Salt affected soils notes uaf

Spring 2013

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M.Nadeem Ashraf M.sc (Hons) Soil Science UAF [email protected]

Salt Affected and Waterlogged soils SES-706

Q1. Write down the equation to calculate the pHc of water and explain its components?

pHc = pk’2_pk’c+p(Ca+Mg)+p(CO3+HCO3) where the

pHc= expected water pH at equilibrium with free CaCO3 in soil.

Pk’2= Negative log of second dissociation constant of H2CO3 corrected for ionic strength.

Pk’c= Negative log of solubility product constant of CaCO3 corrected for ionic strength

P (Ca+Mg) = Negative log of (Ca+Mg, mmolcL-1) in irrigation water.

P (CO3+HCO3) = Negative log of (CO3+HCO3, mmolcL-1) in irrigation water.

Q2. Elaborate the treatment options for water having high RSC?

Dilution: mixing with low CO3+HCO3 or high Ca+Mg

Increase Ca+Mg: by application of Ca-salt,

Neutralize CO3+HCO3: acid or acid forming substances-H2SO4, HCl, S etc.

Gypsum being cheapest and popular amendment

Practice not economical, economic not evaluated by others.

Q3. What is the agriculture significance of Gapon equation?

If we know the SAR of irrigation water then we can guess in how much time our soil become sodic

due to application of that water. SAR calculation is easy to this and we can determine status of soil

and crops.

Q4. Which season is better to initiate the reclamation of SAS in Punjab and why?

Monsoon season is better for reclamation of SAS because good quality surplus water is available.

High temperature to dissolute the lime for Na-Ca exchange etc.

Q5. Enlist the parameters considered important for the classification of SAS according to SSP?

SSP followed the U.S Salinity Lab. Staff followed the limits of pH, EC, SAR additionally Soil Survey

Included some physical, morphological and land form features of soils.

Q6. Enlist the factors affecting solubility of soil applied gypsum?

The activity of Ca2+

in solution, which in turn is governed by the solubility of solid CaSO4 in

soils

The rate of Ca2+

diffusion from solution to exchange sites

The size of the gypsum particles, which affects its specific surface area and thus contact with

water

Electrolyte

CEC

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Q7. Why SCARPs project failed in Pakistan? Explain

a) Under achievement of ambitious targets

b) Inefficient centralized management resulting in technical, operational and maintenance

problems

c) A significant and unsustainable financial burden on scarce public resources

d) Questionable economic performance for tube wells located in useable groundwater areas

e) Pumping of saline sodic water by deep tube wells of 3-5 cusec capacity

f) Inappropriate mixing ratio of saline/sodic tube wells water with canal water

Q8. How plant growth is affected under sodic soil condition?

a) Poor water and air permeability due to soil dispersion

b) Low water availability due to poor air conductance

c) Hindrance for seedling emergence due to hard crust on soil surface

d) Difficult seedbed preparation

e) Sodium toxicity and induced potassium and calcium deficiency

f) Low activity of useful microbes due to high soil pH and SAR

g) Hard CaCO3 layer might hinder root growth.

h) Decreased solubility and thus availability of micro-nutrients like Zn, Cu, Fe, Mn etc.

i) Continuous loss of top fertile soil during rain due to low water infiltration.

Q9. Prove that GR (cmol c kg-1

) = 2GR (mmolc L-1

)

GR (Cmol c kg-1

) = GR (mmolc L-1

) x 100 x 100

1000 x (5) wt. of soil

GR (Cmol c kg-1

) = 2GR (mmolc L-1

)

Q10. Enlist amendments for amelioration of calcareous salt affected soils?

Direct source of calcium

Gypsum; Calcium chloride; Calcium nitrate; Lime; Phospho-gypsum

Indirect source of calcium

Commercial sulphuric acid; Crude sulphur; ferrous sulphate; Aluminium sulphate; Calcium poly

Sulphide.

Organic amendments

FYM; GM; Press mud

Q11. What factors are responsible for the formation of salt affected soils in Punjab?

1. arid and semiarid climate

2. irrigation with low quality water

3. raw city effluent disposal into irrigation water

4. pumping of ground water

5. lack of land levelling-patchy salinity

6. extra crop coverage with same water allocation

7. poor apprehension of water quality guidelines

8. unscientific management practices

9. poor management skill of farmers

10. illiterate farmers

11. absentee landlordism

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Q12. Why SAR increase with the application of irrigation water? Or

SAR higher of soil solution than irrigation water?

Mineral weathering

70-80% ground water is Salt affected

Exchange phenomenon

Dissolution of sparingly soluble salts

Q13. Why gypsum is better than acid for the reclamation of saline-sodic soils?

Addition of acid deteriorates the soil structure and pH fluctuation, but gypsum is gradual soluble,

easy to handle, cheap source, direct source of calcium etc.

Q14. Comment on the statement Conditions that maximize P solubility are, unfortunately, those

that destroy the soil structure?

As pH of soils increases, P availability increases due to formation of Na-phosphate particularly above

pH 9. In acid soils, P is fixed or inactivated by Al and Fe ions. So at high ESP/pH value of sodic soils, P

application could be decreased during initial phase of formation.

Q15. What cultural practices pertaining to water favour crop yields for management of SAS?

Continuous cropping

Choice of crops and cropping pattern

Seed placement

Methods of raising crops

Methods of water application

Frequency of irrigation

Age of nursery

Use of mulches

Root-stock scion relationship

Drainage

Q16. Write down the important considerations to economize the reclamation of saline-sodic and

sodic soils?

a) Ca2+

+Mg2+

from irrigation water could be subtracted from GR.

b) If soil saturation extract contains Ca2+

+Mg2+

subtract it from experimentally determined GR.

c) While deciding final ESP, consider the tolerance for the ESP of the designed crops

d) CEC of soil should consider for the Na-Ca exchange

e) Additional gypsum required to sustain electrolyte concentration in soil solution for better

infiltration of soil in sub-humid to semi-arid regions.

f) Application of gypsum rate could be reduced e.g. if 10 tons/acre of FYM are added

g) Prevailing atmospheric temperatures should be considered.

Q17. Write down the process involved during biological reclamation of salt affected soils?

The biological reclamation includes organic amendments:

The organic manures undergo biochemical oxidation release plant food nutrients, CO2, Variety of

organic acids formation of H2CO3.

H2CO3 + CaCO3 == Ca(HCO3)2

CO2 and organic acid dissolve the soil lime and release the soluble Ca2+

to affect the Na+ desorption.

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Q18. How saline soils provide the parent material for the development of sodic soils? OR

Explain sodication is followed by salination many times?

In saline soils CaCO3 precipitate first upon the concentration of soil solution because of its low

solubility followed by CaSO4 and magnesium silicate then there will be decrease in EC increase SAR

and ESP.Repitions of this process leads to the formation of saline-sodic and sodic soils.

Q19. Why SAR of soil solution is higher than that of applied water?

SAR depends upon the salt concentration of soil solution; the salt concentration will be more in soil.

Mineral weathering and native sparingly soluble salts.

Q20. Why powdery material in winter and crusty in summer on soil surface deposit?

In winter due to less rainfall and low temperature water on the soil surface that evaporates, while in

Summer water few millimetres below the soil surface starts to evaporate due to high temperature.

Q21. Explain SAR increases or decreases by square root times of dilution or concentration

factor. (Principle of dilution factor or valence dilution effect)?

EC Na Ca+Mg SAR

2 10 10 4.48

1 5 5 3.16

4 20 20 6.33

Q22. What are the options for the productive utilization of salt affected soils?

1. Leaching of saline soils

2. Reclamation with organic and inorganic amendments

3. Physical treatments of dense soils

4. Saline agriculture_ Biological means

5. Devotion of these lands for construction.

6. Planting forage and shrubs

Q22. What is human role in the development of salinity or sodicity?

1. Constructions of roads, buildings, dams and canals blocked the surface and sub-surface

drainage so; it develops waterlogging which promotes salinity/sodicity.

2. Irrigation with saline water

3. Mismanagement use of irrigation water

4. Change in cropping pattern

5. High cropping intensity

6. Lack of knowledge

7. Contaminants from agro-chemicals

8. Overgrazing

9. Deforestation in semi-arid climate

Q23. Why the slow release of CaSO4 is beneficial?

CEC of Pakistani soil is low, if all the CaSO4 is dissolute in the water then all unreacted CaSO4 is leach

down.

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Q24. What are the sodium hazards and origin in soils?

The presence of sodium cause deteriorates the hydraulic properties and physical conditions of soil,

dispersions, swelling and de-flocculation of soils, osmotic and specific ion effect, ion imbalance and

ultimately affect crop growth and yield. The sodium originates from the weathering of parent

minerals, improper use and management of land.

Q25. Physical method for reclamation of SAS?

Physical methods of soil reclamation include deep ploughing, sub-soiling, sanding, hauling, and

horizon mixing.

Q26. What are the pre-requisites for the reclamation of SAS?

Good internal drainage

Land levelling

Supply of good quality water etc.

Q27. Discuss osmotic effect on crop yields?

Lower crop yield

Decrease in water absorption

Salts increase the energy requirements of the plants to maintain cell turgor

Physiological drought

Succulence

Altered microbial activity

Q28. What is “Thur tirk”?

Land where salts in the root zone hampers the opening of cotton bolls.

Q29. What is “Thur jusvi”?

Saline land under cultivation having visible patches of salts to the extent of 20%.

Q30. In arid soils of Punjab, the value of KG varies from………………, why?

The value of KG varies from 0.01 to 0.015 (litres mmol-1)1/2 for most of the arid region soils KG values

are affected by the surface charge density of clays and organic matter contents. As SCD increases KG

value tends to decrease and vice versa.

Q31. Write down the mechanism for the formation of sodic soils?

OR

Explain the genesis of sodic/saline-sodic soils under arid land conditions?

In arid regions evapotranspiration will be more than precipitation, in saline soils CaCO3 precipitate

first upon the concentration of soil solution because of its low solubility followed by CaSO4 and

magnesium silicate then there will be decrease in EC increase SAR and ESP. under such conditions a

part of originally absorbed calcium and magnesium is replaced by sodium. Repetitions of this process

lead to the formation of saline-sodic and sodic soils.

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Q32. How moderate saline-sodic water help reclamation of sodic soils?

Moderate saline-sodic water is effective during initial reclamation of sodic soils; high salt water

dilution method is effective. Presence of lime is also important because its provides the calcium

source.

Q33. Ion pair formation in salt affected soil solution chemistry, briefly explain its implication?

The EC of saturated solution with a high proportion of Ca2+ and SO2-4 ions will under estimate

the total soluble salts.

Effect of ion pair formation on EC varies with the type of dissolve salts.

Formation of ion complexes becomes increasingly important as ECe increases.

EC (dSm-1). 10 = TDS or TSS mmolcL-1 concentration is valid for a solution of NaCl, but invalid

for system involving dominantly Ca2+ , Mg2+ or ES>4dSm-1.

Q34. Explain the solubility of gypsum is increased in MgCl2 soil over that in distilled water?

The greater solubility of gypsum in MgCl2 solution is not due to ionic strength but also to the fact

that the Mg-sulphate ion pair is formed which increased gypsum solubility by consuming SO2-4 which

is one of the products of gypsum dissolution.

Q35. Briefly explain the adverse rice and wheat growth responses of crops to sodic soil conditions?

Wheat is sensitive to sodicity which in turn decrease in yield and vegetative growth, rice is termed as

salt friendly crop it is tolerant to sodicity(owing to their less Ca2+ requirement) but if Na+ increases to

threshold level yield may reduce.

Q36. Rice crop is preferred as the first crop for the reclamation of saline-sodic soils in Punjab,

Explain?

Rice is suffers less from sodicity owing to their less Ca2+ requirements. Rice is the most Na+ tolerant

among the cultivated crops, being little affected to ESP value of 50 if climate is suitable.

Q37. Salt affected area is increasing in Pakistan, explain comprehensively?

The location of Pakistan is in arid and semi-arid climatic zones. Global climate change is major factor

for low rainfall pattern which built salts. Moreover temperature variations, poor quality of water,

rise in water table, poor management practices, and small holdings of lands, brackish underground

water and human role playing an important role in increasing salt affected area in Pakistan.

Q38. Why salt affected soils require more application of fertilizer than normal dose?

Availability of plant nutrients is affected adversely in salt affected soils:

Excess of certain ions like Na, CO, and HCO3 suppress the availability of other like Ca, K, P,

Zn, Mn, Fe and B technically it is called antagonistic effect.

An increase in soil pH, especially in soidc soils decreases the overall availability of P and

micronutrients.

Nutrient uptake by the plants in salt affected soils is also reduced due to decreased water

uptake.

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Q39. Differentiate between open and closed systems with examples?

An open system is any system that can exchange material or energy with its environment, plants,

animals and soils are the examples of open systems. A closed system is any system in which no

material or energy can enter or leave. Most systems in life sciences are open.

Q40. What fertilizer management practices are needed in saline-sodic soils?

Salt-affected soils generally have low organic matter and N, 20% of extra N is recommended for salt

affected soils. We should prefer Fertilizers containing Ca (e.g. Single Super Phosphate, Calcium

nitrate).

Q41. A water has EC =3.5 dSm-1, Ca+Mg =8 mmolcL-1, Na=26 mmolcL

-1 and SAR=13. How much 90 %

pure gypsum is required to lower SAR to 10 of a 10 cm-ha irrigation (106L).

We know that,

Na SAR= ---------------- so, 10= 26/ (Ca+Mg/2)1/2 (Ca+Mg/2)1/2 100=676/ (Ca+Mg/2)

Ca+Mg/2 =6.76 and Ca+Mg=13.52 mmolc/L

Additional Ca+Mg required = 13.52 - 8.00 = 5.52 mmolc/L.

100 % pure gypsum required for 10 cm-ha irrigation = (106 x 5.52 mmolc/L x 86 gyp. eq. wt. x 10-6)

= 474.7 kg

90 % pure gypsum = 474.7*100/90

= 527.5 kg

Q42. Example: A water has EC = 3.5 dS/m, 6.0, 29.0, 10.0, 14.0 and 15.0 mmolc/L of Ca+Mg, Na,

CO3+HCO3, Cl and SO4, respectively. Calculate 80 % pure gypsum to lower RSC to 2.5 mmolc/L of 10

cm-ha water (106 L)?.

RSCiw = (CO3+HCO3) - (Ca+Mg) = 10.0 - 6.0 = 4.0 mmolc/L

Decrease required = 4.0- 2.5 = 1.5 mmolc/L or 1.5 mmolc/L of Ca+Mg

Gypsum (100 % pure) required = (1.5 x 86 x 106 L) / (1000 x 1000) = 129 kg

Gypsum (80 % pure) required = 129 x 100/80 = 161.3 kg per 10 cm-ha irrigation.

Q43. Example: A water has Ca2+ = 2.0 mmolc/L and Mg2+ = 4 mmolc/L. Calculate the gypsum (100 %

pure) required to lower Ca: Mg ratio to 1.0 of 10 cm-ha irrigation water (106 L).

Ca: Mg ratio of available water = 1:2, thus additional Ca required = 2 mmolc/L

Gypsum required for 10 cm-ha irrigation = (2.0 x 86 x 106 L) / (106) = 172 kg 100% gypsum.

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Q44. Write down the Main chemical reactions during the treatment of hardness (carbonate and

non-carbonate hardness)?

Non-carbonate hardness: This hardness is usually due to the presence of Cl- and SO42- of Ca2+ and

Mg2+ and requires addition of soda ash (Na2CO3) to affect precipitation of carbonates of Ca2+ and

Mg2+. Main chemical reactions during the treatment of hardness are

CO2 + Ca (OH)2 = CaCO3 + H2O

Ca (HCO)3 + Ca(OH)2 = 2CaCO3 + H2O

Mg (HCO3)2 + Ca (OH)2 = CaCO3 + MgCO3 + 2H2O

MgCO3 + Ca (OH)2 = Mg(OH)2 + CaCO3

MgSO4 + Ca (OH)2 = Mg(OH)2 + CaSO4

MgCl2 + Ca (OH2 = Mg (OH)2 + CaCl2

CaSO4 + Na2CO3 = CaCO3 + Na2SO4

CaCl2 + Na2CO3 = CaCO3 + 2NaCl

Selective removal of Ca2+ and Mg2+ through cation exchange is also a viable option.

Q45. What should be the kind of Crop Selection for Salt-Affected Soils?

Survival Acceptable yield Relative yield Rice should be preferred in sodic and Wheat in case of saline conditions.

Q46. Write down management options for sustainable use of treated waste water for crop irrigation.

a) Water loading rate: A rate of 1.25-10 cm per week is considered optimum.

b) Annual application: About 20.6 m per year application could prove the most suitable.

c) Field area: 3785 m3 per day flow for 230 ha is generally reasonable.

d) Depth of ground water table: A minimum water table depth is 1.5 m.

e) Soil permeability: Moderately permeable soils with good productivity when irrigated are

better.

f) Loss of waste water by evapo-transpiration and percolation should be considered.

g) Climatic restrictions, storage needed for cold weather and run off from irrigation and

rainfall.

Q47. Why rice is preferably grown under flooded conditions and puddling is not recommended

during reclamation of Salt-Affected soils?

Rice is preferably grown under flooded conditions because of internal mechanism of carrying oxygen

through parenchyma cells. Due to puddling soils pores completely clogs so no more salts can leached

down in heavy irrigation.

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Q48. What is the difference between TEC and TUC?

Threshold Electrolyte Concentration (TEC), the electrolyte concentration in the percolating solution

that may cause a 15 % decrease in hydraulic conductivity of a soil at a given SAR or ESP value.

Turbidity concentration (TUC), the electrolyte concentration in the percolating solution that may

cause a dispersion of clay to affect turbid drain water from a soil at a given SAR or ESP vale ( Quirk

and Schofield, 1955)

Q49. What are the management practices to reclaim SAS in Punjab?

1. Choice of crops and cropping pattern

2. Seed placement

3. Method of raising crops

4. Method of water application

5. Frequency of irrigation

6. Root-stock scion relationship

7. Age of nursery

8. Use of mulches

9. Drain

10. Use of plant nutrients

11. Continuous cropping

Q50. How the micronutrients availability in sodic soils can be managed for better rice?

Mixing micronutrients with NPK, uniform application and avoid separate application. Regular

application of organic matter helps to mitigate deficiency of micronutrients. Foliar application should

prefer. Gypsum application for reclamation of calcareous saline sodic soils showed a decrease in Cu,

Zn, Fe, and Mn availability.

Education

Salt affected soils notes uaf