Sect

ionC

SOI
LS

Thi
sisdef
inedasathi
nlay
erofl
ooseunconsol
idat
edmat
eri
alsonthe
ear
th’
ssur
face.I
tpr
ovi
desamedium f
orplant
sandani
malstogrow.

Soilbasi
cal
lyresul
tsfr
om thebr eakdownofparentrockthrough
weatheri
ngprocessesI.
ephy si
cal andchemicalweatheri
ngleadtothe
disi
ntegr
ati
onanddecomposi t
ionofrocksintoregol
it
h.Theweat her
ed
material
mayt henbemodifiedbyot hersoi
lformingprocessestogivea
widerangeofsoilt
ypes.Thesoi lfor
medmaycombi newi t
horganicmatter
togiveanidealsoi
lty
pe.

Soi
l
shavedif
ferentel
ementsorcomponentst
hatmayincl
udeai
r,wat
er,
t
emper
atur
e,organi
cmatter
,inor
gani
cmatter,
l
ivi
ngor
ganismsandother
s.

Organicmat ter;Thisconsi stsoftheremainsofpl antsandani malst hough

muchofi tisder i
vedfrom v egetati
onforexampl eleaves,grass,rootsand
branches.Suchmat eri
alsundergogr adual decomposi t
ionwhi chconv erts
them intohumas.Thehumashasapr onouncedef fectonsoilasi t
'sthe
maj orsourceofpl antnut r
ientssuchassul phur,phosphatesni tr
atesetc
andt hereforesoilfert
il
it
y ,
givessoilalossenessandaer ationcapaci t
ythat
i
sf avourablef orplantgrowt h,
helpssoilt
odev elopandmai nt
ainast ructure.

Inorgani cmat t
er; Thi
sisder i
vedfrom thebreakdownofr ocksieit
consi stsofweat heredrockmat eri
alsandi ti
st hemaj orsour ceofmineral
s
requi redbypl antsandani mal sl
ivi
ngint hesoil.Themi neralsareboth
pr i
mar yandsecondar y.
pri
mar ymineralsarecompoundspr esentinthe
unalt eredr ocksforexampl esili
cate,
si
licon,alumi num, cal
cium ,sodium,
i
r onandmagnesi um whilethesecondar yminer al
sdev elopfrom the
former (pri
mar y
)hav i
ngundergoneal terat
ion.NBi norganicmat terf
or ms
thel argestpor ti
onofsoi l.

SoilAir
;Theairpr
esentinsoili
sat t
ainedfr
om theat mospheref
orexample
corbondioxi
deandmet haneabl esseddayandi nhighlevel
sandoxgenin
l
owl evel
s.Airent
erssoi
lthroughpor espaces.Thisairi
smeantfor
respi
rati
onandgerminati
onaswel lasenabl
ingplantsandanimalsobt
ain
energyformetabol
ism.

Soilwater;Waterinthesoi li
sderi
vedfrom precipi
tationthatisreceivedat
agivent i
meinapar ticularar
eaierainwaterandsnowmel tsenterthesoil
bypercolati
onalthoughsomet i
mesbycapi ll
aryattracti
onwhen
undergroundwat eri
ssuckedupwar dsabovet hewat ertabl
e.soilwateris
responsibl
efordissolvingmineral
sandmaket hem av ail
ableforplants.

Inhumidareasexcessi
vewaterf
aci
li
ti
esl
eachi
ngwhi
leint
heari
dregi
ons
sal
ini
zati
onofsoil
soccursaswateri
sfor
cedtomoveupwardst
husai
ding

1
t
heupwar
dtr
anspor
tat
ionofmi
ner
alst
otheuppersoi
ll
ayer
.

Livi
ngorganisms;Theseincludemicroscopicorgani
smssuchasbact eri
a
thatai
dsinthedecomposi t
ionofor ganicmatt
erinthedesired
componentsnecessaryforplantgrowthandf i
xi
ngni t
rogenintot
hesoil
andmacr oorgani
smssuchasi nsects,eart
hwormst hatcreat
etunnel
sin
thesoi
ltoenhanceaerati
onandpenet rati
onofwaterint
othesoil.

FACTORSI
NFLUENNCI
NG SOI
LFORMATI
ONANDI
TSDI
STRI
BTI
ONI
N
EASTAFRI
CA

Soilfor
mi ngfact
orsref
ertotheelement si
ntheenv i
ronmentthatfaci
li
tate
soi
ldev el
opmentf r
om theparentrock.Thefactorst
hatdeter
mi nethetype,
characterandnatureofthesoil
aswel lastherateofsoi
ldevelopment
i
nclude:

1.Thenat ureoftheparentrock(li
thology),t
hisprovi
desthebasi sf
orsoil
development.Iti
stheparentrockthatbr eaksdownt oform soil
part
icl
es.i
t
al
sodet er
minestherateofsoildevelopment .I
tincl
udessof t
nessand
hardness,color
,miner
alcomposi ti
on,joint
edness.Thechar act
erofthe
parentrockinfl
uencesoilf
ormationint hefol
lowingway s.

 Parentrockmaybehar dori tmaybesof t.Hardparentrocki

s
normall
yr esistanttoweat heri
ngpr ocessesresulti
ngintoskelet
alor
i
mmat uresoi lsanddel ayedsoilformat i
on.Ont heotherhand,
rel
ati
vel
ysof trocksareeasi l
ydisintegr
ated,chemicall
yintosmall
part
icl
est hroughoxi dati
on,carbonat i
on,hydrati
onresulti
ngint
othe
for
mat i
onofdeepormat uresoil
s.

 Themi neralcomposi t
ionoft heparentr ockdet erminesthenat ureof
thesoi lnutr
ientsorsoilferti
li
ty.Rocksofl imest onenatureonce
decomposedt hroughcar bonati
onpr ocesswi ll giveri
set osoi l
sthat
arerichi nli
me.I nadditi
onmi neralcomposi t
ionmaydet ermi nethe
natureandr at
eofchemi caldecomposi tionoft her ocksfor mingdeep
mat uref er
ti
lesoi l
s.Homogeneousr ocksencour agephy sical
weat heringthroughblockdi sint
egrationformi ngskel etalinfert
ile
soil
s.

NB:theminer
alcomposit
ionoft
hepar
entr
ockwi
l
lal
sodet
ermi
net
he
aci
dityandal
kal
ini
tyoft
hesoil
.

 Porosit
yorper meabil
it
yoftheparentr
ockmaydet erminether
ateof
soilf
ormat i
on.Porousrocksal
lowintheagentsofweatheri
ngsuch
asmoi st
ureandai r,
whichacceler
atet
hechemi calbr
eakdownof
rocksthroughprocessesli
kecarbonat
ion,
hydrati
on,oxi
dati
on
formingdeepmat urefert
il
esoil
s.Ontheotherhandnonpermeabl
e

2
 rocksmaytotheformati
onoft hi
nimmaturesoi
lsbecausethey
discour
ageweather
ingprocessesthatwoul
dbreakdownrocks.

 Thecol ouroft hepar entrockal sodet erminesther ateatwhi chsoi l

is
formed.Shi ny/lightcolouredr ocksmaybemor er esistantto
weat her i
ngpr ocessesbecauset heyr efl
ectheatt husl i
mi t
ingt he
rateeatwhi cht heycanbedi sintergratedresult
ingbi ntoskeletalor
thinimmat uresoi l
s.Ont heot herhand, darkcolouredr ocksabsor b
heat ,
expandandl atercontractaf tercoolingleadingt obr eakdown
throughpr ocessesoft emper aturechangesl ikeexf oli
ation,granular
disintegrationhencef ast
errat esofsoi lformation.

 Thepar entrockst ructuremaybechar acterizedbyj oints/l

inesof
weaknessormaybeabl ockofmassi ver ock.Wel l j
ointedr ocksare
susceptibl
et oweat heringandeasilybr eakdowni ntopar ti
clesthat
form soil
s.Joint edrockscaneasi l
ybeper colat edbywat erandai rt
o
causechemi caldecomposi t
ionthr
oughpr ocessesl ikecar bonati
on,
oxidati
on,et.c.Rockj ointscanalsoaidphy sical weat heri
ng
processeslikef rostshatteri
ng,act
ionofpl antr oots,forming
parti
clesthatf orm soil
.Ont hecontrary,massi ver ocksmaynoteasi ly
all
owagent sofweat her i
ngtopenet r
ateandt hereforet hereisalow
rateofweat her i
ngandsoi l
formati
on.

 Theorigi
nandageoftheparentrockdeterminethenatureofthe
soil
sthati
stosay,ol
drocksgiveri
setoferti
l
esoi l
sbecausethey
havebeensubj
ectedtoweatheri
ngprocessesforal ongperi
odof
ti
mewhi l
eyoungrocksgi
v er
isetoskelet
alsoil
sast heyhavejust
beenexposedtoweather
ingprocesses.

QN:Towhatext
enti
ssoi
lfor
mat
ioni
nEastAf
ri
cai
nfl
uencedbyt
hepar
ent
r
ock(25marks)

2.Cl
imat
e(Atmospher
e)i
nfl
uencessoi
lfor
mationt
hroughi
tsr
olei
n
weat
heri
ngthatl
eadst
othefor
mationofsoi
l.

Inareasofheav
yr ai
nfall
andhottemperatures,adequat
emoi st
ureis
provi
dedwhichaccelerat
eschemi calweatheri
ngprocessessuchas
carbonat
ion,
oxi
dat i
on,hydr
oly
sisleadi
ngtof or
mat i
onofdeepsoils
withdevel
opedprofi
les.

I
nar easwheretemperaturesarehotwithli
mit
edr ai
nfal
l,physical
weatheri
ngisaccel
eratedt hr
oughprocessesl
ikeexfoli
ati
on, granul
ar
di
sintegr
ati
onduet oal
ternateheati
ngandcool i
ngleadingtot he
developmentofthi
nskeletalimmaturesoil
s.

3
 I
nv er
ycoldregionsli
kemount ai
ntopsthenatur
eofsoilf
ormationi
s
thr
oughphysicalweatheri
ngprocessesl
ikef
rostshat
ter
ingforming
hil
lcr
eepscreesoilsthatarei
mmat uref
orexampleontheslopesof
mountai
nRwenzor i.

 Heavyrai
nfal
landhi ghtemper atureal
sodeterminethenatur
eof
ani
mal l
if
eandv egetati
ont hatconsequentl
ycontri
butetosoil
for
mationthr
ought headditionofhumust hroughprocessesli
ke
humif
icat
ion,miner
al i
sati
onf ormingfer
ti
lesoil
s.

3.Li
vi
ngor
gani
smsorBi
oti
cfact
ors

Thesei
ncl
udebact
eri
a,i
nsect
s,ani
mal
s,humanbei
ngsandf
act
ors

 Bacteriapl
ayani mport
antr
oleinthebreakdownofrocksthrough
compl expr
ocesses.Organi
smssuchasear t
hworms,ter
mitesalso
breakdownr ocksint
osimpl
er/small
ersubstancest
hatconstit
utesoi
l
.

 Rodent
se.grat
s,moles,
squi
rr
els,
phy
sical
l
ybreakdownr
ocksas
theydi
ghol
esintot
hegroundaidi
ngi
nsoilf
ormati
on.

 Bur rowingani
malscreateholesintherocksandaeratet
hesoi l
sor
rockswhi chaccel
eratesprocessesofchemicalweather
ingespeci
all
y
throughoxidati
onhencepav ingwayforrockdecompositionand
dev elopmentofdeepsoils.

 Maninf
luencessoi
lfor
mati
onthroughact
ivi
ti
esli
kemining/
quar
ryi
ng,
di
ggi
ng.Asar esul
tmassesofr
ockarephysical
l
ybrokendownto
pr
oducesoil
.

 Plantrootsphysi
cal
l
ybreakrocksastheygrowintothegr
ound.Pl
ant
rootsalsosecret
esubst
ancesthatchemical
lydecomposerockst
o
producesoil.

 Plantl
eav es,branchesf alldownanddecayt ofor
m humust hati
s
addedt othesoi lt
hroughsoi l
formingpr
ocessofhumi f
icati
onand
consequent l
ymi neral
isation.Thusareasofthi
ckvegetati
oncov er
havesoilsrichinorganicmat terwhil
eareaswi
thli
mitedv egetat
ion
coverthesoi l
shav eli
mi tedhumus.

Inforestedregi
onswher etherei
sal otofhumussoiler
osi
onis
discouragedandthereforeaccount
ingforthedev
elopmentofdeep
soil
swi thwelldev
elopedpr of
il
es.

QN:towhatext
enthav
eli
vi
ngor
gani
smsi
nfl
uencedsoi
ldev
elopmenti
n
EastAf
ri
ca(25marks)

4
4.Reli
eforTopogr
aphyi
nfl
uencessoi
lfor
mat
iont
hrougher
osi
onand
deposi
tion.

Thenat
ureofr
eli
efi
nfl
uencest
her
ateandnat
ureofsoi
l
sfor
med

 Steepslopesareeasil
yer odedandt hi
simpliesthattheweathered
mat er
ialonthesteepslopeisaswel lremovedt hussoil
stendtobe
skelet
alduet oer
osion.Howev ertherateofsoilformati
onishigh
becauseer osi
onexposest heparentrocktof ur
therweatheri
ng.

 Onthegentl
eslopessoi
lst
endtobedeep,mat ur
eandwi t
hawell
devel
opedprof
il
eduetodeposit
ionofmater
ial
serodedfrom t
he
uppersl
opesanddeeSchemical
weather
ingprocesses.

I
nt hel
owl
andsorfl
atl
andswher
erai
nfal
lishi
ghleachi
ngtakes
pal
aceandmayleadtofor
mat
ionofl
ater
it
esoil
sthatarepoori
n
ter
msofnutr
ient
s.

 Butinar
easwher
ethev
all
eysar
ewat
erl
oggedorpoor
lydr
ainedpeat
soi
lsdevel
op.

5.Ti
me

Soil
for
mat
ioni
ssl
owandcont
inuouspr
ocesst
hatt
akesal
ongper
iodof
ti
me.

Timer eferstothedurati
onoft heint
eracti
onofsoilformingpr
ocessesand
thefactors.Soilfor
mat i
onrequir
esadequat eti
me, t
imeisimport
antinthat
thenatureoft hesoildependsonhowl ongtheprocessesbandfact
ors
havebeeni nt
eracti
ng.

I
faparentrockhasbeenexposedt
otheweat
heri
ngprocessesforalong
t
ime,
soi l
formati
onwil
lbecomplet
eascomparedtoaparentrockexposed
f
orarelati
vel
yshort
erper
iod.

SOI
LPROFI
LE

Thisrefer
stothevert
icalar
rangementofthevari
oussoi
ll
ay er
sf r
om the
toplayerdowntotheparentrockorbott
om lay
er.I
tsavert
icalsecti
on
thr
ought hesoi
lhori
zonsextendingi
ntothebedrock.

I
tdescri
besthesect ionsdownwar dsthroughthesoil
whichcomprisesof
dif
fer
ingcharacteri
sticsi
nt er
msoft ext
ure,col
our,miner
alcomposit
ion,
rat
ioofcombi nati
onofor ganicandinor
ganicmatter,
hardnessandrateof
weatheri
ng.

Thedi
ff
erentl
ayer
sar
eref
err
edt
oashor
izons

Soilhor
izonisawel
l
-def
inedl
ayerwi
thi
nthesoi
lpr
ofi
l
epar
all
elt
othel
ocal
roundsurface.

5
Ther earefourmai
nhorizonsnamely:Ahor i
zon,Bhori
zon, ChorizonandD
horizon.Eachhori
zonhasdiffer
entphysicalandchemi
cal properti
eswhich
resultfr
om vari
oussoi
lformingprocessessuchasweat hering,
i
ntroductionofhumusandmov ementofmi neral
s.

I
tcanbei
l
lust
rat
edasbel
ow:

Aoo-Layerofundecomposedl i
tter.
Ao-Layerofdecomposi ngorganicmat ter
A1-Darkcol ouredlay erri
chinhumusder i
vedf
rom
decomposedor ganicmat ter
.
A2-Bleachedl ayer/zoneduet oLeachi ng.
A3-Transit
ionzone
B1-Transit
ionzone
B2-Layerofmaxi mum deposi t
ionandaccumul at
ionofl
eached
andel
luvi
atedsubst ances/materials
B3-Transit
ionzone
C-Par ti
all
yweat heredrockmat erial
s.

6
D-Fr eshparentr
ockthathasn'
tyetbeenaff
ect
edbyweatheri
ng
processesbutcapabl
eofproduci
ngsoilonceat
tackedbysoi
lfor
ming
acti
viti
es/pr
ocesses.

A-hor
izon

I
tistheuppermostl ayerknownast hetopsoil.Itissubdi vedintoother
l
ayersieAoowhi chismadeupofundecomposedl it
ter,belowAooi sAo
madeupofdecomposi ngor gani
cmatterthatyieldshumus, Aoisfoll
owed
byA1al ayerthatisr i
chinhumushenceadar kcol our.BelowA1i sA2
wheremaxi mum l eachingandeluvi
ati
onoccurmaki ngitabl eachedlayer
wit
hlightcolouredsoi l
sandA3i str
ansit
ionalzonel eadingt oBhorizon.

Bhor
izon

Thisi sknownast hesub-soil

.Nut r
ient
sr emovedf r
om theAhorizon
throughleachi ngandel uvi
ati
onaccumul ateoraredeposi t
edinthis
horizon(B2) .Thepr ocessofplantnutri
entspreci
pitat
ingoraccumulati
ng
i
nt hishorizoni sknowasi ll
uvi
ation.Thishori
zonmayal sobe
char act
eri
zedbyhar dpansduet ot heaccumul at
ionoflargequanti
ti
esof
clayandot hernut r
ients.

Oncei
tisexposed,
itf
ormsduri
crustsasi
tist
hecasewi
tht
hehi
l
ltopsof
t
heBugandahill
s.I
thasadar
kcol our
.

Chor
izon

Thisconsi
stsofpart
ial
l
yweather
edrockknownasr
egoli
th,
thisi
sbecause
weatheri
ngandothersoil
for
mingpr
ocessesmaynotef
fect
ivel
yoper
ateat
thi
sdepth.

Dhor
izon

Thi
sconsistsofthesol
idparentr
ockorinweat
her
edrockorfreshpar
ent
mater
ial
.Iti
salsocall
edthebedrock.I
thasnosoi
lpar
ti
clesbuthas
pot
enti
alforfut
uresoil
formati
on.

NB:theAandBhorizonstoget
hermakeupt
het
ruesoi
landnotal
lsoi
l
s
hav
et hesef
ourhor
izons.

FACTORSAFFECTI
NGTHEDEVELOPMENTOFSOI
LPROFI
LE

Thenatureofthesoil
profi
lemaybesuchthati
tisful
l
ydevelopedor
part
ial
l
ydev el
opedimplyi
ngthatsoi
l
smaybedeeporskeletal,orsoi
l
sof
medium depth.Soi
lprof
il
edevel
opmenti
sinfl
uencedbyanumberof
fact
orsnamel y
.

7
1.Cl
i
mate,rai
nfal
landtemper
atur
edeter
minet
henat
ureandr
ateof
weat
her
ingandsoilf
ormingpr
ocesses

 Areaswi thhight emper atur

esandheav yr ai
nfall
ov er1500mm
encour agedeepv er
ticalweatheri
ngt hr
oughpr ocesseslike
carbonat i
on,hydrolysis,oxi
dati
onr esul
ti
ngintot heformati
onof
mat uresoilsthatarel i
kelytocontr
ibutetothedev elopmentof
compl etesoilprofil
e.Thisisbecausef orest
si ntheseareas
acceleratehumi fi
cationcharacter
izedbyhott emper atur
es.

 Cli
mat ealsodeterminest
hegrowthofpl
antsandanimal
sthat
contr
ibutetothedev el
opmentoft
heAhor i
zonofthesoi
lpr
ofi
le
thr
oughweat heringandhumifi
cat
ion.

 Heavyrai
nfal
landhi
ghtemperatur
esinhumi dtr
opical
envi
ronments
encour
ageleachi
ngandeluv
iat
ionprocessesresponsi
blef
orthe
eluv
ial
zoneintheAhori
zonandani l
luvi
ati
onzonei nt
heBhor i
zonof
thesoi
lprofi
l
e.

I
nari
dareas,wherether
eisli
mit
edrai
nfal
loflessthan5oomm t he
t
emperat
uresarehotandtherei
salotofphysical
weatheri
ng.This
l
eadstoaparti
all
ydevel
opedsoi
lpr
ofil
edevoidofAhor i
zon.

 Coldregi
onsli
kemount ai
nousareas, t
undr aregi
ont her
eisalotof
snowandt her
eforecol
dtemperaturest hatresul
tintheformati
onof
apermanentfrozensubsoil
andt hereforeapar t
ial
lydevel
opedsoi
l
prof
il
e.

2.Par
entr
ock

Theparentmateri
ali
sthenatureoftherockuponwhichweatheri
ngand
othersoi
lfor
mingprocessesoperat
etocreatesoi
l
.Inthefi
rstpl
acethe
parentmater
ial
provi
desthebasisforsoil
profi
l
edevelopment.I
tplay
sthe
rol
ebelow:

 Hardr ocksareresi
stanttoweat heri
ngprocessesandl eadto
developmentoft hi
nsoilswi t
hpoor l
ydevelopedprofi
l
eswhi l
esof t
rocksar eeasi
lyweatheredandact eduponbyot hersoilfor
mi ng
processessuchasl eaching,eluvi
ati
onleadingtotheformationof
deepsoi lswit
hawel ldevelopedprofi
le.

 Joint
edr ocksfaci
li
tatephysi
calandchemi calweatheri
ngprocesses
formingsmal lpar
ti
clesthatar
eacteduponbyot hersoil
forming
processeslikehumifi
cati
on,il
l
uviat
ion,
leadingtoformationoffai
rl
y
deepsoilswi t
hprofi
lesofmedium development.

 Youngpar
entmat
eri
all
eadst
oimmat
uresoi
l
swi
thpar
ti
all
y

8
 devel
opedprof
il
eswhileolderr
ocksthathavehadalongtimeof
exposur
etoweatheri
ngprocessesandprocessesofsoilf
ormat
ion
devel
opint
omat ur
eprofi
leswithcl
earl
ymar kedhor
izons.

 Permeableorporousrocksenabl
eeasypercol
ati
onofagentsof
weatheri
ngli
kerainwater,
airr
esul
tingi
ntodeepweather
ingand
consequent
lydeepsoilswit
hwelldevel
opedprof
il
esunli
ke
i
mper vi
ousrocks.

NB:di
ffer
entsoi
lprof
il
escandev
elopf
rom t
hesamepar
entr
ockunder
di
ff
erentcondi
ti
ons.

3.Rel
i
eforTopogr
aphy
.

 St
eepslopesexperi
encealotofsoiler
osi
onthatremov est
hetopsoi
l
l
eavi
ngshallowskel
etalsoi
l
sthattendtohav
epar ti
all
ydevel
oped
pr
ofi
les.Theyhavethi
nsoil
sanddev oi
dofAhorizon.

I
nfl
atorgent
lysl
opingar
easdeposi
ti
onexceedserosi
onandthey
l
eadtot
heformati
onofdeepsoil
swit
hwelldevel
opedsoi
lprofi
l
es.

Inv
alleys,waterl
oggingdepriv
est hebacter
iaofoxygenandbact er
ial
act
ivi
tieshencepreventi
ngweat heri
ngandhumi f
icati
onprocesses
l
eadingtoapar ti
all
ydevelopedsoilprof
il
e.

 Hi
ll
topstendtoencour
ageleachi
ngandeluvi
ati
onpr ocessesofsoil
f
ormati
onthatl
eadtothebleachi
ngofthetopsoil
leavingitdevoi
dof
t
heAhor i
zonandconsequentl
yapart
ial
lydevel
opedsoi l
profi
le.

4.Li
vi
ngor
gani
sms

 Thickvegetat
ioncov erpr
ovidestheneededorgani
cmattertothesoi
l
throughhumificat
ionprocess.Ital
soprot
ectsthet
opsoilsfr
om
beingerodedawaykeepi ngitinplacef
ormingawelldev
eloped
profi
le.

 Forestedareasalsoacceleratephy si
calandchemi calweatheri
ng
processesthrought hei
rrootspenet r
ati
ngt hroughjoint
edr ocks,
breakingthem i
ntosmal lparti
clesaswel laswi deningthejoint
st o
createpassagesf orwaterandai rthatacceleratedeeperchemi cal
weatheringformingdeepsoi l
swi thfull
ydev elopedprofil
es.

 Man'sacti
vit
iesthroughagricul
turel
ikemonoculture,upanddown
pl
oughing,overgrazi
ngamongot her
sleadtoparti
alsoi lprof
il
e
devel
opmentwhi lesomeact ivi
ti
esdonebymanl ikeaf f
or est
ati
on,
mulchi
ng,ferti
l
izerappl
icat
ion,andforestconser
v at
ion,bush

9
 fal
lowi
ng,encouragecompl
etedevel
opmentofmatur
esoilprof
il
e
becauseweather
ingandsoi
lfor
mingprocessesar
eenhanced.

5.Ti
me.

I
ttakesti
mef orthesoi
lprof
il
etobef ull
ydeveloped.Atypical
orwell
devel
opedprofi
leofsoi
lmusthav eundergoneadequatet i
me, t
her
eforethe
l
ongertheti
met owhichtherocksareexposedt oweatheri
ngandot hersoi
l
for
mingprocesses,t
hemor ethedevelopedprofi
le.

Youngr
ocksnor
mal
l
yyi
eldskel
etal
soi
l
sI.
ewi
thpar
ti
all
ydev
elopedpr
ofi
l
e.

QN:
Whati
ssoi
lpr
ofi
l
e?

Expl
aint
hef
act
orsi
nfl
uenci
ngsoi
lpr
ofi
l
edev
elopmenti
nEastAf
ri
ca

SOI
LCATENA

Thi
sisthesuccessi
vearr
angementorsequenceofarrangementof
di
ff
eri
ngsoilt
ypesalongthesl
opefr
om thehil
ltop(summi t
)totheval
l
ey
bot
tom.

Thissequencevar
ieswi
threl
iefanddrai
nagethoughitmaybeder
ived
fr
om thesameparentmateri
ale.gthesoi
lsatt
hev al
l
eybott
om ar
elikel
yto
bediff
erentfr
om t
hoseofthehil
ltop.

Soil
cat
enamaybeduet
ofact
orsl
i
ker
eli
ef,
cli
mat
e,l
i
vingor
gani
smsand
ti
me.

Acatenausuall
yhasfourtof
ivedif
fer
entsoi
lty
peswi
thv
ary
ing
char
acter
ist
icsasdescri
bedbelow:

a)Hi
l
ltoporUpperl
ayer

b)Thev
ert
ical
slopeort
hef
reef
ace

c)Theconv
exorst
eepsl
ope

d)Thel
owl
yi
ng/
gent
le/
concav
esl
ope

e)Thev
all
eybot
tom

Atthehil
ltop,
ther
earelateri
tecappi
ngwi t
ht hi
nandskeletal
soil
s.Thi
sis
mainl
ycomposedofbearl andwithrocksthatareexposedtoregul
ar
l
eachingandheati
ng.Theseslowlybreakupintofragmentsoftheskel
etal
l
ateri
ti
csoil
sandnormallyformsalateri
ti
ccapping.

10
Belowthehi
l
ltopisafreefaceoraver
ti
calsl
opewhichi
susual
ly
composedofbarerockorsometimesst
onysoil
sduetorapi
dsur
face
runof
f.

Thi
sisfoll
owedbywaxing/conv
ex/
steepslopewi
thcoar
sest
onysoi
l
s
duetoerosi
on.Theyar
eshall
owandinfer
ti
le

Thi
sisf
oll
owedbyt
hewani
ng/
concav
e/gent
lesl
opewi
thdeep

Thesoi
l
sint
hiszonear
enor
mal
l
ydeep,
fer
ti
le,
finegr
ainedi
nnat
ure.

Thevall
eybottom i
schar
act
eri
zedbydar
kgr eyfi
negr
ainedsoi
lswhichar
e
deposi
tedei
therbyri
ver
sorrunofff
rom r
ain.Thesoi
l
sinthevall
eyhave
animpideddrai
nage.

NB.I
nBugandat
hef
latt
oppedhi
l
lsdi
spl
ayat
ruesoi
lcat
ena.

I
ll
ust
rat
ion

FACTORSI
NFLUENCI
NGTHEDEVELOPMENTOFASOI
L
CATENA

1.Topography/r el
i
ef,whichi
st hephysical
appearanceofthel andscape
affectst
hedev el
opmentofsoilcatenainsuchawayt hatdi
fferencesin
rel
iefaff
ectthenatureorsoil
typeduet othefactt
hatt heyi
nfluence
erosion,
depositi
onandhumanact i
vit
ies.

 Hil
l
topshavelater
it
iccappi
ngwi
tht
her
esul
tantt
hin/
skel
etal
soi
lsduetoleachi
ng.

 Thev
eryst
eepsl
ope/
freef
acehar
dlyhasanysoi
l
.Ithasa

11
 bar
erockduet
oer
osi
on

 Thewaxingsl
ope/conv
exsl
opei
schar
act
eri
zedbycoar
se
st
onycreepsoi
lsduetoer
osi
on.

 Thewaningsl
opehasf
air
lydeepcl
ayl
oam soi
l
sduet
o
deposi
ti
on.

 Thelowlyi
ngarea/vall
eybottom hasfi
nepart
icl
esofcl
ay.I
t
i
sdeepandpoor l
ydr ai
ned.Itisgener
all
yazoneof
deposi
ti
onoril
l
uv i
ationiezoneofaccumulat
ion.

Thest eepslopeencour
ageser osionandhencehasshall
owsoi l
s.The
gentl
e slopesarewelldrainedandexperi
encesomedownsl ope
tr
anslocati
onofsoilpar
ti
cleswhiletheval
leybott
om exper
iences
depositi
onhenceaccountingforthedeepclaysoi
ls.

2.Drai
nage,st
eepslopeshaveswifterosi
onandt her
efor
eskelet
al soi
l
s,
gent
lyslopi
ngareashavereduced/sli
ghter osi
onandtheref
oretheyhave
well
drainedsoi
lsthatar
eli
kelytodevelopintomatur
eordeepsoi l
s.

I
nar
easwi
thaccumul
ati
onofwat
er,
peatsoi
l
sar
eli
kel
ytodev
elop.

3.Nat
ureofthepar
entrock,t
hedi
ffer
encesonthesoi
lty
pesalongthe
sl
opecouldbeasaresultoft
hem havi
ngdevel
opedfr
om di
ff
erentpar
ent
mater
ial
s.

4.Cli
mat e:
Thisi
nfl
uencest
hedev
elopmentoft
hesoi
lcat
enai
nthe
fol
lowingways;

Theheav
eyr
ainfal
lencour
agesl
eachi
ngl
eadi
ngt
ofor
mat
ionofl
ater
it
ic
soi
lsont
hehi
llt
ops.

Heaveyrainfallencourageserosiononthesteepsl
opesaccounti
ngfort
hin
skel
etalsoi
ls,anddeposi t
ioninthelowersl
opesandv al
l
eyleadsto
for
mat i
onofdeepdar kloam anddarkclaysoil
s.

Heaveyr
ainfal
lal
soaccount
sforfl
oodi
ngi
nthev
all
eybot
tom andl
ower
sl
opeshencewaterl
oggedsoil
s.

5.Li
vingor gani
smsi epl
antsandanimal
s.Areaswiththi
ckVegetat
ionhav
e
l
oam soi l
sespecial
lyint
hemi ddl
eandlowerslopesduetoplentyf
ul
supplyofhumas.Thi ckveget
ati
onalsoact
sasapr otect
ivecovert
othe
topsoilprevent
ingerosi
on,account
ingf
ordeeploam fer
ti
lesoil
sonthe
waningslope

Humanact ivi
ti
esli
kedef f
orest
ati
on,cropcult
ivat
ionespeci
all
yonhil
l
slopesencourageerosi
onhencet hi
nsoilsonthesteepersl
opeswhil
eon
theotherhanddepositi
onoferodedmat eri
alsoccursonthelowersl
opes
andv al
leybott
om formingdeeploam soil
sthatarefer
ti
le.

12
6.Ti
me,t
hedevelopmentofsoil
catenaneedsampleti
me.Theprocesses
i
nvol
vedtakel
ongandtheref
ore,thel
ongerthegeol
ogi
cal
timescalethe
moredev
elopmentofsoi
lcatenaofanarea.

PROCESSESOFSOI
LFORMATI
ON

Soilf
ormati
onprocessesarethevari
ousacti
v i
ti
esthatactupontheparent
rockandorgani
cmat tert
oproducesoil
.Theseprocessesarearesultofa
combinat
ionofdif
ferentf
actorsi
denti
fi
edalreadyt
hatleadtocreati
onof
profi
l
esandstruct
ure.

Thesepr
ocessesi
ncl
ude:

1.
Weat heri
ng, t
hisi
sthephysical
disi
ntegr
ationorchemical
decomposi
ti
on
ofrocksinsitu.Rocksbr
eakdownt hr
oughv ari
ousphysi
calandchemi
cal
processesleadingtosoi
lfor
mat i
on.

Highrat
eofweat heringr esul
tint
odeepandmat uresoilsmeaningthatwi
th
hi
ghr at
esofweat hering,amat ur
esoilpr
ofil
eiseasi
lyreached.Int
he
tr
opicsweather
ingunderhumi dcondit
ionsleadstodeeplatosol
sand
tr
opicalbl
ackearths.Deeppodzol sinhumidtemperateconditi
ons.Deep
maturetundr
aandAr cticsoil
sinhighl
atit
udezones,etc.

Onthecont
rar
y,ar
easofmor eresi
stancetoweatheri
nghav
eledtoshall
ow
soi
l
sorsoil
sofpart
ial
lydevelopedpr of
il
e.Suchi
ncludet
herecentv
olcani
c
soi
l
s,mountai
nsoil
s,gl
acialsoil
sandmar i
nesoi
l
s

2.Leaching,t
hisistheremovalofsolublemineralnutri
entsf
rom t
heupper
l
ayersoft hesoil
profi
letotheunderlyinglay
ers.Solublenut
ri
ent
sl i
kesal
ts,
i
ron,carbonatesamongot herswhichar er
emov ed/t r
ansport
edina
solut
ionformf r
om theAhor i
zontoot herhori
zons.Somet i
mesthismakes
theAhor i
zonacidic.

3.Eluvi
ati
on,thi
sr ef
erstothemov ementofsol ubl
emat er
ialsi
nsoluti
onor
suspensionfrom oneplacetoanot herwithinthesoil
s.Mov ementcanbe
vert
icalasiti
sthecasewi thleachi
ngorl ateraldependingont he
mov ementofwat erandsoilstruct
ur ewi
thi nagivenarea.I ti
sinf
luenced
bytheclimateandnat ur
eoft hepar entr
ock.ItalsoleadstoapoorA
hori
zonwhi chiscommonl yknownasEl uv i
alzone.

4.Il
luvi
ati
on,thi
sistheaccumul ati
onandprecipi
tat
ionofleachedand
eluvi
atedmateri
alsint heBhorizonoft
hesoilprofi
l
e.Thesol ubl
enutr
ient
s
thatwereremov edfrom Ahorizonaresubsequentl
ydepositedintheB
hori
zon.Itl
eadst othedevelopmentofB2layer(dar
kcoloured)andtherei
s
maxi mum accumulationofcoll
oids.

5.Humi
fi
cat
ion,
thi
sist
hepr
ocesst
hroughwhi
chor
gani
cmat
teri
s

13
decomposedt of
orm humusat askperfor
medbysoill
ivi
ngorgani
smslike
bacteri
a,eart
hwor ms,ter
mitesamongot her
s.I
tisver
ycommoni nhumi d
areaswher ether
eisheavyrainf
all
,for
estsandhott
emperat
ures.I
tmainly
i
nfluencesthedevelopmentoftheA0andA1zonesofAhor i
zon.

6.Mineral
ization,thi
sistheprocessofsoil f
ormationwhichtakespl
acein
ext
remecondi ti
onswher edecompositi
onofor ganicmatterthatf
orms
humusgoesbey ondHumi fi
cati
onsucht hatorgani
cmat teri
sbrokendown
i
ntobasicpar tsandchangedi ntomineralsubstancesli
kecarbondioxi
de,
waterandsi l
ica.Itiscommoni ntheAhor izonbutcanalsooccuranywhere
i
nthesoi l
pr ofil
ewher eorgani
cmat t
erex i
sts.

7.Cal ci
fi
cation,i
tisapr ocesswher eorpr ocesswhi cht akesplaceindry
placesasar esultofupwar dmov ementofcapi l
lar
ywat erwhere
evapor at
ionexceedspr ecipit
ati
on.Theexcessi veev apor ati
oncauses
wat ercontaini
ngdi ssolvedcalcium tomov eupwar dst hroughthesoilby
capill
aryact i
on.Att hesur f
ace,thewat erevaporatesl eavingthesoilt
o
haveorber ichincal ci
tes.Iti
scommoni nthekarstr egionsofEastAf ri
ca
wher eshallowsoi lprofil
eshav edevelopedsoi l
sri
chi ncalcium andthese
soil
sar eknownast hepedocal s.

8.Glei
zat i
on,t
hisoccursinwet/ coolcli
maticr egi
onswi thpoordr ainage
especiall
yintheswampyar eas.Inpolarregionst heper i
frostpr
ov i
desan
i
mper viouslayerwherethet opsoi l
iscir
culatedwi thmel twater.This
reducesoxidationorcausesdi oxidati
onoff erouscompounds.Theyoccur
asbluishgreywi t
hstickyclaysoi l
sandusual lystruct
urel essandt his
processleadst othedevelopmentofshal lowsoi lprofi
le.

9.Laterisat i
on,iti
nvolvesweatheri
ngunderhotanddampcondi tionswithi
n
thetropics.Thi sisapr ocessi
nhumi dar easthati
nvolv
esthemi grati
onof
solublemi neralnutr
ientsfr
om theupperl ay
erstotheunderl
yingl ay
ers.
Sil
icaisl eachedf rom theAhorizonleavi
ngbehi ndir
onandalumi num
whichgi v esrisetoredbr owni
shsoils.Theironhardensonexposur egiv
ing
ri
set olat eri
ti
csoi l
s.

Thisprocessiscommoni
nthet
ropi
cal
regi
onswher
ethef
oll
owi
ng
condit
ionsprevai
l;

-
Abandantsuppl
yandr
api
ddecayofor
gani
cmat
ter
.

-
Deepandi
ntenceweat
her
ingofr
ocks.

Accumul
ati
onofi
ronandal
l
umi
nium .

10.Podzoli
sati
on,
thi
sisacompl exsoi
lfor
mi ngpr ocesst hatoccursunder
coolmoistcli
mati
cregi
onswithconif
erousforests.Iti
nv olvesLeachingof
sal
tsandironcompounds,El
luvi
ati
onandHumi f
icationpr ocessesthatai
d
i
ntheformat i
onofpodozoi
csoil
s.Iti
scommoni nr egionswi thshort

14
summer s(
coolhumi
denvi
ronments)
.Pr
olongedwi
nterwhi
chdoesn’
tal
l
ow
ful
ldecomposi
ti
onofor
ganicmatt
er.

NB:t
hisonei
snotsocommoni nEastAf
ri
caexceptont
het
hreegl
aci
ated
mountai
nsRwenzor
i,Keny
aandKil
i
manjaro.

11.Sal
inizat
ion,isthepr ocessbywhi chsoil
sareenr i
chedwi t
hsalt.Thisis
duetoev aporat
ionf r
om t hesoilsur
facewhichdr awsupsal t
sinsol uti
on
bycapil
larymov ement .Sali
nizati
onmayal sobei nducedbymant hrough
i
ntenseirri
gati
on.Itgivesr i
set osal
inetopsoil
s(i nt
erzonalsoil
s)ofhigh
sal
tconcent r
ati
onespeci al
lyinthesemi ar
idareas.Salini
zati
ongi v
esr i
se
toapoorA-hor izon.

12.Chell
uvi
ation,isthepr ocessthati
nvolveschemicalbondingofmetall
ic
i
onsandor ganicmat ter.Inthiscasewhenor gani
cmat terdecomposesit
rel
easeschelatingagent s(organi
cacids)thatatt
ackrocksthereby
produci
ngiron.,al
umi nium andmagnesi um compoundswhi chthenmov e
downwardsaf fecti
ngsoi lmov ementordev el
opment.Itnormall
yresul
ts
i
ntorichhori
zonAsoi ls.

13.Lessi
vage,i
saprocessofsoilfor
mationespeci
allyt
hebreakdownof
pedswhereclaypart
iclesar
ecarr
ieddownwardsf r
om theuppersoi
lsi
n
suspensi
onformleadingtoanimpoveri
shedA-horizonandhardpansin
theB-hori
zon.

CLASSI
FICATI
ONOFSOI
L

Soi
lty
pesi
nE.
Afr
icaf
all
undert
hreemaj
orgr
oups(
types)namel
y;

Zonalsoi
ls
I
ntra-
zonalsoi
l
s
Azonalsoi
ls

a.Zonalsoi
ls:
Thesearematuresoi
l
swhi
chhav
ewel
ldev
elopedsoi
lpr
ofi
l
es

Theirf
ormat
ionisdomi
nant
lyinfl
uencedbycl
imat
eandv egetat
ion
(or
ganicmat
ter)upont
heparentrockoveral
ongper
iodoftime.

Theyaresaidtohavehadsuffi
cient
lyl
ongper
iodsofexposur
etothesoil
for
mingprocessesandther
efor
ehav ewel
ldev
elopedpr
ofil
eswit
hdist
inct
hori
zons.

Theyareformedongentl
ysl
opingandwelldr
ainedareasinE.Af
ri
casuch
asaroundtheLakeVi
ctor
iabasi
nandalongthefoothil
lsofthehi
ghl
ands
Theyaresubdivi
dedi
ntotwogroupsi.
e.

Pedocal
swhi
char
eri
chi
ncal
cium car
bonat
efor
medi
nar
easofl
ow

15
rainfal
l(semi
ari
dar
eas)
e.gcher
nozems,
chest
nutorbr
ownsoi
l
s,
sierozems,et
c.

Pedalferswhi char
er i
chi nalumini
um andir
on.Theydevel
opi
nareasof
hi
ghr ainfal
l(humidareas).Theyhavelowcalci
um car
bonat
econt
entdue
toleaching.Theyi ncl
udel at
erit
icsoi
ls,t
ropi
calredear
thsandtropi
cal
bl
ackear thsamongot hers.

Thef
oll
owi
ngar
etheTy
pesofZonalsoi
lsi
nEastAf
ri
ca:

Lateri
ti
csoils(Lat
osols):Thesear esoil
sformedinhumidt r
opi
calr
egions
whereheav yleachingtakespl aceal ltheyear.Theyconsistofmai nl
y
hydrat
edi r
onandal uminum oxidesandhav estonypart
icl
esduetot he
l
ossofmi neralnut
rient
sbyr emov alofbasesandsili
cafr
om topsoi
ltothe
underl
yinghori
zon.

Itisformedbyt hel aterali

zationprocess, inwhichsi l
i
cai sleachedoutand
i
r onandal uminum compoundsbecomeconcent r
atedint heAhor i
zondue
toleachingandconsequentdr yi
ng.Thisgi vesrisetolaterit
esoi l
sthatar e
reddishbrownandt endt obest i
ckywhenwetI .eplasti
corcohesi ve.They
hardenwhenexposedt odr yatmospher e.
Ironandal uminum compoundsdon' tdissolveeasilyandt hereforeget
concent r
atedont het opsoil.Thealumi nium andironcompoundsf orm
smal lst
onesorgr av el onthet oporwi thintheweat heredmat eri
alknown
asl at
eri
tegravel.Af tersomet i
met hel ateri
tegraveliscement edtogether
tof or
ml ater
it
e,itismai nl
yusedf orgr adingr r
oads.

Ther
ear e5di visi
onsofl at
osol
snamel
y
1.Weat her edferr
alit
icsoil
s
2.Ferr
ugi noussoi l
s
3.Leachedf err
ali
ticsoil
s
4.Basisols
5.Humi cl atosols

Fact
orst
hati
nfl
uencet
hedev
elopmentofl
atosol
s.

a.Relief
,thi
sisoneoft hemosti mpor t
antfactorsresponsi
bleforthe
devel
opmentofl atosols.Theyform underar easthatarerel
ativ
elywell
drai
nedthatistosayt heydev el
opwel longent lysl
opingareas.Thisis
becausewatercanper col at
eandal l
owt heleachingoftheAhor izonand
theproperdeposit
ionofmat eri
alstoBhor i
zon.Howev ersteepslopesar
e
pronetosoiler
osionwhi chdoesn’tal
lowdev elopment

ofl
atosol
s.

b.Nat
ureoftheparentrock,l
atosol
sfor
mf r
om softr
ockswhichall
ow
qui
ckweatheri
ng.Aparentrockshouldal
socontai
naluminum andi
ron
component
sf oroxi
dati
ont otakepl
ace.

16
Har
drocksdi
scour
agef
ormat
ionofl
atosol
sbecauset
heyar
eresi
stantt
o

weat
her
ing.

c.Drai
nage,
areaswithpoor l
ydr
ainedsoi
l
sdon’
tall
owthefor
mati
onof
l
atosol
swhereaswelldrainedar
easprovi
dei
dealcondi
ti
onsf
ort
he
devel
opmentoflat
osols.

d.Weather
ingprocesses,t
heweather
ingpr
ocessesofoxidat
ionand
sol
uti
onchangethecolorandtr
ansportt
hecementingsil
i
catemater
ial
sto
di
ff
erentar
easresult
ingint
othedevel
opmentoflat
osols.

e.Cli
mate,l
atosolsareformedunderheavyrai
nfal
lamountespeci
ally
above1500mm.t hisRainf
allpr
ovi
deswaterthatact
sasamedi um for
chemical
weatheringprocessesandconsequentl
eachi
ngofsil
ica.

Hottemper
atur
esaccel
erat
ether
ateofphy
sical
andchemi
cal
react
ion
pav
ing

wayf
ordeepweat
her
ingandt
hedev
elopmentofl
atosol
s.

Dr
ycondi
ti
onst
hatt
henenabl
ethel
ater
it
etohar
den.

f.Vegetati
oncover,presenceofforestshel
ptoholdthesoil
part
icl
es
togetherandall
owweat heri
ngprocessesespeci
all
ychemicalweather
ing
totakeplaceinsit
ur esult
ingint
oHumi fi
cat
ionther
efor
eaidingl
atosolst
o
devel.

g.Humanacti
vi
ties,f
orexamplecl
ear
ingofv
egetati
on,
mining,f
armi
ng
exposet
hesoilt
ot heful
lfor
ceofrai
nandheataidi
ngl
atosolst
ofor
m.

Somehumanact
ivi
esi
nter
ruptt
hedevel
opmentoflat
eri
ticsoil
sfor
exampl
emini
ng,
far
mingtendtoret
ardt
hefor
mationoflatosol
s.

h.Time/geologicalperi
od,l
atosol
srequi
realonggeol
ogi
calperi
odto
al
lowtheformationandaccumul at
ionofoxi
detotakepl
aceforexample
areaswit
hlactosolsineastAfri
caarebel
i
evedtohavedevel
opedinter
ti
ary
peri
od(250years)

Latosol
sar
egoodmat
eri
alsi
nmaki
ngr
oadsast
heycont
aincar
bonoxi
de
and

i
ronor
e.

Tropi
calr
edearths:Thesearefor
medint r
opi
calr
egionswit
hdefi
nitewet
seasonsdur
ingwhichheav yl
eachi
ngtakespl
ace.Theyarechar
acteri
zed
byaloamymi xt
ureofclayandquart
z

Tr
opicalbl
ackear
ths:Thesearesoi
lsfor
medi nhumi
dt r
opicalr
egions
wher
et her
earebasal
trocksforexamplepar
tsofKenya.Itisblackin

17
col
ourduetohi
ghcont
entoft
it
ani
um sal
tsi
nthebasal
tbedr
ockor
par
entr
ock.

Reddeser
tsoi
ls:Thesear
esoilsthatar
ereddi
shincol
our.Theyar
e
for
medinhotanddryregi
ons.Theyaresandyandcont
ainalotofsal
ts.

b.I
ntr
azonalsoi
ls:

Thiscategoryofsoil
soccurswher especialcondi
tionsoftheparentrock,
drai
nageandr eli
efexer
tast rongerinf
luence/eff
ectont heresult
antsoil
ty
pet hanotherf
actorsl
i
keclimateandv egetati
on.Thiscoul
dbei nfor
m of
presenceofmuchwat er
,lar
geamount sofsal t
setc.

Theyexi
sti
ndi
ff
erentpar
tsoft
hewor
ldr
athert
hani
nspeci
fi
czones.

Int
razonal
soi
l
sar
eint
ermedi
atebet
weent
hezonal
soi
l
sandt
heazonal
soil
s.

Theyshowprofil
eswhicharedist
inct
,anindi
cat
ionthatt
her
ehasbeena
dominantcont
rolfactori
nt hei
rf or
mati
on i
.e.par
entrockmater
ialor
drai
nageot
herthancli
mate.
Theymainl
yoccurincoastalar
easofeastAfri
ca(bogandpeat)
,inr
iver
fl
ooded pl
ains (
sil
tand mud)and sali
ne soil
sin semidesertar
eas
(cal
car
eous).

Exampl
esofI
ntr
azonalsoi
lsi
ncl
ude:

Sali
nesoi l
s:Thesear ethesoilswhi
chhav ehighlevel
sofsolublesal
ts.
Theyar egreybecauseoft hesal
tcontentandtheyoccurinr egi
onsor
areaswher eevaporat
ionisveryhi
gh.Theyaresocommoni nsemideser t
areas.Theyincl
udesolonchaksandsolonet
zsoil
s.Theyareal
soknownas
Halomor phi
csoils

Peatsoils:Thesearesoi l
swhichoccuri
nwaterlogged( marshy)areaswi
th
almostnoai rspacet oal l
ow easywaterpercol
ati
onori nfi
l
trati
on.The
decomposi ngplantremai nsaccumulat
eontopoft hisimpervioussoi
lto
form peatorbogsoi lf orexampleinswampsandv all
eysaswel lasthe
coastalareasofE. Afr
icasuchasmeadow soi lsandgl eysoi
ls.Theyare
alsocall
edHy dromorphicsoi l
s
Relat
edly,meadowsoi l
s( sil
tandmud)occuri
nr i
verfloodplai
ns

Calcar
eoussoi ls:Thesearesoilswhi charef
ormedf r
om l
imestonerocks.
They include Rendzi na soil
s whi ch are dark-
col
our
ed,l oamy soils
contai
ningchalkorl imestonef r
agment sfor
medunderhumi dcondi
ti
ons
and Ter r
arossa soil
s whi ch arer eddi
sh resi
dualsoi
lst hatnormally
accumulatei nlimestonedepressionsusuall
yundersemi-ar
idcondit
ions.
Theyareal soknownasCal cimorphicsoil
s

18
c.AzonalSoi
ls:

Theyareimmatureory
oungsoi
l
swhi
chshowchar
act
eri
sti
csoft
hei
r
ori
ginal
parentr
ock.

Thei
rdevel
opmentisincomplete,
thati
swhyt
heydon’
thav
ewel
lmar
ked
hori
zonsi
.etheyhav
enocl earsoi
lprof
il
e.

Theyaresoi
l
swhichhav
enotbeenexposedtosoil
formingpr
ocessesfor
alongti
metodev
elopmatur
echaract
eri
sti
cshencetheyarei
mmat ur
e
soil
s.

Theyar
eskelet
alsoi
lswit
hshall
owprofi
lessotheyr
eflect(show)si
mil
ar
char
act
eri
sti
csoftheori
ginal
parentr
ockhence,t
heyresistchange

Azonalsoil
scanbedescri
bedastr ansport
edsoi
lswhi
charedeposi
tedby
theagentsofer osi
onbecauset heyar ederi
vedfr
om unconsoli
dated
materi
alssuchasall
uvi
um,sand,
vol cani
cashamongother
s
Azonal
soi
l
sar
edi
vi
dedi
ntot
wo(
2)cat
egor
iesi
.eLi
thosol
sandRegosol
s

Li
t hosolshaveahi ghcontentofi
ronandalumi
num, mai
nlyfoundin
tr
opi cal
rainforests
Rogosol scompr iseunconsol
idat
edparentmater
ial
ofal
luvi
alori
gin
der i
vedfrom unconsoli
datedmateri
alsuchasall
uvi
um,sand,vol
canicash,
etc.

Exampl
esofazonalsoi
lsi
ncl
ude:

Mountai
nsoil
s/Screesoi
ls:Thesear esoil
swhi charestonyconsist
ingof
l
argerockfr
agment st
hatweat herdownbyf r
ostaction.Theyarecoarse
grai
ned(t
ext
ured)andheavil
yleached.Theyaref oundonmountainslopes
formedfr
om t
heaccumulati
onofweat heredrockf r
agments

All
uvialsoil
s:Thesearedeposi
tedsoil
sconsist
ingofamixt
ureofsand,sil
t,
mudandcl ay(r
iverbor
nemateri
als)
.Theyarefi
netext
uredandsui
tablefor
agri
cultur
e.

Marinesoi
ls:Theyarecommoni ncoastalar
easassoci
atedwithwat
er
bodiesf
orexamplelakes,seasandoceansformedasar esul
tofwave
act
ionsuchasmudandcl ay.

Volcani
csoi
ls:Theyaret
hesoil
spr oducedbyweatheri
ngofvol
cani
crocks.
Theyarehi
ghlyacidi
candfer
ti
leforexamplerecentl
avaandashsoi
ls.

Glaci
alsoils:Theyar esoil
sf ormedasgl aci
aldepositedmateri
alsfor
exampl et
il
lsoil
s,fl
uvi
alglaci
alsoil
s,gr
avelsandclayaswellasoutwash
sands deposit
ed in gl
aci
all akes byglaci
ers and r
iversf
lowing f
rom
glaci
atedhi
ghlands.

Wind-bl
ownsoils(Aeoli
n):especi
all
ysandsheet
s,drysandysoi
l
s,sand
dunesandloess.Theyareblownanddeposit
edbywi ndinari
darease.
g
Koti
doandMor ot
oi nKaramojaregion,t
heri
ftval
l
eyregioninWester
n
UgandaandChalbideser
tinKenya.

19
 FACTORS/
CONDI
TIONS/
PROCESSESRESPONSI
BLE
FORTHEFORMATI
ONOFAZONALSOI LSINE.
AFRICA:

Denudat
ionpr
ocesses(
Erosi
on,
transpor
tat
ionanddeposi
ti
on)

Weat
her
ingoft
hepar
entr
ockl
eadst
othef
ormat
ionofscr
eesont
he
mount
ain sl
opes.Thesesoi
l
snor
mal
l
yshow char
act
eri
sti
csoft
hei
r
or
igi
nal
par
entmat
eri
alandr
esi
stchange.

Wav
edeposi
ti
onr
esul
tsi
ntot
hef
ormat
ionofmar
inedeposi
tsandt
he
r
esul
tantsoi
l
sincl
udemud-
fl
atsoi
l
s/mar
inecl
aysoi
l
se.
gal
ongt
heEast
Af
ri
cancoastatMombasa.

Gl
aci
aldeposi
ti
onr
esul
tsi
ntot
hef
ormat
ionoff
luv
io-
glaci
alsoi
l
se.
g
t
il
ls,
out
washsands,
grav
elandcl
aydeposi
tedi
ngl
aci
all
akese.
gLac
duSpekeonMt
.Rwenzor
i.

Ri
v erdeposi
ti
onresul
tsint
otheformati
onofalluvi
alsoi
lspar
ti
cul
arl
y
si
ltandmude. galongthebanksofri
verPanganiandriv
erRufi
gii
n
Tanzania.

Wi
ndact
ionr
esul
tsi
ntot
hef
ormat
ionofwi
ndbl
ownsoi
l
sli
kesand
sheet
s,sanddunesandl
oess.

Cli
mate
Heavyamount
sofr
ainf
all
causef
loodsandseal
evel
changesf
ormi
ng
al
l
uvi
alsoi
l
sinl
owercour
sesofr
iver
se.
gal
ongRi
verRuf
igi
andRi
ver
Pangani
aswel
lasmar
inesoi
l
sincoast
alar
eas.

Heav
yrai
nfal
lal
socausessev
ereer
osi
onal
ongt
hest
eepsl
opesof
hi
ghl
andse.
gRwenzor
ianddeposi
ti
oni
nlowl
andsf
ormi
ngsoi
l
ssuchas
si
l
t,mudl
i
kei
nsomepar
tsofKasese.

Temper
atur
echangesi
nmount
ains/hi
ghl
andsl
i
keRwenzor
iandMt
.
Keny
acausef
rostact
iont
otakepl
aceconsequent
lyf
ormi
ngscr
ee
soi
l
sormount
ainsoi
l
s.

Di
ff
erencesi
npressur
ewithi
ndesert/semi desertar
eascausest
rong
wi
ndstoblowresul
ti
ngint
owi nder
osionthatformsloesssoi
ls

20
Rel
ief

Thesteepsl
opesofhi
ghlandspromoteweat
heri
ng,
erosi
onandmass
wast
ingtotakepl
acehenceformingscr
eesoi
ls

Vall
eys/lowl
andsencour
agedeposi
ti
onofer
odedmat
eri
alst
ofor
m soi
l
s
l
ikesil
tandmud

Vol
cani
cact
ivi
typr
oducesv
olcani
csoi
l
ssuchasl
ava,
ash/
cinder
set
c

Nat
ureoft
hepar
entr
ock(
Rockst
ruct
ure)

Dar
kcol
our
edr
ocksar
eeasi
l
yweat
her
edt
ofor
m scr
eesoi
l
s

Wellj
oint
edr
ocksi
nhi
ghl
andar
easar
eeasi
l
yweat
her
edt
ofor
m scr
ee
soi
l
s

Sof
trocksar
eeasil
yer
odedbyr
iver
sandgl
aci
erst
ofor
m al
l
uvi
alsoi
l
s,t
il
l
soi
l
samongot her
s

Loose/l
i
ghtrockpar
ti
clesar
eeasi
l
yblown,t
ranspor
tedanddeposi
ted
tofor
m wind-
blownsoi
lssuchasl
oessandsanddunes

Bi
oti
cfact
orsi.
emanandt heeff
ectofburr
owingani
mals
Humanacti
vi
ti
esli
keagr
icult
ure,
quarr
yingandmini
ngleadt
obr
eakup
oft
hepar
entr
ocki
ntosmal
lpar
ti
clest
her
ebypr
oduci
ngl
ooseorun
consol
i
dat
edmat
eri
alswhi
chf
orm scr
eesoi
l
s.
Manal sodumpswast ematerialsthatmayresul
tint
oweat her
ingof
therockhencef or
mingazonal soi
ls.
Deforestat
ion,
bushburni
ng,ov erstocki
ngandovergrazi
ngexposet he
parentrocktoweather
ingprocessest hatl
eadtofor
mat i
onofy oung
soil
s.

Ti
me

Azonal
soi
l
sar
eyoung(
immat
ure)soi
l
simpl
yi
ngt
hatt
heyar
e
exposedt
othesoi
lfor
mingpr
ocessesf
orashor
tper
iodoft
ime
dur
ingt
hei
rcour
seoff
ormat
ion.

Qna)Di
sti
ngui
shbet
weenaz
onal
soi
l
sandi
ntr
azonal
soi
l
s

b)Accountf
ort
hef
ormat
ionofazonal
soi
l
sinEastAf
ri
ca

OR

21
Qn.Exami
net
hecondi
ti
ons/
fact
ors/
processesr
esponsi
blef
ort
he
f
ormat
ionofazonal
soi
l
sinEastAf
ri
ca.
a)Di
sti
ngui
shbet
weenAzonalandI
ntr
a-zonalsoi
ls.

Azonalsoi
l
sar esoi
lswhi
charey oungandwithoutacl
earsoilpr
ofi
l
e.They
aresoi
lswhichhavenotbeenexposedt osoi
lfor
mingprocessesl
ong
enoughtodevelopmatur
echaracteri
sti
cs.

Theyar
eskelet
alsoi
l
si.
e.wi
thshal
l
owpr of
il
esandshowcharact
eri
sti
csof
thei
ror
igi
nal
parentr
ockwhi
chweather
edandresi
stchange.

Theyar
edi
vi
dedi
ntot
wogr
oupsi
eli
thosol
sandr
egosol
s.

Theyar
ederi
vedf
rom unconsol
i
dat
edmat
eri
alse.
g.al
l
uvi
um,
sand,
and
vol
cani
cash.

Azonalsoi
lsi
ncl
ude,

Scr
eesoi
l
sonmt
.sl
opes.

Mud-
fl
atsoi
l
s/mar
inesoi
l
s.

Fl
uvi
o-gl
aci
alsoi
lse.
g.t
il
l,
out
washsandandgr
avel
andr
esor
tedcl
ayl
aid
downingl
aci
all
akes.

Wi
ndbl
ownsoi
le.
g.sandsheet
,dunesandl
oess

Lav
a/ashsoi
l
s,ci
nder(
vol
cani
c).

Fact
ualmar
king03mks

I
ntr
a-zonalsoi
ls

Int
ra-zonalsoi
lsoccurwher
especi alconditi
onofreli
eforparentrockexer
t
astrongerinfl
uenceontheresult
antsoiltypethanotherfactorsegcli
mate
andv egetat
ionegbog/peat
/gleyedsoilsinmar shyareasofEastAfri
ca
suchascoast alregi
ons,
meadowsoi l
sint heri
verfl
oodpl ai
ns(sil
tand
mud) ,
sali
nesoilsinsemi
-desertareas,

Fact
ualmar
king02mks
05mks

b)Accountf
ort
hef
ormat
ionofAzonalsoi
lsi
nEastAf
ri
ca.

Weat her
ingoftheparentrockl
eadstofor
mati
onofscr
eesonmt.
slopes,t
hesoilsusual
lyshowcharact
eri
sti
csoft
hei
ror
igi
nal
par
ent
rockandr esi
stchange.

Tect
oni
cdeposi
tsofl
avat
hroughv
olcani
cact
ionl
eadsi
tsf
ormat
ion

22
ofl
avaashsoi
l
s,ci
nder
,pumi
ce.

Material
smaybet ransport
edelsewherebyhi
ghrateoferosi
onand
agents,deposi
tedt
hroughwav eactionl
eadi
ngtoformati
onof
marinedeposit
s.Thesoilsher
ei ncl
ude:

Mudsoi
l
sormar
inecl
aysoi
l
s.

Windacti
onleadi
ngtot hef
ormat
ionofwi
ndbl
ownsoi
l
sli
kesand
sheet
s,dunesandloess.

Gl
acialact
ion(f
luv
io-
glaci
al)r
esul
ti
ngintot
heformati
onoffl
uvi
o-
gl
acial
soil
s,sandandgravelandr
e-sort
edclay
s(deposi
tedi
nglaci
al
l
akes)

Ri
veract
ionl
eadst
ofor
mat
ionofal
l
uvi
al.

Cl
i
mat
e,

Hi
ghamountofrai
nfal
lcausesr
iverf
loodst
hatl
eadt
odeposi
ti
onof
al
l
uvi
um i
nthelowercourse.

Equal
l
y ,
highr
ainfal
lcauseer
osi
ononst
eepsl
opesanddeposi
ti
onof
mater
iali
nthelowlands.

Temperat
urechangesi
nmt
.sl
opesi
nfl
uencephy
sical
weat
her
ing
thusf
ormingscr
ees.

Rel
ief
,thenatur
eofrel
iefmai
nlyi
nfl
uenceserosi
onofscr
eesonmt
.
sl
opeandt hei
rdeposi
ti
onfor
mingnewsoils.

Timel
apse;
Azonalsoi
lsar
eimmaturesoi
l
sandmai
nlydepends
upont
heshortper
iodoft
imeint
heirf
ormati
on.

Humanactivi
ti
esli
ke,quarr
yingandminingl
eadst
othebreaki
ngof
t
heparentrockint
osi
mpl erpart
icl
es,l
eaveal
onedumpi
ngofwaste
mater
ial
,henceformi
ngAzonal soi
l.

Def
orestat
ion,
bushbur ni
ngandovergr
azingexposet
heparentrock
t
oweat her
ingprocessesthatl
eadt
otheformat
ionofyoungsoi
ls.

I
mpr
essi
onmar
king 20mks

Tot
al 25mks

23
 SOI
LEROSI
ONI
NEASTAFRI
CA:

Soiler
osionistheprocessofwashingawayorr emovalofthetopthinlay
er
ofsoilbyagentsli
ker unni
ngwater,wind,i
ce(glaci
ers)andmanf rom one
pl
ace to another.The eroded soil
s aretranspor
ted and deposit
ed to
anotherarea.

Ther
ear etwo(
2)t
ypesofsoi
ler
osi
onnamel
ygeol
ogi
calandaccel
erat
ed
soi
lerosi
on.

Geologi
calsoilerosionisregar
dedasnor maler osi
onwhicht akespl
ace
whenevertherei
saf l
owofenergyont hesurf
aceoft heeart
h.Itisaslow
processinwhicht heremovalofthesurfacesoilmaybemat chedbythe
formati
onofnewsoi l.I
tist
heref
orenotdangeroustothesoi
landoccursin
areaswithveget
ationcover
.

Acceler
atedsoiler
osionoccurswhengeologi
calsoi
lerosi
onisspeededup
byman’sactiv
iti
es.Inthiscaset
herateofsoill
ossisgreat
erthantherat
e
ofsoilf
ormati
on.Thist ypeofsoi
lerosi
ontakesplaceinallenvi
ronment
s
whichhavebeendisturbedbyman.

Areas af
fected by soilerosion i
ncl
ude:Slopes ofMt.Elgon,Kigezi
hi
ghlands i
n Kabale and Kisoro,Kot
ido and Mor
otoin Nort
h Easter
n
UgandaandAnkol eMasakacor ri
dor
.

I
nKenya,
itoccursinMachakos(Masail
and),
Nyanzapr
ovi
nce,
Tur
kana
l
and,
Chalbideser
tandtheKenyahighl
ands.

I
nTanzani
a,i
tisexper
iencedi
ntheKondoaregi
on,Mi
ombowoodlands,
Mt
Ki
li
manjar
osl
opesandar oundt
heSouther
nhighl
andsamongot
hers

Gener
all
y,soi
ler
osi
onoccur
sint
hehi
ghl
andanddr
yar
easofE.
Afr
ica

TYPES/
FORMS/
PROCESSESOFSOI
LEROSI
ONI
NEASTAFRI
CA:

1.Wi
nder
osi
on/
Def
lat
ion

Thisistheremov alofl
ightsoilpart
icl
esfrom onepl
acetoanot herbyt
he
acti
onofwi nd.Thesoilparti
clesareblownawaybywi ndandlat er
deposit
edt oform sanddunes.I t
’sver
ycommoni ngener
all
yflatanddry
(semiarid)areaswithnoorlessv egetati
oncovere.
gChalbidesertof
Kenya,KotidoandMor oto(Kar amojaregi
on)

2.Sheeter
osi
on

Itistheuni
formremov alofathi
nlayerofsoi
loveralargear
eaby
runni
ngwat erandwind.Thismainl
yoccurswhenrainfall
sonagent
le
slopewhichisbarewithoutanyv
egetati
one.ginNakasongola,
Mbar ar
aandBusheny i

24
3.Ri
ller
osi
on

Thisistheunevenremov alofsurfacesoi lbyr

unningwat erinwhich
numer oussmallchannels(f
urrowsorr i
l
ls)ofafewcent i
met ersindept
h
areformed.Thi
soccur songent leslopeswher evegetati
onhasbeen
cl
eared.Iti
smor efrequentinareast hatrecei
vefrequentrainfal
le.
g
aroundLakeVictori
ainMukono, Kampal a,WakisoandMt .Elgonsl
opesin
Mbale.

4.Gul
leyer
osi
on

Itiswheredeepandwi dechannel s/
groovesarecreatedbyr
unning
waterontheeart
h’ssurface.Itiscommoni nsteepslopeswhich
recei
veheavyrai
nfal
lespeciall
ywher evegetat
ionhasbeendestroy
ed
e.gKabal
e,Kisor
oandKabar oleinUganda.

5.Spl
asher
osi
on

Iti
scausedbyt heimpactofr ai
ndr opswhi
chdisl
odgesoi lpart
icl
esand
scatt
erthem i
ndi f
ferentdi
recti
ons.Thespl
ashedparti
clesar el
aterpul
led
downbygr avi
ty.Therefor
eraindropsdonotonlydetachloosesoi l
part
icl
esbutalsoaf f
ectthehorizontal
movementofthet hoseparti
cles

CAUSESOFSOI
LEROSI
ONI
NEASTAFRI
CA:

Soi
ler
osi
oni
sinf
luencedbybot
hPhy
sicalandhumanf
act
ors.They
i
ncl
ude:

a)Phy
sicalf
act
ors:

Climate
Prolongedandheavyr
ainfal
lespecial
l
yinhighl
andar
eascr
eatesexcessi
ve
surfacerunof
ft hati
ncreasest heerosi
veenergyoftherunni
ng water
result
ingi
ntori
l
landgull
eyerosion

Pr
olongedbutgent
le/
moder
ater
ainf
all
leadst
omi
nimal
rat
esofer
osi
on

Str
ongwindsespeci
all
yinsemi
ari
d/ar
idar
easwi
thv
eryl
i
ttl
erai
nfal
lcause
defl
ati
on(wi
nderosi
on)

Vegetat
ion
Areaswithl
imit
ed( t
hin)vegetat
ioncoverexper
iencehighrat
esofer
osion.
Scantyvegetat
ion encouragesexcessivesurf
acer unoffhencecausi
ng
winddefl
ati
on,ri
ll
andgul l
eyerosion

Ar
easwi
ththi
ckvegetat
ioncoverar
eassoci
atedwi
thmi
nimum r
atesof
er
osi
onsuchasaroundMabira

25
Topography /
rel
ief
Steepslopesinhighlandareasaccel
erat
ehighratesoferosionespeciall
y
gull
eyerosion.I
notherwords,thel
ongerandsteepert
heslope,thegreater
thevel
ocity(speed)anderosiv
epoweroft hesur
facerunoffhenceleading
togull
eyerosion.

Gent
lesl
opesencour
agesheeter
osi
on

Natur eoft
hesoils
Porousand un consol idated soil
sespeci all
yy oung v
olcanicsoil
sand
sandysoi l
sofferl essresist
ancet otheer osionalagentslikewindand
runningwaterhencecausi nghighr at
esofer osion.Suchsoil
sar ev
eryli
ght
i
nnat ur
ethat’
swhyt heyar ehi ghlysusceptibletoerosionespecial
lyat
KotidoandMor oto.Youngv olcanicsoil
sar ef oundatBuduudahence
promot i
nggull
eyerosion

Bioti
cf actor
s
Thepr esenceofhar v
est erantsandwi l
dani mal
sinpastoralandsemiar i
d
areasl eadstorapidl ossofv eget
ationcov erespeci
all
ygr assesleav
ing
suchar easbareandl essr esi
stanttoer osi
on.Thisisresponsibl
eforwind
defl
ation and splash er osi
on in areas like Machakos,Ankol e-
Masaka
corri
dor ,
NakasongolaandKar amojaar eas

Prolongeddrought
Thislimit
sthegr owt
hofnaturalveget
ati
oncov erhenceleavi
ngtheland
bareandexposedt oagent
sofsoiler
osionli
kestrongwindsandheavyrai
n
drops.Thisi
sv er
yseri
ousinKaramojar
egion,Turkanal
and,Masai
landand
Miombowoodl ands

Humanf actor
s:
Deforest
at i
on
Theexcessi vecutti
ngdownorclearingawayoft r
eesbymanr educesthe
prot
ectiv
ecov erofsoi
landencouragesrunoffsubsequent
lyr
esul
ti
nginto
soil
erosioninf or
m ofsheetandgul
leyerosi
on

Shifti
ngculti
vation
Thisisanagr icult
uralpract
icewhichinvolvescutt
ingdowntr
ees,planti
ng
cropsont helandandt hereaft
erabandoningitwhenitl
osesi
tsfert
il
it
y.The
soiliseasil
yer odedoncet hebarelandisabandonedbyt hefarmerswho
shiftt
ootherv i
rginlandswhicharesti
llproduct
ive

Overst
ocking/overgr
azing
Lar
genumber sofanimalsleadtot heemergenceofbar
epat chesofl
and
l
eavi
ngt helandhighl
ypronetoer osi
onespeci
all
ywinddef
lat
ion.Thi
sisso
commoni nnomadi cpastor
alareas

Overcroppi
ng
Itref
erstocont
inuedcul
ti
vat
ionofcropsonthesamepi eceoflandfora
l
ongt i
mewi t
houtgivi
ngi
trest.I
tcausessev
eresoi
lexhausti
on.Thesoil
s
ult
imatel
ybecomel ooseandar eeasil
ywashedawaybyt heer osi
onal
agents

26
Upanddownsl opecultivat
ion
I
ft here’
spersi
stentploughingofhighl
andsl
opeswithoutusingproper
met hodsofcul
ti
vati
on,itencour
agessurf
acer
unofft
herebyresul
ti
nginto
ri
l
landgul l
eyer
osion

Miningandquarry
ing
Open castmining i
nv ol
vesthe r
emovalofl
argequant
it
iesofsur
face
vegetat
ionandthisleavessuchareasbar
eandpronetosoi
ler
osi
onby
windandrunni
ngwat er

Construct
ionwor ks
The establi
shmentofr oads,mot orabl
et rucks and r
ailway invol
ves
removalofv egetat
ion and exposest hesoi ltotheharmf uleff
ectsof
rai
ndrops,runningwat erandwi nd.Inaddit
ion,runni
ngwat ereasi
l
ytakes
advantageoft r
ansportroutest
ocr eategul
li
eshencesoilerosion

Swampr eclamati
on
Thisinvolvesthedraini
ngofswampsf oragr
icul
turalpurposes.Fl
oods
especial
lyinrai
nyseasonsoccurwhi
chcarr
yawayt hesoile.ginBusoga,
Tororo,andpartsofBuganda

Bushburning
Thi
sismai nlydonebythepastor
ali
stsli
ketheBahi mai nUganda, Masaii
n
Kenyaaswel lasTanzaniaandculti
vator
sl eadi
ngt ot hedestructi
onof
nat
uralvegetati
oncover.Thi
sexposest hetopsoi ltoagentsli
ker unni
ng
waterandwi ndsleadi
ngt owinddefl
ati
on,riller
osion,sheeterosionand
spl
asherosion

Monocult
ure
Thisi
sthepersi
stentgr
owingofasingl
et y
peofcroponapi
eceoflandf
or
alongperi
odoftime.Thismakesthesoill
ooseandeasi
l
ycarr
iedawayby
theagent
sofer osione.gKikuy
ul andinKenya,MukonoandLugaziin
Uganda

Growi
ngofpoorcovercrops
Somecropssuchascottonandt
obaccoleavebar
elandi
nbetweenthe
rowsandthi
sinci
dent
all
yencour
ageserosi
onofthesoi
lbyr
unningwater
.

AcasestudyofKondoaarea
Iti
sfoundi
nDodomai ncentr
alTanzani
a.I
texperi
encesmai
nlygul
l
y
erosi
onandthemaincausesofsoil
erosi
onincl
ude:

Steepnatur eoft helandscape

Therainyseasonsexper iencedfr
om Decembert oApri
l
Thedryseasonwhi chlastsforoversevenmonths
Highpopul ationdensityof20-40personspersquareki
lometer
Theov ergrazi ngandpr i
mitiv
eculti
vati
onwit
habi gnumberofcat
tl
einthe
area.
Thescant yv egetati
oncov erdominatedbygrassl
andandacaci
atr
ees.

27
Highlyporoussoil
sthatcaneasil
ybeeroded.
Extensiv
edef or
estat
ionofthefewexi
sti
ngtreestopr
ovidef
irewood
Thepr evai
li
ngdrywindespecial
lyt
hesouthEaster
lyt
radewinds.
Thet oomuchbushbur ning.

Acasest udyofKigezihi ghland

Iti
sfoundinsouthwest ernUgandai nKigezir
egionandthecausesof
soil
erosi
oni nthi
sregioni ncludethefol
lowing
Heavyamount sofrainfallreceiv
edthroughouttheyearover1500mm
Highpopulati
onpressur eonl and
Thehil
ly/mount ai
nousst eepslopes
Pri
miti
vemet hodsoff armi ngforexamplecult
ivati
onalongtheslope
Thereisalotofdeforestation
Thesocialfact
ors,polygamousf amil
ies

EFFECTSOFSOI
LEROSI
ON:

Negat
iveef
fect
s:

Soi
ler
osi
onresul
tsint
owashingawayofthefi
nestandmostfert
il
esoils
whi
chareri
chinorgani
cmatter
.Thi
sresult
sint
oinfer
ti
le(
unproduct
ive)
soi
l
swhichcausel
owcr opy
iel
dshencel
eadingtofami
ne.

Soilerosionphysi
call
ydestroy
st hesoi
lsurf
acebycreati
nggulley
sand
therefor
ecausingwast eLandsleadi
ngtolossoffarmland.Equal
ly,t
he
wast eland/badlandswi thgull
ieshi
ndertr
anspor
tandcommuni cati
on
aswel lasmechanizat
ion

Soi
lerosi
oncanr
esul
tint
olandsl
idesespeci
all
ywheregul
ley
sar
eformed.
Thesegul
ley
sweakenthest
abil
it
yofaslopetherebyl
eadi
ngtol
andsl
i
des.

Soiler
osionresul
tsintopol
luti
onofwat erbodi
ese.g.springs,wel
lsand
ri
versthr
oughdeposi t
ionofsil
tandsandi ntothewat erbodies.I
tadds
otherimpuri
ti
esintothewat erwhi
chmaybehar mf ultohumanheal th.
Relat
edly
, wi
nderosi
oncausesairpol
lut
ionduetoexcessivedust

Areaswithrampantsoilerosionarei
nfert
il
e.Theyarether
eforeassoci
ated
withli
mited vegetat
ion coversinceheav i
l
yer oded soi
l
sar eunablet o
supportplantgrowth.Thisr esul
tsintoreducedev apot
ranspi
rat
ion,l
ow
rai
nfal
landscarcit
yofpast ur
efortheanimals

Soilerosionalsocausesfloodinginbr oadri
verval
leysandlowlandsdueto
sil
tati
onofr iver
sandot herwat ersources.Thi
sultimat
elyresul
tsint
oloss
ofhumanl if
eanddestructi
onofpr oper t
y
Itcostsal otofmoneyandef fortstoindivi
dual
sandgov er
nment sto
control.Farmersal
soloset hei
rcropf i
eldsbecauseofsoiler
osion

I
tmayalsol
eadtosil
ti
ngofl
akesandi
rr
igat
ioncanal
s.Thi
sint
urnaf
fect
s
f
ishi
ngandagr
icul
tur
e

28
Thedustparti
clescarri
edbywi ndar
edeposi
tedaroundsoci
al
i
nfrast
ruct
urelikeroads,bui
l
dingsamongother
sleadingt
oincr
eased
costsofmaintenance

Posi
ti
veef
fect
s:

Soiler
osi
onleadstoremovaloft
opsoilt
husexposi
ngthefr
eshpar
ent
rockstot
heagentsofweat
heri
ngl
eadi
ngtofor
mationofnewsoi
l
shence
i
tfacil
i
tat
essoi
lfor
mati
on.

Itleadst otr
anspor
tat
ion,deposi
ti
onandaccumul at
ionoffer
til
ealluv
ial
soilsinthelow l
andareaswhichareuti
li
zedforagri
cul
tur
e/cr
opf ar
ming
e.g.RiverManaf
waatDohoi r
ri
gati
onscheme.

Itleadsto exposureofphysi
callandf
ormssuch asinsel
bergswhich
attr
acttour
ist
st huspr
omoti
ngt hedevel
opmentofthetour
ism i
ndustr
y
e.g.i
nMubendeandNakasongola.

Soiler
osionexposesmi neral
snearert
otheear
th’
ssur
faceandthi
smakes
them easytoextr
acte.g.li
mestonerocksi
nToror
o.Whentheyare
exported,
revenueisearned

St
epst
akent
ocont
rolsoi
ler
osi
oni
nEastAf
ri
ca:

Affor
estat
ionandr e-
affor
estati
onprogr
amsar ebeingencour
agedand
peopleareplant
ingtr
eesinfreshareasandinareaswher
ef or
estswere
clear
ed.Thismakessoi lpar
ticl
esonhighl
andslopestobehel dti
ght
ly
toget
herbythetreer
oots.

Terr
aci
ngmet hodoff ar
mingonsteepslopesisbeingusedwhereby
benchl
ikestepsarecutal
ongahighl
andsl
opeandthesebecomegar
dens.
Thesestepsbreakthespeedoft
hewaterandit
senergyt
owashawaythe
soi
l.

Cont ourploughing i
susedwher ebycul tiv
ationonsl opesf ol
lowst he
heights oft he sl
ope so t
hatareas oft he same contours/heightare
culti
vatedtogetheracr
ossaslope.Thi
sr educesthesur f
acerunof fasthe
raisedridgesbreakthefl
owoftherunningwat erforexampleintheKeny a
highlands.

Cropr otat
ionsystem off
armingisbei
ngappli
ed.Thisi
nvol
vessuccessi
ve
cul
tiv
ationofdifferentcr
opsi nthesamefiel
df ol
lowi
ngchangesi nthe
season.Thishel
pst omaintai
nthesoi
lstr
uct
ureandsoilf
ert
il
it
y.

Str
ipcult
ivat
ionisbeingpracticedonsteepsl
opeswherethegardensare
separ
atedbyst r
ipsofuncult
ivatedgr
ass.Thi
sbreakssoi
ler
osionbecause
aswaterbeginstorun,i
tsspeedi sbr
okenbyenter
ingi
ntoagrassstr
ip.

Useofcov ercropsespeci
all
ythosecr
opswhichspr
eadastheygrowand
covert
hesoilsuchasbeans,sweetpot
atoes,
pumpki
nsandotherl
egumes.
Thesebreakdownt hespeedoft her
unningwat
erandi
tsenergytoer
ode
andwashawayt hesoi
l
.

29
Mixedori ntercr
oppingsyst
em offarmi
ngwherediff
erenttypesofcrops
aregrowni nthesamef i
eldatt
hesametimeforexamplecropslikemaize,
beans,groundnut sandIr
ishpotat
oesar
eint
er-
plant
edandt hisassi
ststo
bi
ndt hesoilpart
icl
es

Rest
ri
ctedorcontr
oll
edgrazi
ngwhichinv
olv
escont
roll
i
ngthenumberof
ani
malsgrazi
nginapar t
icul
arar
easoast omaket hesoi
lremainwit
h
somegrasstohol
ditandprot
ecti
tfr
om er
osi
onf
orexamplezerogr
azi
ng.

Bushfall
owi
ngsystem ofrot
ati
onalfar
mingwher esomepi ecesofland
ar
el ef
tunderfal
low orrest
,in or
dertor egai
nf ert
il
it
ynatural
l
y.This
i
mprovesthesoi
lstruct
urewhi
chmakesi thardforthesoilt
obeer oded
away.

Additionoforgani
cmanur eandotherart
if
ici
alf
ert
il
izer
stoimpr
oveonthe
soilfert
il
it
yandstruct
ure.Thesoi
lpart
icl
esbecomecohesiv
eandtoohard
forrunningwatert
owasht hem away.

Qn.Di
scusst
hecausesandef
fect
sofsoi
ler
osi
oni
nEastAf
ri
ca.

Geogr
aphyDepar
tment

30