18 Questions
What is the primary effect of active hydrogen ions on plant growth?
They directly affect plant growth
What is the pH range considered optimal for soil?
5.5 - 7.5
Which of the following is a cause of soil acidity?
Deposition of acid rain
What is the effect of high soil pH on plants?
It decreases the ability of plants to uptake water
What is the relationship between active hydrogen ions and exchangeable hydrogen ions?
They are in equilibrium
What is the effect of low soil pH on the biological transformation of ammonium to nitrate?
It slows the rate of transformation
What is the primary purpose of adding barium to the soil in the reserve hydrogen computation?
To replace the exchangeable hydrogen ions
What is the role of phenolphthalein in the titration process?
It serves as an endpoint indicator in the titration process
What is the units of reserve hydrogen in the given formula?
g H+/g soil
What is the effect of high CEC and low base saturation on a soil's pH?
It makes the soil more resistant to pH changes
What is the purpose of adding copper cations to the soil in the CEC measurement?
To fill all the soil's exchange sites
What is the method used to determine the concentration of copper in the soil?
Developing a characteristic blue color in a basic solution
What is the wavelength used to analyze the solution via UV/Vis spectrophotometer?
540 nm
What is the temperature used to evaporate water from the soil sample to determine moisture?
105oC
What is the purpose of heating the soil sample in a muffle furnace at 550oC for 3 hours?
To determine the organic matter content
What is the relationship between organic matter content and CEC?
Higher organic matter content relates to higher CEC
Why is it necessary to use moisture-free soil for dry combustion analysis?
To prevent water loss during ashing
What type of soils tend to have higher organic matter content?
Soils from wet areas
Study Notes
Soil Analysis
- Soil is analyzed using a UV/Vis spectrophotometer at 540 nm or compared visually.
- Cation exchange capacity is determined by measuring the concentration of copper ions in soil (ppm Cu/g soil).
Determination of Moisture
- Moisture is determined by heating the soil sample in an oven at 105°C to evaporate the water.
- The weight lost after heating is taken as the amount of water, and divided by the weight of the soil to be presented in percentage.
- Moisture relates to pH.
Determination of Organic Matter Content
- Organic matter content is determined by dry combustion analysis.
- Soil is heated in crucibles at 550°C for 3 hours to oxidize organic matter to CO2 and H2O.
- Weight lost is used to determine organic matter content, while weight remaining is used to determine inorganic matter content.
- Moisture-free soil must be used to avoid water loss during ashing.
Reserve Hydrogen
- Reserve hydrogen comprises all bound aluminum and hydrogen in soil minerals.
- Barium replaces exchangeable hydrogen, forming acetic acid.
- Filtrate is titrated with NaOH using a phenolphthalein endpoint.
- Reserve hydrogen is calculated using the formula: Reserve hydrogen = VNaOH × NNaOH / Vleachate × 1.008 g H+ / mass of soil.
Cation Exchange Capacity (Exchangeable Acidity)
- Cation exchange capacity is the ability of soil to exchange cations.
- CEC is measured by removing cations and determining their concentration.
- Copper (Cu2+) cations are used to fill all exchange sites, replacing other cations.
- Ammonium (NH4+) cations are then used to displace copper, and its concentration is determined by developing the characteristic blue cupric color.
Types of Soil Acidity
- Active Hydrogen content: affects plant growth, directly determined using a pH meter.
- Reserve Hydrogen: comprises bound aluminum and hydrogen in soil minerals.
- Exchangeable Acidity (Cation Exchange Capacity): ability of soil to exchange cations.
Effects of Soil pH
- Controls availability of essential nutrients like nitrogen, phosphorus, sulfur, calcium, magnesium, sodium, and molybdenum.
- Determines abundance of soil microorganisms.
- Determines which plant species will grow.
- Low soil pH slows biological transformation of ammonium to nitrate.
- High soil pH decreases ability of plants to uptake water and leads to a high cation exchange capacity.
This quiz covers the concepts of soil acidity, including active hydrogen ion content, reserve hydrogen, and exchangeable acidity. Learn about the importance of soil pH and its optimal range. Test your knowledge of soil chemistry and analysis!
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