Agriculture Reference
In-Depth Information
decomposition rates (Sims and Frederick, 1970; Ambes and Jensen, 1997; Angers and Recous,
1997). During the initial decomposition, microbial colonizers must penetrate the straw epidermis
with its protecting cuticula and then the layers of strongly lignified sclerenchyma of the internode
before colonizing less lignified parenchymatic cells (Ambus and Jensen, 2001). Breaking up plant
material may therefore facilitate microbial attack (Amato et al., 1984). In addition, finely ground
plant material mixes more intimately with the soil accelerating microbial breakdown (Angers and
Recous, 1997). Furthermore, fine particles may also be physically protected against decomposition
by adsorption to clay and other soil constituents (Jensen, 1997). Ambus and Jensen (2001) reported
that adequate management of crop residues may regulate soil N mineralization-immobilization and
match the N release synchronously with the crop requirement.
Incorporation of crop residue into the soil improves soil fertility, including N, and crop produc-
tivity by increasing C sequestration and reducing the emission of greenhouse gases among other
parameters (Biau et al., 2013). Wilhelm et al. (2004) and Lal (2005) also reported that the incor-
poration of stover has many benefits, including the prevention of soil erosion, maintenance of soil
organic matter and soil structure by humification, and as a source of energy for soil biota. Stover is
also an important source of macronutrients (NPK) and micronutrients such as S, Cu, B, Zn, and Mo
(Mubarak et al., 2002). Stover improves soil organic carbon (SOC), which is a key of the CO
2
sink,
maintaining the productivity of agriculture while reducing greenhouse gas emissions and mitigat-
ing global climate change (Christopher et al., 2009).
The benefits of high SOC levels include the sequestration of atmospheric CO
2
as well as bet-
ter soil quality (Blanco-Canqui and Lal, 2009; Benjamin et al., 2010). Plant residues influence N
cycling in soils because they are the primary sources and sinks for C and N (Dinnes et al., 2002).
Incorporation of crop residues into the soil provides substantial amounts of nutrients, including
N for succeeding crops (Carranca et al., 1999; Ambus and Jensen, 2001). In the long term, straw
incorporation has resulted in the increased N mineralization potential in rice and nonrice systems
(Bacon, 1990). Sustained increases in the microbial biomass have been observed following many
seasons of straw incorporation compared with burning (Powlson et al., 1987; Bird et al., 2000).
When plant residues having C/N ratios greater than 20/1 are incorporated into the soil, the avail-
able N is immobilized during the first few weeks by the decomposing microbial populations present
(Doran and Smith, 1991; Somda et al., 1991; Green and Blackmer, 1995). However, some workers
have reported that net immobilization is likely to occur following the addition of plant material
with C/N ratios above ~25:1 (Brady and Weil, 2002; Burgess et al., 2002). Cereal straws (rice, corn,
wheat, and barley) usually have high C/N ratios (Table 8.5) and may induce temporary N deficiency
in crops due to N immobilization by soil microbial populations when straw is not incorporated or
decomposes in advance. However, this temporary adverse effect of N immobilization can be allevi-
ated by applications of about 15 kg N ha
−1
under most cropping systems (Fageria and Baligar, 2005).
Legume crop residues are effective sources of N (Bremer and Van Kessel, 1992; Haynes et al.,
1993). When released in synchrony with the crop N demand, crop residue N is a particularly desir-
able source of N as losses to the environment are minimized (Stute and Posner, 1995; Soon et al.,
2001). Legume residues generally have high N contents and lower C/N ratios compared with cere-
als (Table 8.5). During the mineralization of leguminous materials, up to 50% of the amount of N
can be released within 2 months of incorporation into the soil (Kirchmann and Bergqvist, 1989).
Besides providing N, crop residues can provide effective weed control and consequently improve
N use efficiency if managed properly. Winter weed residues reduced weed seedling emergence by
45% (Crutchfield et al., 1986) and biomass by 60% in corn (Wicks et al., 1994). Crop residues sup-
press weed emergence by reducing light penetration and soil temperature fluctuations (Teasdale and
Mohler, 1993).
Optimizing the N fertility level and water availability can influence residue production and the
SOC sequestration potential (Follett, 2001; Halvorson et al., 2006, 2009; Halvorson and Jantalia,
2011). Crop residue production under no-tillage and irrigation should be sufficient to increase SOC
storage in the semiarid central Great Plains (Varvel and Wilhelm, 2008; Halvorson et al., 2009;
