ORGANIC
CARBON
SEQUESTRATION
EFFICIENCY
OF
SUSTAINABLE
MANAGEMENT PRACTICES UNDER RAINFED MEDITERRANEAN CROPS
Martínez-Mena, Mª., de Vente, Jª., Boix-Fayós, Cª., Garcia-Franco, Nª., Melgares de Aguilar, Jb.
Gonzalez, Db, Almagro, Ma.
a
b
CEBAS-CSIC, Campus de Espinardo, Murcia
Consejería de Agricultura de la Región de Murcia
1. Introduction
According to the UNEP-UNDP-UNCCD (2008) Sustainable Land Management practices (SLM) are
a fundamental tool to combat desertification. There is a growing interest in evaluating their
effectiveness for carbon sequestration in semiarid areas. The objectives of this presentation are to
evaluate the effect of several SLM practices under organic rainfed crops (almond and cereal)
representative of Mediterranean areas on: a) soil carbon sequestration; b) runoff and erosion
control, c) soil water storage capacity, and d) crop yield.
2. Material and Methods
The experimental areas were established in October 2008 in two sites in the Murcia Region with
similar climatic and lithologic characteristics and under organic rainfed almond and cereal crops.
The management practices evaluated were: conventional tillage (CT), reduced tillage (RT),
reduced tillage plus green manure (RTG), and no tillage (NT). The green manure consists of
Avena sativa L.and Vicia sativa L.in 1:3 proportion at 150 kg ha-1, manually sown during early fall
and cut off in May/June. After cutting the green manure is incorporated into the soil by ploughing
with a cultivator. In the no tillage (NT) treatment, the weeds are manually cut off in May/June and
left on the soil surface. The experimental design consisted of randomized-block design with three
replicates for each treatment. Open erosion plots (3 per treatment) were installed in one of the
areas in order to quantify organic carbon mobilization by erosion. Runoff and sediments were
collected after each rainfall event and analysed in the laboratory. In order to determine the capacity
of carbon sequestration under each tillage practice the following aspects have been studied: i)
distribution of organic carbon pools in soil aggregates (by wet sieving and density fractionation); ii)
soil CO2 emissions to the atmosphere (soil respiration measurements before and after tillage
operations using a Licor 8100 closed chamber system), and iii) carbon exported by erosion (OC
analysis in sediments) and size of mobilized particles (particle analyser, coulter LS).
3. Results and Discussion
Reduced tillage and green manure incorporation proofed to be very efficient measures for
atmospheric carbon sequestration in these semiarid areas. This efficiency is largely determined by
the activation of both carbon and nitrogen cycles, which have enhanced the formation of
aggregates and therefore improved the physical protection of organic carbon within them. In fact,
while 70% of labile organic carbon (POC) was protected within macroaggregates (> 63 m) under
RTG, this percentage was reduced by approximately 15% in both RT and NT treatments. The
higher protection of OC within aggregates found under RTG was consistent with the observed
lower rates of soil CO2 emissions to the atmosphere after tillage (27% reduction compared to RT;
Figure 1), and with the 1.31 times lower sediment enrichment of OC (ERco) compared to RT. The
reduction in tillage intensity (RT) resulted in an increase of SOC stock (1.50 and 1.16 fold higher
than CT for the almond and cereal, respectively), but not in the outputs of OC by erosion (Table 1).
Table 1. Improvement in soil carbon stock and yield productivity parameters with the implementation of
sustainable management practices in organic rainfed crops: comparison with conventional practices.
Erosion control
OC outputs
OC Stock
Crop productivity
Runoff
Sediments Erosion Soil
Soil
Aggregates Yield
Percentage
Respiration
crop
of kernel
RT
RTG
NT
*
+
+
-
-
=
*
*
+
+
+
+
+
+
+
-
-
RT: reduced tillage; RTG: reduced tillage + green manure; NT: no tillage; +: improve; -: reduce; =: no change respect to conventional practices.
*: no data
A clear reduction in soil CO2 emissions to the atmosphere under NT was observed during the
studied period compared to the RT and RTG practices (Figure 1). Moreover, a reduction of about
63% and 44% in soil CO2 emissions under NT compared to tillage treatments (RT and RTG
respectively) was observed after tillage performed in December 2012. Regarding crop productivity,
a higher percentage of kernel was obtained under RTG as compared to RT. On the other hand,
both RT and RTG treatments were more efficient in crop yield than the most intensive tillage
practice (CT). However, NT caused a decrease in yield productivity parameters, as was also
reported by other authors (e.g. Lampurlanés et al., 2001).
Reduced Tillage + Green Manure (RTG)
No Tillage (NT)
Reduced Tillage (RT)
3,5
Soil respiration in g C m
-2
-1
day
3,0
a
a
a
2,5
a
b
ab
2,0
b
b
a
a
1,5
a
1,0
a
b
a
a
b
c
b
b
0,5
0,0
d
3r
2
2
2
2
2
2
2
2
12
12
12
01
01
01
01
01
01
01
01
20
20
20
t2
y2
c2
c2
c2
c2
v2
p2
ly
ec
ne
Oc
Ju
De
De
De
De
No
Se
Ma
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dD
h
h
d
h
h
h
h
h
r
t
t
t
t
t
t
t
r
h
5
5
10
7t
12
n3
n4
n5
n7
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eo
eo
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eo
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ag
ag
ag
lag
ag
ti l l
till
till
till
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t
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Po
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Fig.1. Pre- and post-tillage soil respiration rates under almond orchard at the Burete experimental site.
4. Conclusion
In semiarid areas, where soils are very prone to compaction, minimum tillage (for cereals) plus the
incorporation of green manure (for rainfed almonds) is recommended due to the improvement
observed in the soil structure and in its efficiency in sequestering carbon from the atmosphere.
References
Lampurlanes J., Angás, P. and Cantero-Martínez, C. 2001. Root growth, soil water content and
yield of Barkly under different tillage systems on two soils in semiarid conditions. Field Crops Res.
69 27-40.
UNEP-UNDP-UNCCD. 2008. Technical Note for Discussion at CRIC 7.