Agriculture Reference
In-Depth Information
TABLE 4.4
Management Practices to Improve or Stabilize OM Content of Soils
i. Conservation tillage
ii. Crop rotation
iii. Use of an adequate rate of fertilizers
iv. Liming acid soils
v. Use of organic manures
a. Cover crops/green manuring
b. Farmyard manures
c. Municipality compost
d. Recycling crop residues
vi. Keeping land under pasture
4.8.1 a
doptInG
C
onservatIon
t
IllaGe
s
Ystem
Conservation tillage is defined as any tillage sequence, the objective 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 residues on the surface (Soil Science Society of America,
2008). Minimum tillage, NT, or zero-tillage terms are also used in the literature. According to the
Soil Science Society of America (2008), 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 for conventional tillage
(CT). Similarly, minimum 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 harvest of the previous crop. In this
process, usually a special planter is necessary 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.
Conservation, minimum tillage, or NT is widely adopted in developed as well as developing coun-
tries in recent years for crop production. Horowitz et al. (2010) reported that about 35% of row crop
hectares in the United States was planted using no till in 2009 and that the median rate of adoption
from 2000 to 2007 was roughly 1.5% year
−1
, a trend that shows no sign of declining. It is projected that
conservation tillage will be practiced on 75% of cropland in the United States by 2020 (Lal, 1997).
Kern and Johnson (1993) reported that increasing conservation tillage to 76% of planted cropland would
change agricultural systems from C sources to C sink. No-till management is generally recognized as
an effective strategy to sequester C (West and Post, 2002; Franzluebbers, 2005; Spargo et al., 2012), and
it has also been shown to conserve soil organic N (Franzluebbers, 2004; Spargo et al., 2008).
Intensive tillage disrupts the soil structure and also increases the oxidation of SOM because
of the increased aeration and microbial activity (Vance, 2000). Hence, it depletes the SOC stocks
through erosion (Blanco-Canqui and Lal, 2008). It has been reported that conversion of natural sys-
tems to agroecosystems can deplete the SOC stock by as much as 40% for soils under the forest to
about 60% for those under grassland (West and Post, 2002; Blanco-Canqui and Lal, 2008). The NT
system has been used in the Corn Belt soils of the U.S. Midwest for more than a century (Wander
et al., 1998) to enhance corn and soybean production (Kumar et al., 2012). Therefore, this system
is being promoted as an alternative to more intensive tillage systems to restore SOC stocks and to
improve soil properties (Blanco-Canqui et al., 2009).
There is a general concept that tillage decreases aggregate stability by increasing mineraliza-
tion of OM and exposing aggregates to additional raindrop impact energies (Tisdall and Oades,
1982; Elliott, 1986; Angers et al., 1992; Amezketa, 1999; Balesdent et al., 2000; Park and Smucker,
