Agriculture Reference
In-Depth Information
the atmosphere because of respiration by roots and microorganisms (section 3.4).
In addition to CO 2 , traces of other gases such as methane (CH 4 ), nitric oxide
(NO), and nitrous oxide (N 2 O), the by-products of various microbial metabolic
processes (chapter 5), are produced.
Summary Points
1.5
This chapter explores the relationship between soil and its environment. The main
points are summarized as follows:
Soil forms at the interface of the atmosphere and consolidated or loose rocks of
the earth's crust. Physical and chemical weathering, denudation and redeposition,
plus the action of colonizing plants and animals mold a distinctive soil body. The
process of soil formation culminates in a remarkably variable differentiation of soil
material into a series of horizons that make up a soil profile . The intimate mixing
of mineral and organic materials to form a porous fabric, permeated by water and
air, creates a favorable habitat for plant and animal life.
The five soil-forming factors are parent material , climate , organisms , relief , and time .
Where only one set of factors has operated during soil formation, the resultant
soil is said to be monogenetic . Polygenetic soils, which are much more common,
arise when there is a significant change in one or more of the factors. Studies on
the role of these factors, and their interactions, have helped scientists understand
why certain types of soil occur where they do. This concept has also been the ba-
sis of early attempts at soil classification . But modern systems of soil classification
rely as much on the measurement of actual soil properties as on the inferred gen-
esis of a soil.
Parent material affects soil formation primarily through the type of rock miner-
als, their rate of weathering, and the weathering products. These products are re-
distributed by the action of water , wind , ice , and gravity . Generally, the parent
material of soils formed on transported material (especially alluvium) is more het-
erogeneous than that of soils formed on weathering rock in situ (residual soils).
Many vineyards of the world are located on alluvial deposits (old river terraces),
colluvial deposits (rock slides), and solifluction deposits.
Climate affects soil formation through rainfall, evaporation, and temperature. Cli-
mate also influences grape-growing directly. Climate interacts with organisms , par-
ticularly through its effect on the type of vegetation.
Organisms are the vegetation and the animals that live on and in the soil. Human
activity can exert a profound effect on the soil, for good or bad, through the clear-
ing of natural vegetation and the use of soil for agricultural and other purposes.
Relief and its effects are obvious in old, weathered landscapes. Slope has an im-
portant effect on runoff and soil drainage, which is important for viticulture.
Drainage in turn influences the balance between oxidation and reduction of Fe
compounds in the soil profile.
Time is important because the value of a soil-forming factor may change with time
(e.g., global climate change), and profile differentiation depends on the length of
time that a soil has been forming. A soil profile may attain a steady state if the rate
of natural erosion matches the rate of weathering of the parent material. Soil-plant
ecosystems developing since the last Pleistocene ice phase appear to have attained
 
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