By Francis Belohlavy and Steve Hartung
Introduction:
The following demonstration shows how salts move to the surface of the soil and form salt crusts. It also demonstrates how some salts may be removed from soils.
Materials:
- Plastic syringes
- various soil materials
- string
- various salts (NaCl, CaCl2, KCl, MgSO4, etc)
- container for suspending syringes
- wire
- water
General Information on Saline & Alkali;
Saline Soil (white-alkali)
- Highly soluble salts magnesium sulfate *sodium chloride *sodium sulfate calcium chloride magnesium chloride
- Insoluble salts calcium sulfate **calcium carbonate **magnesium carbonate
- pH less than 8.5
- Exchangeable sodium percentage is less than 15%
* high concentrations are detrimental to soil structure
** main constituent of lime
Reclamation of Saline soils
- lower the water table to at least 4.5-5 feet
- leach with water which has sufficient calcium and magnesium cations present to prevent exchangeable sodium concentrations exceeding 15%
- problem - leaching without sufficient calcium and magnesium allows the exchangeable sodium concentration to reach a point it hydrolyzes to form sodium hydroxide and eventually an alkali soil.
- leaching: 6"/ft root zone -- removes 50% salts 12"/ft root zone -- removes 80% salts 24"/ft root zone -- removes 90% salts
Alkali soils (black-alkali)
- Exchangeable sodium concentration is greater than 15%
- pH 8.5-10 (degraded alkali in western US have low pH)
- Dispersed soil colloids
- soil solution - dominantly sodium, less calcium and magnesium
anions usually sulfate, chlorides, carbonates and bicarbonates
sodium clays ----hydrolyzes----> sodium hydroxide ---CO2---> sodium carbonate
(high pH) (soil air)
sodium carbonate ---organic matter---> black solution forms black crust on surface - 'black-alkali'
Reclaiming Alkali soils
- Lower water table to at least 4.5-5 feet
- Add gypsum or sulphur (with lime)
- gypsum + sodium clays ------> calcium clays
- sulphur ---oxidizes---> H2SO4
(moist soil) - CaCO3 + H2SO4 ---------> gypsum + carbonic acid + calcium carbonate
- Leaching: 6"/ft root zone -- removes 50% 12"/ft root zone -- removes 80% 24"/ft root zone -- removes 90%
- Apply practices that build soil structure
Literature:
Salt Tolerance in Plants, E.V. Maas
Applied Agricultural Research, vol 1, No. 1, pp. 12-26
Reclamation and Management of Salt-Affected Soils after Drainage
J.D. Rhoades, U.S. Salinity Laboratory, Riverside California
Effects of Salts on Soils and Plants, J.D. Rhoades
U.S. Salinity Laboratory, Riverside California
Controlling Saline Seeps By Intensive Cropping of Recharge Areas
A.D. Halvorson & C.A. Reule, Montana Cooperative Extension Bulletin 1132
Diagnosis and Improvement of Saline and Alkali Soils
USDA Salinity Laboratory Staff, Soil Conservation Service
Agricultural Handbook No. 60, 1954
Reclamation of Saline-Alkali Soils by Leaching - Delta Area, Utah
R.C. Reeve etal., Utah Experiment Station, Bulletin 335
Availability of Water to Crops on Saline Soils
USDA Agricultural Information Bulletin No. 210
Chemical Amendments for Improving Sodium Soils
USDA Agricultural Information Bulletin No. 195
Diagnosing Soil Salinity
USDA Agricultural Information Bulletin No. 279
Salt Problems in Irrigated Soils
USDA Agricultural Information Bulletin No. 190
The Salt Problem in Irrigation Agriculture
USDA Miscellaneous Publication No. 607
Tolerance of Crops to Exchangeable Sodium
USDA Agricultural Information Bulletin No. 216
Salt Tolerance of Grasses and Forage Legumes
USDA Agricultural Information Bulletin No. 194
Salt Tolerance of Vegetable Crops In The West
USDA Agricultural Information Bulletin No. 205
Gypsum and Other Sulfur Materials for Soil Conditioning
California Agricultural Experiment Station