N2O EMISSIONS FROM TWO MEDITERRANEAN
AGRICULTURAL SOILS WITH SUB-OPTIMAL IRRIGATION
REGIME AND DIFFERENT N-INPUT MANAGEMENT
A. Forte1, A. Fierro1, M. Riondino1, A. Virzo1, M. Fagnano2, N. Fiorentino2, A. Piccolo2,
S. Ranucci3, L. Ottaiano3, T. Bertolini3, P. Di Tommasi3, M. Oliva3, L. Vitale3, V.
Magliulo3
1
2
3
Dipartimento di Biologia Strutturale e Funzionale, Università di Napoli Federico II, Italy, anforte@unina.it
Dipartimento di Ingegneria Agraria e Agronomia del Territorio, Università di Napoli Federico II, Italy,
nunzio.fiorentino@unina.it
CNR-ISAFoM, Naples, Italy, silviaranucci@gmail.it
Introduction
In the last decades the increased N-input and the large use of irrigation, have greatly
increased N2O emissions from croplands (IPCC, 2007). Scanty data are available about N2O
effluxes from irrigated croplands of Mediterranean countries, despite the extension of these
areas and their potential as high N2O emitters via bacterial denitrification and/or nitrification,
due to the combined effect of irrigation and high soil temperature, especially after N
fertilization (Sanchez et al., 2001; Vallejo et al., 2004). Indeed irrigation appears to play a
key role in the evolution of N2O from cropped soil under Mediterranean condition and
recently it has been underlined (Sánchez-Martín et al., 2008) that the reduction of the amount
of water applied and the optimization of its distribution into the soil profile can effectively
mitigate N2O emission from Mediterranean irrigated cropland
The aim of this study was to investigate the influence of sub-optimal irrigation scheduling on
nitrous oxide emissions from the soil of two Mediterranean irrigated croplands under
different N-input.
Materials and Methods
N2O fluxes were measured from the soils of two near by Mediterranean maize based cropping
systems in Campania Region, South Italy (Borgo Cioffi BC and Torre Lama TL). The sites
are located 10 km apart and were therefore subjected to the same meterological environment.
At BC the most of cropped soil presented a silty-clay texture with 1% organic carbon, while
TL was characterized by a clay-loam textured soil with 1% organic carbon. Tillage
(mouldboard ploughing) and irrigation pattern (sub-optimal regime with 350 mm of total
water applied) were the same for both sites. On each irrigation session the amount of water
ranged from about 20 to 30 mm (calculated on the basis of crop evapotranspiration rates) and
was supplied by means of sprinkler irrigation systems (only at TL replaced by a drip
irrigation system towards the end of the maize growing cycle). N input was instead different:
130 Kg N ha-1 by urea at sowing for TL and 65 Kg N ha-1 by ENTEC NP 25-15 at sowing
followed by 119 Kg N ha-1 by ENTEC 35 + 84 Kg N ha-1 by urea at stem elongation for BC.
Data were collected in 2008 by means of an automated closed static chamber coupled to a
1412- Photoacustic in TL and thorough manual closed static chambers coupled to gaschromatography in BC. Measurements to determine top soil physico-chemical properties
were performed as well.
Results
Up to 45 days after maize sowing TL and BC showed comparable N2O emission patterns
(Fig.1), clearly as a consequence of similar trends of soil mineral N and WFPS, mostly close
by 40% except soon after irrigation events. During this first stage of maize growing season
kg N 2 O - N h a -1
the highest fluxes were detected at both sites soon after the first irrigation, which therefore
led to a steeper increase on the ramp of total N2O efflux from soil (Fig.1).
Afterwards, as shown in
Fig.1 the fertilization at
0 ,7
stem elongation determined
0 ,6
E F B C = 0 ,0 0 2 3
a second N2O peak and
consequently a second
0 ,5
inflexion point on the curve
0 ,4
of the cumulative amount of
E F T L = 0 ,0 0 2 8
N2O evolved from the soil
0 ,3
in BC. As a result total
0 ,2
N2O-N emissions in BC
TL
were 67% higher compared
0 ,1
BC
with TL (0,371 and 0,620
0 ,0
-1
Kg N2O-N ha for TL and
0 10 20 30 40 50 60 70 80 90 00 10 20 30
1
1
1
1
BC respectively).
D a ys fro m m a iz e s o w in g
N2O fluxes ranged mostly
Fig. 1. Cumulative N2O fluxes from the soil of TL and BC throughout
around low-medium values
the maize crop cycle. The fertilization at sowing, the first irrigation
(from 0 to 50 g N2O-N m-2
post sowing and the fertilization at stem elongation (only for BC) are
-1
h ) at both sites and even
represented by arrows with arrow end, dotted end and arrow-line end
after key events such as the
respectively. The emission factors as relates to the maize cultivation at
first irrigation after sowing
both BC (EFBC) and TL (EFTL) sites are reported as well.
or the late fertilization, the
highest values detected at
midday were always below 200 g N2O-N m-2 h-1. This was likely due to the restrained water
management and the consequent low values of soil WFPS, which even soon after irrigation
never exceeded 68%. As a consequence denitrifying processes, likely major contributors to
N2O evolution from soil at both BC and TL sites were limited,.Notwithstanding the different
N input, BC and TL exhibited similar emission factor (EF1) for N2O emissions from N inputs
throughout the maize cultivation, (kg N2O–N/ kg N input, according to the 2006 IPCC
Guidelines for National Greenhouse Gas Inventories). Moreover in both cases, the value of
the EF1 appeared lower than the default value of 1% reported in the current IPCC
methodology (0,23% and 0,28% for BC and TL respectively).
Conclusions
Mineral N availability played a key role in the evolution of N2O from soil, as evidenced by
the total N2O-N emissions – which were more than doubled in BC compared with TL.
Overall low values for N2O efflux from soil and N2O emission factor were detected at both
sites, despite the highest N input supplied at BC. Fhese findings confirm that a proper
management of irrigation can restrain N losses from Mediterranean agroecosystems, reducing
N2O production by soil microbial processes.
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