Title: Soil Salinity Testing
Introduction:
By definition, a saline soil contains excess soluble salts that reduce the growth of most crops or ornamental plants. These soluble salts contain cations such as sodium (Na+), potassium (K+), calcium (Ca2+) and magnesium (Mg2+) along with anions chloride (Cl-), sulfate (SO42-), nitrate (NO3-), bicarbonate (HCO3-) and carbonate (CO32-). Soils may become saline as a result of land use, including the use of irrigation water with high levels of salt. Seawater is also a source of salts in low-lying areas along the coast through tidal estuaries or when rainfall in coastal regions mixes with sea spray. Saltwater intrusion into freshwater aquifers may occur when wells are close to the coast and water is pumped to the surface for various purposes, including irrigation. Irrigating from salt-impacted wells or saline industrial water may lead to the formation of saline soils. High salt levels reduces water absorption from the soil. Even thought the soil may contain adequate water, plant roots are unable to absorb the water due to unfavorable osmotic pressure (the difference in water pressure due to the abundance of water molecules). Plants are generally most sensitive to salinity during germination and early growth. Excessive amounts of salt can also enter the plant through the transpiration stream and injure leaf cells, which further reduces growth, restricts root growth, causes marginal or leaf tip burning/ browning, slows down flowering, reduces vigor and reduces crop yields.
Aim: To test a sample of water for salinity (total soluble salt concentration).
Materials:
Water sample
500 mL beaker
500 mL Erlenmyer Flask
Filter paper (fine textured)
Method:
Place the sample of water into a 500 mL beaker and allow it to settle for up to 24 hours.
Place a filter funnel within a dry 500 ml Erlenmyer flask.
Place a a double layer of fine textured filter paper within the funnel, and wet the paper with a few drops of the water sample.
Ensuring that the sediment in the beaker is not disturbed, filter about 400 ml of the water sample through the filter paper.
Shake the beaker vigorously until all the sediment is in suspension and, by rapidly pouring the suspension through the funnel, attempt to transfer as much as possible of the undissolved material into the funnel. Do not add additional water to the beaker to aid in this operation.
Allow the water to completely filter through the paper but do not allow the paper to become dry nor wash the residue on the filter paper.
d) add about 0,5 g of dry filter paper pulp to the filtrate and stir until the paper pulp has disintegrated completely and is in suspension. Cover the residue in the Buchner funnel with a glass fibre filter paper of fine texture1 and filter the filtrate through the Buchner funnel again, using low vacuum, into a clean and dry suction flask. Do not wash the residue in the Buchner funnel.
The filtrate should now be clear and contain no undissolved material in suspension. If this is not the case, repeat (d) above. 3.2 Recovery of water-soluble salts a) By means of a pipette transfer 200 ma of the filtrate to a beaker of capacity about 400 ml, boil until the volume of the solution is about 50 ml, and transfer quantitatively to the dry tared evaporating dish, washing the beaker three times with warm water and adding the washings to the solution in the evaporating dish. b) Evaporate the contents of the evaporating dish to dryness on a water bath, then transfer the dish to an oven maintained at a temperature of 105-110 EC and dry for 1 h Cool the evaporating dish and its contents to room temperature in a desiccator, determine its mass, and calculate the mass of the contents of the evaporating dish. 3.3 Blank determination . Carry out a blank determination by following the procedures given in 3.1 and 3.2 but omitting the 25 g of test specimen. Subtract the mass of any residue found in the evaporating dish from the mass found in 3.2(b) above and record this corrected mass (Mass A) as the mass of water-soluble salts in the 200 ma of filtrate. SECTION 4. CALCULATION 4.1 Calculate, as follows, the water-soluble salts content of the fine aggregate or the fines (as relevant): Total water-soluble salts content, a (m/m) = A x B x x 5 2 100 where : a = mass of soluble salts found in 200 ml of the extract, g b = mass of the specimen taken for extraction, g
References:
Soil Salinity Testing, Data Interpretation and Recommendations. University of Georgia Extension website. <https://extension.uga.edu/publications/detail.html?number=C1019&title=Soil%20Salinity%20Testing,%20Data%20Interpretation%20and%20Recommendations
Method B16 T: The Quantitative Determination Of The Total Water-Soluble Salts In Soils and Aggregates <http://asphalt.csir.co.za/tmh/b16t.pdf>.