To calculate the Aggregate Instability Index (AII) of the soil, we can use the following formula:
\[ \text{AII} = \frac{\text{MWD}{\text{dry}} - \text{MWD}{\text{wet}}}{\text{MWD}_{\text{dry}}} \]
Where:
- \( \text{MWD}_{\text{dry}} \) is the mean weight diameter for dry sieving,
- \( \text{MWD}_{\text{wet}} \) is the mean weight diameter for wet sieving.
Given:
- \( \text{MWD}_{\text{dry}} = 4.37 , \text{mm} \)
- \( \text{MWD}_{\text{wet}} = 2.5 , \text{mm} \)
Now, plug in the values:
\[ \text{AII} = \frac{4.37 , \text{mm} - 2.5 , \text{mm}}{4.37 , \text{mm}} = \frac{1.87 , \text{mm}}{4.37 , \text{mm}} \approx 0.427 \]
So, the Aggregate Instability Index (AII) is approximately \( 0.427 \) or \( 42.7% \).
Interpretation of Results
-
High AII (>0.3): An AII value greater than 0.3 typically indicates a significant level of instability in the soil aggregates. This instability may lead to increased susceptibility to erosion and degradation, particularly during wet conditions.
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Moderate AII (0.1 - 0.3): Values in this range suggest that the soil has moderate aggregate stability, which implies some resilience but may still experience issues under certain conditions, especially when saturated.
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Low AII (<0.1): An AII below 0.1 indicates that the soil has good aggregate stability and is less likely to suffer from erosion or degradation.
In this case, with an AII of approximately \( 0.427 \), it indicates that the soil exhibits high instability. This could suggest a greater risk of erosion or degradation under wet conditions, and strategies aimed at improving soil structure, such as adding organic matter or employing conservation tillage methods, may be warranted to enhance overall soil stability.