73 prolonged milling, resulting in a reduction in surface area relative to unmilled
material Table 2.1 so that dissolution in soil may be restricted by inadequate exposure to soil solution and associated slow diffusion of dissolved ions to and from
reacting surfaces. Table 4.2. Distribution of the values of coefficient correlation r for the linear
relationship between dissolution of basic cations from the SRFs in 0.01M acetic- citric acid for 1 hour, 1 day, and 56 days E
1H
, E
1D
, and E
56D
versus the average dissolution that occurred in 23 soils for 2 months E
2M
. Distribution of r values
soils with r 0.95 SRF
Dissolution Variables
Max Min
Mean Sd
significant at p 0.05 Basalt
E
1H
v E
2M
E
1D
v E
2M
E
56H
v E
2M
1.00 1.00
1.00 0.51
0.45 0.48
0.85 0.84
0.84 0.16
0.17 0.15
35 35
30 Dolerite
E
1H
v E
2M
E
1D
v E
2M
E
56H
v E
2M
1.00 1.00
1.00 0.74
0.73 0.78
0.95 0.95
0.96 0.06
0.06 0.05
70 65
78 Gneiss
E
1H
v E
2M
E
1D
v E
2M
E
56H
v E
2M
1.00 1.00
1.00 0.93
0.93 0.93
0.99 0.99
0.98 0.02
0.02 0.02
87 87
91 K-feldspar
E
1H
v E
2M
E
1D
v E
2M
E
56H
v E
2M
1.00 1.00
1.00 0.89
0.89 0.85
0.98 0.98
0.97 0.02
0.03 0.04
96 96
94
4.3.4. Dissolution of SRFs versus Soil Properties
Simple and multiple regression analyses were employed to identify relationships between the amounts of dissolved elements Eo, E
2M
, E
10M
, E
0-2M
, and E
2-10M
from the SRFs in soils and the soil properties listed in Table 4.1. The dissolved elements involved in the analysis are Ca + Mg for basalt and dolerite
SRFs and K + Na for gneiss and K-feldspar SRFs. Results of simple-linear regression Table 4.3 indicate that soil properties
which are significantly correlated to dissolution of SRFs in soil are commonly different for each SRF, milling time, and incubation period, with correlation
coefficients r being mostly smaller in magnitude than 0.70. Thus single soil properties mostly indicate 50 of the variation in dissolution of basic cations
from SRFs in the soils. No single soil property is highly predictive of dissolution in soils for any SRF, incubation time, or milling time.
74 Table 4.3. Soil properties with significant-linear bivariate relationships p 0.05
with dissolution of basic cations from the SRFs in 10 soils for each milling time. Dissolution is presented as of Ca + Mg and K + Na dissolved in 10 soils
relative to total content of these cations in SRF.
SRF cations
Dissolution of total
Soil Properties Correlation Coefficient
Basalt Ca + Mg
Eo E
2M
∆E
0-2M
∆E
2-10M
org. C -0.45 only for T0 sand -0.48 to -0.67 and clay +0.44 to +0.62
EC +0.40 to + 0.62, CEC +0.43 to + 0.48, sand -0.45 to -0.59, and clay +0.43 to +0.64
sand -0.63 and clay +0.65 only for T60
Dolerite Ca + Mg
∆E
0-2M
sand -0.41 to – 0.53 and clay +0.48 to +0.52
Gneiss K + Na
Eo E
2M
∆E
0-2M
sand -0.41 to -0.53 and clay +0.48 to +0.52 EC +0.70 to +0.86, CEC +0.45 to + 0.57, sand
-0.52 to -0.59, and clay +0.43 to +0.62 EC +0.79 to +0.85, sand -0.50 to – 0.71, and
clay +0.57 to +0.75
K-feldspar K + Na
Eo E
2M
E
10M
∆E
0-2M
∆E
2-10M
org C +0.47 for T10 and +0.44 for T60 pH
H
2
O
-0.46 for T60 and -0.52 for T120, and org C +0.43 for T0 and T10
pH
H
2
O
-0.62 to -0.82, EC +0.70 to +0.83, CEC +0.65 to +0.80, and exch. acidity +0.69 to +0.93
pH
H
2
O
-0.44 only for T60 CEC +0.83 for T10, CEC +0.91 and exch. acidity
+0.93 for T60.
The stepwise multiple regression method was employed to evaluate if incorporation of several variables improved the predictive relationships between
dissolution of basic cations from the SRFs and soil properties. Values of dependent E and
∆E and independent soil properties variables were also incorporated as log and square root transformed values to test for non-linear relationships. Examples of
results from multiple regression analysis expressed as predictive equations with coefficients of determination R
2
0.50 are presented in Table 4.4.
75
76 In general there is no substantial improvement in the prediction of
dissolution by use of relationships generated by multiple regression compared to the results for simple bivariate regression analysis, but a few quite predictive equations
were generated. The variables sand negative and clay positive appear several times in both the bivariate and multivariate relationships. It appears that
dissolution of ground silicate rocks is greater in clay rich soils. Both CEC and exchange acidity are positively related to the extent of dissolution of alkali elements
from K-feldspar in soils. This outcome parallels that observed by Hughes and Gilkes 1994 who found only poorly predictive bivariate relationships between the
percentage dissolution of rock phosphate in soil and single soil properties for 228 soils from south-western Australia. Multiple regression analysis indicated a
combination of titratable acidity positive and sand negative explained about 61 of total variation in percentage dissolution of rock phosphate in soil. In the
present work, exchange acidity positive and sand negative also appear in several of the multivariate equations.
4.3.5. Percentage Dissolution versus SRF Properties
