MR 1 Study Guide - Soil Chemistry Flashcards
What are redoximorphic features, what do they indicate? What are some examples of redoximorphic features?
Variegated color patterns of dull gray and bright orange, indicative of seasonal saturation
Black soil
Humified (highly decomposed) organic matter
Brown soil
Combination of Fe-oxides, oxyhydroxides, and OM
Red soil
Oxidized iron, hematite (Fe2O3)
Gray soil
Reduction of Fe3+ to Fe2+ and loss of Fe2+, anaerobic conditions WITH leaching,
Grayish colors indicative of iron depletion
Blue-green soil
Reduction of Fe3+ to Fe2+ and retention of Fe2+, anaerobic conditions WITHOUT leaching
Pale bluish or greenish-yellow colors are indicative of prolonged saturation, but reduced iron is not leached away
White soil
Carbonate or evaporite accumulation OR strong eluviation leaving non-pigmented light-colored minerals
How are metamorphic rocks formed?
They are formed when rocks undergo extreme heat, pressure, hot mineral-rich fluids, or any combination of these factors
How are sedimentary rocks formed?
Compacted or cemented particles weathered from any type of preexisting rocks
How are igneous
rocks formed?
Formed from molten magma
What soil properties are determined by the characteristics of the parent material?
Fertility and coarseness of the soil
What are the two main types of weathering of parent materials? Give some examples of each
Physical and chemical weathering
ex of physical: wind abrasion
ex of chemical: organisms
What is a mafic rock? What is a felsic rock?
Mafic is made of heavy elements, felsic is made of light elements
How does element composition in the parent material affect soil properties?
Affects mineral composition, soil fertility, rate of weathering, texture, hydrology, vegetation
How does grain size in the parent material affect soil properties?
Parent material with larger grain size will generally produce coarser soils while smaller grain size will produce finer soils
Explain the main properties of granite and how they drive the properties of soil
Granite is a felsic rock
Quartz: resistant to weathering and doesn’t contain minerals
Feldspars and muscovite: more easily-weathered but still contain few nutrients
Soils derived from granitic rock are coarse-textured and have low fertility
Explain the main properties of basalt and how they drive soil properties
Basalt is a mafic rock
Dominated by small-grained, easily weathered, nutrient-rich minerals including hornblende, augite, biotite.
Parent materials and soils derived from basaltic rock are fine-textured and fertile
What are the three main characteristics of soil colloids?
Small, highly reactive, and massive surface area
The hydrolysis of feldspar is an example of ________ weathering that forms _______, a secondary mineral
chemical, kaolinite
The oxidation of Pyroxene, is an example of __________ weathering that forms, ________, a secondary mineral
chemical, iron oxide
During the processes of chemical weathering from primary to secondary minerals there is generally an ______ (increase/decrease) in Si4+ in the mineral structures
Decrease
The attraction between colloids and water molecules is called:_____
adhesion
The attraction of water molecules to each other is called:______
cohesion
How does the charge of the cations determine how strongly they are attracted to the colloids?
Higher charge = stronger attraction
How does the size of the hydrated cations determine how strongly they are attracted to the
colloids?
Smaller size = stronger attraction