Reference soil Kenya 01: Nitisol

KE001

Nitisols occur mainly in the tropics and subtropics, as well as in areas with a Mediterranean type of climate. They are associated with basic rocks (e.g. basalts) or hard limestone or dolomite deposits.

Characteristics

Soils having a nitic horizon (a horizon with pronounced nut-shaped soil structure and significant amount of active iron) within 100 cm from the soil surface, and gradual to diffuse horizon boundaries between the surface and the underlying horizons. They do not have a ferric, plinthic or vertic horizon within 100 cm from the soil surface.

Distribution of Nitisols (rough estimation supplied by soilgrids)

Reference soil KE001: Nitisols

Authors: Kenya Soil Survey (KSS), officers Rachilo and Michieka. Topography and landform: The area has an almost flat topography, the slope gradient increasing to the North and East to gently undulating, thus inducing a N-NE aspect of land. Situated on a broad interfluve at an altitude of 1700 m the landform is characteristic for a large area East of the Rift Valley, which has been named "broad ridge topography" by Scott (1963), or as "volcanic ridge landscape". The ridge on which NAL is located is bordered to the South by the valley of the upper Nairobi river, which flows from West to East and to the North by a canalized stream following the same direction. Both streams contribute to the Athi river. Vegetation and land use: The original vegetation of bushed and wooded grassland with characteristically broad-leaved trees such as Combretum and Croton macrostachys with mostly evergreen shrubs made way a long time ago for arable cropping and exotic tree and bush species. Present cropping experiments on the station include plants like maize, sunflower, pulses, tomatoes, irish potatoes and flowers. Prior to these coffee (Arabica) was grown. These and other crop trials may have influenced the fertility status of the (top)soils. Brief description of the profile: The typical soil at the NAL is described as well-drained, very deep, dark reddish brown to dark red, friable clay. Additional notes on profile description: Ah: in the upper 5 cm weak sealing occurs; AB: also many fine and few medium pores. In a thin section taken from the Bt2 at 110-120 cm micro-cutans are obseved and occasionally clay filling occur. There is also common soil fauna activity mainly by termites and millipeds, as evident from channels and aggrotubules. Rooting is very deep, the bulk of roots is concentrated in the top 60 cm. Climatic data: mean monthly potential evaporation in mm; period 1921-1962 and 1965.

Classification

WRB 2006

WRB 1998

Acric- Nitisol (Humic Dystric Rhodic)

Rhodi-Humic- Nitisol (Dystric)

37-150 cm

nitic horizon

0-37 cm	ochric horizon
37-150 cm	nitic horizon

FAO-UNESCO-ISRIC 1988

FAO-UNESCO-ISRIC 1974

Dystri-Rhodic Nitisol

Humic Nitosol

0-37 cm	ochric A horizon
37-150 cm	argic B horizon
-	nitic
-	strongly humic

0-37 cm	ochric A horizon
37-150 cm	argillic B horizon
-	high organic matter content in B horizon

Other classification

USDA-NRCS (1999)	Rhodic Paleustalf
USDA-SCS (1975)	Rhodic Paleustalf ustic clayey kaolinitic isohyperthermic

More images

Land use

Major crops	maize
Land improvements ; Guidelines for soil description - Fourth edition (FAO, Rome, 2006)	land clearing
Main type of irrigation; Guidelines for soil description - Fourth edition (FAO, Rome, 2006)	no irrigation
Land use or vegetation in the immediate vicinity of the site	high level arable farming
Remarks on Land Use / Vegetation	VEGETETATION: The original vegetation of bushed and wooded grassland with characteristically broad-leaved trees such as Combretun and Croton macrostachys with mostly evergreen shrubs made way a long time ago for arable cropping and exotic tree and bush species. LANDUSE: Used for cropping experiments,and garden. Present cropping experiments include maize, sunflower, pulses, tomatoes, irish potatoes and flowers. Prior to these coffee (Arabica) was grown. These and other crop trials may have influenced the fertility status of the (top) soils.
Status of vegetation; Guidelines for soil description - Fourth edition (FAO, Rome, 2006)	modified
Major vegetation type; Guidelines for soil description - Fourth edition (FAO, Rome, 2006)	woodland

Physical characteristics

Particle size distribution

Depth (cm)	Gravel % v/v	very coarse sand % w/w	coarse sand % w/w	medium sand % w/w	fine sand % w/w	very fine sand % w/w	Total sand % w/w	coarse silt % w/w	fine silt % w/w	Total silt % w/w	Clay % w/w
0-15	-	0.1	0.6	1.7	2.4	1.4	6.2	7.1	16.5	23.6	70
15-30	-	0.0	0.6	1.6	2.6	1.5	6.3	6.4	12.7	19.1	74.6
30-60	-	0.1	0.4	1.0	1.7	1.1	4.3	5.2	9.0	14.2	81.5
65-100	-	0.0	0.5	0.8	1.4	1.0	3.7	3.8	8.7	12.5	83.8
100-150	-	0.1	0.4	0.7	1.6	1.2	4	2.1	8.8	10.9	85.1

Water retention characteristics

Depth (cm)	Bulk density kg/dm³	Spec. Surf. Area m²/g	COLE cm/cm	Water disp. clay %	Clay % w/w
0-15	-	-	-	14.7	70
15-30	-	-	-	13.1	74.6
30-60	-	-	-	14.8	81.5
65-100	-	-	-	4.2	83.8
100-150	-	-	-	0.0	85.1

Chemical data

Depth (cm)	pH H2O	pHKCl	EC 1: 2.5 dS/m	CaCO3 % w/w	C % w/w	N %	C / N	Exch. Acid cmol(c)/kg	Exch. Al cmol(c)/kg	Ca cmol(c)/kg	Mg cmol(c)/kg	K cmol(c)/kg	Na cmol(c)/kg	Sum Cations cmol(c)/kg
0-15	5.8	4.9	0.15	-	2.33	0.18	13	-	-	7.9	1.9	2.1	0.0	11.9
15-30	5.4	4.3	0.14	-	2.14	0.16	13	0.2	0.0	5.4	1.5	1.4	0.0	8.3
30-60	5.4	4.5	0.08	-	1.02	0.09	11	0.1	0.2	6.5	1.6	0.9	0.0	9
65-100	5.9	5.0	0.08	-	0.81	-	-	-	-	7.1	2.6	0.4	0.0	10.1
100-150	6.3	5.3	0.07	-	0.73	-	-	-	-	6.3	3.4	0.4	0.0	10.1

Depth (cm)	Base sat. %	CEC soil cmol(c)/kg	CEC clay cmol(c)/kg	CEC org cmol(c)/kg	ECEC cmol(c)/kg	Al sat. %	ESP %
0-15	46	25.7	37	8.2	-	-	0
15-30	33	24.8	33	7.5	-	0	0
30-60	40	22.7	28	3.6	-	1	0
65-100	43	23.7	28	2.8	-	-	-
100-150	55	18.5	22	2.6	-	-	0

Depth (cm)	pH NaF	P Retention %	ODOE	Al o % w/w	Si o % w/w	Fe d % w/w	Al d % w/w	Fe p % w/w	Al p % w/w	C p % w/w	Fe o % w/w
0-15	-	-	-	0.3	0.0	7.2	0.3	-	-	-	0.4
15-30	-	-	-	0.3	0.0	7.6	0.3	-	-	-	0.4
30-60	-	-	-	0.3	0.0	7.1	0.2	-	-	-	0.4
65-100	-	-	-	0.3	0.1	7.2	0.3	-	-	-	0.4
100-150	-	-	-	0.3	0.0	7.7	0.3	-	-	-	0.4

Clay mineralogy

Depth (cm)	Chlorite	Feldspar	Gibbsite	Goethite	Halloysite	Hematite	Kaolinite	Mica / illite	Mixed-layer	Quartz	Smec	Vermiculite
0-15	-	very weak to weak	-	very weak to weak	-	-	weak to medium	-	weak	very weak to weak	-	-
15-30	-	very weak to weak	-	very weak to weak	-	-	weak to medium	-	weak	very weak to weak	-	-
30-60	-	weak	-	very weak to weak	-	-	weak to medium	very weak	weak	very weak to weak	-	-
65-100	-	weak	-	very weak to weak	-	-	weak to medium	very weak	weak	very weak to weak	-	-
100-150	-	weak	-	very weak to weak	-	-	weak to medium	very weak to weak	weak	very weak to weak	-	-

Profile description

Ap 0-18 cm	dark reddish brown (5YR 3/4, dry) dark reddish brown (5YR 3/3, moist)clay,moderate to strong fine subangular blocky and moderate to strong medium subangular blocky,hard firm sticky plastic,patchy thin clay cutans,non calcareous,gradual smooth boundary to,
18-37 cm	dark reddish brown (2.5YR 3/4, dry) dark reddish brown (2.5YR 3/4, moist)clay,strong medium subangular blocky and strong coarse subangular blocky,hard friable sticky plastic,broken moderately thick clay cutans,common micro pores and many pores,non calcareous,gradual smooth boundary to,
Bt1 37-66 cm	dark red (2.5YR 3/6, dry) dark reddish brown (2.5YR 3/4, moist)clay,strong medium angular blocky and strong coarse angular blocky,hard friable sticky plastic,continuous thick clay cutans,many micro fine common medium pores,non calcareous,diffuse smooth boundary to,
Bt2 66-116 cm	dark red (2.5YR 3/6, dry) dark reddish brown (2.5YR 3/4, moist)clay,strong medium angular blocky and strong coarse angular blocky,hard friable sticky plastic,broken thick clay cutans,many micro fine common medium pores,non calcareous,diffuse smooth boundary to,
Bt3 116-180 cm	dark red (2.5YR 3/6, dry) dark reddish brown (2.5YR 3/4, moist)clay,strong medium angular blocky and strong fine angular blocky,firm,broken thick clay cutans,many micro fine common medium pores,non calcareous,

Kind 1 (parent material) ; Parker (eds), 1984	fine-grained intermediate igneous rock
Mode of accumulation or deposition of parent material	residual material
Remarks on Parent Materials	quartz trachyte
Soil Depth	180cm
Texture of parent material	clayey
Weathering Resistance	moderate
General characterization of the status of weathering of solid rock	highly

Occurrence of soil aggradation (McDonald et al., 1984)	absent
Slope stability	stable

Altitude	1700m
Physiographic Unit	volcanic ridge landscape
Physiographic position of the site	middle slope
Regional landform; McDonald, R.C., Isbell, R.F. et all, 1984; Australian soil and land survey Field Handbook, Inkata Press, Melbourne.	plateau
Slope	4%
Slope Aspect	north-north-east
Topography; Guidelines for soil description - Fourth edition (FAO, Rome, 2006)	undulating

Drainage class ; FAO (2006) - Guidelines for soil description	well
Dry From - To	0-180cm
Flooding frequency (FAO, 1986)	never
Kind of ground water table (USDA, 1979)	no groundwater table observed
Estimated permeability (class) of least permeable part of the profile	high
Estimated run off (class)	medium

Evidence of alkali ; Soil Survey Manual USDA, 1951	non-alkaline
Surface cracking	no cracks observed
Slaking of aggregates by tillage, rainfall or frost (USDA/SCS, 1979)	surface partly slaked, round smooth aggregates
Microrelief pattern	none
Rock outcrop class (FAO (2006) - Guidelines for soil description)	none
Evidence of salt; Soil Survey Manual USDA, 1951	non-saline
Surface stoniness class (FAO (2006) - Guidelines for soil description)	none

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Reference soil Kenya 01: Nitisol

Characteristics

Reference soil KE001: Nitisols

Classification