Transcript Unit 3: Water - Kaskaskia College

Unit 3: Water
Chapter 6
Unit 3: Water

Unit 3 Objectives:





Understand the role and characteristics of
water
Knowledge of the concepts of transpiration
and its relationship to plant water needs
Plant water needs
Explain water movement within the plant
Describe symptoms of water shortage
Unit 3: Water

Characteristics of Water


Ex. A 1 ton load of fresh cut alfalfa would
weigh only 520 lbs. w/out the water
What molecules combine to form water?


How much of each?
Exists in 3 forms



Liquid - 32° - 212°F
Vapor - >212°F
Solid - <32°F
Unit 3: Water

Resistant to temperature changes


Requires the most heat energy to raise temp
1°C
Universal solvent


Can dissolve almost anything
Powerful, yet gentle


Dissolve rock
Hold an enzyme, medium for biochemical reaction
Unit 3: Water

Water is the determining factor regardless
of the temp zone




Productivity
Growth
Survivability
Role of Water


Necessary part of cells and tissues
Biochemical medium that helps move and
dissolve nutrients from roots to shoots, and
storage
Unit 3: Water




Chemical reactant in chemical processes
(photosynthesis)
Cell turgor
Responsible for stomata function and
maintaining plant turgidity
Coolant/temp buffer
Unit 3: Water

Plant classification based on their water
needs

Xerophytes – grow in dry places



Mesophytes – grow in moderately wet areas


Conserve/store water
Ex.? Sorghum, millet
Most cropping plants
Hydrophytes – best in very wet/flooded regions


Water lily
Rice
Unit 3: Water

Precipitation



Precipitation forecasts are most useful for
planning
Measurable precipitation must be .01” or
more
Weather forecasters calculate the
probability of rain within a system and the
area by which it may cover
Unit 3: Water


Computer modeling is now very common
to help predict rain, amounts, etc.
Help make management decisions on:




Planting
Harvesting
Irrigation
Weather Outlooks



6-10d
30d
Longer?
Unit 3: Water


Normal temp and precipitation is a 30yr.
Avg. calculated every 10 yrs.
Water Loss in Plants



Directly proportional to the amount of
exposed surface area
Gases and water vapor can be exchanged
through the leaf stomata
How do plants adapt their leaf structures
to deal with the climate?
Unit 3: Water


Most water absorbed through the root
hairs
Wilting occurs when water loss>water
uptake





Life processes may slow or stop
Stunting
Yellowing
Drop leaves
Death
Unit 3: Water


Can result in yield loss and decreased
profit
Water stress risk




High in a germinating seed
High at flowering or fruit set
Pollen may not develop properly
Indications of water shortage


Plant will often display before damage is done
Greenish-blue tint (leaves)
Unit 3: Water

Wilting/rolling



May occur only during the day and recover at night
 Need water, but not emergency
Stays wilted through the night
 Immediate need for water
 High damage risk
Reducing water loss from the soil


Proper plant spacing
Till soil appropriately so plants may grow to
subsurface moisture
Unit 3: Water






Avoid tillage during growth that may damage
roots and open soil for moisture escape
Leave lay fallow
Control weeds
Use mulches
Early planting
Sometimes, water must be supplied
through irrigation

What are the different types of irrigation
systems?
Unit 3: Water

Excess water


Reduces availability of oxygen and carbon
dioxide
Can run the risk of:




Diseases
Root and seed rot
Death
Symptoms




Yellowing
Stunting
Leaves dropping
“Spongy”, slimy feeling to the plant
Unit 3: Water

Crop selection and management should be
carefully considered based on what type of
soil conditions you have


Crop
Soil management




Ridge till
Raised seedbeds
Planting time
Other options
Unit 3: Water

Water for Plants

500 lbs. of water/lb. dry plant material



Only 5lbs. actually used in the plant
Other 495lbs. lost through leaf stomata by
transpiration
Plants use capillary water

Capillary water moves freely in the soil
Unit 3: Water

Water sources NOT available to plants



Gravity water – lost to drainage
Hygroscopic water – bound to soil particles
Movement of Water

Translocation


Transported water from roots to shoots via
xylem
Carries nutrients and metabolites

Metabolites are products of chemical reactions or
metabolized substances of the plant
Unit 3: Water

Moves phloem to transport sugar produced
from photosynthesis to all parts of the plant


Water adds turgor (stiffness) to the cells






Roots have no other means of nourishment
Provides support to new leaves and tissue
Assists w/ keeping the plant’s shape
Carries transpiration
Buffers temp changes
Stabilizes pH in metabolism
Facilitate chemical reactions
Unit 3: Water


Maintain cellular cytoplasm
Transpiration





Evaporation of water from leaf and plant
surfaces
Last step of the water pathway
Plant respiration & photosynthesis result in
water and heat
Transpiration cools the plant
>90% of all water entering a plant is given off
through this process
Unit 3: Water

Water lost through the leaf stomata



Free exchange/release of water vapor
Close at night and during stress
Water in the Soil

Evapotranspiration


Water removed from soil by soil evaporation
and plant transpiration
Soil evaporation can account for 20-30% of
total ET
Unit 3: Water



Soil evaporation rates are higher after rainfall
and irrigation
Evaporation & transpiration are driven by the
atmosphere’s influence to dry the soil
Just like water drawn through the plant, it’s
drawn to the atmosphere


High conc. ---- Low conc.
ET & Crop Yield

Crop yield directly related to ET
 Increases linearly w/ increase in ET to maximum
 Extra water above ET demand will not increase
yield
Unit 3: Water



Ability of plant to transpire water varies w/ climate
and variety
All water can’t be turned into ET and yield
Factors Affecting ET

Weather
 Power of atmosphere drives soil evap. & crop
transpiration
 Air temp, humidity, solar radiation, wind
 What types of days would result in increased ET?
 Crop and soil may or may not be able to meet
atmospheric ET demand
Unit 3: Water
Sets the demand for crop ET
 Helps us to make irrigation decisions
Crop type
 Different crops use different amounts of water
during a growing season
 See tables 6-1 through 6-6
 Why is alfalfa so high?
 Differences in corn, SB are due to planting dates
and days to maturity


Unit 3: Water


Crop Growth Stage
 ET related to leaf surface area
 Which would transpire more, a large plant or a
small one?
 Maximum ET just prior to the reproductive stage
 Avg. max ET for corn, SB, wheat ~.3-.35”/d
Crop Variety
 Relative maturity has most impact on seasonal
ET needs
 Ex. 120d corn will need more water than 85d
corn
 Difference is total water use, not daily amount
used
 Why might this be important?
Unit 3: Water


Crop Population
 What population do you plant?
 Do you think that ET would be higher or lower if
you decreased population by 25%, 50%?
 What might be different w/ dryland farming?
Irrigation?
Surface Cover & Tillage
 Cover crops, mulch will help decrease ET
 Even as crops grow and shade the soil ET
continues
Unit 3: Water


Availability of Soil Water
 Relates to ability of the soil to transport water to
the root zone
 Speculate what types of soils will have more/less
trouble w/ providing the plant sufficient water
Estimating ET



Need weather stations to calculate temp, humidity,
wind, radiation
Can calculate potential ET
Most important if you are irrigating
 Why?
Unit 3: Water

Irrigation

Water can be lost in two ways:



Runoff – rainfall rate exceeds soil’s infiltration
rate
Deep percolation – rainfall exceeds the soil’s
water holding capacity
Irrigation systems

Selection of a system should be matched w/:

Land slope, water intake rate and holding capacity,
crop water tolerance, wind
Unit 3: Water

Flood Irrigation





Used on leveled land
Orchards, vineyards, hay, pasture, cereal grains
Slope of .1 to .4’/100’
Water enters through a head ditch and released into
the field bound by levees
Furrow Irrigation





Very widely used
Water moves through furrows between plant rows
Infiltrates the soil through capillary action
Efficient, but expensive and labor intensive
Very uniform crop maturation
Unit 3: Water

Sprinkler & Drip Irrigation



Pumping unit, control head, mainline and pipes,
lateral pipes
Emitter – very small openings (pinhole size), misting,
fogging, drip, etc.
 Low psi (5-40)
 Lower flow rate (.5-15g/hr)
Sprinkler – more of a spray
 Rotating, stationary nozzles, perforated pipe
 Can operate from 5-80psi depending on nozzle
size
Unit 3: Water
Discharge varies from few gpm to 1000gpm
 Coverage area up to 500’
Things to consider:
 Nozzle size, jet angle, wind, overlap, sprinkler
rotation
 Important for determining application rates,
spacing, droplet size
 50-60% overlap



Irrigation Efficiency

Not all water sprayed reaches the ground

~15% lost to direct evaporation
Unit 3: Water



Drip systems may lose only 10%
Sprinklers may lose 25%
Timing of Irrigation




Water-holding capacity of soil and available
plant water or keys for determining timing
Must know how much water is in the bank
When should irrigation begin?
Determining irrigation needs


Feel test
Electrical conductivity
Unit 3: Water






Moisture probe
Evaporation pans
Computer program
Water budgets
Tensiometers
Climate Concerns

More difficult to manage irrigation in humid
regions



Why?
What is the difference?
How would we change our irrigation strategy?
Unit 3: Water

Arid & Semiarid Regions



What dependence will we have on irrigation?
What will the return be?
Water use can be .25”/d
Unit 3: Water

Unit 3 Assignment:

Ch. Review questions pg. 137


Nos. 6-9, 11, 12, 14, 16
Each will be worth 2 pts for a total of 16 pts