Soil Organic Matter Quiz

Study Notes

Natural Supply of Nitrogen

Rates of natural nitrogen supply vary, with values ranging from 6-30 kg N/ha.

Available Nitrogen

Easily available nitrogen is classified as less than 250 kg N/ha.
Nitrogen levels between 250 and 500 kg N/ha are considered medium availability.
High nitrogen availability is indicated by levels exceeding 500 kg N/ha.

Forms of Phosphorus in Soil

A significant portion, 25-80%, is in the form of Phytin or organic forms.
Within humus, 40-80% of phosphorus exists as Phytin, while only 0-10% is found as nucleic acid.

Importance of Humus in Phosphorus

Humus aids plant uptake through the formation of phospho-humic complexes.
It facilitates the anion replacement of phosphate (PO₄³⁻) by humate ions.
Humus coats sesquioxide particles, reducing the soil's phosphate-fixing capacity.
It forms stable complexes with iron (Fe) and aluminum (Al), preventing their interaction with phosphorus.

C : N : P Ratio

The C : N : P ratio is approximately 100:10:1.
When the C : P ratio exceeds 100:1, immobilization of phosphorus occurs, which limits its availability.

C : S Ratio

A C : S ratio below 200 leads to the accumulation of sulfate ions (SO₄²⁻) in the soil.
A C : S ratio over 400 results in sulfate ions being tied up in soil organic matter.
Ratios between 200 and 400 indicate that sulfate may either be released or tied up.

Mineralisation of Organic Nitrogen

The process consists of three steps, beginning with aminization.
Aminization involves the hydrolytic decomposition of proteins by heterotrophic bacteria such as Bacillus and Pseudomonas in anaerobic conditions.
This decomposition process converts organic matter into polypeptides, releasing amines, amino acids, carbon dioxide (CO₂), energy, and other compounds.

Description

Test your knowledge on soil organic matter and its components, including available nitrogen and forms of phosphorus. This quiz covers essential concepts regarding nitrogen supply and the role of organic matter in soil fertility.