Agriculture Reference
In-Depth Information
include: solution formation, solution concentration, solids formation, solids finishing,
screening, coating, bagging and/or bulk shipping.
As mentioned previously, the steam produced from the exothermic reaction allows a
significant reduction in the energy consumption in AN production. The average consumption
in Europe is 0.7 GJ/ton but a modern plant may consume 0.09-0.22 GJ/ton AN.
Calcium ammonium nitrate is obtained from an AN solution by mixing it with dolomite,
limestone or calcium-carbonate. Subsequently its production requires a higher energy
consumption due to the grinding process of dolomite or other raw materials (European
Commission, 2006).
Many studies on the GHG emissions from AN and CAN have reported that the majority
of these emission are made up of CO
2
emission from the ammonia synthesis and N
2
O
emission from nitric acid production. The latter accounted for an estimated 60-78% and 52-
61% of total CO
2
emission from AN/CAN respectively (Wood & Cowie, 2004). Emissions
arising from processing of intermediate products (i.e., ammonia and nitric acid) into final
products (i.e., CAN, AN etc.) were of relatively minor importance (Patyk & Reinhardt, 1996;
Davis & Haglund, 1999).
E
FFECT OF
N
ITROGEN
F
ERTILIZATION ON
S
OIL
O
RGANIC
M
ATTER
T
URNOVER AND
R
ESULTING
S
OIL
CO
2
E
MISSION
Depletion of soil carbon content, recorded over the past 100 years, has been mainly due
to conventional tillage practices, which increase soil organic matter (SOM) mineralization
rate.
Agricultural soils have lost, compared with native soil, their natural capability to
accumulate carbon (C), thereby releasing CO
2
into the atmosphere (Schlesinger, 1984).
Depletion of soil carbon content, globally recorded over the past 100 years, has been mainly
due to conventional tillage practices, which increase soil organic matter (SOM)
mineralization rate.
Matson et al. (1997) reported SOM decline, often by 50% or more. Practices to improve
C storage in cropping systems are: (1) improve C capture and (2) decrease SOM respiration.
When agronomic practices increase SOM, CO
2
is removed from the atmosphere in the long-
term (Lal et al., 1998 and 2003). In the last few decades a belief was developed in the
scientific community that agricultural soils have the potential to increase C sinks and reduce
CO
2
emissions if better management practices (BMPs) are adopted. Cole et al. (1997)
estimated that it would be possible to increase the amount of C stored in the agricultural soils
of the planet by 0.44 to 0.88 billion tons annually over a 50-year period.
SOM degradation is the main source of soil CO
2
emission, even if vegetation contributes
to the total CO
2
emission with root and rhizo-microbial respiration. For this reason, the total
soil CO
2
emission cannot be considered a direct measure of SOM oxidation, in spite of the
fact that some studies continue to interpret it in such a manner (Hanson et al., 2000).
Therefore, the so-called ―basal respiration‖ refers to the CO
2
evolved by the degradation of
SOM in roots-free soil. Three different C pools as sources of CO
2
from soil have been
identified (Kuzyakov, 2006): (1) SOM; (2) above and below ground dead plant residues; (3)
organic substances released by living roots such as exudates, secretions and sloughed-off root
Search WWH ::
Custom Search