Page 66 - Soil Degradation, Conservation and Remediation

52 2 Physical Deterioration of Soil

conservation farming: (1) to improve the physical and chemical conditions of the
soil and (2) to shield the soil surface from the destructive force of the raindrops
using mulches or protective cover. Integration of these two approaches commonly
produces encouraging results. Cover crops and mulch reduce water loss and erosion
appreciably.

Tillage Management

Tillage management for crusted soils includes choice of tillage implements, axle
load, tillage operations such as number of turns of plow, and timing of tillage opera-
tions in relation to wetting and drying.

2.2.3 Soil Compaction

Soil compaction is the physical consolidation of the soil by an applied force, usually
by tillage implements, that destroys soil structure, compresses soil volume, increases
bulk density, reduces porosity, and limits movement of water and air within the soil.
Surface sealing, crusting, and hardsetting are actually some sorts of soil compaction
occurring in the surface soil by slaking of soil structure. Sometimes soil consolida-
tion is distinguished from soil compaction. Soil consolidation is regarded as a pro-
cess by which a saturated soil is compressed under a long-term load accompanied
by a reduction in porosity with expulsion of water. In contrast, soil compaction is
considered to be a process in which an unsaturated soil is compressed by a load
applied for a short time with no expulsion of water. However, such a distinction in
compacted soil management does not seem practical.
Stunted plant growth, shallow and malformed plant roots, standing water, for-
mation of large clods after tillage, and physically dense soil are the signs of soil

compaction. Soil compaction has been described as one of the five threats to sus-
tained soil quality by the EU Soil Framework Directive (Commission of the
European Communities 2006 ). There is about 68.3 M ha compacted soil globally,
which accounts for 4 % of anthropogenic soil degradation (Oldeman et al. 1991 ).
In Europe, compaction accounts for about 17 % of the total degraded area. It is a
complex problem in which machine/soil/crop/weather interactions play an impor-
tant role and may have economic and environmental consequences for world agri-
culture (Soane and van Ouwerkerk 1995 ). Soil compaction is a global problem
commonly associated with mechanized agriculture. It has caused yield reductions
of 25–50 % in some regions of Europe (Eriksson et al. 1974 ) and North America
and between 40 and 90 % in West African countries (Charreau 1972 ; Kayombo
and Lal 1994 ). On-farm losses through soil compaction in the USA have been
estimated at US$1.2 billion per year (Gill 1971 ). Oldeman et al. ( 1991 ) suggested
that compaction is by far the most important type of physical deterioration of
agricultural soils.