Page 67 - Soil Degradation, Conservation and Remediation

2.2 Surface Sealing, Crusting, Hardsetting, and Compaction (Pc) 53

Fig. 2.1 Soil moisture level High
and susceptibility to
compaction Moist soil
Susceptibility to compaction compactible
is most

Low
Low Water content High

There are two types of soil compaction: shallow and deep. Shallow compaction
occurs near the soil surface and can be broken up by normal tillage. Surface crust
and hardsetting are a kind of shallow soil compaction. Deep compaction is caused
mainly by axle load. Compacted layers below the plow depth are known as tillage
pans or plow pans. Van den Akker and Schjonning ( 2004 ) suggested that extensive
areas have undergone subsoil compaction due to use of heavy farm machineries.
Deep compaction may extend as far as 75 cm below the surface. It is extremely dif-

ficult to correct since it is below the normal tillage zone. Deep compaction reduces
water and air storage in the deeper part of the soil profile and hamper the growth of

all types of crops. Developing full root system of deep-rooted crops such as corn
and alfalfa is hampered by deep compaction.

2.2.3.1 Factors Affecting Soil Compaction

Any process that reduces pore space causes soil compaction. Farm machineries

including tractors and other implements can compact soil when traveling across a

field. Livestock and even human can compact soil. The extent of soil compaction
depends on many factors: soil physical conditions as well as weight and design of
the load on soil, distribution of the load over the number of axles and tires, and, to a
lesser degree, number of trips made over the field. Soil texture, structure, organic

matter, and water are important soil factors that determine susceptibility of soil to
compaction. Soils made up of particles of about the same size compact less than soil

with a variety of particle sizes. Smaller particles can fill the pores between larger
particles resulting in a denser soil. A sandy loam soil is more easily compacted than
a sandy or clayey soil. A soil with a higher level of organic matter generally has a
better structure. Hard, dense, low organic matter soils suffer more from compaction
than loose, friable, high organic matter soils. A dry soil is not easily compacted. Soil
compaction increases with the increase in soil water content during tilling. A soil
saturated with water resists compaction because water occupies the pores and water
is not compressible. Soils are easily compacted at soil water contents slightly higher

than field capacity. Figure 2.1 shows the relationships of soil water with soil
compaction.