Soil Ec and Ph Using 3 Types of Extractant Solutions on Different Soil Samples
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Submitted By bj3vincent Words 1548 Pages 7
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Soil EC and pH using 3 types of extractant solutions on different soil samples
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Ben Vincent
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AGR2IlS subject coordinator: Dr Gary Clack
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INTRODUCTION
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pH is in general terms the about the acidity or alkalinity in a soil or growing medium, technically pH refers to the ratio concentration of H+ ions to OH- ions in a medium (Handreck & Black 1984) and given in the formula pH= Log10(H=). Considering H2O is neutral the pH will be lower if the concentration of H+ is higher and vice versa. The pH is important because it will determine the availability of nutrients to plants, amounts of nutrients held in soil, toxicities in soil and life of microorganisms (Handreck & Black 1984). Dramatic changes in a soils pH will cause stress to life that is held within it, this is where the desirable ability of pH buffering plays its role. This pH buffering is the ability of a soil to resist dramatic changes to pH levels in order to avoid plant stress (Handreck & Black 1984). Measurement of pH is one of the first and most important tests done on a soil, however there can be a variety of difficulties as in nature and agriculture not everything is in a standard condition. There can be large differences that affect the data recorded with pH measurement techniques (Dolling P J, & Richie 1985). To help decipher some of these variations the size of the sampling area and the method used to conduct the pH test along with an EC test need to be taken into account. Obtaining knowledge of salt content is critical to predicting plant growth, as high salt content in the soil will disrupt water intake into roots due to unfavourable osmotic pressures (Brady & Weil 2008). In turn starving the plant of nutrients and water it requires for healthy growth no matter how much fertilizer is applied or what the pH is (Handreck & Black 1984). A method used to raise a pH is to incorporate lime into an acidic soil, the aim of this experiment is to contrast the pH and EC in two soil samples with increasing lime contents from different locations as well as examining the differences in data using different extractant solutions.
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MATERIAL & METHODS
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Details described in (AGR2ILS, 2014)
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The measurements with KCl have been left out as the data was incomplete
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Cas numbers
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Calcium Carbonate (CaCO3) 1317-65-3
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Calcium Chloride (CaCl2) 10043-52-4
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Potassium Chloride (KCl) 7447-40-7
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Results
Different results using different methods of pH testing between distilled water vs. 0.01M CaCl2
In both Cranbourne and Kinglake soil samples showed an upward trend as more lime was added. Between the results, using distilled water as and an extractant constantly resulted in a higher pH than using 0.01M of CaCl2 (Fig.1) (Fig.2). In the Cranbourne sample the largest variance was observed in soil that had no lime added, at this point Cranbourne showed a variance of pH 4.81 with pure H2O in contrast to a pH 3.81 with 0.01M CaCl2 (Fig.1) which is 1 unit of difference. As added lime increased past 2000mg/kg the variance in the units tracked with a much smaller difference showing an average of 0.4 units differences between the two different solutions (Fig.1) (Fig.2).
Fig.1. Cranbourne soil mixed with increasing amounts of CaCO3, contrasted in a soil suspension between 2 methods of pH testing - 1:5 distilled water vs. 1:5 CaCl2 at 0.01M
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The upward trend in the Kinglake sample was slightly different to the data recorded in the Cranbourne sample given in (Fig.2). The greatest variation was found at the 2000mg/kg point, furthermore the lowest variation was found at 0mg/kg. Overall the difference in pH between the two extractant was higher than what was found in the Cranbourne sample.
Fig.2. Kinglake soil mixed with increasing amounts of CaCO3, contrasted in a soil suspension between 2 methods of pH testing - 1:5 distilled water vs. 1:5 CaCl2 at 0.01M
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Comparison of soil EC between soil samples from Cranbourne and Kinglake
As lime was added EC had an upward trend. The Cranbourne sample showed its upward trend in a wave formation in contrast to Kinglake which showed a hockey stick formation. Interestingly at 2000 mg/kg the Cranbourne sample dramatically rose above the Kinglake sample and this difference doubled at 4000 mg/kg, only to drop back to a similar level at 8000mg/kg. Then at 16000mg/kg of lime added the Kinglake sample surprisingly overtook and rose dramatically above the Cranbourne sample. One data point needed to be removed as there was a significant standard error.
Fig.3. EC levels of Soil samples from Cranbourne and Kinglake contrasted against increasing amounts of added CaCO3
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Calculations for question 4
10,000m2 per hectare × 0.1m depth = 1000m3 of soil
Bulk density = 1.33. 1.33 × 1000m3 = 1330kg of soil
37mol/tonne
Molecular weight of CaCO3 = 100g
37 × 1330 mol (+) = H+/2
Mass of lime = (37 × 1330/2) × 100g
2,460,500 g/ha
2.46 t/ha
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The incorporation of calcium carbonate has been shown to increase the pH of both samples of soil at a relatively similar rate (fig1.) (fig.2.), however the electrical conductivity of both soil samples rose as well (fig.3.), which is important to take into account when applying lime to agricultural fields. At high levels of calcium carbonate application undesirable amounts of salt content could arise. It is noteworthy that EC levels did not dramatically rise until 8000mg/kg were added. The reason for this rise in EC could be from H+ ions being replaced by Ca2+ ions, and because EC does not measure H+ but does measure Ca2+. Hence, rising electrical conductivity.
Question 2,
Three methods used in determination of pH involve different extractants, 1) pure water, 2) 0.01M Cacl2, and 3) 1 M KCl. These solutions are used in standard ratios of solution to soil (Brady & Weil 2008). Using pure water can give misleading results as fertilizers or salt accumulations in the soil can lead to variations in results (Brady & Weil 2008). By using a solution of 0.01M CaCl2 this inaccuracy can be avoided, because of the Ca+ ions in the solution minimizing these variations (Fig.2.). Therefore results using this method usually give readings that are 0.2 to 0.5 units lower than pure water (Brady & Weil 2008). The third method uses a 1M KCl solution. In this method cations in the soil are completely exchanged with K+ ions in the solution in turn pH measured this way is completely unaffected by salt concentration variations (Brady & Weil 2008). Using this method will usually give a reading of 1 unit lower than using pure water (Brady & Weil 2008). These three methods are used in different parts of the world therefore when interpreting pH results the method used in testing is required knowledge (Brady & Weil 2008).
Question 3,
Differences in the buffering capacity of soils are dependent on their composition, soils with higher amounts of clay particles, different types of clay particles and or hummus will give a soil a greater buffering capacity than soils with less. Hummus has multiple sites of holding capacity for H+ ions, this is to do with its complex structure and its ability to hold H+ ions at different strengths (Brady & Weil 2008). To raise pH a material is needed to soak up H+ ions, in the case of CaCO3 (lime) being added Ca+ will disassociate H+ will form H2O with 1 oxygen atom from CO3, and CO2 will be released as a gas, resulting in soaking up of H+ ions meaning a rising pH. However as the pH rises more H+ will be released from hummus particles to offset the application of lime where a soil with more organic matter means more H+ ions released which means higher buffering capacity. In the case of clay particles enhancing buffering capacity of a soil it is to do with aluminium and silicon particles attracted to colloid surfaces that hold H+ ions with relation to the OH- concentration. In acid soils Al3+ ions are much more common than H+ ions on colloid surfaces and these Al3+ ions will split H2O to form H+ ions (Handreck & Black 1984). Higher concentrations of OH- ions will induce the release of H+ ions from these sites (Brady & Weil 2008). Therefore the difference in the curves in (fig.3.) will be representative of the amount of organic matter and clay particles in the two soil samples. Therefore it will be easier to change the pH of a sandy soil than a clay soil. Therefore more clay particles and organic matter ate present in the Cranbourne soil sample.
Ref,
Brady N C, Weil R, (2008) The Nature and properties of soil Pearson Prentice Hall, Upper Saddle river, New Jersey.
Handreck K, Black N, (1984) Growing media for ornamental plants and tur,f New South Wales University Press, New South Wales Australia.
Dolling P J, Ritchie G S P, (1985) Estimates of soil solution Ionic strengths and the determination of pH in West Australian Soils, Australian Journal of Soil Research
