsum is only slightly soluble, but it
releases sufficient sulphate to support
plant growth
 Phosphate ions may bind to soil particles
containing aluminum or iron because the
positively charged iron and aluminum ions
have hydroxyl group that exchange with
phosphate

21.  As a result, phosphate can tightly
bound, and its mobility and availability in
soil limit plant growth
 Once the nutrients are in the soil
solution ,they can be adsorbed by the
plant’s roots
 The soil solution is the medium by which
most soil nutrients are supplied to
growing plants

22.  The soil solution can be neutral ,acid, or
alkaline this is called soil pH
 When the soil solution contain more H ions it is
acidic
 When there are fewer H ions the soil solution
is alkaline
 The level of the acidity and the alkalinity in
a soil affects the availability of soil nutrients

23.  Hydrogen ion concentration (pH)is an
important property of soil because it
affects the growth of plant roots and
soil microorganism
 Root growth is generally favored in
slightly acidic soil,at pH values between
5.5 and 6.5

24.  Soil pH determines the availability of
soil nutrients

25.  CO2 is produced from decaying organic
matter
 CO2 is also released from the respiring
roots
 It dissolves in water and forms
carbonic acid which lowers the pH of
the soil
 Ammonia and hydrogen sulphide
released from decaying organic matter
ultimately get oxidized to form nitric
acid and sulphuric acid

26.  When the soil becomes acidic it will
promotes the weathering of rocks that
releases ca, Mg, K and Mn and
increases the solubility of carbonates,
phosphates and sulphate
 There for , the solubility of nutrients
facilitate and are more easily available
to roots

27.  Major factors that lower the soil pH
are decomposition of organic matter and
the amount of rain fall
 Carbon dioxide is produced as a result
of the decomposition of organic
materials and equilibrates with soil
water in the following reaction:
CO2 +H2O H+HCO3

28.  This reaction releases hydrogen ions,
lowering the pH of the soil
 In arid regions, the weathering of rocks
releases ca, Mg, K and Mn to soil, but
because of the low rain fall, these ions
do not leach from the upper soil layers,
and the soil remains alkaline
 Iron is absorbed best in acidic soil
whereas molybdenum is absorbed best in
alkaline soils

29.  Verma.V, (2008) Text book of plant
physiology, published by Ane books india
 Kochhar P.L, KrishnamoorthyH.N,(1985), Text
book of plant physiology ,published by ATMA
RAM and Sons Delhi
 Jain, V.K,(1990)fundamentals of plant
physiology, published by S.Chand and Company
 Lincoln Taize,Eduardo Zeiger, (2002),plant
physiology, 2 nd edition, Sinaeur associates
publishers