Soils - Physical Flashcards
What is soil fertility?
- Ability of soil to grow and sustain plant growth.
What is texture of soil?
Mix of particle sizes in soil.
What factors influence soil fertility?
- Drainage.
- Thermal capacity (higher levels of water = longer to warm up).
- Aeration.
- Nutrient levels (wash away easier in sand/silt).
- Root penetration
- Capillary action (clay particles smaller so draw water up by cohesion and adhesion).
Why is dead organic matter important for fertile soil?
It releases plant nutrients as it decomposes. Also increases water retention and provides food for soil biota.
What is a ped? Are crumb ped soils or platy ped soils more fertile? Why?
Soil particles that form aggregates.
Crumb ped soils.
Have better drainage, aeration, have easy root penetration.
How does ploughing/drainage affect soil fertility?
- Increases it.
- Soil more aerobic = increases nitrogen fixation, nitrification, and decomposition.
How are nutrient levels affected by soil texture?
- Nutrient ions absorb easily onto clay particles.
- Sand prone to leaching.
How is temperature affected by soil texture?
- Clay is colder as it is wetter.
- Sand has a greater temperature range.
How is drainage affected by soil texture?
- Sand is well drained.
- Clay is poorly drained.
How do you measure soil texture?
1) Dry soil in oven.
2) Remove large pieces of material.
3) Remaining dry soil placed in water-filled cylinder and soil is left to settle for a few days.
4) Sand will sink to base, then silt, then clay.
5) Each layer is measured in heigh and the relative proportions (%) are worked out.
How do you measure the pH of soil?
1) Take a soil sample.
2) Add distilled water to it and mix.
3) Use pH paper.
4) Compare it.
How do you measure soil moisture?
1) Soil is weighed.
2) Placed in an oven at 100 degrees c overnight.
3) Soil is weighed again.
4) Soil is returned to oven again and repeatedly weighed until constant mass is reached.
5) The difference in weight is soil moisture content.
6) Percentage of soil moisture calculated with: (Difference in mass/original mass) x 100
Why should collected soil be kept in a plastic bag and placed in the refrigerator?
- Prevent water loss.
- Stop action of microorganisms.
How do you measure the bulk density of soil (mass of dry soil per unit volume)?
1) Collect known volume of soil.
2) Dry soil (heat at 100dc) then weigh.
3) Mass/volume = bulk density.
What is standard deviation?
- A measure of the variation of data about the mean.
- A higher standard deviation value means a wider variation around the mean.
