<u>Answer</u>:
1. <u>Phosphorus</u> in soil originates from (white arrows):
- plant residue,
- animal manures and biosolids
- atmospheric deposition (dust)
- mineral fertilizers
These sources all add to the phosphorus found in soil in both organic or inorganic forms.
2. <u>Phosphorus</u> from soil is released to (red arrows):
- <u>organic phosphorous</u> through:
<em> -->plant uptake</em> in the form of soluble P. This soluble form has several of its own sources such as primary minerals, mineral surfaces, secondary compounds etc.
--> <em>immobilization</em> where microorganisms convert and absorb inorganic P
- <u>phosphates in solution</u> through:
-->runoff and erosion
-->a small portion though leaching