Unit 3: Water

1. Unit 3: Water Chapter 6

2. 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

3. 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

4. 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

5. 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

6. Unit 3: Water • Chemical reactant in chemical processes (photosynthesis) • Cell turgor • Responsible for stomata function and maintaining plant turgidity • Coolant/temp buffer

7. 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

8. 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

9. 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?

10. 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?

11. 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

12. 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)

13. 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

14. 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?

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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?

26. 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

27. 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?

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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?

34. Unit 3: Water • Arid & Semiarid Regions • What dependence will we have on irrigation? • What will the return be? • Water use can be .25”/d

35. 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