unit 3: water chapter 6. unit 3: water unit 3 objectives: understand the role and characteristics of...
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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
Conserve/store water Ex.? Sorghum, millet
Mesophytes – grow in moderately wet areas 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 Roots have no other means of nourishment
Water adds turgor (stiffness) to the cells 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