Environmental Engineering Reference
In-Depth Information
examined for P, Ca and Mg. P was measured by a Tu-1810 spectrophotometer (PERSEE,
China), using the ascorbic acid molybdenum blue method.
Table 1. Characteristics of the soil samples
Total-P
g/kg
Fe-P
%
Soil
type
Clay
(%)
Silt
(%)
Sand
(%)
TOC
(g/Kg)
Al-P
(%)
Ca-P
(%)
pH
A
7.81
3.39
63.63
32.98
2.98
0.83
7.39
10.69
53.17
B
5.56
4.67
45.06
50.27
1.21
0.27
19.03
4.2
52.03
Ca and Mg were analyzed on an atomic absorption spectrophotometer (TAS-990, China).
Reaction time was also studied. The treatments were the same as described above, except that
the concentration of organic acids was 1 mmol/L and the reaction times varied from 2 to 50 h.
The extraction pH ranges from 3 to 8 were also studied on P, Ca and Mg release from alkaline
soil.
2.3. Statistical Analysis
All the data are averaged values of three replicates. All statistical analyses were
performed using SPSS 17.0. The effect of each factor on P, Ca and Mg release from soils was
tested by one-way ANOVA. The significance level was p <0.05.
3. R ESULTS
3.1. P Desorption Influenced by Concentration of Organic Acids
The results obviously revealed that P solubility was highly dependent on the organic
acids type and concentrations (Figure 1). In soil A, the P solubility was small at low organic
acids concentrations (0-1 mmol/L) while the release of P was significantly increased at higher
concentrations (2-20 mmol/L). Compared with control, citric acid increased more P by 21.7
fold, oxalic acid being 11.7 fold, malic 6.8 being fold and acetic 2.7 being fold. In soil B,
slight increases (about 3 fold) had taken place in soluble P concentrations as organic acids
increased from 0 to 0.05 mmol/L.
In addition, the soil P release content increased by 11.9 fold for citric acid, 14.9 fold for
oxalic acid and 7.3 fold for malic acid when organic acids increased from 1 to 20 mmol/L.
For both two soils, acetic acid did not follow the same trend as the other organic acids
because release of P was only significant at relatively higher concentration (≥10 mmol/L).
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