# 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.