World’s Soil Resources

is among the top options in the portfolio of technologies to reduce tillage costs, conserve soil and water,
increase soil organic carbon (SOC) pools, and reduce net CO 2
emissions, which contribute to global warming
(Lal et al., 2004). Despite the numerous benefits of NT, there is no consensus yet on its role in alleviating
soil compaction: some researchers report increased compaction associated with the practice (Bueno et al.,
2006) and others a decrease in compaction (Gregory, Shea and Bakko, 2005). Increasing soil organic matter,
as practiced in conservation agriculture, reduces soil compactibility (Thomas, Haszler and Blevins, 1996), but
residue availability remains a key challenge, especially in Africa.
6.9.2 | What is the extent of deep soil compaction?
Soil compaction affects mainly topsoils (Balbuena et al., 2000; Flowers and Lal, 1998) but can also affect
subsoils at depths >30 cm. Most subsoil compaction occurs when the soil is wet and field equipment weights
exceed 10 tons per axle. The average weight and power of vehicles used on farms has approximately tripled
since 1966 and maximum wheel loads have risen by a factor of six (Chamen, 2006). While remediation of
shallow compaction is possible, for example by ripping and subsoiling, correcting soil compaction at depths
below 45 cm is challenging (Batey, 2009; Berli et al., 2004). Both topsoil and subsoil compaction have been
acknowledged by the European Union as a serious form of soil degradation, estimated to be responsible
for degradation of up to 33 million ha in Europe (Akker and Canarache, 2001). Similar compaction problems
have been reported elsewhere, including in Australia, Azerbaijan, Japan, Russia, China, Ethiopia and New
Zealand (Hamza and Anderson, 2005). The total amount of compacted soil worldwide has been estimated
at approximately 68 million ha or around 4 percent of the total land area (Oldeman, 1992; Soane and Van
Ouwerkerk, 1994). Nearly 33 million ha is located in Europe, where the use of heavy machinery is the main
cause. Cattle trampling and insufficient cover of the top soil by natural vegetation or crops account for
compaction of 18 million ha in Africa, and 10 million ha in Asia (Flowers and Lal, 1998; Hamza and Anderson, 2003).
Agricultural mismanagement (80 percent) and overgrazing (16 percent) are the two major causative factors of
human induced soil compaction (Oldeman, 1992).
6.9.3 | Solutions to soil compaction problems
Soil compaction, like soil chemical characteristics, should be monitored routinely and corrected as part of
soil management (Batey, 2009). Although soil compaction effects on soil biodiversity and related functions
and processes depend on several site and soil properties, a threshold of effective bulk density of 1.7 g cm–3 is
the maximum above which only negative effects are observed (Beylich et al., 2010). Managing soil compaction
can be achieved through appropriate application of some or all of the following techniques: (a) addition and
maintenance of adequate amount of soil organic matter to improve and stabilize soil structure (Heuscher,
Brandt and Jardine, 2005); (b) guiding, confining and minimizing vehicular traffic to the absolutely essential
by reducing the number and frequency of operations, and performing farm operations only when the soil
moisture content is below the optimal range for the maximum proctor density (Kroulik et al., 2009); (c)
mechanical loosening such as deep ripping (Hamza and Anderson, 2005); and (d) selecting a rotation which
includes crops and pasture plants with strong tap roots able to penetrate and break down compacted soils
(Hamza and Anderson, 2005). Promoting macrofauna activity can accelerate creation of channels for water
infiltration and root growth. Arbuscular mycorrhiza can to some extent alleviate the stress of soil compaction.
This effect has been observed on wheat growth following increased root/shoot ratio of wheat under
compaction (Miransari et al., 2008). In the long-term, soil compaction can be reduced by natural processes
that cause the soil to shrink and swell such as wetting and drying (Shiel, Adey and Lodder, 1988), and freezing
and thawing (Miller, 1980).
Soil moisture lower than the plastic limit is desirable for cultivation. Traffic should be avoided or restricted when
condition are otherwise. For farmers, a simple test to avoid soil compaction involves squeezing a small lump of
soil into a ball and rolling it into a rod about 3 mm in diameter. If a rod can be made easily, the soil is too wet and
will compact if it is worked or has animals or machinery on it. If the rod is crumbly the water content should allow
traffic and cultivation without compaction. If a rod will not form at all, the soil could be too dry for tillage in a sandy
or loamy soil. This test should be run at several points over the full depth of any proposed cultivation.
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