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AGRI 2220 > Soil Salinity + Sodicity > Flashcards

Soil Salinity + Sodicity Flashcards

1
Q

What is an example of an ancient civilization that did so much damage to their soils through salinization that they had to abandon their fields? how?

A

Mesopotamia

over-irrigation, no drainage, evaporation left behind salts on surface = soil became unusable

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2
Q

What are the 3 types of salt affected soils?

A
  1. Saline
  2. Saline-sodic
  3. Sodic
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3
Q

what is saline soil?

A

soil that has excessive soluble salts in it that can move through the soil with water

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4
Q

What is saline-sodic soil?

A

Soil that is already saline and is not being treated for remediation and is in the process of becoming sodic
(an in-between stage)

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5
Q

What is sodic soil?

A

soil that is very high in sodium
the sodium in this soil is BOUND to the particles (not free moving like saline) making this a very unstable soil when wet as the aggregates will burst apart, erode the soil, create restricted water movement, and surface capping

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6
Q

What are 4 causes of salts in soil? which is the most common?

A
  1. mineral weathering
  2. inorganic fertilizers (are salts)
  3. salts in irrigation water (most common source)
  4. direct addition of salts in water
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7
Q

What could be the first sign of salt issues? give 2

A

a decline in plant growth or the growth of specific kinds of salt-tolerant plants like couch grass

also, livestock licking the soil or bare patches on your field

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8
Q

How does mineral weathering cause salts in soils?

A

Parent materials that are high in salts (like Ca, Na, Mg, K, nitrate, chloride) will release salts when they are weathered

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9
Q

What are 3 natural ways salts occur in soils?

A
  1. Mineral weathering
  2. climate
  3. texture of soil
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10
Q

How does climate naturally cause salts in soil? examples of climates?

A
  • areas that have less precipitation increases salts being drawn up to the surface through capillary movement of water
  • higher evaporation rates increase the accumulation of salts on the soil surface
    ex. arid or semi arid climates

also, coastal areas can be effected by winds carrying salts from the ocean

low lands have poor drainage, this will increase the amount of salt accumulation on the surface

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11
Q

How does texture naturally cause salts in soils?

A

clay soils that have a high CEC (ex. smectite), have restrictive interspatial layers that prevent the leaching of salts so the salts accumulate in the interspatial layers of clay particles

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12
Q

How does salt water intrusion increase salts?

A

salt water can intrude into aquifers if well is placed close to the ocean because it will pull up salt water rather than fresh water
ex. Mediterranean

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13
Q

How does irrigation increase salinity?

A

irrigating with saline water will increase salinity of soil and will encourage progression into sodic soil

irrigating in too little amounts can allow the soil to dry out and prevent salts from leaching, leading to salt accumulation

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14
Q

How does the conversion of natural land to conventional agricultural land increase soil salinity? where is an example of this?

A

native, perennial vegetation with deep roots are removed and replaced by annual crops with short roots causing the water table to rise and bring groundwater salts with it into the rooting zones

Ex. Australia

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15
Q

How do inorganic fertilizers increase soil salinity? What is an example of the direct addition of salts?

A

inorganic fertilizers, especially in excessive amounts and especially Nitrogen, contain salts
examples: Soil amendments like gypsum or composts and manure contain salts
di-icers for icy roads are salts that can run off into water ways or soils

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16
Q

What are 3 early warnings of high salinity in soils?

A
  1. bare patches/crop yield production decrease/stunted growth
  2. growth of specific grasses like couch grass
  3. animals will lick the area
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17
Q

T or F: if you see salt crystals on your soil surface, it is too late to remediate the soil

A

TRUE once salt crystals begin to form, your soil is so wrecked

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18
Q

What are 7 ways high salinity affects plants?

A
  1. water stress - plants are not able to extract sufficient water –> crop yield reduction and stunted growth
  2. nutritional disorders - imbalances of soil nutrients caused by the high concentration of salt ions
  3. salts will inhibit microbial activity which will impact important soil processes that plants depend on
  4. ion toxicity
  5. oxidative stress
  6. alteration of plant’s metabolic processes
  7. plant membrane disorganization
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19
Q

Osmotic stress and ion toxicity effects on plants from salinity?

A

Osmotic stress on plants means more water particles are bound to soil particles more tightly, reducing the available water content and can actually pull water out of the plants and into the soils (because water moves from [ ]s of high to low)

Ion toxicity:
Na and Cl can become very toxic especially to fruit trees
and Boron can become toxic

20
Q

6 issues farmers will have with high salinity levels?

A
  1. decline in soil productivity and crop yields
  2. increased requirement and use of inputs (like seeds, water, fertilizers) - could be adding more salts this way
  3. low crop yield per unit of input used
  4. crop suitability is reduced (may not be cash crops)
  5. reduced water use efficiency
  6. in severe cases, land cannot be used anymore for production and must be remediated
21
Q

What 5 characteristics distinguish saline soils?

A
  1. high concentration of soluble salts that can move through the soil water and adversely affect most plant growth
  2. electrical conductivity reading of above/around 4dS/m
  3. Most of the salt cations are NOT sodium but Ca, Mg, Bo, etc.
  4. pH is 8.5 or less
  5. if it has gotten bad, white crusts can be seen as salts move through capillary action to the surface
22
Q

How do we measure salinity levels?

A

Electrical conductivity

23
Q

When testing for salinity using the electrical conductivity method on a saturated paste extract, what levels would be concerning?

A

anything around or above 4 dS/m

24
Q

What 7 characteristics distinguish sodic soils?

A
  1. it is NOT saline = salts are BOUND not free-moving
  2. Mostly only Na and not many other salts
  3. pH of more than 8.5 (very alkaline) = H+ from water absorbs onto soil particles and leaves OH- in the soil solution
  4. sodium binds to the interspatial layers of clay molecules so they burst apart when water is added making it VERY UNSTABLE
  5. can have toxic levels of Na
  6. can cause serious erosion
  7. can have a columnar soil structure
25
Q

What is flocculation? why is it desirable?

A

when particles “flock”/stay together - aggregates

desirable because water moves through large pores in aggregates

26
Q

What is dispersion?

A

when particles are dispersed from their flock

27
Q

T or F: Calcium and Magnesium promote flocculation and tighten soil whereas Na disperses soil particles?

A

TRUE

Sodium binds with the inner layer of some clay particles and disperses them –> losing aggregate stability

28
Q

What are 4 effects sodicity has on plants?

A
  1. Na will react with water to form NaOH (sodium hydroxide)
  2. pH is very alkaline = 8.5 or higher
  3. Na destroys the soil structure
  4. Plants can take up Na and damage tissues
29
Q

5 ways Na destroys soil structure?

A
  1. colloids separate
  2. disperse aggregates
  3. seals surfaces/pores/crusts
  4. columnar structure in subsoil = poor drainage
  5. effects are worse in fine textured soils
30
Q

What 6 characteristics distinguish saline-sodic soils?

A
  1. high in salinity and have a high proportion of Na salts (relative to Ca and Mg)
  2. EC higher than 4dS/m
  3. pH less than 8.5
  4. less dispersal of clay - better water infiltration than sodic
  5. structure will be okay until there are heavy rains/high irrigation to leach out Ca and Mg, leaving Na = becomes sodic
  6. it is in between saline and sodic and if not remediated, it will become sodic
31
Q

Two easy ways to distinguish saline vs. sodic?

A

EC! Saline >4; Sodic <4

pH! Saline <8.5; Sodic >8.5

32
Q

What are the 3 different ways to measure salinity?

A
  1. saturated paste extract
  2. 1:1 extraction
  3. EC test
33
Q

What is Exchangeable Sodium Percentage (ESP)? what does it indicate?

A

the portion of total exchangeable cations that are sodium

ESP indicates the risk for Na-induced soil dispersion

34
Q

T or F: an ESP of greater than or equal to 15% indicates a sodic soil?

A

TRUE

35
Q

What is SAR? What is it used for? How does it work?

A

Sodium Absorption Ratio is used to evaluate the sodicity of a soil
it compares concentrations of Na to that of Ca and Mg in water

36
Q

T or F: if a soil has a SAR of 13, it will likely have poor permeability?

A

TRUE

37
Q

T or F: a soil with high SAR (>15) will be unstable? why?

A

TRUE bc that means it is sodic as it has measured higher in concentrations of Sodium than of Ca and Mg
higher Na concentrations means the soil particles are more dispersed

38
Q

T or F: a soil with a low SAR (<6) will be stable? why?

A

TRUE because that means that the proportion of Na to Mg and Ca isn’t concerningly high and the soil particles will be flocculated together by Ca and Mg concentrations –> better aggregate stability

39
Q

At what SAR reading would remediation efforts begin?

A

at or above SAR 6

40
Q

What 2 treatments can be used to remediate sodic soils? Which is better?

A

Gypsum is the best option - H+ and Ca sources replace the Na so it can be leached out
- this is the cheaper, more available, and more rapid option

or sulphur (but only good in calcareous soils) - when it oxidizes it becomes sulphuric acid and will allow H+ ions to replace the Na and lower the pH

  • this must be leached with water and have good drainage
  • can only be used if there are tolerant crops (barley, halophytes)
  • can take several years
41
Q

How can saline-sodic soils be remediated?

A

Gypsum treatments can help remove the Na concentrations by adding Mg and Ca to replace Na in its bond to the soil particles
Will need excessive water to leach out Na after CE and good drainage

42
Q

5 ways to remediate saline soils? which is the best?

A
  1. growing salt tolerant crops (not a long term solution, but will help remediate)
  2. irrigating with high quality water and knowing the salinity levels of that water
  3. keeping the soil moist/drip irrigation: water dilutes salts and allowing soil to dry out will increase capillary action to bring more salts from the groundwater to the root zone and surface
  4. Over-irrigate to leach salts out of root zones (only if there is good drainage)
  5. MULCHING (BEST OPTION): prevents evapotranspiration
43
Q

What are 5 management techniques to prevent salty soils?

A
  1. avoid over-fertilization
  2. plant positioning: ex. plant on ridge shoulders or plant lower than the top of the ridges
  3. MULCHING
  4. monitor with soil testing and monitor irrigation water
  5. recognizing areas that have been effected and acting immediately
44
Q

How to remediate saline soils?

A

Leach out salts with good, non-saline water

45
Q

What are 6 ways to avoid salination?

A
  1. not using synthetic fertilizers
  2. measuring the pH and salinity of irrigation water if you’re going to irrigate
  3. No till system
  4. cover crops
  5. adding SOM! (as long as it’s not too salty - manure and compost can be)
  6. understanding the topography of the field - is there a depression? flat? drainage?

AGRI 2220 (9 decks)

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