1. Give one example of a condition which tends to increase net nitrogen immobili
ID: 119051 • Letter: 1
Question
1. Give one example of a condition which tends to increase net nitrogen immobilization (relative to nitrogen mineralization)?
2. Under what soil conditions do you expect to see the highest rates of nitrogen mineralization? (Name at least two critical factors necessary to achieve these high rates).
3. (a) The dominant end-product of carbon mineralization in well aerated soils is ______________.
(b) The end-products of carbon mineralization in water-logged bog soils are ________________.
(c) Explain this difference.
4. In the figure below, inorganic nitrogen pools were monitored over a one-year experiment in two soil samples. Both soil sample A and B originated from the same site and were treated identically except that soil A was amended with organic matter (arrow 1). Nothing was added to soil B, the control soil. Other than this difference, consider A and B identical at the start of the experiment (before arrow 1).
a) What type of organic matter do you think was added to soil A (arrow 1)? Explain.
b) Explain the change in the shape of the inorganic nitrogen curve of soil A marked by arrow 2. What microbial process(es) in soil explain the change in inorganic nitrogen concentrations?
c) What can you say about the native soil organic matter being degraded in soil A and B at time = 0 (before amendment)?
2 B (control)Explanation / Answer
1. Immobilization is the process by which the inorganic compounds are converted into organic compounds by micro-organisms or plants and it is prevented from being accessible to plants. Net nitrogen immobilization or mineralization depends on the C/N ratio of the plant residues. If the C/N ratio of the plant residue is 30:1 means very little amount of nitrogen, then the soilmicrobial poplulation takes the nitrogen in mineral form i.e. nitrate form.This is immobilized and causes deficiency in the plant residue.
2. Plants absorb nitrogen in two forms : nitrate and amonium ions. Nitrification is effected by aerobic autotrophs while the production of amonium is carried by heterotrophic organisms such as fungi, bacteria and actinomycetes. It has been found that nitrogen mineralization is more under water logged condition rather than under aerobic condition.
The facors that influence the nitrogen mineralization are :
i. Soil pH
ii. Percentage of organic C and N
iii. Temperature
iv. Moisture &
v. Salt content.
3. a) The dominant product of carbon mineralization in well aerated soil is nutrients.
b) The dominant product of carbon mineralization in well logged soil is carbon di-oxide.
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