Soil moisture conservation role of mulching and hydrophilic polymers; Methods to conserve moisture, mulch types, polymer types, importance, advantages and disadvantages

1. Soil Moisture Conservation: Role
of Mulching and Hydrophilic
Polymers
Sukhjinder Singh Mann

2. SOIL MOISTURE
• Water contained in soil is called soil moisture.
The water is held within the soil pores. Soil water
is the major component of the soil in relation
to plant growth
• Not all the water, held in soil, is available to
plants. Much of water remains in the soil as a thin
film. Soil water dissolves salts and makes up the
soil solution, which is important as medium for
supply of nutrients to growing plants

3. Soil moisture constants

4. • The amount of water that a soil contains at each of these
equilibrium points is known as soil moisture constant.
• Gravitational water:- when water in the macropores
moves downward under the influence of gravity beyond
the root zone.
• Hygroscopic water:-Evaporation from surface and
moisture absorption by growing plant further reduce the
amount of water in the soil until water no longer moves
because of capillary force .it is held so tightly as thin film
around soil partical that it cannot be used by plants. This
water is called hygroscopic water
• Capillary water:-when supply of water in soil is
stopped,water continue to drain from the larger pores for
one or two days and become negligible thereafter .The
macropores are again filled with air .The micropore are
still filled with water and moves due to capillary forces.
This water is called capillary water

5. • There are two more constants
• Field capacity
• Wilting cofficient
• With the downward movement of water all macro and micro
pores are filled up. It is the amount of water held in the soil
when all pores are filled. Sometimes, after application of water
in the soil all the gravitational water is drained away, and then
the wet soil is almost uniformly moist. The amount of water
held by the soil at this stage is known as the field capacity or
normal moisture capacity of that soil
• As the moisture content falls, a point is reached when the water
is so firmly held by the soil particles that plant roots are unable
to draw it. The plant begins to wilt. At this stage even if the
plant is kept in a saturated atmosphere it does not regain its
turgidity and wilts unless water is applied to the soil. The stage
at which this occurs is termed the Wilting point and the
percentage amount of water held by the soil at this stage is
known as the Wilting Coefficient.

6. Soil moisture losses
Evapotranspiration (ET)
1. Evaporation losses occur directly from the soil.
2. Transpiration losses are through plants.
• The potential evapotranspiration (PET) is the
maximum amount of water that could evaporate
and/or transpire when moisture is not limiting.
• When the PET is high, plants must draw heavily on
soil water and transpiration can occur faster than the
plants can draw water from the soil which may
eventually cause wilting.

7. Soil moisture conservation
• Organic matter
• Green manuring
• Crop rotation
• Mulching
• Hydrophilic polymers

8. Methods to conserve moisture
 Organic matter:-
• It influences many of the physical, biological and chemical
properties of soil.
• Soil organic matter generally has a positive relationship on
water availability, regardless of the soil texture.
• Crop residues left on the soil surface can conserve
moisture by reducing evaporation. Most evaporation from
soil occurs when the soil is wet.
• The presence of crop residues protect the soil from solar
energy and acts as a windbreak to reduce evaporation
• Residues also aid in moisture retention by reducing water
losses due to runoff. As with mulches, crop residues also
intercept rain drops, thus reducing soil detachment,
dispersion and compaction.

9. Crop rotation:-
• Growing a different crop each year prevents organic
matter loss, improves soil structure and reduces the
incidence of weeds and pests.
• The better Crop rotations can also lead to greater
efficiency in soil water utilization.
• For example, deep rooted crops following shallow
crops can take advantage of the extra reserve of
deep moisture which was unavailable to the shallow
rooted crop.
Green manuring
• Improved soil structure help for more moisture
conservation through better infiltration and water
holding capacity.

10. Mulching
a protective covering is placed over the ground.
 Advantages
• Conserves soil moisture
• Moderates soil temperature
• Controls weed growth
• Reduces soil compaction
• Reduces soil erosion
• Preventing leaching of fertilizers
• Reduces incidence of soil-borne diseases
• Reduces fruit rot by eliminating contact b/w fruit & soil
• Reduces winter injury
• Provides conducive environment for plant growth
Lkecki et al (1997)

11. TYPES OF MULCHING
ORGANIC MULCHES
• The organic materials such as
crop residues & by-products
from farm manure &
byproducts of timber industry,
when used for mulching.
• Examples- Dry leaf mulch,
Paddy straw mulch, Paddy
husk mulch, Jowar trash, Saw
dust, Dry grass, Dry sugarcane
leaves, Dry coconut leaves,
Dry coconut husk, Paper
mulch
INORGANIC MULCHES
• The inorganic mulches such
as plastic films, when used
for mulching are k/as
inorganic mulches.
• Examples- plastic film,
metal foil, sand, stone,
gravel, etc.

12. INORGANIC MULCHES OVER
ORGANIC MULCHES
• The organic mulches, though beneficial, were
found to have inherent weaknesses & not
easily available in large quantities. The plastic
films, however, are easily available, easy to
handle, transport & lay

13. ORGANIC MULCH
MATERIAL
THICKNESS OF
MULCHING
COMPOST 3-4 INCHES
GREEN LEAVES 3-4 INCHES
DRY LEAVES 6 INCHES
GRASS CLIPINGS 2-3 INCHES
BARK 2-4 INCHES
WOOD CHIPS 2-4 INCHES
NEWSPAPER ¼ INCH
ONION/GARLIC SCALE 2-3 INCHES

14. TYPES OF PLASTIC MULCHES
• Black plastic mulch film: helps in conserving moisture, controlling
weed problem and reduces the outgoing radiations (Lamont, 1999; Aniekwe
et al. 2004)
• Transparent plastic film: increases the soil temperature and mostly
used for soil solarization (Lamont, 1999; Coleman, 1995)
• IRT mulch: Infra Red Transmitting (IRT) mulch results in warmer soils but
less than black plastic but cooler soils than clear plastic. Mostly used to retard
weed growth (Lamont, 1999)
• Red mulch: new color mulch investigated recently. Results in reducing
early blight of tomato (Lamont, 1999)
• Photodegradable plastic mulches: formulated to break down after a
certain no. of days of exposure to sunlight
• Bio degradable plastic mulches: broken down by microbes
(Rangarajan et al., 2003)

15. EFFECT OF PLASTIC MULCH
• Soil temperature: Based on colour of plastic mulch. Black mulch
increases the temp than control (Anikwe et al., 2007)
• Soil water content: black plastic mulch maintain high soil water
contents than control (Li et al., 2001)
• Improve water use efficiency by reducing soil water evaporation and
exploiting deep soil water and support shoot biomass accumulation
(Li and Zhao, 1997)
• Drip irrigation along with plastic
mulch increases the water and
nutrient use efficiency and also
control weed (Vazquez et al., 2006).
Plastic mulch with drip line
in case of Mango tree

16. Mulch working

17. Moisture content (%) (0-15 and 15-30 cm) below soil surface
Kumar et al, 2014

18. Soil moisture content at 15 and 30 cm depth under mulches in Nagpur mandarin
Shingure et al,2003

19. Disadvantages of mulches
• Mulches have been found to increase Phytophthora
root disease in apple orchards (Merwin et al., 1992)
• Rodent damage in orchards (Prokopy, 2003)
• Costs for growers, making mulch systems less
profitable than conventional orchard management
(Edson et al., 2003).
• Disadvantage of mulching is spring frost damage of
flowers in early cultivars of strawberry (Plekhanova
and Petrova, 2002)

20. HYDROPHILIC POLYMERS
• Hydrophilic polymer are class of polymers which dissolve or
swollen by water.
• Together they form three dimensional network of
macromolecules carbon chain which have tremendous capacity to
absorb solution as much 100 times their weight (Ekebfe 2011)
• Polyacrylamides in soil were also able to reduce the amount of
water lost from the soil through evaporation (Al-Omran & Al-
Harbi, 1997).
• When mixed with the soil, they form an amorphous gelatinous
mass on hydration and are capable of cyclical absorption and
desorption over long periods of time, hence acting as a slow-
release source of water in the soil.
• Under rain fed conditions they may be expected to increase the
survival of seedlings by increasing the time to wilting between
rainfall events

21. • Types of Hydrophilic polymers
Natural HPs: polysacharides, polyuronids,
Aljinic acids
Synthetic HPs : polyveneyl alcoholes (-
CH2OHOH-)n or
polyacrylamids (-CH2CHCONH2-)n.

22. Groups of HPs
Synthetic polymers are used more than natural
polymers because they are more resistant to
biological degradation
• SCP (starch polyacrylamide graft copolymers)
• PVA (venylalcohol-acrylic acids)
• PAM: Polyacrylamides (acrylamides sodium acrylate
copolymers)
(Peterson, 2002)

23. HPs used in agriculture
• Aquasorb: Cross-linked copolymers of acrylamide and
potassium acrylate from SNF Floerger, France
• Agrihope: Gel-conditioner, cross-linked sodium polyacrylate,
Nippon Shokubai Co., Japan
• Broadleaf P4: High molecular weight, cross-linked PAM,
Agric. Polymers Ltd. UK
• Hydrogel: Starch copolymer, Potassium acrylate, Finn
Corporation, USA
• Hydrosource: Cross-linked PAM, potassium or sodium
acrylate
Bhatt et al. 2009

24. Synthetic polymeric materials: Major classes
• Water-soluble polymers are linear soluble hydrophilic or ionic
polymers used as wetting agents leading to more effective water-
holding capacity
• and more stable soil aggregates.
• PEG, PVA, CMC, H-PVAc, H-PAN, PiBMA, NaPAA, PVAcMA, and
water-soluble PAAm.
• PVAcMA and H-PAN are used for preventing soil surface crusting
and for moisture retention.
• Polyelectrolytes improve the chemical, physical, bacteriological, and
agronomical aspects of soils aside from supporting reclamation of
saline and alkaline soils.
• Linear PAAm and cationic guar derivatives (polysaccharides) have
been applied in sprinkler irrigation water to sandy soils to maintain
stability, infiltration, and preventing surface crusting.
• However, the use of water-soluble polymers in reclamation of clayey
soils reduces root growth of plants as a result of inadequate aeration.

25. Effect of super-absorbent polymers and drought
Tango et al. (2014)

26. Importance of HPs
• Improving nutritional and water status of the plant
• Improving soil physical properties
• Aiding seed germination and emergence and
increasing seed survival
• Increases soil water holding capacity, yield and water
use efficiency of plant
• Decreases the negative effect of soil salinity on plant

27. Conclusion
• Mulches are the simplest and cheapest method to
conserve soil moisture
1. Organic mulches_____________25%
2. Inorganic mulches ____________75%
• Hydrophilic polymers are recent advancements in soil
moisture conservation, application with the growing
media on nursery level
• Under Punjab conditions water use efficiency
increases by the use of laser leveling, drip irrigation
and mulching