GREENHOUSE GAS EMISSIONS AFTER ORGANIC AND MINERAL FERTILIZATION
FROM MAIZE IN GALICIA
Louro, A., Báez, M.D., Garcia, M.I.
INGACAL-Centro de Investigaciones Agrarias de Mabegondo (CIAM). Apartado 10, 15080.A Coruña, Spain.
1. Introduction
Crop production systems with high inputs of nitrogen (N) fertilizer can be an important source of greenhouse
gases (GHG). This fact takes importance in Galicia, the primary milk production region of Spain, due to
its production is associated with a feed management system based on own-grown crops (as
maize) and concentrates. The aim of this study was evaluate the influence of the conventional
fertilization with mineral and slurry fertilizers on GHG emissions.
2. Materials and Methods
The experiment was carried out in 2010 at the experimental farm of CIAM in Galicia, Spain (43ºN
latitude, 8ºW longitude, 94m altitude), during the growing season of maize (Zea mays L.) on a silt
loam soil. A randomized block design was established with three replicates and four treatments: no
N application or control (C); mineral fertilizer (M); injected cattle slurry (CS) and, injected pig slurry
(PS). A rate of 200 kg N ha-1 was applied in each N fertilizer treatment, entirely distributed just
before sowing (25th May 2010) in CS and PS, and split in two doses in M: 125kg N ha-1 as NPK
fertilizer at sowing (25th May 2010) and 75 kg N ha-1 for the top dressing (16th July 2010) as
granulated urea 46%. Nitrous oxide (N2O) fluxes were monitored in the completely maize grown
season and methane (CH4) and carbon dioxide (CO2) within the first nine days after sowing. GHG
were monitored using the closed chamber method and analyzed by a gas chromatography with an
electron capture detector and a flame ionization detector equipped by a methanizer to analyze
CH4. In addition, soil samples at 10 cm depth were taken for the measurements of moisture as
Water Filled Pore Space (WFPS) and mineral N.
3. Results and Discussion
Low N2O fluxes were observed immediately after the fertilization which was carried out in May
previously to maize sowing (Figure 1a), despite high nitrate (NO3-) contents were observed in the
top soil consequence of the high nitrification occurred immediately after the application of the N
fertilizers. Also, the same patter was observed after the application of urea at the top dressing in M
where ammonium (NH4+) and NO3- contents remained high in the soil. During the growing season
low rainfall events were recorded (rainy was 16% less than the last 10 years monthly average) and
the soil remained dry throughout most of the maize growth season with WFPS values of up to 27%
(Figure 1b). This fact resulted in low N2O fluxes of up to 1000 µg N2O-N m-2 h-1 consequence of the
limited denitrification activity. In terms of type of fertilizer, no differences in N2O emissions were
observed between the use of the mineral fertilizer or slurries, which was in agreement with
previous experiments developed in the same area by Louro et al. (2012) and in other countries as
Pelster et al. (2012). Slurries application in soils with low C contents can provide organic carbon
which enhances microbial growth, promotes oxygen consumption and creates temporary
anaerobic microsites for N2O production by denitrification. It seems like in our study soil C content
was not a limiting factor for N2O emission.
Methane (CH4) emission (production) was observed only from slurries application and they were
short-lived, occurring 1h 30min after the application into the soil, resulted from the dissolved CH4 in
the slurry. In terms of type of slurry, PS showed significant higher CH4 release (17.7 mg CH4 m-2 h1
) compared to CS (6.0 mg CH4 m-2 h-1). The difference on chemical characteristics of both slurries
affected the amount of CH4 released. As Loyon et al. (2006) reported, the higher the ammonium
and organic matter contents in the slurry the higher the emissions of CH4, CO2 and also, NH3,
which denoted that the composition of slurries played an important role in the amount of CH 4
produced. Despite organic matter was higher in CS than PS (780 versus 545 g kg-1), total
ammonium nitrogen applied with PS was approximately 2 times greater than CS (134 versus 63 kg
N ha-1). Also, lower dry matter content of the PS respect to CS (1.5 versus 7.7%) enhanced the
anaerobic conditions into the soil due to the better infiltration of the material, stimulating the activity
of the methanogenic bacteria and thus, CH4 production. During the rest of period studied, CH4
fluxes were not significant different to those rates recorded in M and C plots. Zero or negative
values of up to -0.06 mg CH4 m-2 h-1 were observed, denoting CH4 consumption and acting the soil
as a sink of this gas. High CO2 peaks of up to 862.3 and 403.0 mg CO2-C m-2 h-1 were observed
within 25 hours after application of PS and CS, respectively. The amount of CO2 released probably
was related to the CO2 dissolved and produced in the slurry, no in the soil, due to in the following
samplings slurry treated plots recorded similar CO2 rates as C and M plots.
As is showed in Table 1, the contribution of N2O emissions to the global warming potential (GWP)
was higher than CO2 and CH4 emissions in the first nine days measured after fertilization. In terms
of type of fertilizer, PS increased 87% and 46% the contribution of GWP with respect to M and CS.
Similar N2O emissions were found for the three N-fertilized treatments in the short period
measured after fertilization and during the whole growing season.
3500
a)
C
3000
M
CS
PS
b)
120
C
M
CS
PS
100
%WFPS
µg N2O m-2h-1
2500
2000
1500
1000
80
60
40
500
20
0
-500
0
Time after fertilization
Time after fertilization
Figure 1. a) Temporal variation of N2O fluxes resulted from the treatments studied during the maize crop season in 2010
and b) soil WFPS at 10 cm depth.
Table 1. N application rates (N input, kg N ha-1), N2O, CH4 and CO2 emissions during nine days after fertilization just
before maize sowing (kg C ha-1 or kg CO2 eq ha-1), and N2O fluxes during the whole crop season (Mg CO2 eq ha-1).
Nine days after fertilization
Maize growth season
Treatment
N input
N2O-N
CH4
CO2-C
N2O-N
kg N ha-1
kg CO2 eq ha-1
Mg CO2 eq ha-1
C
156.5b
-0.6c
0.2c
1.6b
M
200
184.2a
0.1c
0.2c
2.3a
PS
209
264.2a 106.5a
0.5a
2.6a
CS
183
213.6a
56.3b
0.4b
2.6a
Treatments followed by the same letter do not differ at p<0.05
4. Conclusion
During the maize growing season mineral fertilizer produced similar N2O emissions than cattle and
pig slurries applications. The results suggest that fertilization with cattle slurry can involve lower
contribution to the total global warming potential with respect to pig slurry.
References
Louro A., Báez D., García M.I. Castro J. 2012. Nitrous oxide emissions from two maize crop seasons in
northwestern Spain. In: Richards K.G., Fenton O., Watson C.J. (Eds). Proceedings of the 17 th International
Workshop. Innovations for sustainable use of nitrogen resources, 26th-29th June 2012, Wexford, Ireland, 190191.
Loyon L., Guiziou F., Béline F., Peu P. 2006. Gaseous emissions (NH3, NO2, CH4, CO2) during pig slurry
biological aerobic treatment and treatment by product storages. International Congress Series 1293, 299302.
Pelster D.E., Chantigny M.H., Rochette P., Angers D.A., Rieux C., Vanasse A. 2012. Nitrous oxide emissions
respond differently to mineral and organic nitrogen sources in contrasting soil types. J.Environ. Qual.,41,
427-435.