Page 99 - Soil Degradation, Conservation and Remediation

86 3 Soil Erosion by Water

3.4.3 Conservation Tillage

Tillage refers to the mechanical manipulation of soil for cultivation of crops.
Tillage involves a series of mechanical operations including plowing and harrow-
ing to prepare a good seedbed. The main objectives of tillage are inverting the soil,
incorporating crop residues and amendments, controlling weeds, and harvesting
crops. Tillage systems may be grouped into conventional tillage and conservation
tillage.
Conventional tillage is any tillage system that inverts the soil and alters the natu-
ral soil structure. It includes loosening soil, incorporating residues, preparing a
seedbed, controlling weeds, and mixing lime, fertilizer, and other chemicals. It pri-
marily involves the moldboard plowing. The introduction of moldboard plow
increased food supply particularly in developed countries. But intensive plowing
has caused soil erosion, depleted soil fertility, and reduced biological activities.
Moldboard plow chops and buries the residues in the soil. Because plowing leaves
little or no residue cover, it increases soils’ susceptibility to wind and water erosion.
Because of its adverse impacts, use of moldboard plow has decreased since the
1970s, especially in the USA, Canada, Brazil, Argentina, Australia, etc.
Conservation tillage is any system that reduces the number of tillage operations,

reduces the area of tilling in the field, and maintains residue cover on the soil sur-

face. The Soil Science Society of America (SSSA 2008 ) defines conservation tillage
as a tillage system that leaves at least 30 % of residue cover on the soil surface.
When combined with prudent management of crop residues, crop rotations, and
cover crops, conservation tillage is a useful technology for protecting soil and sus-
taining crop production (Blanco and Lal 2008 ). Conservation agriculture occupies
about 100 M ha of land worldwide (Derpsch 2005 ). Conservation tillage includes
no-till and reduced or minimum tillage systems such as mulch tillage, strip tillage,
and ridge tillage. Cropping with no-tillage or limited tillage is not as popular as with
tillage. But for negative impacts of conventional tillage, including exposure of the
soil surface to wind and water erosion, and loss of soil organic matter through oxi-
dation, conservation tillage is gaining popularity. These management strategies
have proved effective for controlling soil erosion and improving soil quality.
In no-tillage, crops are planted directly in the residues of the previous crop with
no prior tillage (Fig. 3.9 ). For row crops, a slit is made in the soil in which the seed
is sown. Minimum tillage involves the minimum manipulation of soil. It is actually
a localized tillage. For example, strawberry in Fig. 3.10 has been grown by tilling
only the soil of the rows. Minimum and no-tillage leave more residues on the soil
surface than conventional tillage, resulting in enhanced infiltration and reduced run-

off and soil erosion for which they are called conservation tillage. A strip 30–45 cm
wide is tilled in the row between undisturbed spaces during strip tillage. Strip-till is
less effective than no-till and subsoil systems, because bare soil exposed in the tilled
strip is susceptible to erosion. It can be made effective by covering the exposed part
with organic residues. Conservation tillage systems have some disadvantages too.
Yield of crop tends to be lower and weed infestation is a major problem.