The document discusses how soil characteristics influence nutrient availability for plants. It describes the solid, liquid, and gaseous phases of soil and how they interact with mineral elements. Nutrients are obtained by plants from the soil solution, and their availability depends on factors like soil texture, particle size and charge, pH, and cation exchange capacity. Finer textured soils with more clay tend to store more nutrients due to their larger surface area for adsorption. Soil pH also affects nutrient availability and solubility.

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