Water Resources and Irrigation - Soils and Soil Supplements - Lecture Slides, Slides for Biology. Ankit Institute of Technology and Science

Biology

Description: These are the lecture slides of Soil Supplements. Key important points are: Water Resources and Irrigation, Importance of Irrigation, Application Methods, Relating to Irrigation Efficiency, Stabilizing Water Resources, Profitability, Quality of Water, Earliest Days, Circulated Water, Precipitation
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Unit 15: Water Resources & Irrigation

Unit 15: Water Resources & Irrigation

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Objectives

• Facts, issues, & importance of irrigation • Amounts of water needed for crop production • Application methods for irrigation • Issues relating to irrigation efficiency • Stabilizing water resources

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Introduction

• Water tends to be determining factor in profitability

• Quantity & quality of water are critical all over the world – Aren’t we lucky?

• Irrigation dates back to the earliest days of farming

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Water Resources for Irrigation

• Earth contains ~327 mi3 of water – 97% in oceans – 2% in glaciers & icebergs – .03% in circulated water

• Precipitation, transpiration, evaporation • Includes all surface water, atmospheric water vapor,

etc. • Hydrologic cycle

• Supply of water not evenly distributed – Can you give some examples?

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Water Resources for Irrigation

• Water Scarcity – Looming problems w/ water supplies

• Rapidly growing populations • Effects of global climate change • Conflicts over water resources

– Agriculture is, by far, largest user of water » Account for >70% of water withdrawals

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Water Resources for Irrigation

• Fresh Surface Waters – 60% of avg. annual river flow in U.S. is in stored

reservoirs w/ dams – Dam building in U.S. has basically ended

• Fewer sites available w/ substantial impact for the cost – Environmentalists despise dams

• Why, what impact do they have? • Are they the only ones?

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Water Resources for Irrigation

– Water quality varies • Depends in the geology through which the water flows • Most suitable for irrigation

– Diversion of surface flow waters cheaper than pumping subsurface waters

– Currently ½ of irrigation water from wells

• Groundwaters – Responsible for greatest increase in quantity of

irrigation water = aquifers • May be small to miles long/wide

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Water Resources for Irrigation

Vadose zone – area from soil surface to water table

• Includes capillary fringe – depth from bottom of root zone to top of water table

• Good for collecting/filtering contaminants – Total groundwater storage ~25x more abundant

than surface waters • Supplies ~25% of all groundwater used

– 50% of U.S. citizens obtain their drinking water from ground – 95% of rural households depend on it totally

– Costs more to use groundwater than surface water due to expense of pumps & drilling

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Water Resources for Irrigation

• Mining Aquifers – Rate of recharge – growing concern

• Some fill very quickly, some quite slowly – Depends on source of recharge – Soils

– Water removed > water recharged = mining • Low water tables may cause

– Dry wells – Land subsiding

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Water Resources for Irrigation

• Groundwater supplies ~40% of AZ’s water – Being pumped out 5x rate of recharge

• AR, OK, TX areas overdraft water ~60%

• Irrigation Trends – Irrigated lands comprise ~16% of cropland, but

produce 33% of total harvest – China, India, U.S. – biggest irrigators

• 70% of grain in China irrigated, 50% in India • U.S. – irrigation use declining

– Due to costs, water quality, improved efficiency of irrigation systems

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Irrigation Water Quality

• Water quality continuum: – Drinking water – swimming – industry – irrigation – Irrigation water can contain considerable

contaminants & still be used, if managed carefully – Turbidity – water cloudiness caused by suspended

solids of clays, silts, sands, organic materials • Can fill irrigation canals, seal soil pores, clog irrigation

systems – Water temp – limited concern to irrigators

• Except if cold enough to reduce growth

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Irrigation Water Quality

Hardness – elements in water – generally favorable for irrigation

Biological Oxygen Demand, Chemical Oxygen Demand (BOD, COD) – measures of amounts of oxygen & chemicals dissolved in water

• High BOD’s – decreased oxygen availability – High BOD water can kill fish, decrease soil oxygen

Pathogenic organisms – disease causing agents present in water

Pesticides – even slightest levels bad in drinking water

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Irrigation Water Quality

• Salinity – Most important criteria for irrigation water – Most detrimental affect from irrigation water

• What problems can it cause? • Only takes small amounts to cause detrimental effects

– If salt levels low, adequate leaching ability in soil still necessary to rid salts

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Irrigation Water Quality

• Sodium Hazard (Sodicity) – High levels of Na causes aggregate dispersion – Seals soil pores – decreases permeability

• Toxicities – B – most common toxicity in irrigation water

• Relatively low window from deficient to toxic – Can easily have trouble either way, depending on soil

– Cl – may cause damage in fruit/vegetable crops

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Meeting Water Needs of Plants

Consumptive Use – water evaporated + water transpired + water in the plant tissue – Increases w/ conditions that favor more

evaporation – Dailey consumptive use - .1” - .6”/d Evapotranspiration (ET) – evaporated water +

transpired water • Easier to measure due to no measurement of plant

tissue water

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Meeting Water Needs of Plants

• Plant Roots • Depth influenced by access to water & air • Most water absorbed in upper 1-2’

• When to Irrigate – Recommended when ~50% of available water lost

from root zone – Computer-aided equipment can help predict

when • Can be very expensive, unless you have extensive

irrigation

– Two mathematical methods also (see pg. 421)

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Methods of Applying Water

• Border-Strip & Basin Irrigation – Ridges direct water through a strip of land – Works well w/ nearly level soils, gentle slope w/

water flow – Loss of 20-45% of water, if no collection & reuse – Basin Irrigation

• Each area, tree has own basin • Flood basin

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Methods of Applying Water

• Furrow Irrigation – Oldest form of irrigation – Water flow from main (head) ditch through

furrows to end of each row – Crop best if planted on ridges – Accounts for ~40% of all irrigation – Problems

• Deep percolation • Runoff losses • Erosion on soils >2% slope

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Methods of Applying Water

• Slope should be <.25% – Many of these lands are laser-leveled

– Advantages • No moving equipment • Can catch excess water • More efficient use of water

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Methods of Applying Water

Sprinkler Methods  Simulates rainfall Can irrigate variety of land Can be portable More uniform soaking of soil Precise application  Fertigation possible Can be expensive  Foliar diseases can be caused Water quality is critical What can go wrong?

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Methods of Applying Water

– Sprinkler irrigation methods • Lawn sprinklers • Solid-set pipe systems • Center-pivot • Wheel move • Travelling gun

– VRT can be used to improve efficiency • Drip Irrigation

– Most efficient irrigation method – Drip, trickle, microirrigation Docsity.com

Methods of Applying Water

– Frequent, slow, small amounts of water applied – Little/no water lost to surface flow or evaporation

• Savings of 20-50% on water – Installation/maintenance costs high – Greatest improvements in yields, w/ least water

usage – More flexible w/ salt levels – Commonly used in orchards, vineyards,

vegetables, greenhouses – Emitters can plug easily – Difficult to use w/ field cropping Docsity.com

Special Irrigation Techniques

• Irrigating Clay Soils – Difficult due to impermeability, shrink/swell,

stickiness – Major problems

• Inadequate aeration • Rapid infiltration through surface cracks • Slow infiltration once soil is wet • Limited moisture range suitable for tillage

– More frequent, smaller quantity irrigations more effective

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Irrigating Efficiently

Water Use Efficiency – portion of added water used by the plant Average efficiency ~40%  Surface irrigation ~50-65%  Sprinkler ~60-70% (85% if well designed &

managed)  Low flow w/ drops closer to soil surface 91-96%

How to improve efficiency: Reduce water evaporation  Improve equipment, technology, engineering Optimize total crop management

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Increasing Water Supplies

• Revert to dryland farming, deep rooted & drought resistant crops

• Reduce water pollution • Use catch basins for catching excess water,

plant trees/etc.

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Assignment

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