c stocks and spectroscopic assessment of c stability in kenyan soils
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# LIF index estimated as the ratio of area under fluorescence emission (430 - 800 nm) by total organic carbon content. This index is associated with C stability. The stability is highest for the native vegetation and lowest for the forest. Stability also increases with soil depth
C STOCKS AND SPECTROSCOPIC C STOCKS AND SPECTROSCOPIC ASSESSMENT ASSESSMENT
OF C STABILITY IN KENYAN SOILSOF C STABILITY IN KENYAN SOILSAline Segnini1,2, Adolfo Posadas*1,2, Roberto Quiroz1, Lieven Claessens3,
Carla Gavilán1, Débora M.B.P. Milori2 & Ladislau Martin Neto2
INTRODUCTION Soil carbon stocks (CS) and soil carbon stability data are required to make decisions to guarantee sustainable land use in intensively cropped areas. The present study reports the findings of a comparative analysis in different agro-ecologies in Embu – Kenya, where soils under different uses – e.g. native vegetation, forest, tea, coffee, and crops under different rotations - were sampled. Carbon stocks were analyzed in 3 areas for different soil land uses and native vegetation as reference. Whole soil samples were also characterized using the Laser-Induced Fluorescence Spectroscopy (LIFS) to assess the carbon stability
1International Potato Center (CIP) – Lima, Peru; 2 Brazilian Agricultural Research Corporation (EMBRAPA)/ Embrapa Agricultural Instrumentation - São Carlos-SP, Brazil. 3CIP - Nairobi, Kenya. *a.posadas@cgiar.org
Figure 1. Map from study sites in Embu District - Kenya representing soil sampling in different land uses from a transect of approximately 50 km. Examples of crops and native vegetations.
Table 1. Mean characteristics of soil sampling sites (0-30 cm).
# CARBON STOCKS = (C × d × T); C is the carbon content in g kg-1; T the sample layer thickness in meters and d the soil layer bulk density in Mg m-3;
Table 2. Soil carbon stocks (kg m-2) by soil layer and total (0-30 cm). Data from soils sampled in different cropping systems in Embu/Mbeere - Kenya.
EXPERIMENTAL
RESULTS
DISCUSSION
ACKNOWLEDGEMENT
Figure 2. Humification index of whole soils obtained through Laser Induced Fluorescence Spectroscopy (LIFS).
Kenya Agricultural Research Institute (KARI)
Area 1 Area 2 Area 3
sites Forest Tea Coffee + eucalyptu
s
Coffee Native vegetation
#
Rotationsystem*
Native vegetatio
n#
Rotationsystem†
Altitude (m) 2012 2002 1387 1387 741 738 1198 1118
Sand (%) 36 32 16 16 74 58 18 14
Silt (%) 20 22 16 12 8 10 22 18
Clay (%) 44 46 68 72 18 32 60 68
Soil class clay clay clay clay Sandy loam
S. C. loam Clay clay
Natural vegetation
Rotation
system
AREA 3AREA 3
Natural vegetation
Rotation
system
AREA 2AREA 2
AREAAREA 11
Forest
Tea
Coffee + Eucalyptus
Coffee
CARBON STOCKS# (kg m-2)
Area 1 Area 2 Area 3
sites depth (cm)
Forest Tea Coffee + eucalyptu
s
Coffee Native vegetation
Rotationcrops
Native vegetation
Rotationcrops
0-2.5 1.8 0.1 0.6 0.0
0.6 0.0 0.5 0.0 0.3 0.0 0.7 0.1 1.0 0.0 0.5 0.1
2.5-5 1.3 0.1 0.3 0.0
0.6 0.1 0.5 0.0 0.2 0.0 0.7 0.1 0.8 0.0 0.5 0.1
5-10 2.4 0.1 1.2 0.1
1.3 0.3 1.0 00 0.5 0.0 1.3 0.1 1.4 0.0 0.9 0.1
10-20 4.1 0.6 2.1 0.0
2.1 0.1 1.8 0.2 0.8 0.1 2.1 0.4 2.8 0.1 2.0 0.3
20-30 3.1 0.3 2.1 0.0
1.9 0.1 1.8 0.2 0.8 0.2 1.7 0.2 1.8 0.1 1.3 0.1
Total (0-30)
12.7 1.2
6.3 0.1
6.4 0.5 5.6 0.4
2.6 0.4 6.5 0.9 7.8 0.3 5.1 0.6
# natural vegetation: transition between forest and savanna; * rotation crops: maize, peas, green grams, cow peas, pumpkin; † rotation crops: maize, beans, mango, banana, cassava, papaya, peas, green grams.
fore
st (1
)
tea (
1)
coffee +
eucaly
ptu
s (
1)
coffee (
1)
natu
ral v
egeta
tion (
2)
rota
tion (
2)
natu
ral v
egeta
tion (
3)
rota
tion (
3)
0 - 2.5
5 - 1020 - 30
01020
3040
50
60
70
80
90
LIF index (a.u.) (x1000)
Land use
depth (cm)
0 - 2.5
2.5 - 5
5 - 10
10 - 20
20 - 30
BIBLIOGRAPHY• MILORI, D.M.P.B., H.V.A. GALETI, L. MARTIN-NETO, J. DIEKOW, M. GONZÁLEZ-PÉREZ,
C. BAYER and J. SALTON. 2006. SSSAJ. 70:57-63 • SEGNINI, A., A. POSADAS, R. QUIROZ, D.M.B.P. MILORI, S.C. SAAB, L. MARTIN NETO,
C.M.P. VAZ. 2010. SSSAJ. 74(6) DOI: 102136/sssaj2009.0445..
Soil sampling location: Southeastern slopes of Mount Kenya, Embu District - Eastern Province of Kenya.
Topography: Hilly highlands
Soils: Nitisols (17%), Cambisols (12%), Phaeozems (12%), Andosols (10%) and Ferralsols (8%);
Conventional soil C analyses plus LIFS (Milori et al., (2006); Segnini et al., 2010)
The results showed wide variations in the levels and stability of carbon stored in the soil depending on factors such as land use, crops grown, water content, elevation, and agricultural practices. Soils under trees and shrubs presented the largest C stocks but lower stability;
Portable instruments for analyzing C contents in whole soils samples (laser-induced optical device developed by EMBRAPA-Agricultural Instrumentation) and stability (LIFS) are useful and reliable for field assessments;
SC and C stability must be taken into account for decision making about alternative land uses.
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