LH1 WaterPlant and Soil Water Relationships

Many Plants are 90% Water•Water is essential for chemical reactions of plants, especially the process of photosynthesis

•Water keeps cells rigid so that they don’t collapse

•Water is the primary vehicle for transporting plant nutrients, sugars, hormones and all other biochemical molecules within the plant

Water Moves Through Plants From Areas of High Water Potential to Low Water Potential

•Water Potential is essentially the same as Water Concentration

•Areas of High Water Potential include very wet or moist soils or where the molecules of water are greater than molecules of dissolved minerals

•Areas of Low Water Potential include leaf tips where water is actively evaporating, also any tissue such as roots which have high concentrations of dissolved minerals and molecules

OsmosisThe process which water enters the

Root System

•Water is absorbed by the roots through the process of osmosis, which is the diffusion of fluid through a semi-permeable membrane until there is an equal concentration on both sides of the membrane

•Roots and other plant parts contain high concentrations of solutes: molecules dissolved in water necessary for all biochemical reactions.

•Water moves into roots from an area of high water potential to low water potential in an attempt to equalize the contents of the plant cells

Water Travels Upwards in Plants through the Xylem Through Cohesion and

Adhesion

• Cohesion is the attraction water molecules have for other water molecules.

• Adhesion is the attraction between water molecules on mineral particles

Xylem is formed by sections of long ultrathin segments known as vessel

elements or tracheids

Water lost through Stomatal Pores when they are open for

gas exchange is known as TRANSPIRATION

•In temperate climates, due to extreme water loss, at 92-94 deg F, stomata start to close, at 100 degrees all stomata close and the plant “shuts down” and photosynthesis cannot occur

•Stomata close if a dark cloud passes overhead during the day and they close at night.

Stomates are primarily located on the underside of leaves

Transpiration of Water into the Atmosphere is fueled by the Sun’s Radiant Energy and the process of the movement of water through a plant is known as

Transpirational Pull

Each water molecule is “connected” to other water molecules due to attraction of Hydrogen and Oxygen of different molecules

Transpiration increases if:

•Air has low humidity•Temperatures are high• Under warm and windy conditions•If there is full sun, as opposed to cloudy conditions or plants growing in shade

Plants Have Adapted Many Mechanisms to prevent water loss and survive periods of drought

Waxy coating to prevent loss of water Specialized water storage stems

Needle-like Leaves Reduce Surface Area Loss of Water

Summer Dormancy in Mediterranean Climates

Babiana corms grow during wet winters and … Are dormant in the summer

Water Movement in Soil• Gravitational Water: water that moves down

through the soil due to the effect of gravity

• Capillary Water: Water that is held on soil particles and aggregates which can be used by plants

• Hydroscopic Water: Water that is bound tightly to soil particles and not available to plants

A Totally Saturated SoilOccurs During a Rainstorm

Field CapacityA measure of the amount of

water a soil retains after gravitational water drains

•Water is held is small pores between soil particles

• This water is held against the pull of gravity by the forces of adhesion, the attraction of water molecules to other particles

•This water is known as Capillary water. It is the available water in the soil which plants can suck off of soil particles

•Capillary forces can move water laterally or upward through the small soil pores through the cohesion of water molecules from areas of high water potential to low water potential

When all available water is removed by plants or has evaporated there remains

Hydroscopic Water•Hydroscopic Water is held tightly by the soil particle through adhesion

•Plant root hairs cannot obtain this water from the soil particles

Soils differ in their ability to retain water, both capillary and hydroscopic water

•Sandy soils have the lowest field capacity

•Adding organic matter to sandy soils can significantly increase its field capacity

•Clay soils hold more capillary water and also hydroscopic water

•At the point where plants cannot obtain water from a soil they will wilt

•If they are not quickly watered they may reach their PWP (Permanent Wilting Percentage) and die!

With Clay soils, water must be applied more slowly and more water must be applied to water at the same depth as a sandy or

loamy soil

•A clay soil will hold more water in a smaller volume of soil, closer to the surface

*Clay soils take longer to saturate due to its small pore spaces. But when it is saturated it holds onto the water more tightly and water drains less well

More water must be applied to a clay soil to reach the same depth as

sandy or loamy soil

Movement of Water into Soil is

known as Infiltration

*When the application of water is higher than infiltration then run-off will occur

*Infiltrometer gauges how fast water will penetrate soil. Will give you an idea of soil texture.

How to Determine the Water Content of the Soil?

Tensiometer is an airtight, hollow tube filled with water with a porous end inserted into the soil

A vacuum gauge at the other end measures the pull exerted by the soil on the water. The greater the pressure the drier the soil

Hand-Feel Test

Practical Hand-Feel TestAvailable Water

SAND SANDY LOAM CLAY LOAM CLAY

Close to 0%Field capacity

dry, loose grains

dry, loose dry clods break into powder

hard, baked, cracked clods

50% or less(about time to water_

Will not form ball with pressure

appears dry, will not form a ball

crumbly, will hold together

Somewhat pliable, will form a ball

50%-75% Same as above Will form ball but not hold together

Forms ball, a little plastic

Forms ball will form ribbon test

75% to field capacity

Sticks together slightly, forms weak balls

Weak balls, breaks easily

Forms pliable balls

Feels slick

Field Capacity No free water Appears when Squeezed, but moist

Water Quality

Misc. Water Quality ParametersWater Quality Parameter

Oakland Richmond San Leandro

Alkalinity, mg/l bicarbonate

27 - 40.4 53.3 97.4

Alkalinity, mg/l carbonate

1 – 1.2 0.8 2.3

Calcium (mg/l) 4 - 13 12 - 14 23 - 30 60 mg/l aver.

Hardness (mg/l CaCO3) 16 - 24 46 - 60 96 - 130

60-180 acceptable

Magnesium(mg/l)

0.9 – 3.3 3.7 – 4.2 7.1 - 12 125 mg/l maximum

pH 8.7 – 9.3 8.5 – 8.9 8.7 – 8.8 6.8 -7.5 aver.

Potassium (mg/l)

0.5 – 1.0 0.8 – 0.9 1.2 – 1.5

Silica (mg/l) 9.4 – 12.0 8.6 – 11.4 4.1 – 10.9

Sodium (mg/l) 5.6 - 12 16 - 18 22 -28 EPA 20 mg/l

Hard vs. Soft Water

• Hard Water is due to high levels of dissolved minerals, commonly calcium and magnesium

• Causes spots on dishes, scale on shower heads, and can clog drip irrigation emmiters

• Hard Water is worse in S. California • Soft Water has

Guidelines for Using Grey Water in the Garden

• Mix washwater with rinse-cycle water before using on plants

• Some plants are more sensitive, eg. Azaleas and strawberries

• Do not use wash water for potted plants with restricted root zones

• Do not pour directly onto base of plants which may cause crown rot

• Use of black water not allowed by law

• Chlorine in Bleach will damage plants, let water stand overnight before using to let chlorine dissipate

• Boron will burn leaf edges. Fabric softeners contain either boron or metaphosphates containing sodium. Use natural detergents.

• Phosphates will generally not hurt plants, usually acts as a fertilizer, but can cause algae blooms in lakes and streams.

Watering and Irrigation

Hunter Sprayers used for some Large Landscape Installations but wasteful

Underground Watering Systems(E.g. Netafim)

Micro-Sprayers

Microsprayer Set-up

My Microsprayer Set Up!

•Independent Irrigation Timer run by batteries

•Filter

•Pressure Reducer

Many Different Types of Sprayers are Available

Swale Gardens

How Deep to Water?LEAFY VEGETABLES

AND ANNUALS 6 inches – 1 foot

SMALL SHRUBS, COOL SEASON TURFGRASS,

CORN, TOMATOES1 feet – 2 feet

LARGE SHRUBS, TREES, WARM-

SEASON TURFGRASS1.5 feet – 5 feet

Soil Auger to test how deep you are actually watering

How Much Water Do Plants Require?

• Water is loss from plants through TRANSPIRATION

• Water is also lost from the soil surface through EVAPORATION

• Total water loss from plants and soil is known as EVAPOTRANSPIRATION

WATER LOSS THROUGH EVAPOTRANSPIRATION MUST BE REPLACED FOR HEALTHY PLANTS

AVERAGE SEASONAL EVAPOTRANSPIRATION RATES VARY BY LOCATION IN CALIFORNIA

•Evapotranspiration rates are established for different regions of the state

•Coastal Areas have lower evapo-transpiration rate

•Northern California generally has lower evapotranspiration rates than S. California

How Much to Water and How Long to Water?

It all depends on:

• Soil texture• Type of plant and root depth• Evapotranspiration Coefficient,• Wind, heat, rainfall• Topography: slopes usually require more water,

also Southern exposures• You type of irrigation system

Measure Water Application Rate and Depth of Penetration

•Put tuna cans out in various locations

•Turn on irrigation system for 20 min., measure inches of water & multiply by 3 to determine inches of water per hour

•If the amounts vary by more than 15-20% your irrigation system needs adjusting

•Run normal irrigation time or until run-off starts. Check to see how deep the water has penetrated

•Adjust water time to allow water to penetrate proper depth

What time of Day to Water?

Morning is best• Less evaporation, better water pressure• Plants begin using water as soon as sunrise• Fewer disease Problems, no children

Midday is worst• High evaporation, • Low water pressure• Wind, children

Evening has problems• Low water pressure• Disease and rots

• Wind, less water Pressure

How to Conserve Water in a Drought?

• Prune back large plants to reduce water need and loss• Move container plants to shade and out of wind• Mulch to reduce water evaporation• Water deeply and infrequently• Remove weeds, remove your lawn• Plant drought tolerant natives and Mediterranean

Plants• Do not fertilize heavily to avoid lush growth• Create berms to localize water