Water and Plant Growth

1
Water and Plant Growth

• All water used for irrigation contains some
  dissolved materials. Some water has none
  dissolved materials
• Salt has the biggest effect.
• Weed seeds

2
As a user

• One should know the effects that your water
  quality irrigation practices used have on
• Salt content (salinity) of the soil.
• Sodium status (sodicity) of the soil.
• Rate of water infiltration.
• Toxic elements content of the soil.
• Soil nutrient status and groundwater quality.
• Plugging of micro irrigation system.

3
Irrigation

• We irrigate to replenish the water that is lost
  due to
• Evaporation.
• Used by growing plants.
• Transpiration.
• Drainage passed the root zone.

4
Irrigation method used.

• Application method depends on
• Type of crop being grown.
• Soil texture depth.
• Water cost.
• Topography.
• Water cost.
• Water quality.

5
Irrigation Frequency

• Once again, one must consider several factors.
• Type of crop being grown.
• Soils water holding capacity.
• Leaching requirements.
• Climatic considerations.
• To assist you, you can go to this web site.
• www.cimis.water.ca.gov

6
How does water enter the soil?

• through pores in the soil
• sandy soils have the largest pores, but are often
  filled with other material
• medium textured soils (loamy) have good water
  entry properties
• clays, pores swell shut when they get wet

7
What is Adhesion?

• it is the attraction of two different molecules
  (water to soil)

8
What is Cohesion?

• it is the attraction of two similar molecules
  (water to water)

9
What is the importance of adhesion and cohesion
in soils?

• water molecules are strongly attracted to soil
  minerals and organic materials due to adhesion
• water molecules are also strongly attracted to
  each other due to cohesion
• soil holds a thin layer of water, that layer
  holds a thin layer of water etc., the farther
  away from the soil particle you get, the looser
  the water is held

10
What is the importance of adhesion and cohesion
in soils?

• -water then tends to move from wetter places to
  drier places. Roots remove water, then water is
  drawn from surrounding areas
• in dry conditions, water moves slowly and only
  fractions of an inch, thus roots must be well
  distributed

11
How is soil water classified?

• 1) Hygroscopic Water is held so strongly by the
  soil particles (adhesion), that it is not
  available to the plants
• 2) Capillary Water is held by cohesive forces
  greater than gravity and is available to plants
• 3) Gravitational Water is that water which cannot
  be held against gravity
• as water is pulled down through the soil,
  nutrients are"leached" out of the soil (nitrogen)

12
Saturation Percentage

• Immediately following an irrigation, the film of
  water is thick, and smaller pores are full of
  water. The soil particles can not hold the
  water. It is easily lost to the plant.
• 1/10 Atmosphere (Near Saturation)

13
What is Field Capacity?

• when the soil contains the maximum amount of
  available water, the greatest amount of water it
  can hold against gravity.
• 1/3 Atmosphere
• ½ saturation

14
What is Permanent Wilting Point?

• the soil has so little water, that plants can no
  longer recover from wilting.
• roots can no longer take in water.
• 15 Atmospheres.
• ¼ Saturation

15
What is Available Water?

• the amount of water between field capacity and
  wilting point

16
What is Water Table?

• the level beneath the soil which the soil is
  saturated with water
• marshes develop where the water table is just
  below the ground surface
• if the water table is not too low, dryness tends
  to correct itself through capillary movement

17
What affect does soil particle size have on its
water holding ability?

• the smaller the individual particles are, the
  more surface area there is, thus it will hold
  more water
• consider a book compared to all of its pages

18
What factors determine the amount of soil
moisture?

• amount of snow, rain, irrigation
• rate which soil permits water entry
• water storage capacity of soil
• evaporation rate
• height of water table
• rate which water can move within the soil
• amount and type of vegetation

19
How is soil moisture measured?

• soil is weighed dry, then wet (expressed as a
  percent of dry wt)
• electrical conductivity

20
When to irrigate

• 1. Tensiometer measures in atmosphere
• 2. Electrical Resistance Blocks (gypsum blocks)
  electrical resistance
• 3. Neutron probe neutrons collide with
  hydrogen atoms soil (water in soil)
• 4. Thermal dissipation sensor measures
  dissipation of heat
• 5. Time domain reflector high speed microwave
  pulse

21
How can we increase the amount of available water
to the plant?

• Precipitation better utilize snow and rain by
  keeping the water on the soil surface.
• windbreaks
• keep snow in place (cover)
• strip cropping
• contour strips
• grassland farming
• Irrigation may not be practical
• Water entry reduce cultivation, green manures,
  correct alkaline soils

22
How can we increase the amount of available water
to the plant?

• Storage capacity increase O.M. (manures)
• -Evaporation conservation tillage, shelter
  belts, strip cropping
• -Water movement in soil O.M.
• -Vegetative covering holds water

23
Water Analysis Terminology

• Dissolved salts ions
• Cations positively charged ions
• Anions negatively charged ions
• pH expresses the acidity or alkalinity
• Total Salt Content electrical conductivity
  (EC) also reported as decisiemens per
  meter (dS/m)1
• Total Dissolved solids (TDS) total salt content

24
Water Analysis Terminology

• Parts per million (ppm) 1 part of salt to 1
  million parts of water.
• Milliequivalents per liter (meq/L) is a
  meacurement of charge concentration per liter.
• Most meaningful method of reporting chemical
  components of water. It takes the atomic weights
  divided by the valence.

25
Cations determine the physical as well as
chemical properties of soil.

• Calcium Ca
• Magnesium Mg
• Sodium Na
• Potassium K

26
Anions indirectly affect the physical
properties of soil by altering the ratio of Ca
and Na attached to the clays.

• Bicarbonate HCO3-
• Carbonate CO3
• Chloride Cl-
• Sulfate SO4
• Nitrate NO3-
• Boron B

27
Evaluating Irrigation Water

• Saline soil contains soluble salts in such
  quantities that they interfere with plant growth.
• Sodic Soil contains enough sodium adsorded on a
  clay particle to interfere with plant growth.

28
Evaluating Irrigation Water

• Salinity hazard irrigating can lead to a build
  up of soluble salts in the root zone.
• Sodium or permeability hazards results in
  reduced rates of water penetration.
• Applying gypsum, reduce pH bicarbonate of water
  by adding sulfuric acid, and incorporating sulfur
  into problem soil if adequate free lime is
  present.

29
Toxic Constituents

• Boron Hazard
• Chloride Hazard
• Sodium Toxicity

30
Salt movement in soil.
31
Salt movement in soil.
32
Drainage

• What do we do with our tail water?
• What is the problem with tail water?

33
Water for sprinkler

• Benefits
• Less loss of water.
• Deep percolation of water may be less.
• Problems
• Not for every crop.
• More loss of water.

34
Water for low volume

• Benefits
• Tail water runoff can be completely eliminated.
• Evaporation may be reduced.
• Total volume of soil wetted is usually less
• Deep percolation of water may be less
• Problems
• Plugging caused by insoluble calcium carbonate,
  algal growth, suspended solids, reactions to
  injected fertilizers.