Agriculture Reference
In-Depth Information
The other advantages of composting include killing pathogens and most weed seeds, and improv-
ing the handling characteristics of manure by reducing the volume and weight. The disadvantages
of composting include nutrient loss, specifically N, and requirements for time, money, equipment,
and labor. Eghball et al. (1997) found that as much as 40% of the total beef feedlot manure N can
be lost during composting, and significant losses of K and Na (>6.5% of total K and Na) occur in a
runoff from composting windrows not protected from rainfall. Overall, the benefits of composting,
however, have many disadvantages. Besides, intensively cropped systems may also slowly increase
the SOM content, thereby improving the long-term plant environment (Bowman et al., 1999).
4.8.9 r
eCYClInG
C
rop
r
esIdues
Crop residues are portion of plants remaining after seed harvest, refers mainly to grain crop residue,
such as corn stover, or of small grain straw and stubble (Crop Science Society of America, 1992).
Crop residue management affects the biological and chemical processes that govern the conversion
of C and N into SOM and the residual availability of N into succeeding crops (Bird et al., 2003). In
general, the incorporation of plant residues in soil can affect the soil microclimate and increase the
plant residue contact with soil. This will increase the residue decomposition and OM transformation
(Beare et al., 1992; Cambardella and Elloitt, 1993). Bird et al. (2001, 2002) reported that sustained
increase in soil microbial biomass, C, N, and SOM pools after four seasons of straw incorporation
compared with straw burned. Crop residues are important in the formation of SOM (Wilhelm et al.,
2004).
Recycling or incorporating crop residues into the soil after harvest of grain is an important
management practice to improve organic carbon. Crop residues not only add organic carbon but
also supply essential nutrients depending on crop species or genotypes within species. Carter et al.
(1998) and Kay (1998) reported that the addition of OM to the soil in the form of crop residues
increases the level of low-density macroorganic matter, which can represent up to 45% of total
SOM. This form of SOM functions in improving the mechanical properties of soil (Carter, 2002).
Kern and Johnson (1993) and Paustian et al. (2000) reported that agricultural management prac-
tices, such as crop residue incorporation, are being promoted to increase biomass incorporation into
SOC pools, enhance soil quality, and sequester atmospheric CO
2
. The frequent incorporation of
straw into soils, particularly when combined with mineral nitrogen fertilizer, results in an increase
of SOM (Amberger and Schweiger, 1991). Johnson et al. (2004) reported that crop residue is an
important source of new C for building and maintaining SOM.
Singh et al. (2004b) reported that burning of rice straw is cost-effective and the predominant
method of disposal is in areas under combined harvesting in the Indo-Gangetic Plains (IGP) of
India. Burning of straw can accelerate losses of SOM and nutrients, increasing C emissions, caus-
ing intense air pollution, and reducing soil microbial activity (Biederbeck et al., 1980; Rasmussen
et al., 1980; Kumar and Goh, 2000). Singh et al. (2004b) reported that 113.6 million Mg of rice and
wheat residues, containing about 1.90 million Mg of nutrients, are available in the IGP of India. In
the Punjab state of India alone, about 12 million Mg of rice straw are burned annually, which causes
about 0.7 million Mg of N loss. The gas emissions from burning of rice straw are 70% CO
2
, 7% CO,
0.66% CH
4,
and 2.09% N
2
O (Singh et al., 2004b). These figures show that burning crop straw not
only reduces the soil quality (SOM) but is also responsible for environmental pollution. Hence, it
should be incorporated into the soil rather than burned.
Mann et al. (2002), Wilhelm et al. (2004), and Hooker et al. (2005) reported that the use of
corn stover as a source of ethanol for fuel in the United States may negatively impact agricultural
sustainability if SOC levels and soil quality decline as a result. Wilhelm et al. (2004) reported
that crop residue as a feedstock for biomass ethanol production is an appropriate solution for
fuel production and reducing greenhouse gases in the atmosphere. However, residues are neces-
sary to protect the soil from erosion and contribute to SOC levels, a key factor in most desirable
characteristics of soil quality, and are positively related to soil and crop productivity. Supply of
