Geoscience Reference
In-Depth Information
Fig. 11.4
Scheme of nitrifi cation and denitrifi cation
terminology are related to the reaction, and we use the term phosphate with descrip-
tive modifi ers. The phosphate ion (PO
4
3−
) exists in strongly basic conditions. In
weakly basic conditions, we fi nd the hydrogen phosphate ion (HPO
4
2−
). In weakly
acid conditions, there is dihydrogen phosphate ion (H
2
PO
4
2−
). In strongly acidic
conditions, trihydrogen phosphate (H
3
PO
4
) prevails. See also Fig.
11.5
.
Phosphate is important in conserving energy and in taking part in the release and
transport of energy within a plant's body, as we have seen in the example on the
cycle ATP
ATP, Sect.
11.1
. Adequate P availability for plants
stimulates plant growth rates especially during their early development as well as
hastening their maturity. Phosphorus defi ciency is diffi cult to diagnose because
other growth factors give similar symptoms. A laboratory soil test calibrated with
tissue tests for specifi c crops is the best method to determine the need for phospho-
rus fertilizers.
The phosphate used by living organisms is incorporated into organic compounds.
When plant residues are returned to the soil, this organic phosphate is slowly
released. A certain portion of it is incorporated into more stable organic forms and
becomes part of the soil humus. The release of inorganic phosphate from organic
phosphates is called mineralization. The breaking down of organic compounds is
mainly realized by microorganisms. The activity of microorganisms is highly infl u-
enced by soil temperature and soil moisture. The process is most rapid when soils
are warm, moist, and well drained - not waterlogged.
→
ADP and ADP
→
