Agriculture Reference
In-Depth Information
after tillage, soil erosion and transport of SOC-rich sediment off of the sloping plots
contributed substantially (29%-39%) to these SOC losses.
Surface sealing and soil crusting from raindrops on the soil consolidate the sur-
face layers when crop residues are removed. After the surface seals, erosive forces
increase, leading to sheet and rill erosion. Surface soil properties are sensitive to
the maintenance of stable soil aggregates, which are created through the continual
addition of organic material. To prevent surface sealing, it is necessary to maintain
surface residue (Ruan et al. 2001). Tillage practices, for example, NT, which main-
tain crop residue on the surface and application of compost and manure as sources of
organic materials, reduce surface sealing and crusting (Cassel et al. 1995; Pagliai et
al. 2004). Blanco-Canqui et al. (2006a) observed in soils without residue cover that
crusts with a thickness of 3 cm and cracks with widths of 0.6 cm were formed during
periods with no rainfall. Removal of crop residue affects the stability of aggregates,
which depends upon the maintenance of SOM concentration at the surface (Blanco-
Canqui et al. 2006b; Rhoton et al. 2002). Changes in the soil structural stability are
rapid, and often, degradation of the surface soils occurs within the first year after
the residue is removed (Blanco-Canqui and Lal 2009). A regional study by Blanco-
Canqui et al. (2009) comparing different tillage systems observed that aggregates
under NT systems were more stable under rain but did not show any effect on dry
aggregate stability. The formation of stable aggregates and exposure to the forces of
raindrops under a rainfall event will lead to increased resistance to the soil erosion.
Since erosion is one of the major causes of soil degradation, any change in a soil
property to diminish the impact of intense rainfall events on the soil surface will
have a positive effect on reducing soil erosion.
Tillage decreases the SOM content in the surface soil and creates conditions fos-
tering a corresponding decrease in soil biological activity (Mahboubi and Lal 1998).
Mahboubi and Lal (1998) found a seasonal response to tillage effects on aggregation
and soil structure, suggesting that any assessment of tillage on soil properties must
account for seasonality. Removal of crop residue from the soil surface decreased the
soil microbial biomass C and N concentrations (Salinas-Garcia et al. 2001). Doran
et al. (1998) observed a loss of soil C from three tillage systems in a Nebraska
study; however, the loss from NT was less than from conventional tillage. In the NT
system, they observed an increase in soil microbial activity near the soil surface.
Karlen et al. (1994) concluded from a comparison of different systems that removal
of crop residue caused soil aggregates to be less stable and decreased soil biologi-
cal activity. The advantage of the NT system was the maintenance of the protective
soil cover and partially decomposed organic material near the soil surface, which
reduced the rate of soil degradation. Reeves (1997) concluded that maintenance of
SOM is critical for soil quality. SOM is a critical component of the soil. Loveland
and Webb (2003) reviewed the literature from around the world and concluded that
when organic C declines below 2%, there will be a decline in soil quality. Papiernik
et al. (2007) evaluated a glacial till landscape in west central Minnesota as affected
by long-term tillage and found that areas of the field with greater than 20 Mg ha
-1
year
-1
erosion had shallower soil profiles and reduced inorganic C content. They
also observed that SOC and total N in the cultivated areas were less than half of
those in adjacent uncultivated areas. The effect of the long-term tillage (over 40
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