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 Figure 4.19 Dry Sieve Test.
Wet sieve test (laboratory)
The wet sieving test is used to determine the grain composition of the smaller particles <63 μm. This test is also done in the laboratory. When 10 % or more of the soil is smaller than 63􏰀m then it is necessary to use a wet sieving test.
4.2.3 Chemistry and Morphology
Chemistry and soil morphology are intimately related. Essentially, the soil looks the way it does due to chemical reactions. Three types of reactions, redox reactions, podzolization, and cementation, are important as is the resulting morphology, and interpretation. Other reactions do occur but these three are the most critical in regards to soil evaluation for our purposes.
Redox reactions are short for oxidation-reduction reactions. These reactions occur in all soil but are most common in seasonally saturated and hydric soils. It is these reactions that are responsible for many of the soil colors observed in soil. Other than color redox reactions control organic matter contents and are related to soil water chemistry. The general redox principle is that as OM decomposes it releases electrons. These electrons are taken up by (or given to) another element or compound. The compound that gains an electron is said to be reduced as the electron has a negative charge thus the overall charge or the element or compound is reduced by 1. Conversely a substance that looses an electron is said to be oxidized.
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