Soil aeration Flashcards
What is soil Aeration?
It is the process by which soil air is replaced by atmospheric air.
What percentage of soil is pores?
50%. If 25% of the 50% pores are filled with water and the other 25% is filled with air then this is called field capacity.
What is the biggest difference between soil air and atmosphere air?
Soil air has a lot more CO2 compared to atmosphere air.
What are some characteristics of oxygen in soil?
- Slightly lower O2 in soil compared to atmosphere.
- May drop to less that 5% in the lower soil horizons after a heavy rain.
What are some characteristics of carbon dioxide in the soil?
- Soil air CO2 is 10-100x higher than atmospheric air.
- It usually increases with depth.
- Proportion of soil CO2 depends on SOM.
- If soil air CO2 is greater than 10% it can be toxic to plant roots.
What are some other gasses that can be found in soil air?
CH4 and H2S can be formed under water logged conditions, by anaerobic microbial metabolism.
N2O as GHG
Why is a 50/50 mix of air and water in the soil ideal?
Because oxygen can move much faster in air than water.
What is oxidation.
It is the loss of an electron
What is reduction
It is the gain of an electron.
What is a redox reaction?
It is when an oxidation and reduction reaction occur together. One has donated electron the other has accepted electron.
What are the two methods of expressing available electrons in a system?
- Electron activity : pe = -log(e-)
- Electrode potential : Eh=0.059pe
What does a high pe value mean?
Electron poor, normal, aerobic, oxidized environment. Oxic
What does a low pe value mean?
Electron rich, anaerobic, waterlogged, reduced environments. Anoxic
What is the difference between oxic and anoxic?
Oxic means abundant in oxygen, Anoxic means not abundant in oxygen.
What is the order of electron acceptors used by microorganisms?
O2 > NO3- > MnO2 > Fe(OH)3 > SO4 2-
What happens to nitrogen and sulfur in the absence of oxygen due to flooding?
Gaseous losses of N and S increase in flooded, anaerobic soil due to reduction.
N5+ → N0
S6+ → S2-
What happens to Mn and Fe in suboxic environments?
Precipitated forms of nutrients are converted to soluble plant-available forms. Mn and Fe dissolve in solution which leads to an increase in electrons in the flooded anaerobic soils due to reduction.
Mn4+ → Mn2+
Fe3+ → Fe2+
How many times more soluble is Mn2+ to Mn4+?
10^30 times more soluble.
What are some management practices for suboxic soils?
- Improved drainage.
- Selection of crop species and variety to tolerate nutrient deficiency/toxicity caused by poor aeration.
- Careful selection of form, timing and placement of Nitrogen fertilizer.
What are three ecological effects of soil aeration?
- Effects on organic residue degradation
- Effects on element availability and behavior
- Effects on activities of higher plants.
What kind of effects does soil aeration have on organic residue degradation?
- Poor aeration slows down rate of decay.
- Partially oxicdized products such as alcohol, ethanol and organic acids are toxic to plants.
What kind of effects does soil aeration have on element availability and behaviour?
Nutrients: More Mn and Fe are available in the reduced form as they are more soluble.
Toxic elements: Reduced form of cadmium and arsenic are most mobile and toxic. Accumulation in rice grain is a health issue.
What can soil color tell us about aeration conditions?
- Red, yellow, reddish brown are characteristics of well oxidized conditions.
- Subduded shades such as blues and greys are characteristics of reduced conditions.
What are the effects of soil aeration on activity of higher plants?
- Plant growth: reduced shoot growth. But different plants have different tolerance to flooding.
- Nutrient and water uptake: Low airation leads to low oxygen uptake. Toxic substances such as H2S harm plant roots.
