Soil Lab Quiz
What is the net charge of each soil sample?
A smaller volume of each soil sample is required to absorb Crystal Violet, a positively charged dye, than an equal amount of Eosin Y, a negatively charged dye. Therefore, the net charge of each soil sample is negative.
What type of soil could be added to your unknown sample to regulate its water-holding capacity?
Adding clay or humus could be added to increase the water-holding capacity. Sand could be added to decrease the water-holding capacity.
What are the causes of nutrient depletion in soil?
Chemical weathering and nutrient uptake by plants causes nutrient depletion.
Which soil particle type could you add to your unknown sample to increase it ion exchange capacity?
Clay would be the best soil type to add, because of its high ion exchange capacity.
Why is it important for soil to be able to exchange ions?
Exchanging ions is a way of measuring a soils capacity to gold different macronutrient ions. Soils that can hold more ions will me more productive over a period and require less addition of fertilizers then soils with low levels of macronutrient ions.
What can be done about nutrient depletion in soil?
Fertilizers can be added to soil to replace depleted nutrients. Also adding a layer of humus will replenish the nutrients as it decomposes.
What advantages would soil have if it was composed mostly of sand and had high capillary action rate?
If water penetrated below the surface but pooled at the bedrock, a soil with a sand composition would be able to suck water up to the roots of plants if surface water is scarce.
Why is soil acidity associated with nutrient depletion?
In natural weathering and nutrient depletion, nutrient cations such as K+ are replaced by H+. Soil has a defined cation exchange capacity. Low soil pH means that more and more cation binding sites are occupied by acidic cations rather than nutrient cations.
Was your soil most deficient in N, P, or K?
N
What happened to the soil particles in the jar overnight?
Overnight, the soil particles settled. The heaviest particles settled first, and the lightest settled last. The sand settles first and the clay settles last.
In a prolonged, heavy downpour, which ditch would be more likely to flood (sandy soil or high clay)?
Rain on sandy soil will be quickly absorbed, while rain on clay will be more likely to run off. Therefore, the ditch at the bottom of the clay soil field would be more likely to flood.
What soil particle type could be added to your unknown soil sample to increase the soil's permeability?
Sand, having the highest permeability rate, would increase the soil's permeability. Humus also has a high permeability rate, due to its irregularly shaped pieces.
Rank the soil samples you tested in order of increasing ability to hold macronutrient ions.
Sand, sand and humus, sand and clay.
What characteristic of soil is most important in determining water-holding capacity?
Soil texture determines water capacity. Clay holds more water, as texture is a function of particle size.
What role does water-holding capacity have in agriculture?
Soil that can hold more water requires less water from rainfall or irrigation. In times of drought, the soil with higher water-holding capacity is important for farmers. Soils with excessive water-holding capacity can be damaging to plants (root rot or drowning) due to lack of air.
Explain the relationship between particle size and percolation rate.
The smaller the particle size, the slower the percolation rate.
Crystal Violet is retained near the top of the soil column, whereas Eosin Y is retained through the length of the column. Why?
The soil samples have more negative charged ion-binding sites per volume that positively charged ion-binding sites. Therefore, a small volume of soil easily retains all the Crystal Violet but a large volume is needed to retain the Eosin Y.
What causes soil to become acidic?
Weathering, exchange of nutrient cations for H+ by plant roots, and acid deposition cause soil to become acidic.
