受盐害的土壤课件.ppt

Salt-affected Soils,1.通常發生於semiarid and arid regions annual precipitation evapotranspiration2.Natural sources of soil salinity a)Mineral weathering b)Fossil salts c)Atmospheric precipitation3.Local salt accumulation Soils in low-lying areas,4.Human ActivitiesSalts from areas of over-irrigation accumulate in poorly drained areas.Relatively saline irrigation water are used.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 mgL-12.Electrical Conductivity(EC)C(conductance)(mho)=C=L L(specific conductance)(mho/cm)1 S(Siemen)=1 mho 1 dSm-1=1 m mho/cm,3.Water Quality Relations(a)TDS(mg/L)EC(dSm-1)640(b)Sum of cations or anions(m mole(+or-)L-1)EC(dSm-1)10(c)OP(bars)EC(dSm-1)(-0.36)(d)Hardness=Ca 2+Mg2+Alkalinity=HCO3-+CO32-,Sodium Hazard,1.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 water2.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.,Conc.Unit:m moles(+)/L,來表示relative sodium status of irrigation water and soil soln.,Conc.Unit:m mole/L,assume only Na and Ca in the system,ESR(Exchangeable Sodium Ratio)=,Exch.cation conc.Unit=m mole(+)/kg,所以,KG(Gapon exchange coefficient):The range of KG is commonly 0.0100.015(L/m mole)-1/2,Ca2+and Mg2+behave quite similar同理 ESR=KGSAR,If considering Na+,Ca2+,Mg2+in the system,Unit:m mole(+)/L,Bicarbonate Hazard,High HCO3-conc.High pHironother micronutrients deficiencyResidual sodium carbonate(RSC)conc.unit=m moles(+or-)/L 可用來predict the tendency for calcium carbonate to precipitate from high-bicarbonate water.RSC 2.5 hazardous 1.25 RSC 2.5 potentially hazardous RSC 1.25 generally safe Empirical but worked reasonably well,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),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,Conc.單位：m moles(+)/L,Effects of salts on soils and plants,1.Main effect on plantsOsmotic Effect,Water,Semipermeable membrane,High salt conc.,Outside the membrane,High salt Osmotic potential 愈負,Water potential 愈負,Difficult to,extract water,Osmotic adjustment,Production 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 Effect3.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),Ddw:Amount of drainage water,Diw: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),DdwECdw=DiwECiw ECdw(allowable EC of the saturation extract)can be obtained from existing salt tolerance data(Table 9.2).e.g.Soybean ECdw 5.5 dsm-1 at 25,Reclamation,1 Saline,non-sodic soils Leaching ponding-inefficient basin-furrow method,Reclamation,2 Saline-Sodic Soils;Sodic soils a)Decrease ESP application of gypsum(CaSO42H2O),or tillage(深耕)bring subsoil lime to the surface 對calcareous-sodic soils 施用S,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,