(i) To determine the relationship between organic resource quality/quantity and the quantity/quality of the SOM pool and distinct SOM fractions for a set of soils and climates relevant for the target benchmark areas (ii) To evaluate the impact of inherent soil properties (e.g. texture) and climate on the relationships between organic resource quality/quantity and the quantity/quality of the SOM pool and distinct SOM fractions (iii) To quantify the effect of fertilizer N and growing crops on the relationships between organic resource quality/quantity and the quantity/quality of the SOM pool and distinct SOM fractions;
The experiment aims at unravelling relationships between the quality of organic resources and the quantity/quality of the SOM pool and distinct SOM fractions as affected by various modifiers of the decomposition process.
Data Access Statement
Available to collaborators only
Data Access Notes
Anyone interested in using the data from SOM trials in Kenya needs to contact Bernard Vanlauwe and then it will be discussed if a collaboration is possible and access for free can be provided versus no collaboration with the cost to the data access will be agreed.
Data license
No data license
Data policy
research organisation
ETH Zurich
research organisation
funding agency
Bernard Vanlauwe
principal investigator
Consultative Group on International Agricultural Research, Nayrobi, kenya
Magdalena Necpalova
data manager
ETH Zurich
Department of Environmental Systems Sciences
Waswa Wycliffe
experiment manager
International Centre for Tropical Agriculture(CIAT), Kisumu, Kenya
Monicah Mucheru-Muna
experiment manager
Kenyatta University, Nairobi, Kenya
Joahn Six
principal investigator
ETH Zurich, Switzerland

Site: Embu

research station field
Embu District
Geographic location
-0.5148611, 37.4557557
© OpenStreetMap contributors
1350 Metres
Visits permitted?
Visiting arrangements
By arrangement with Monicah Mucheru-Muna
Integrated soil fertility management. The organic residues are applied only at the start of the first season. Each plot receives 60 kg P/ha and 60 kg K/ha per growing season. Tillage by hand
Soil type
Soil description
Well drained, extremely deep, dark red to reddish brown, friable clay, well structured; an ABC sequence of horizons with gradual to diffused and smooth boundaries. Strongly humic, umbric A horizon and an argillic B horizon with reddish colours and nitic properties. Clay cutans are present in the B horizon. Parental material: Mt Kenya phonolites (Kenyete); Geology: Phonolites; Physiography: Volcanic footridges; Effective soil depth: Very deep >150cm.
Soil properties
VariableDepthValue (range)UnitsRef yearEstimated?Baseline?
total soil nitrogen0 – 15 Centimetres0.3 Percent2002
soil total carbon0 – 15 Centimetres2.9 Percent2002
plant available phosphorous0 – 15 Centimetres2.54 parts per million2006
soil pH0 – 15 Centimetres5.43 2002
cation exchange capacity0 – 15 Centimetres16.03 kilogram per mole202
sand content0 – 15 Centimetres3 Percent2002
silt content0 – 15 Centimetres22 Percent2002
clay content0 – 15 Centimetres75 Percent2002
soil density0 – 15 Centimetres1.26 gram per cubic centimetre2004
Climatic type
Climate properties
VariableTime periodValue (range)Units
air temperature 2002 – 2007 19.57 (14.41 – 19.57) degree Celsius
precipitation 2002 – 2007 1346.1 (683.5 – 2151.9) millimeter
solar radiation 2002 – 2007 19.29 (17.83 – 23.79) megajoule per square meter

Design period: Main period (2002—)

Design Type
split split plot
Plots measure 6 x 6 m
Number of blocks
Number of plots
Number of subplots
Number of replicates
Number of harvests per year
CropYears grown
maize 2002—
Factor name
Factor levels
crop residue management exposure
Tithonia diversifolia  (1.2 t/ha)
Tithonia diversifolia  (4 t/ha)
Calliandra calothyrsus  (1.2 t/ha)
Calliandra calothyrsus  (4 t/ha)
maize stover  (1.2 t/ha)
maize stover  (4 t/ha)
sawdust  (1.2 t/ha)
sawdust  (4 t/ha)
farmyard manure  (1.2 t/ha)
farmyard manure  (4 t/ha)
control exposure
No residues of any form applied
nitrogen fertilizer exposure
Plot application: Whole plot
control exposure  (0 kgN/ha)
nitrogen  (120 kgN/ha)
cropping system
Plot application: Whole plot
bare fallow
grain yield traitmaizet/habiannualall cropped plots
core biomassmaizet/habiannualall cropped plots
stover biomassmaizet/habiannualall cropped plots
plant biomassmaizet/habiannualall cropped plots
soil organic carbonSoil%irregularsample per site
total soil nitrogenSoil%irregularsample per site
total soil phosphorousSoil%irregularsample per site
soil pHSoilcropped plots
concentration of nitrate in soilSoilmg/kgcropped plotsCollected 3 times during 2018 rainy season
concentration of ammonium in soilNot specifiedmg/kg