Mass flow, diffusion, root interception, factors affecting nutrient availability

1. Dr.AB Jadhav, AC, Pune
Topic No. 25 & 26
 Mechanism of nutrient transport from soil to plants
roots
 Factors affecting nutrient availability to plants.
 Measures to overcome deficiencies and toxicities.
Marks: 06
Dr. Anand. B. Jadhav,
Assistant Professor
College of Agriculture, Pune
abjadhav1234@rediffmail.com

2. Dr.AB Jadhav, AC, Pune
Nutrient Uptake by Plants
Mechanisms for transport of
nutrients form soil to root
rhizosphere/surface
Mechanisms for Nutrient uptake
by the plants (Inside the cell)

3. Dr.AB Jadhav, AC, Pune
Nutrient uptake by
plants
Exchangeable ions +
surface adsorption
Soil Air
Solid phases +
minerals
OM + Microbes
Rainfall + Evaporation
+ Drainage, addition
of fertilizers

4. Dr.AB Jadhav, AC, Pune
Mechanism of Nutrient Transport from Soil to Root
Mass flow Diffusion Root Interception

5. Dr.AB Jadhav, AC, Pune

6. Dr.AB Jadhav, AC, Pune

7. Dr.AB Jadhav, AC, Pune
Mass flow occurs when plant nutrient ions and other dissolved
substances are transported in the flow of water to the root that
results from transpiration water uptake by the plant
Mass flow can also take place in response to evaporation and
percolation of the soil water
Amount of nutrients reaching to roots by mass flow is determined
by
Rate of water flow
Water consumption of plants
Average nutrient concentration in soil solution
1) Mass Flow

8. Dr.AB Jadhav, AC, Pune

9. Dr.AB Jadhav, AC, Pune
2) Diffusion
 Diffusion occurs when ions moves from an area of high
concentration to one of low concentration
 As plant roots absorbs nutrients from the surrounding soil
solution, the nutrient concentration at the root surface decreases
compared with the bulk soil solution. Therefore a nutrient
concentration gradient is established that causes ions to diffuse
towards plant roots
 A high plant requirement for a nutrient results in a large
concentration gradient, favoring a high rate of ion diffusion from
sol solution to the root surface

10. Dr.AB Jadhav, AC, Pune
Diffusion is governed by Fick’s Law
The rate of nutrient diffusion is directly proportional to the
concentration gradient
dc/dt = De A dc/dx
dc/dt = Rate of diffusion (Change in concentration C with time t)
dc/dx = Concentration gradient (Change in concentration C with distance
x
De = Effective diffusion coefficient
A = Cross sectional area through the ions diffuse

11. Dr.AB Jadhav, AC, Pune
3) Root Interception

12. Dr.AB Jadhav, AC, Pune
Factors Affecting
Nutrient Availability
1) Soil Texture
2) Soil Structure
3) Soil Reaction
4) Soil
Temperature
5) Moisture
Supply
6) Composition of
Soil Air
7) Soil Available
Nutrients
8) Total Nutrients
Content
9) Microbial Activity
10) Soil Organic Matter

13. Dr.AB Jadhav, AC, Pune
1. Soil Texture
Texture
Relative proportion of sand, silt and clay has profound
effect on different properties of soil
Light textured soils Fine textured soils
Low water capacity High water capacity
Less water holding capacity High water holding capacity
Less organic matter content More organic matter content
Little or no swelling or
shrinkage
High swell and shrinkage in
soil
High leaching of nutrients Less leaching

14. Dr.AB Jadhav, AC, Pune
2. Soil Structure
Structure
Arrangement of soil separates is called …….
Despite adequate nutrient supply, unfavorable physical
condition resulting from a combination of the size, shape
arrangement and mineral composition of the soil particles,
may lead to poor crop growth and activity of microbes.
Basic requirement for crop growth in terms f physical
conditions of soils are…..
Adequate soil moisture
Aeration
Optimum soil temperature
Freedom from mechanical stress

15. Dr.AB Jadhav, AC, Pune
Adequate soil moisture
Aeration
Optimum soil temperature
Tillage/Mulching/Irrigation
Incorporation of OM
Liming o other
amendments
Root penetration,
microbial activity
Soil Structure Indirectly Affects….

16. Dr.AB Jadhav, AC, Pune
Component Per cent
1 Mineral matter 45
2 Soil water 25
3 Soil air 25
4 Organic matter 5
Soil Composition (Volume basis)

17. Dr.AB Jadhav, AC, Pune

18. Dr.AB Jadhav, AC, Pune
Optimum pH: for more availability of nutrients in soil 6.5 to 7.5
Acidic pH : More availability of Fe, Mn, Zn and Cu
Alkaline pH: less availability of P, Fe, Mn, Zn and Cu
More availability of Mo and B at high pH
Continuous and slow persisting action of this acid removes large quantities of
Ca and Mg by dissolution and leaching. This release of acids
Decomposition of organic matter releases
Organic acids like
carbonic acids
Inorganic acids like
Sulphuric and nitric acids
3. Soil Reaction (pH)

19. Dr.AB Jadhav, AC, Pune
4. Soil Temperature
Soil temperature affects most of he physical chemical and
biological properties of soil
Physical Properties
Indirectly affects soil
texture and structure
Chemical Properties
Nutrient availability,
pH
EC
Dissolution
Precipitation
Biological Properties
Decomposition
Root growth
Microbial growth/population
Germination
Suitable temp. for microbes
25 to 350C

20. Dr.AB Jadhav, AC, Pune
5. Soil Moisture
Nutrient availability &
root penetration
Root inerception, mass
flow, diffusion
Soil moisture affects
various phenomenon
soil
Moisture at FC-
optimum nutrient
availability
Excess moisture-
leaching losses
Mineralization
Microbial
activity/decomposition

21. Dr.AB Jadhav, AC, Pune
6. Soil Air
Soil
reaction
Microbial
activity &
population
Decomposition/
mineralization
Symbiotic
N-fixation
Nutrient
availability
Root growth

22. Dr.AB Jadhav, AC, Pune
Composition of Soil Air

23. Dr.AB Jadhav, AC, Pune
Mineralization
Leaching losses
Immobilization Fixation of
nutrients
Clay
Al-P
Fe-P
Soil Available
Nutrients

24. Dr.AB Jadhav, AC, Pune
Total Nutrient Content
• Total nutrient content may be high in soil but its
availability may be less
• Conversion of total to available is a biochemical
processes mediated by microbes.
• Microbes and OM content plays imp. role for
mineralization
• Soil may have higher nutrient content but to make
them available various factors are involved.
• Some soils have high fertility but may not be
productive.

25. Dr.AB Jadhav, AC, Pune
Organic
Matter
Mineralization/im
mobilization
Decomposition
causes nutrient
release
Microbial activity
& population
Symbiotic N-
fixation/Chelating
agent
Release of fixed
nutrients
Improvement in
physical properties
& Enhances WHC

26. Dr.AB Jadhav, AC, Pune
Plant
Species
Variety
Rooting
pattern
Climate
Season
Humidity
Temperature

27. Dr.AB Jadhav, AC, Pune
Irrigation
• Quality
• Management
• Type of irrigation
Fertilizer
• Application method
• Type of fertilizer
• Time of application

28. Dr.AB Jadhav, AC, Pune
Management/cultivation
• Tillage
• Compaction
• Problematic soil

29. Dr.AB Jadhav, AC, Pune
Measures to Overcome Deficiencies and Toxicities.
Maintenance of soil physical properties of soil
Soil test based use of fertilizers
Irrigation water testing
Organic manure application
Use of multi-nutrient containing fertilizers
Use of micronutrients as per the deficiency symptoms through foliar spray

30. Dr.AB Jadhav, AC, Pune
1] pH affects the stability and performance of insecticides
Pesticide performance (especially insecticides) can be dramatically affected if the water
you use is alkaline (with a pH between 7.5 and 9.0). This can lead to alkaline hydrolysis,
which causes the pesticide to decompose to an inactive form – resulting in poor insect
control.
The solution:
Decomposition can be slowed or prevented by using an acidifying product solution to
achieve a pH level of 6.0 or below. Acidified pesticide sprays frequently provide improved
initial pest control and longer residual control.
CLICK HERE for list outlining recommended pH levels for a number of common
insecticides, fungicides and herbicides (by product name and active ingredient).
2. Your pH impacts solubility and nutrient uptake.
Nutrients must be present in water-soluble form for effective plant uptake. Fertilizer and
nutrient products that have a neutral pH and low water solubility make it hard for plants
to immediately absorb the nutrients.
The solution:
Acidifying the water to a safe level will increase solubility of nutrients within the spray
tank, making them more readily available for plant uptake. Where quick response is
desired, such as in fast-growing crops or where deficiency correction is urgent, this effect
is especially important.

31. Dr.AB Jadhav, AC, Pune
3. Foliar sprays require an acidic pH for proper absorption.
Foliar absorption is pH dependent. The pH level regulates the complex electrostatic
repulsion and attraction phenomena within the plant’s cuticle. For example, it is believed
that the optimal pH level for phosphate absorption and utilization is between 3 – 3.7. There
is evidence that zinc is absorbed best at a pH range between pH 4.1 – 4.9. While much
research needs to be done, it is clear that optimal pH levels vary according to each nutrient
and its carrier.
The solution: Again, acidify the water and seek the advice of an agronomy professional if
required.
4. Extreme pH imbalances can burn the plant surface.
Plants are generally tolerant of sprays with a wide range of pH. Naturally, extremes at
either end of the pH scale should be avoided.
Phytotoxicity is a chief concern. A spray solution with a significant pH imbalance can
“burn” the plant, and result in soft tissue death, stunting, russeting, leaf spotting, dead leaf
tips, dead areas between leaves and distortion of the leaves and reproductive organs
The solution: Avoid extreme pH levels in a spray solution. Spray solutions should not be
acidified if they contain lime, lime sulfur, or fixed copper products where copper may
become solubilized by the acidity resulting in possible plant injury.
Note: Other factors besides pH that affect phytotoxicity are concentration, salt index,
chemical reactivity, and weather conditions.

32. Dr.AB Jadhav, AC, Pune
Management of pH for Spray Solution
 As a general practice, spray solutions work best in an acidic solution (pH 4.0 – 6.0).
 Pesticides are most effective at a pH of 6.0 or below.
 Phosphate is absorbed best at a pH slightly below 4.0.
 Most spray products become more soluble as pH decreases.
 Extremely high or low pH levels can cause leaf burn.
 Spray solutions should not be acidified if they contain lime, lime sulfur, or fixed copper
products, carbonate, hydride.
 Acid spray solutions help control certain fungi and may be a factor in maintaining
populations of some beneficial insects.
It starts by knowing the pH level of your water supply. When it comes to product mixing and
compatibility, always follow the labels and consult with your farm supply retailer if you have
any questions. They may recommend use of an acidifying product or a tank mix adjuvant
designed to improve solubility, compatibility and efficacy.

33. Dr.AB Jadhav, AC, Pune
Soil & Plant Critical limits for Micronutrients
Micronu. Critical limit
(ppm)
Fertilizer Application method
Soil Plant Soil
(kg ha-1)
Foliar -
simple salts(%)
Chelated
Fe < 4.5 < 50 FeSO4 10-40 0.5 0.2
Mn < 2.0 < 20 MnSO4 10-40 0.5 0.1
Zn < 0.6 < 20 ZnSO4 10-40 0.5 0.2
Cu < 0.2 < 4 CuSO4 10-40 0.1 0.1
B < 0.5 < 2 Borax 5-10 0.2 --
Mo < 0.05 < 0.1 Na2MoO4 1-2 0.1 --

34. Dr.AB Jadhav, AC, Pune