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