Environmental Engineering Reference
In-Depth Information
3.6. Ca and Mg Desorption Influenced by pH of Organic Acids
The Ca and Mg release capacity influenced by pH-dependence of four individual organic
acids was presented in Figure 6. Generally, the release of Ca and Mg had the decreasing trend
with decreasing soil acidity for the two soils.
1000
Mg
Ca
Mg
Ca
1000
750
750
500
500
250
250
0
0
3
4
5
6
7
8
3
4
5
6
7
8
citric a cid pH
oxa lic a cid pH
1000
Mg
Ca
1000
Mg
Ca
750
750
500
500
250
250
0
0
4
5
6
7
8
3
4
5
6
7
8
a cetic a cid pH
ma lic a cid pH
Figure 6. The effect of pH-dependence of four organic acids on cations releases in the alkaline soil.
Symbols represent mean ± SEM.
3.7. Relationships between Nutrients and Solution pH
Figure 7 showed the changes of soil pH after adding different amounts of organic acid in
two soils. For soil A, pH was decreased when high concentrations of organic acids (≥ 5
mmol/L) were added into the soil. For soil B, the response was more apparent because the soil
was greatly acidized with the increasing content of organic acids (>1 mmol/L).
For soil A and B, P solubility was negatively related to extraction pH ( p <0.05) and
positively related to Ca and Mg ( p <0.05) with some exception for acetic acid and oxalic acid.
Meanwhile, Ca and Mg solubility were negatively related to extraction pH (p<0.05) except
for oxalic acid in two soils.
4. D ISCUSSION
Generally, organic acids (e.g. citric acid, malic acid and oxalic acid) exuded from roots
can accelerate soil P release from soils. Meanwhile, the effectiveness of an organic acid to
mobilize soil P highly depends on the type, concentration, reaction time and pH of organic
acids and soil type [13, 17].
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