Agriculture Reference
In-Depth Information
Table 1.1
Summary of Soil Forming Factors and their Effects
Factors
Components
Characteristics and active agents
Features of soils formed
Parent material
Parent material in place
Igneous rocks—derived from volcanic
activity
Acidic rocks, e.g., granite, rhyolite,
rich in quartz and pale-colored Ca
a
,
K, and Na feldspars
Basic rocks, e.g., basalt, dolerite, low
in quartz and rich in dark-colored
ferromagnesian minerals
Varying size of rock particles forming
mudstones (small), sandstones,
shales, and conglomerates (large);
fine-grained chalk and limestone
Granite metamorphosed to gneiss,
sandstone to quartzite, shale to
schist, limestone to marble
Soils on granite have a high proportion of
quartz grains, often coarse; well drained
if deeply weathered; low fertility
Soils on basalt often high in clay and Fe and
Al oxides; can be poorly drained unless
old and well weathered; generally fertile
Soils on mudstone often poorly drained;
soils on sandstone and conglomerates of
low fertility; soils on limestone vary with
the content of impurities
Variable weathering and properties,
depending on the original rock that was
metamorphosed
Sedimentary rocks—weathered rock material
deposited under water or by wind and
subsequently compressed
Metamorphic rocks—igneous and
sedimentary rocks subjected to heat and
pressure that has changed the original rock
structure and minerals
Transported parent material
Weathered rock materials moved from their
original place
Water, gravity, ice and wind deposits;
when compressed, can form
sedimentary rocks
Alluvial (water) and colluvial soils
(gravity), loess (wind); usually well
drained and fertile
Climate
Macroclimate—the regional climate
applicable over tens of kilometers
Mesoclimate—applicable to a subregion or
site, such as a valley or slope
Microclimate—very local, as within the
canopy of a vineyard
Modified by latitude and elevation,
temperature affects the rate of
organic matter decomposition
and other biochemical reactions;
moisture availability affects
weathering, leaching, and clay
movement down the soil profile
Current and past climates are reflected in
present-day and buried (“fossil”) soils
through differences in depth, color,
organic matter, structure, translocation
of clay, organic compounds, salts, and
oxides, and ultimately the profile form
(see box 1.1)
(continued)
