Salt-affected Soils1. 通常發生於 semiarid and arid regions

∵annual precipitation< evapotranspiration

2.Natural sources of soil salinity

a) Mineral weathering

b) Fossil salts

c) Atmospheric precipitation

3.Local salt accumulation

Soils in low-lying areas

Evaporation

Capillary risewater table

4.Human Activities

a) Salts from areas of over-irrigation accumulate in poorly drained areas.

a) Relatively saline irrigation water are used.

a) Oil-field development, waste-spreading operation, and crop fertilization

灌溉水質1.Total Dissolved Solids (TDS)

大部分之灌溉用水 TDS < 1000 mg‧L-1

2.Electrical Conductivity (EC)

C (conductance) (mho) =

C =L L (specific conductance) (mho/cm)

1 S (Siemen)=1 mho 1 dS‧m-1=1 m mho/cm

1R Resistance (ohm)

Ad

d

soln.

Area A

3.Water Quality Relations

(a) TDS (mg/L) ≈ EC (dS‧m-1) × 640

(b) Sum of cations or anions (m mole (+ or -) ‧L-1) ≈EC (dS‧m-1) ×10

(c) OP (bars) ≈ EC (dS‧m-1) ×(-0.36)

(d) Hardness = [Ca 2+ + Mg2+ ]

Alkalinity = [HCO3- + CO3

2- ]

Sodium Hazard1.Irrigation water (High Na content) high ESP of soil

Soil crust badly and swell or disperse

greatly decreasing the hydraulic conductivity or permeability of soil to water

2. 為何不以 Na concentration 直接來表示？ 不能表示出 ESP. 因為 ESP 之決定不僅在於 Na+在 soln.

之濃度，而是在於 Na+和 Ca2+、 Mg2+爭取 exch. sites 。3.SAR(sodium adsorption ratio), U.S. Salinity Lab.

1/222

]]2

MgCa[[

][NaSAR

Conc. Unit : m moles (+)/L來表示 relative sodium status of irrigation water and soil soln.

1/222 )Mg(Ca

)(NaSAR

21/2 Ca

2

1NaXNaXCa

G1/2

1/22

KX))(Ca(Na

)(NaX)(Ca

Conc. Unit : m mole/L

＊ assume only Na and Ca in the system

SAR

1

)(Na

)(Ca 1/22

SAR1 ． G

1/2

KX)(Ca

)NaX(

XCa

NaX

NaX-CEC

NaX

1/2

ESR (Exchangeable Sodium Ratio)

= Exch. cation conc. Unit = m mole (+)/kg

GKESRSAR

1

ESRKSAR G

所以

KG (Gapon exchange coefficient):

The range of KG is commonly 0.010~0.015 (L/m mole)-1/2

∵ Ca2+ and Mg2+ behave quite similar同理 ESR=KG SAR ‧

100CEC

NaXESP

XMgXCaNaX

NaX

CEC

NaXESF

1/21/2

ESR

1ESR

ESR

11

ESF

1

If considering Na+, Ca2+, Mg2+ in the system

ESR

11

NaX

XMgXCa1

NaX

XMgXCaNaX

ESF

1 1/21/21/21/2

1ESR

ESRESF

ESR1

ESR 100100)

1ESR

ESR(ESP

ESPESR)

2MgCa

(

NaSAR

1/222

Unit : m mole (+)/L

Bicarbonate Hazard• High HCO3

- conc.High pHiron ＆ other micronutrients deficiency• Residual sodium carbonate (RSC) conc. unit = m moles (+ or - )/L

可用來 predict the tendency for calcium carbonate to precipitate fr

om high-bicarbonate water. RSC > 2.5 hazardous 1.25 < RSC < 2.5 potentially hazardous RSC < 1.25 generally safe

Empirical but worked reasonably well

22-23

-3 MgCa-COHCORSC

223

-3

2 COOHCaCO2HCOCa Increasing SAR of water

項目 限值 項目 限值

pH 值 6.0 ~ 9.0鈷 (Co) m

g/L 0.05

電導度 μmho/cm 25℃ 750銅 (Cu) m

g/L 0.2

懸浮固體物 mg/L 100

鉛 (Pb) mg/L 0.1

氯化物 (Cl-) mg/L 175

鋰 (Li) mg/L 2.5

硫酸鹽 (SO4-2) mg/

L 200錳 (Mn) m

g/L 2

總氮量 (T-N) mg/L 1

汞 (Hg) mg/L 0.005

清潔劑 (ABS) mg/L 5

鉬 (Mo) mg/L 0.01

油 脂 mg/L 5

鎳 (Ni) mg/L 0.5

鋁 (Al) mg/L 5

硒 (Se) mg/L 0.02

砷 (As) mg/L 1

釩 (V) mg/L 10

鈹 (Be) mg/L 0.5

鋅 (Zn) mg/L 2

硼 (B) mg/L 0.75 鈉吸著率 (SAR) 6

鎘 (Cd) mg/L 0.01

殘餘碳酸鈉 RCS (meq/L) 2.5

鉻 ( 總 ) (Cr) mg/L 0.1 水溫℃ 35

表 3.1 台灣省灌溉用水水質標準 (67.7.5 府建水字第 59931 號公告 )

附註：天然之水質若超過本標準之限值，得不受本標準之限制。

Characterization of Salt-affected Soils

• 1.Na-status

(i) ESP (Exchangeable Sodium Percent)

100CEC

[NaX]

直接測定 ESP 費時麻煩，且常有誤差

(ii) SAR (Sodium Adsorption Ratio) Soil Soln.

做為 exch.-Na status 之 index

1/222 ]/2]Mg[[Ca

][NaSAR

SAR KESR G

ESR1

ESR 100ESP

Conc. 單位： m moles(+)/L

ESP SAR

NaX-CEC

NaXratio) Na (exch. ESR

Effects of salts on soils and plants

1. Main effect on plants—Osmotic Effect

WaterSemipermeable membrane

High salt conc.

Outside the membraneHigh salt Osmotic potential 愈負

Water potential 愈負

Difficult to extract water

Osmotic adjustmentProduction of organic acids or update of salts

使 osmotic potential 愈負 water potential 愈負然而消耗 energy ，並發生葉

組織細胞不斷之分裂但不增長之現象

Possible to continuously obtain water

Water potential

Inside the membrane

2.Specific-ion effects

Plants are sensitive to specific ions in irrigation water or soil soln.

Boron, Chloride, ESP Effect

3.Nutritional imbalances

e.g. bicarbonate toxicity 是由於 high pH 引起 iron 或其他 micronutrients 之 deficiency, 而不是 bicarbonate直接引起之 effect.

• Other toxic Solutes

B, Li, Na and Cl

B (Boron)

缺乏～毒害 之間只相差 a few mg/L

Leaching Requirement (LR)

dw

iw

iw

dw

EC

EC

D

DLR

Ddw: Amount of drainage waterDiw: Amount of irrigation water

ECiw: Electrical conductivity of irrigation water

ECdw: Electrical conductivity of drainage water

為了維持 Salt balance (Salt entering = Salt leaching)所需之 Leaching fraction ( 假設 no salt propitiation, no salt dissolved from soil minerals, and no salt taken up by the crop)

• Ddw EC‧ dw=Diw EC‧ iw

ECdw (allowable EC of the saturation extract) can be obtained from existing salt tolerance data (Table 9.2).

e.g. Soybean

ECdw 5.5 ds m≦ ‧ -1 at 25℃

Reclamation

1 Saline, non-sodic soils Leaching

ponding-inefficient

basin-furrow method

Reclamation2 Saline-Sodic Soils ; Sodic soils

a) Decrease ESP application of gypsum (CaSO4 2H‧ 2O)

NaX-CaX-NaCa2

11/2

2

or tillage ( 深耕 ) bring subsoil lime to the surface

對 calcareous-sodic soils 施用 S4222 SO2HO2H3O2S

224423 COOHCaSOSOHCaCO

424 SONaCaXCaSO2NaX

b) Leaching

SAR 60 (High-salt water)

Soil ESP=40-50

2nd leaching with 1st fourfold dilution of the high-salt water

150 m mole(+) L‧ -1 salt conc., SAR 30

3 Sodic soils High-salt water-reclamations

1st leaching with 600 m moles(+) L‧ -1 salt conc.

3rd leaching with 2nd fourfold dilution of the high-salt water

37.5 m mole(+) L‧ -1 salt conc., SAR 15

4th leaching with 3rd fourfold dilution of the high-salt water

9.4 m mole(+) L‧ -1 salt conc., SAR 7.5

Problem: Drainage facilities need to be adequate to remove large quantities of salty drainage water.