salt-affected soils 1. 通常發生於 semiarid and arid regions ∵ annual precipitation<...
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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.
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