C STOCKS AND SPECTROSCOPIC ASSESSMENT OF C STABILITY IN KENYAN SOILS

1. C STOCKS AND SPECTROSCOPIC ASSESSMENT OF C STABILITY IN KENYAN SOILS Aline Segnini1,2,Adolfo Posadas*1,2, Roberto Quiroz1, Lieven Claessens3, Carla Gavilán1, Débora M.B.P. Milori2 & Ladislau Martin Neto2 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 INTRODUCTION RESULTS 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 Table 1. Mean characteristics of soil sampling sites (0-30 cm). EXPERIMENTAL • 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) # 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. Table 2. Soil carbon stocks (kg m-2) bysoillayer and total (0-30 cm). Data from soils sampled in different cropping systems in Embu/Mbeere - Kenya. #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; # 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 Forest Tea AREA1 Coffee + Eucalyptus Figure 2. Humification index of whole soils obtained through Laser Induced Fluorescence Spectroscopy (LIFS). DISCUSSION Coffee • 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. Natural vegetation AREA 2 Rotation system Natural vegetation 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. • . AREA 3 Rotation system ACKNOWLEDGEMENT • Kenya Agricultural Research Institute (KARI) 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.