Agriculture Reference
In-Depth Information
8.4.1 u
se
of
C
onservatIon
t
IllaGe
Conservation tillage is related to tillage operations. Hence, it is logical to first define what tillage
is. Tillage is defined as the mechanical manipulation of the soil profile for any purpose, but in agri-
culture it is usually restricted to modifying soil conditions and/or managing crop residues and/or
weeds and/or incorporating chemicals for crop production (Soil Science Society of America, 2008).
Conservation tillage, on the other hand, can be defined as any tillage sequence, the object of which
is to minimize or reduce the loss of soil and water operationally, a tillage or tillage and planting
combination that leaves a 30% or greater cover of crop residue on the surface (Soil Science Society
of America, 2008). In addition to conservation tillage, no-tillage or zero tillage terms are also used
in the literature and these terms are related to conservation tillage and need to be defined. No-tillage
or zero tillage is defined as a procedure whereby a crop is planted directly into the soil with no
primary or secondary tillage since the harvest of the previous crop; usually a special planter is nec-
essary to prepare a narrow, shallow seedbed immediately surrounding the seed being planted. NT
is sometimes practiced in combination with subsoiling to facilitate seeding and early root growth,
whereby the surface residue is left virtually undisturbed except for a small slot in the path of the
subsoil shank (Soil Science Society of America, 2008).
Two other terms—minimum tillage and conventional tillage—are also frequently used in the soil
preparation operations. Hence, these terms should also be defined to correlate with conservation till-
age. Minimum tillage is defined as the minimum use of primary and/or secondary tillage necessary
for meeting crop production requirements under the existing soil and climatic conditions, usually
resulting in fewer tillage operations than for conventional tillage (Soil Science Society of America,
2008). Similarly, conventional tillage is defined as the primary and secondary tillage operations
normally performed in preparing a seedbed and/or cultivating for a given crop grown in a given
geographical area, usually resulting in <30% cover of crop residues remaining on the surface after
completion of the tillage sequence (Soil Science Society of America, 2008). Conservation tillage is
practiced on approximately 95 million ha worldwide, with the largest area in South America (approx-
imately 47%), North America (approximately 40%), and Australia (approximately 9%); the remaining
areas are located in the rest of the world, including Asia, Europe, and Africa (Mchunu et al., 2011).
Several studies have shown that the use of conservation tillage in cropping systems can improve
soil organic matter, soil moisture, and total available soil N (Sharifi et al., 2008; Lafond et al., 2011;
Zakeri et al., 2012). Zakeri et al. (2012) reported that the use of conservation tillage improves not
only C and N but also the overall soil quality. Across the three major soil zones of Saskatchewan,
continuous NT increased potentially mineralizable soil N by 16-40 kg ha
−1
compared to conven-
tional tillage (Liang et al., 2004). In the black soils of this province, Schoenau et al. (2008) mea-
sured greater soil-available N and P following 28 years of continuous no-tillage compared to 5
years of continuous NT history in the same field. As a result of the improved soil quality and soil
moisture, the biological nitrogen fixation of legume crops has gradually increased in NT systems
(Matus et al., 1997; Van Kessel and Hartley, 2000). Blanco-Canqui and Lal (2008) and Wuest and
Schillinger (2011) reported that NT is an attractive method of farming because it can lower produc-
tion costs, leave the soil in a less erodible condition, and improve the soil quality compared with
tillage-based systems. Wust and Schillinger (2011) further reported that wheat farmers in many
regions of the world have developed NT systems that are economically and environmentally supe-
rior to tillage-based systems.
Improved soil and crop management practices, such as reduced tillage and continuous crop-
ping, can increase dryland N storage to a depth of 20 cm compared to a traditional farming system
(Sherrod et al., 2003; Sainju et al., 2006). Besides reducing N mineralization, NT can conserve sur-
face residues and soil water more than conventional tillage (Farahani et al., 1998). As a result, crops
can use soil water more efficiently in conservation tillage (Deibert et al., 1986; Aase and Pikul,
1995), which can reduce or eliminate summer fallow by increasing cropping intensity (Farahani
et al., 1998; Peterson et al., 1998).
